Co ncret ncrete e Ground Floo loorrs & Pa vement vementss for Commer ommerci ciaa l & Ind ndus ustt ria l Us e Pa rt One One Contents A more-detailed contents list is provided at the beginning of Chapters 1, 2 and 3, listed below.
Introdu In troduction ction ................................................. ........................................................................................... .......................................... 5
Chapter 1: 1: Design Design .......................................................... ................................................................................... ......................... 7
Chapter 2: Constr onstructi uction on .................................................. ........................................................................ ...................... 35
Chapter 3: 3: Guide to Specifi Specification cation ....................................................... ......................................................... .. 53
Appendix A: Glossary of Term ermss ....... ....... ...... ....... ....... ....... ...... ....... ....... . 75
Appen ppendix dix B: Design Examp xample le ............................................ ................................................................ .................... 77
Appendix C: Effect Effect of Chemic Chemicals als on Concrete Concrete Pa vemen vements ts ....... ....... ....... .. 81 © 1 99 99 9
Appendix D: Determinat Determinat ion of Amount of Shrinkag Shrinkag e Reinforcement Reinforcement .... .. 87
CEMENT&C ONCRETE CEMENT&CONCRET ASS OCI OCIAT ATION OF NEWZEAL NEW NEWZ NEWZEA ZEAL EALA AN ND D
Appendix E: E: Effect Effect of Various Fa Fa ctors on Abrasion Abrasion Resista nce .... ... ... .... .. 88
Level 6, 142 Fea Fea thers ton S t, Welling to ton. n.
Appendix F: Subgrade Subgrade and Subase Evaluations Evaluations ...... ....... ....... ....... ....... ... 90
PO Box 448, Welling to n. Tel el:: 0-40 -4-499 499 8820 8 820,,
Refer eferenc ences es ..................................................... ........................................................................................... ...................................... 95
Fa x: 0-40-4-499 499 7760. E-mail: ad
[email protected] rg.nz
Bibli Bib liography ography ................................................... ........................................................................................ ..................................... 96
ISSN: 1171-0748 ISBN: 0-908956-11-8 TM 26 26 First Pub lishe d Novembe Novembe r 1999
CEMENT&C ONCRETE CEMENT&CONCRET ASS OCI ATION OF NEWZEAL NEW NEWZ NEWZEA ZEAL EALA AN ND D OCIAT
Concrete Ground Ground Floor Floors s a nd Pa vements : Pa rt 1
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Co ncret ncrete e Ground Floo loorrs & Pa vement vementss for Commer ommerci ciaa l & Ind ndus ustt ria l Us e Pa rt One One Contents A more-detailed contents list is provided at the beginning of Chapters 1, 2 and 3, listed below.
Introdu In troduction ction ................................................. ........................................................................................... .......................................... 5
Chapter 1: 1: Design Design .......................................................... ................................................................................... ......................... 7
Chapter 2: Constr onstructi uction on .................................................. ........................................................................ ...................... 35
Chapter 3: 3: Guide to Specifi Specification cation ....................................................... ......................................................... .. 53
Appendix A: Glossary of Term ermss ....... ....... ...... ....... ....... ....... ...... ....... ....... . 75
Appen ppendix dix B: Design Examp xample le ............................................ ................................................................ .................... 77
Appendix C: Effect Effect of Chemic Chemicals als on Concrete Concrete Pa vemen vements ts ....... ....... ....... .. 81 © 1 99 99 9
Appendix D: Determinat Determinat ion of Amount of Shrinkag Shrinkag e Reinforcement Reinforcement .... .. 87
CEMENT&C ONCRETE CEMENT&CONCRET ASS OCI OCIAT ATION OF NEWZEAL NEW NEWZ NEWZEA ZEAL EALA AN ND D
Appendix E: E: Effect Effect of Various Fa Fa ctors on Abrasion Abrasion Resista nce .... ... ... .... .. 88
Level 6, 142 Fea Fea thers ton S t, Welling to ton. n.
Appendix F: Subgrade Subgrade and Subase Evaluations Evaluations ...... ....... ....... ....... ....... ... 90
PO Box 448, Welling to n. Tel el:: 0-40 -4-499 499 8820 8 820,,
Refer eferenc ences es ..................................................... ........................................................................................... ...................................... 95
Fa x: 0-40-4-499 499 7760. E-mail: ad
[email protected] rg.nz
Bibli Bib liography ography ................................................... ........................................................................................ ..................................... 96
ISSN: 1171-0748 ISBN: 0-908956-11-8 TM 26 26 First Pub lishe d Novembe Novembe r 1999
CEMENT&C ONCRETE CEMENT&CONCRET ASS OCI ATION OF NEWZEAL NEW NEWZ NEWZEA ZEAL EALA AN ND D OCIAT
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Preface The uninterrupted use of any factory is very depen dan t on the perform ance of the pavem en t.Th e surface shou ld not dust or abrade u nder the action of fork lifts or trolleys.Joints shou ld no t break d ow n un der w heelload ing.A ny repair necessary to the pavem ent m ay involve closing dow n the factory,at least in part,for a considerab le p eriod.Therefore, the im portan ce of a high -qu ality factory pavem en t cannot be over-em phasised.In a sim ilar w ay it is im portan t that grou nd floors in offices and com m ercial buildings perform in a w ay that is satisfactory. W hilstthis m anual has been prod uced to give building ow ners an d d esign ers guidan ce on the design ,detailing an d con struction of com m ercial an d industrial pavem en ts inside bu ildings,they w ill find that the d ocu m en t m ay b e u sefulfor the d esign of external pavem en ts carrying norm al veh icle load ings,such as sem i-trailers.
DIS CLAIMER Apar t f rom any f air deali ng for th e purposes of pri vate study, research, cri ti cism or r evi ew, no part of thi s publi cati on may be reproduced, stored i n a r etr ieval system or tr ansmit ted in any form or by any m eans, electr onic, mechanical, photocopying, recordi ng or oth erwi se wi thout
To aid bu ilding ow ners and design ers the A ssociation has produced this,Part1 of the m an ual,to p rovide gu idan ce on em pirical procedures (i.e.non-specific d esign ) and construction considerations.It replacesDesign of Concrete ,IB26,first Ground Floors for Commercial and I ndustri ali zed use published 1980,reissued 1984. A separate Part2 o f this m an ual deals w ith specific engineering d esign w here a m ore in-dep th design analysis is undertaken ,particularly considering the subbase conditions and load ing configu rations. Th e assistance of the N ew Z ealand C on crete S ociety is acknow ledged in prod ucing this m anu al.
wr itt en permission. Enqui ries should be ad- dr essed to the publ isher. The Associat ion i s a non-profi t organi sati on sponsored by the cement i ndustr y i n N ew Zealand to provide informat ion on the many uses of cement an d concrete. Thi s manual is publi shed by the Associati on for th at pur pose and was prepared by the Associat ion with i nput fr om independent consult ants. Since the in form a- ti on provi ded is intended for general gui dance only and in no way r eplaces th e servi ces of professional consult ants on part icular projects, no legal l iabi li ty can be accepted by t he Associa- tion. Remember, when w orki ng wi th cement and concrete/mort ar or manu factur ed or pr efabri - cated concrete products, ALW AYS foll ow t he manuf acturer’s in structions and seek advi ce about worki ng safely wi th t he products from th e manuf acturer, or your nearest OSH Offi cer. Acknowl edgement is made to C & CA of Austral ia f or permi ssion to use their manual T48 as a basis for developing a simi lar document specif ically for N ew Zealand condit ions. Concrete Ground Floors a nd Pa vements : Pa rt 1
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Introduction SCOPE T h is m an u al cov covers ers th e select ecti io n an d d et etai ail lin g o f con cr cret ete e in d u strial an d com m er erci cial p avem en ts,bo th in ter ern n ally an d extern exter n al all ly.It has ha s bee b een n p rep ared to assist en gin ee eers rs, ,arch archi itects ects, ,sp speci ecif fiers an d b u ild in g co con n tractors by p ro vi vid d in g an o u tlin e of o f th e pr p ro cess of d et etai ailin g an a n d d esign ,an d th e m ajo r fact actors ors in m eet eeti in g d esign p er erf fo rm an ce. Th e content content has been sequenced sequ enced to en cour courage age th th e d esign er to co con n sid er servi servicea ceab b ility requ req u irem en ts bef be fo re slab th ick ckn n ess is establ estab lish shed ed .It is th e A sso ssoci ciatio n ’ s exp erien ce th at th e com m on di dist stress m od es of in d ust ustr rial p avem en ent ts are are related to jo in ts,jo in t lay ayo o u t an d th e sel selectio n o f ap p rop riate con co n cr crete ete pr p ro p erties that th at avo id su sur rface d eter eteri io ratio n .T h is m an u al al’ ’ s go al is to to p ro vi vid d e in in fo rm atio n o n co cost st-ef -eff fective tech n iq u es fo r th e det d etai ail lin g an a n d d esign o f con cr cret ete e in d u strial an d com m er erci cial p avem en ts to ach achi ieve th th e req requ u ired p er erf form an ce in in service. A n em p irical,n on -s -sp p ecific engi en gin n eerin g p avem en t d esign is pr p ro vi vid d ed to assist d esign ers w ith va var rio u s pr p ro ject sizes an an d fu n ct cti io n s. Fo r th e pu p u rp o se of th is m an u al al, ,b o th in terna ernal l flo o rs and an d exter ext ern n al p avem en ts are are ref refer err red to as a s pavem pave m en ts.T h e m an u al covers p lain an a n d rein forced con cr cret ete e pavem pav em en ts,bu t d o es no t cov cover er p rest estr ressed o r p o st-ten sio n ed con cr cret ete e pavem ent ents s.For pavem en ent t th ickness gr great eater th an 200m m , th e desi de sign er sho u ld u se sp sp ecialised com m er erci cial com p u ter erise sed d design techn echni iqu es for deter determ m ini ning ng op tim um pavem ent th ickn ess w h ich fo rm th e sub su b stan tive text text o f PartTw o o f th e m anual. T h e p rin cip les an a n d d et etai ail ls pr p rov ovi id ed are ap p licab cabl le to p avem en ent ts likel kely y to to b e fou fou n d in in a w id e ran range ge of o f com m er erci cial an d in in d u strial b u ild in gs in clu d in g:
• foo d p rocessin g p lan ts. Fo r exam p le,for gu id an ce on For o n coo cool l stores ref refer er to G u id elin es fo fo r th e S p ecificat cati io n ,D esign an d C o n stru ct cti io n o f C o ld 1 S to re Fl F lo o rs .
INTENDED US U S E OF P AVEMENT M an any y in in d u strial p avem en t p roj oject ects s are are p ar art t o f a p rop er ert tyd evel evelop op m en t p ackag ackage, e,an d o ften th e pr p ro ject d esign er h as little o r no kn o w led ge o f fu tu re tenan ten an ts an d th ei eir r operat op eratin g req u irem en ts.S el electi ectin g the th e lo w est est-i -in itial al-co -cost st sol solu u tio n m ay p rovi ovide de sho rt-ter erm m p er erf form an ance ce and m eet n orm al op er erat ati in g req equ u irem en ts in th e fi firstfew years years. .H ow ever ever, ,a ch an ge o ten enan ancy cy an d th th e in trod u ction of m echan icalequ ip m en ent tm a cau se suf su fficien t d ist stress ress to d isrup t th e u se of o f th e bu b u ild in u n til rep un epai airs have b een com p let eted ed. .It is recom m en d ed th a t h e d esign er con sid ers th e li th life-cycle cost co st o f th e p avem en t in clu d in g in in itial co con n st str ru ct cti io n co cost sts, m ai ain n ten an ce an d isr di sru u p tio n cost costs s to th e bu b u sin ess,w h en select ecti in g the p avem en t sys syst tem Th e d es esi ign er shou ld alw ays ask ask to to be m ade aw ar are e of o f th pavem pa vem en t op er erat ati in g requi requ irem en t an d stat state e th th is on th p avem en t layo pavem ayou u t d raw in g. A lso, th e d esign er w ill n eed t consi con sid er con stru ction loa oad d in g, an d th th at th e pavem p avem en t m a b e su b jected to sem i-t be -tr rai ail lers and an d fo rk lift truck rucks s du d u rin g an af aft ter th e com co m p let eti io n o f th e b u ild in g
ELEMENTS OF A TYP YPIC ICA A L COMMERC CO MMERCIAL IAL OR ICAL AL IND US TRI INDUS RIAL RIA AL AL CO CONCRET CONCR NCRET ETE PA P AVEMENT Wearing surface Topping (if used)
• w ar areho eho uses and stor ores es; ; • m an anuf ufact acturin g p lan ant ts;
SLAB
• eng in eer eeri in g w or orkshop kshop s and gar garages; ages;and • of off fices an and d sho shop p pi pin n g com pl plexes exes. . H ow ever ever, ,p avem en ts su su bj bject ect to speci sp ecial loa oad d in gs or con co n d itio n s,an d /o r h avi avin n g sp eci ecial al req u irem en ts fo r resist stan ce to to ab abr rasion or agg ress essi ive ch em icals need n eed ad add d ition al con sid er erat ati ion an d ar a re ou o u tsid e th th e sco sco p e of o f th is docum do cum en t. T h ese in clu d e th th o se associ associat ated ed w ith : • coo cool l stores and freezi eezin n g w orks; • ab atto irs rs; ; • d ai airi ries; • p igg eries; • che chem m icalp lan ts;an d
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SUBBASE
Reinforcement (if used) Vapour barrier (if used)
SUBGRADE
T h e elem en ent ts of a typi typical calcon cret ete e pavem p avem en ent t ar are e sho w n in th e fi figu re ab ove ove. .Fo For r th is m an u al th e key k ey term term s are are d ef efi in ed as fo llo w s: cret ete e pavem pav em en t laid in in o n e piece piece and an d Panel A u n it of con cr b o u n d ed o n all sid es by fr free ed e d ge ges s or jo in ts. ein n fo rcin g b ars or rei ein n fo rcin g fabri fab ric Reinforcement R ei 2 3 com pl plyi ying w ith N Z S 3402and a nd N ZS 3422 3422 resp ec ect tive vel ly (n ote a joi oin n t A S /N Z S tan d ar ard d for steel m esh an d ba bar rs is in preparation).
INTRODUCTION
ent t of th e con cret ete e pavem p avem en ent t. Slab Th e m ain stru ctu ral elem en Subbase A layer of select m at ater eri ial be bet tw een th e sub grade an d th e slab. Subgrade T h e nat n atu u ral or prepa prepar red form form at ati ion on w h ich th th e p avem en t is con stru cted ed. . Topping A n in teg egr ral o r ap p lied layer used to in cr crease ease abr ab rasio n (w ear) resistan ce an d /o r ch ch em ical resistan ce of of th e slab slab. . Vapou r barrierThe Th e m em br brane ane p lace aced d b eneat eneath h the slab to to p reven t w at ater er vap vapou ou r risin g th th rou gh th e subgrade sub grade to th th e pavem en ent t sur surf face.
e surface w h ich com co m es in con cont tact w ith Wearing su rfac rfaceeTh traf aff fic usin usin g the p ave avem m en t. A dd ition alter erm m s used in th th is m anu aland com m on for in du strial p avem en ent ts are are d ef efi in ed in A p pe pen n d ix A .
ALTERNATIVE MATERIALS T h is m an u al p rov ovi id es in form at ati ion ab abou ou t p lain an a n d rein forc orced ed con concr cret ete e pavem p avem en ent ts.O th er con cret ete e p avem en ent t typ ypes es n ot covered in this this d ocu m en t in clu d e: • Prestressed concrete paveme nts w ill p ro vi vid d e large large jo in t-free areas an a n d th ey are gen g en erally th in n er pavem pa vem en ts (r (ref efer er to th e B ib lio grap graph h y fo fo r fu rth er reading).
• Steel-f Steel-fibre ibre reinforc reinforced ed concrete w illal also so freq equ u en tly gi give ve ad advan van tag ages es in in th ickn ess desi d esign , red u ce pl p last asti ic sh sh rin ka kage ge crackin crackin g, an d im im p rov ove e th th e flexu ral st str ren gth ,fatigu e str stren gth an d resistan ce to im p act lo ad s (r (ref efer er to to th e B ib lio grap h y for fu rth er rea read d in g).T h e m ovem ent effec ect ts of the pavem ent ar are e un chan ged w hen u sin g fib res in con cr cret ete e an a n d th e spaci sp acin g o f jo in ts need n eed s to to b e assess a ssessed ed to en sure success su ccessf fu l jo in t b eh avi avio o u r.Fo r d esign gu id an ce,ref efer er to th e fi fib re m an u facturer’ s do d o cu cum en tat ati io n .Po Pol lyp ro py pyl len e-f e-fi ib re rein fo rced con cr cret ete e red u ces pl p last asti ic shrin ka kage ge cr crack acki in g. R esearch h as asnoted noted th at fib res ad d ed to con cr cret ete e u n d er con tro lled con d itio n s an d fo r lim ited site con co n d itio n s red u ce th th e pr p ro b ab ility of of cracki crack in g in th e p lastic state state an an d ,to a lesse lesser r exten exten t,in th e h arde arden n ed state.R ef efer er to th e fi fib re m an u facturer’ s do d o cu cum en ent tat ati ion for design gu id an ance. ce. Shrinkage nkage comp ensati ensating ng cements and ad mix mixtures tures • Shri are ar e u sed to to p rod u ce con cr cret ete e w h ich exp expan an d s in th e fi first few d ays aft after castin g, p ro d u cin g a fo fo rm o f p rest estr ress w h ich is rest restr rai ain n ed w ith steel rei ein n fo rcem en t.T h e restrain ed early exp expan an sion ap app p roxi oxim m at atel ely ba bal lan ces subsesub sequ en ent t n orm al shr shri in kag kage. e.T h e expan sion of cem en ent t pa past ste can resu esul lt fro m th e fo fo rm at ati io n o f et ett trin gi git te an d b ecau se th is req requ u ires a lar large ge am ou n t of w at ater er, ,con tin u ou s w et curi cu rin g o f th is typ e of o f exp an sive co n cr crete ete is nece n ecessar ssary y to to achieve achi eve o pt pti im u m results.
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DESIGN
Cha pter 1: Des ign 1. PRO CED U RE
8
2 . D ES I G N FO R S ERVI CEAB I LI TY
9
2 .1 JO IN TS A N D JO IN T LAYO U T
9
2.1.1 General ........................................................... 9 2.1.2 Joint types ..................................................... 10
2.1.2.1 Free movement joints ........ ......... ........ ........ 10
3 . D ES I G N FO R S TREN G TH
23
3 .1 O B JECTI VES
23
3 .2 S U B GRA D E AN D S U B B AS E
23
3.2.1 Site conditions ...............................................23 3.2.2 Site investigation ...........................................23 3.2.3 Subgrade strength ......................................... 24
2.1.2.2 Tied joints ......... ......... ......... ........ ......... ...... 12
3.2.4 Subgrade uniformity ...................................... 24
2.1.2.3 Construction joints ........ ......... ........ ......... ... 13
3.2.5 Subbase materials a nd thickness ....................24
2.1.3 Joint layout ..................................................... 13
3 .3 S I M PLI FI ED TH ICK N ESS D ES IGN
25
2.1.4 Joint sealants ................................................. 15
3.3.1 General ........................................................... 25
2.1.5 Joint protection ...... ....... ....... ...... ....... ....... ...... . 16
3.3.2 Loading ........................................................... 25
2 .2 CO N CRETE P RO PERTIES
16
2.2.1General ........................................................... 16 2.2.2 Abrasion resistance ........................................ 17 2.2.3 Corrosion resistance ....................................... 17 2.2.4 Freeze-thaw resistance ................................... 17 2.2.5 Resistance to chemical atta ck ......................... 17 2 .3 S U RFACE FI N IS H ES
18
2.3.1 General .......................................................... 18 2.3.2 Single-course versus two-course pa vements ... 18 2.3.3 Surface finish ................................................. 19
3.3.3 Designing for shrinkage movements ...... ....... .. 26
3.3.3.1 Design process for linear movement ........ .. 26 3.3.3.2 Design process for warping movement ....... 27 3.3.3.3 Design proces s for selection of joint types .. 30 3.3.3.4 Design process for special conditions ........ 31 3.3.3.5 Design &construction process for design ... 32 3.3.3.6 Influence of fixing slab to foundation ......... 32 3.3.4 Design process for linear movement for unreinforced panel construction ....... ...... ....... . 32 3.3.5 Design process fo r linear movement for reinforced panel construction ............................... 33
2.3.4 Toppings ........................................................ 19 2.3.5 Surface treatments and coatings .................... 19 2 .5 GRAD I EN TS A N D S U RFACE D RAIN AGE
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1. P ROCEDURE A s m en tioned in the Introduction,this C hapter has been sequ en ced to en sure that design ers address the serviceability requirem en ts first,follow ed by the p avem en t thickn ess requirem en ts.Table 1.1 p rovides a concise gu ide for the design proced ure o f industrial pavem en ts. TABLE 1. 1
DES IGN PROCEDURE FOR CONCRETE COMMERCIAL AND INDUSTRIAL PAVEMENTS ACTION
REFERENCE
STAGE 1 Define Intended Use of Slab /Pa vement • Load ing condition • Internal/external • Subgrad e conditions • Surface wear and finish STAGE 2 Determine Properties of Concrete Sla b/Pa vement Ste p 1: Step
Select suita ble concrete
Section 2.2
Step 2:
Nomina te a suita ble concrete finis h
Section 2.3
Step 3:
Determine s ubba s e thickness
Section 3.2; Ta ble 1.9
Step S te p 4:
De te rmin e co nc re te sla b /pa ve me nt th ickn es s
S ec tio n 3.3; Ta b le 1. 10
STAGE 3 Choose Choos e the Des ign Method Options: Options : Unreinforced
Section 2.1.3 Section 3.3.4
Reinforced - Strip-pour Method
Section 3.3.3.5
Reinforced - Continuous-pour Method
Section 3.3.3.1
Reinforced - Pa nel Strip Method
Section 3.3.5
Reinforced - Pa nel Continuous Method
See Pa rt 2
Step S t ep 5: 5:
De te rm in e Re in fo rce me nt fo r Lin ea l Mo ve me nt
S e ct io n 3.3. 3. 1; Ta b le 1. 12
Step 6:
Design for Wa rping Movement
Section 3.3.3.2
Step 7:
Select Joint Type
Section 3.3.3.3; Fig. 1.22; Fig. 1.23
STAGE 4 Prepare Slab /Pa vement Drawings, S howing Pos itions, types of Joints and Reinforcement
8
• Check sla b res tra ints
Sections 3.3.3.4; 3.3.3.6
• Specify sla b fla tness
Section 2.4
• Allow for gra dients a nd s urfa ce dra ina ge
Section 2.5; Ta ble 1.12
DESIGN
2.
DES IGN FOR SERVICEABILITY
2. 1 JOI JOINT NTS AND JOINTLAYOUT JOI NTLAYOUT
2.1.1 General U sers of floo rs are becom ing increasingly aw are of the m any issues that need addressing at the tim e of the d esign an d detailing o f a n ew floor slab on grou nd.Joints are a m ajor con sideration and som etim es the need to m inim ise or elim inate form ed joints m ay be m ore im portant than floo r flatness or levelness,for exam ple w here floors are h ighly trafficked by h eavily load ed pallet trucks w ith sm all solid rub ber w heels. Joints,w hich develop vertical displacem en t over tim e, im pact on : •Floo r m aintenance (progressive joint edge dam age)
ends to bow dow nw ards. W arping can cause p rob lem s by effecting the flatness of the floo r an d slabs can crack across an unsup ported edge un der w heel load s. A perm eable dry subg rade w ill redu ce m oisture w arping by allow ing d rying to take place from the bottom of the slab as w ellas the top. C on versely po uring on a w et sub grade or on po lythene sheet m ay aggravate w arping. B ecause m oisture w arping causes upw ard cu rling at a free slab ed ge,the effect of w arping is apparen t at every m ovem en t joint –see figu e 1.1. FIG URE 1. 1
Moisture warping of sla bs
LEVEL
•Fo rklift operator perform an ce (unable to carry out the job satisfactorily) •Po ten tial spillage o f tran spo rted go ods •Sm all solid w heeldam age an d con sequ ential m aintenan ce
CURLING
Ideally,pavem en ts should b e joint free except w here they abut other structures.H ow ever,in practice, concrete pavem ents need to b e jointed for a num ber of reasons, including con struction con siderations,m inim ising the risk of unplan ned shrinkage cracking, an d to avoid con flict w ith other structures an d/or pen etrations.It is desirable to m inim ise the n um ber of joints,as these not only affect the even ness of the pavem en t in m ost instan ces bu t they also ten d to b e the area m ost vulnerable to w ear and requiring repairs.
CRACKING
To understan d the u se an d positioning of joints it is im portan t to u nderstan d the basic factors that cause concrete m ovem ents. M ovem en ts in con crete w hich can result in cracking if not con trolled can be categorised as follow s: • Early movements prior to final set: P lastic cracking cau sed through the con crete drying too rap idly. Plastic cracks are discon tinuous and ran dom in nature,but can lead to co ntinuous shrinkage cracks at a later age. P lastic crack ing is con trolled by protection of the slab surface from rap id drying an d/or the u se of fibres 4 in the concrete (R efer to Gui de to Concrete Constr uction ). • Movemen ts commen cing 14 hours after casting: D ifferential tem perature or differential m oisture conten t throu gh the thickn ess of a slab can cause the slab to w arp (or curl). H eat of hyd ration effects,w hich can be significan t w ith slabs over say 200m m thick, w ill result in a positive tem perature gradien t from the expo sed surface of a slab to the underside causing the slab to b ow up w ards at the ends. A sim ilar effect w ill occur as the top surface of a slab starts to dry out after curing h as ceased. Th e heating o f pavem en t surfaces from the sun w ill cause the
• Long term drying movements due to concrete shrinkage: A s the excess w ater w hich is used in con crete to give the m ix ad equate w orkability evaporates ou t of the concrete, the concrete shrinks. To this extent,the greater the am ount of w ater in the initial m ix,the g reater w ill be the drying shrinkage. The design er can influen ce this by specifying structural concrete m ixes using appropriate com paction m ethod s for low slum p con crete (e.g. vibrating screed ). By com parison ,a pu m ped con crete m ix w ith a h igh er slum p and sand con tent could exhibit 50% high er ultim ate shrinkage. Vacuum dew atering reduces lon g-term drying shrinkag e further by rew orking an d com pacting of the slab after this excess w ater has been rem oved.
C oarse aggregate has a significan t role in restraining con crete shrinkag e. M axim ising the coarse agg regate size allow s a low er san d con ten t for a given w orkability w hich low ers the w ater dem and. L ow shrinkage con crete types are available in m ost areas utilising h igh coarse aggregate volum es and n atural sands. W here joint op enings need to be kep t to a m inim um ,to redu ce w ear from w heeled
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DESIGN
traffic for instan ce,concrete for such slabs should be specified w ith a m axim um 56-day d rying shrinkage lim it of below 750µm (A S 1012.13)5. Theoretically,shrinkage w ould not be a problem if there w as n o restraint existing to prevent the concrete sh orten ing. In a floor slab w e h ave the restraint of the subbase cau sed by friction w ith the underside of the slab. If this friction w as uniform an d lim itless,shrinkag e w ould not be a problem either,as the stresses resulting w ould be tran sferred straigh t into the grou nd an d not taken by the con crete. H ow ever,neither of these extrem es is the real w orld. Th e concrete w ill crack if the stress resulting from the restraint to shrinkage exceeds the ten sile stren gth of the con crete. Typically,con crete shrinkag e is accom m od ated by allow ing the slab to m ove freely at predeterm ined m ovem ent joints,w ith allow ance betw een the joints typ ically using reinforcing steelto avoid uncontrolled cracking from stress buildup due to a frictional restraint. A lternatively,jointless solutions rely on relatively h igh levels of reinforcem en t to en sure that cracks resulting from shrinkage restraint are very n arrow an d at close centres (1 to 2m ). A typicalcon crete shrinkage of say 7m m in 10m length could be reduced to around 4.5m m due to the restraint of the reinforcing. For a 100 –150m m thick slab d rying ou tdoo rs,50% of this could be expected to take p lace in the first four m on ths drying and 90% after tw elve m on ths. A w et w inter,how ever,w ill slow the rate of drying an d hen ce the initial shrinkage rate significan tly. Floors indoors are likely to shrink at a faster rate, particularly if the en vironm en t is air conditioned . C uring of concrete w ill not effect the sh rinkage p oten tial to an y extent,how ever it w illoptim ise concrete stren gth gain to resist cracking from shrinkage restraint. There are a n um ber of design op tion s w hich cater for con crete m ovem en t. The app rop riate option w ill con sider the clien t’ s brief in conjunction w ith both construction costs and m aintenance costs. A con crete floor slab has to be sub divided into sm all areas for tw o reason s: 1. To con trolten sile stresses due prim arily to m oisture chan ge an d therm al con traction of the slab, an d thus to lim it ran dom cracking. 2. Fo r con ven ien ce during construction . Th e size of the area m ay be governed by practical con siderations arising from the m ethod of con struction an d resou rces available. There are a num ber of alternative solutions available for floor layo ut an d control of slab m ovem en t. The ‘ success’ is often judged b y design er preference an d clien t expectations. A s m ovem ent joint m aintenance can b e sign ificant for con ditions of heavy-w heeled traffic,the spacing of m ovem en t joints can be increased w ith an increased risk of cracking betw een the joints,w hich is acceptable if the
10
reinforcem en t is detailed to en sure the crack w idths are lim ited. O n the other hand,m ovem ent joints w here hard urethan e w heeled traffic is used should be restricted in w idth to avoid edge dam age under trafficking b y lim iting the joint spacing. Flatness specifications for such floors also dictate closer joint spacing to red uce the effects of curling. The type o f joint,the layout of joints,the sealan t required,an d the am ount of reinforcem en t in the pan els (w hen used) are inter-related .Fo r exam ple, increasing the am ou nt of reinforcem en t w ill perm it w ider spacing o f free m ovem en t joints but w illm ean that the joints w ill exp erience w ider m ovem ent.These factors are d iscussed separately below an d the d esign er is encouraged to read them all to get a clear un derstan ding o f the prob lem . L oad tran sfer m ech an ism s are available to tran sfer load s across a joint to ad jacent pavem en t pan els,resulting in low er flexural stresses in the p an el than those occurring at free ed ges w ith no effective load tran sfer.They also serve to prevent differential vertical m ovem en ts of adjacen t pan els and so avoid stepping. L oad tran sfer in con traction joints m ay b e p rovided by: aggregate interlock across the rou gh crack faces; keyed joints;dow els;or a com bination of these. If the o pen ing is greater than 1m m ,as m ay be expected w hen the pan els len gths exceed about 5m ,load tran sfer by aggregate interlock or keyw ays cann ot be relied upon an d an effective loadtran sfer device for these situations installed .The A C 6I recom m ends that keyw ays not be u sed for slab thickness less than 150m m .It also sugg ests that for dow els to b e fully effective the slab thickn ess should b e at least 125m m .
2.1.2 Joint Joint type typess There are tw o prim ary types of joint used:free m ovement joi n ts and tied joints
2.1.2.1 Free movement joints ISOLATION JOIN TS: These joints perm it horizontal an d verticalm ovem en t betw een abutting elem en ts,allow ing the elem ents to beh ave independen tly o f each other.Th ey shou ld be p rovided betw een a pavem ent panel and fixed parts of the building (such as colum ns,w alls,m ach inery bases,pits,etc).Isolation joints should also be p rovided at the junction w hen an exten sion is being m ade to an existing pavem en t,an d at junction s betw een internal an d external pavem en ts,to p reven t the develop m en t of stresses that m ay result from differential m ovem en ts.H ow ever,provision for load tran sfer m ay w ell be requ ired w here such exten sion s occur and the d esign er needs to address the d etailnecessary to ach ieve this.
Isolation joints are generally form ed by casting against a com pressible,preform ed filler m aterial (eg self-exp an ding cork) over the full dep th of the joint to provide a com plete sep aration.Typ ical details of this typ e o f joint are p rovided in Figu re 1.2.
DESIGN
m aintained b y dow els or other devices such as sleep er beam s.O therw ise the slab thickness should be design ed as a free ed ge.See Par t 2.
FIGURE 1. 2
FREE-IS OLATION JOINT Sealant Filler
D
Abutting pavement or other structure
EXPANSION JOINT Dowel bar size: see Table 1.2 20mm wi de joint sealer
Half bar coated with bondbreaking compo und or use sleeve
0.5D D
C ontraction joints are u sually constructed either by form ing a groove in the top of the freshly-placed con crete (Form ed Joint) or by saw ing o ne in the pan el after the con crete h as harden ed bu t before uncon trolled cracking occurs (Saw n Joint). • Sawn jointsare con structed after the concrete h as harden ed sufficien tly that it w illnot be d am aged by the saw ing, bu t before shrinkag e cracking can occur.The approp riate tim e for saw ing varies w ith the m any con dition s,eg con crete stren gth an d am bien t tem perature,that influen ce the h arden ing of con crete.The initial saw cut should be 3 to 5m m in w idth.If required ,for the installation of a joint sealer,the joint can be w iden ed later.See Figure 1.3. FIGURE 1.3
20mm wide compressible filler board
100mm
20mm
FREE CONTRACTION JOINTS (INDUCED)
Dowel cap, end filled with compressible m aterial
EXPANSIO N JOINTS: Expan sion joints are u sed in pavem ents to provide for therm al and m oisture-induced m ovem ent of the slab.H ow ever,these joints m ay also be required in areas or room s subject to large tem perature fluctuations.D esigners should satisfy them selves that there is a definite need for expan sion joints,thereby m inim ising their unnecessary installation an d the relatively w ide gap required b etw een pan els.In m any instan ces expan sion joints w ill not be requ ired becau se the d rying shrinkage is the d om inant linear m ovem ent.These joints w ithin pavem en ts req uire the provision of load tran sfer,usually by the provision of dow els fitted w ith a cap to accom m od ate the m oving d ow el as the joint op en s and closes.See Figu re 1.2. CO NTRACTION JOIN TS: C ontraction joints con trol the ran dom drying shrinkag e cracking of con crete by inducing the slab to crack at the contraction joints.They allow horizontal m ovem en t of the slab at righ t an gles to the joint an d act to relieve stresses w hich m igh t otherw ise cause ran dom cracking. In order to en sure that shrinkag e cracking occurs at a contraction joint,a p lan e o f w eakness m ust be created by form ing (using crack-inducing tapes or form ers) or cutting a groove to a d ep th of at least one-quarter of the slab thickness.See Fig 1.6.
H ow ever,if the cut can be form ed early en ou gh ,by a suitable grooving tool or early-age saw cutting, som e reduction in the groo ve dep th m ay be w arranted. The spacing o f contraction joints in jointed unreinforced pavem en ts shou ld b e selected to suit the geom etry of the pavem ent being constructed,bu t should be such that the joint m ovem ent do es not m ean that load transfer by ag gregate interlock is lost.If it is,load tran sfer h as to be
0.25D
Sealant reservoir and sealant with bond- breaking backing tape
D
Induced crack
UNDOWELLED JOINT – jointed un reinforced pavements
Bond-breaking compound or sl eeve
0.5D D Dowel (length, L)
0.5L
0.5L + 25 DOWELLED JOINT – jointed u nreinforced pavements 75
75
0.5D D Dowel (length, L)
Bond-breaking compound
0.5L 0.5L + 25 DOWELLED JOINT – jointed reinforced pavements
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DESIGN
• FORMED JOIN TScan be constructed by form ing a groove using a T-section an d inserting preform ed filler (eg fibreboard or self-exp an ding cork).This can be installed using vibratory equipm en t after the finishing operations are com pleted ,but w hile the con crete rem ains plastic. A lternative m ethod s such as preform ed inserts can also be u sed.If req uired ,a sealer can be installed in form ed contraction joints by rem oving the filler m aterial after the pavem ent has been com pleted.In reinforced p avem ents, the reinforcem en t m ust not interfere w ith the form ed joint.This m ay necessitate the reinforcem en t being term inated sh ort of the joint.See F igure 1.4.
R ecom m end ed d ow eldim ension s are given in Table 1.2. TAB LE 1.2
Recommended dimensions (Grade 300 Bars) for dowels placed a t 300mm centres Slab thickness (mm)
Dowel diameter (mm)
Dowel length (mm)
150 to 190
20
400
200 to 240
25
450
2.1.2.2 2.1.2. 2 Tied Joints FIG URE 1. 4
Tied joints are used in tw o w ays:
FREE CONTRACTION JOINTS (FORMED) Formed or sawn joint with sealant and bo nd-breaking tape
Bond-breaking compound or sleeve
•to restrict the m ovem en ts at the joint in unreinforced pavem ents;and •to provide relief for w arpim g stresses in reinforced pavem ents. Typical details of tied construction joints are show n in Fig 1.5.
0.5D FIGURE 1.5
D Dowel (length, L)
25mm
DOWELLED JOINT Formed joint with sealant and bond- breaking tape
TIED CONSTRUCTION JOINTS
0.5L 0.5L + 25
75
0.5D D
75
Deformed tie bar (length, L)
0.5D
TIED JOINT (NOT USED AT A CONTRACTION JOINT LOCATION) reinforced and unreinforced pavements
D Dowel (length, L) DOWELLED JOINT 25mm (suitable for use at a contraction joint location) reinforced and un reinforced pavements:
Bond-breaking compound
0.5L
NOTE: In reinforced pavements, the reinforcement may be carried through the joint
D 5-10mm wide sawn or moulded groove sealed as required
BUTT JOINT D
2m m
0.3D
0.5D
R
0.3D D/6 but ≥ 20mm
W hen do w els are used,they should not prevent the joint from op en ing or closing, otherw ise an uncon trolled crack m ay o ccur in the vicinity of the joint.Fo r exam ple,dow els crop ped at bo th ends should n ot be u sed as the end d eform ation m ay interfere w ith the open ing o r closing o f the joint.D ow els shou ld be coated w ith a suitable bon d-breaker or sleeve on on e side o f the joint an d sho uld be align ed parallel to the longitudinal direction of the p an el an d to the surface of the slab to w ithin close tolerances.
12
0.4D 1 0.2D
D FREE KEYED JOINT
4
Deformed tie bar (length, L) TIED KEYED JOINT
0.4D
0.1D
0.5L
K eyed longitudinal joints should b e held together w ith deform ed tie-bars.H ow ever,such tie-bars shou ld not be used in panels w ith a total w idth of m ore than 10m un less dow elled longitudinal con traction joints are also provided at a spacing n ot exceeding 10m .
DESIGN
The tie bar spacing relates to the overalldesign of the slab betw een free joints.Typical bars and centres u sed are D 12 at 300m m for slabs up to 150m m thick,or D 16 at 350m m for slabs over 150m m .M ore details are provided in Section 3.3. The o ther joint often used to deal w ith w arping is the induced con traction joint form ed by saw ing the concrete after harden ing to cau se a w eak ness.This joint has reinforcem en t passing through it an d is show n in figu re 1.6.
subgrade n ot subject to vo lum e chan ges,or over a bo und sub base o r stabilised sub grade.If the p avem en t is thicker or m ore heavily-load ed ,longitudinal con struction joints should be p rovided w ith som e form of load-tran sfer device such as dow els.Typ ical details of this typ e o f joint are p rovided in Figure 1.4 A keyed joint w ill not function properly as a load transfer device if the joint op ens up m ore than 1m m .
2.1.3 Joint layout FIG URE 1. 6
The joint layo ut w ill gen erally be controlled by tw o factors, con struction m ethod an d pavem en t type.It w ill also n eed to take into account the d esirability o f uniform paving runs, continuity of joints,construction crew size, an d the constraining effects of colum ns,rack system s and any m achinery on,or pen etrations throu gh ,the pavem en t.
TIED INDUCED JOINT (The mes h must be s et b elow the D/4)
5-10mm wide sawn or moulded groove sealed Mesh
CONSTRUCTION METHOD: The slab w idth w ill be influen ced by the m ethod of pavem en t con struction,taking into account the constraints im po sed by equipm ent dim ension s,m axim um placing rates,etc.
≥D/ 4
D Induced crack
There are tw o p referred m ethod s of placing concrete for pavem en ts (see Figu re 1.7):
2.1.2.3 Construction Joints: L on gitudinal con struction joints are u sed to form the edges of each p ou r and to separate areas of con crete p laced at differen t tim es.Transverse co nstruction joints are required at plan ned locations,such as at the end of each day’ s placing, an d at the location of unplan ned interruption s such as m ay be caused by adverse w eather con dition s or equ ipm ent breakd ow ns.C on struction joints can be either free m ovem en t or tied joints. For longitudinal construction joints,sim ple tied butt joints betw een ad jacent pan el strips w ill often be satisfactory provided the p avem en t is ligh tly-loaded,not m ore than 150m m thick,an d con structed over a firm ,unyielding
• Long-strip:The m ethod of placing in lon g con tinuo us strips betw een form s m axim ises placing efficien cy an d provides tighter surface tolerance. • Continuous-pour:Thi s m ethod requ ires the use oftem po rary form s or w et screed s to achieve surface levelcontrol. Th e chequ erbo ard m ethod of casting alternate squ are or rectan gu lar pan els w as a p opular form of con struction for m any years,bu t is no lon ger recom m ended. G enerally,the long-strip m etho d is used,as it sim plifies construction an d allow s tigh ter con trol of pavem en t surface tolerance.L ong strips of con crete h ave o nly tw o sides w hich h ave to be m atched in level,w hereas squ are o r rectan gu lar pan els con structed indepen den tly in ch equerbo ard fashion have levels on all fou r sides to be m atched.The con tinuou s-pou r
FIGURE 1.7
Pavement construction methods NOTE: Joint details and reinforcement have been om itted for clarity
Direction of placing
Direction of placing
LONG-STRIP METHOD (preferred)
CONTINUOUS-POUR M ETHOD
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DESIGN
m ethod is the m ost efficien t in placing con crete over large areas,but accurate level con trol is difficult to ach ieve, an d this m ethod is not recom m end ed w hen tigh t surface toleran ces have to be m et. In the long-strip m etho d,the w idth of the strip (typ ically 4.5m ) is gen erally go verned by practical con siderations,an d con struction equipm en t.Pan el w idths larger than 4.5m require special vibrating equ ipm en t an d low er slum p con crete w hich m ake the con struction op eration s m ore difficult.It is reco m m en ded that the strips are parallel-sided an d that careful con struction plan ning is carried out. PAVEMENTTYPE: The joint spacing will be influenced by the
pavement type selected; ie jointed-unreinforced, joint edreinforced or continuously-reinforced pavement – see Figure 1.8. • Jointed un reinforced :In this type ofpavem en t,tran sverse con traction joints are closely spaced ,in the range of25 to 30 tim es the slab thickn ess.The close spacing controls cracking by relieving shrinkage and therm alstresses,so that steel reinforcem ent is not required. Long,narrow ,unreinforced con crete panels tend to crack into sm aller pan els of approxim ately squ are d im ension s. Therefore,the len gth:w idth ratio should not exceed 1.3:1. • Jointed r einforced:In this type of pavem ent there are tw o op tion s: (i) Tied joints at approxim ately 8 to 10m are provided betw een panels to form a connected strip o fup to 32 to 40m in len gth betw een free joints. The reinforcem en t required is based on the totallen gth betw een free joints,i.e.32 to 40m . A llshrinkage m ovem ent is transferred to the free joint positions w ith only w arping hairline cracks at the 8 to 10m joints. (ii) Free joints at approxim ately 8 to 10m are provided betw een panels usually requiring the use of a dow elled form of joint. The reinforcem en t required is based on the len gth of individualpanels,i.e.8 to 10m . The shrinkage m ovem ent of the slab takes place at each joint. In com parison ,type (i) uses h igh er levels of slab reinforcem ent and concentrates the shrinkage m ovem ents prim arily to tw o positions at the free joints. Th e tied joints require m inim um m aintenance. Type (ii) uses substan tially less steel in the overallslab area and avo ids significant shrinkage m ovem ent at tw o p osition s by distributing the m ovem ent. H ow ever,the m ovem ents taking p lace at each joint require the use of dow elled joints since aggregate interlock m ethods w illno t w ork on ce the joints open u p by m ore than 1m m . The choice is,therefore,influen ced by the final use ofthe floor as related to the accep tan ce of differen t joint typ es.The m ajor advan tage of the secon d m ethod is in continuou sly pou red con struction w here the dim ension restriction s of strip construction do n ot apply. H ow ever,greater sop histication ofdow el joints is needed. Th is is discussed further in Part 2 ofthe M anual.
14
FIGURE 1. 8
Joint requirements for various pavement t ypes
W, to suit paving equipment and/or pavement geometry L = 5m maximum
W
Direction of placing
W
Direction of placing
L
L:W = 1.3:1 max. Transverse contraction jo in ts (d ow ell ed or undowelled) Longtudinal construction jo in ts
JOINTED UNREINFORCED W, to suit paving equipment and/or pavement geometry L = 8 to 10m recommended
L
L:W = 1.8:1 max. Dowelled transverse contraction joints Longtudinal construction jo in ts
Dowels
JOINTED REINFORCED
Tie induced joints sawn after hardening Direction of placing
JOINTED REINFORCED
• Continuou sly reinforced:In this type of pavem en t,no con traction joints are provided .A m uch high er reinforcem en t con ten t is used (in the rang e o f 0.6 to 0.9% ) to lim it the w idth of any fine cracks w hich are design ed to o ccur at spacing o f arou nd 1 to 2m .See Part 2.
DESIGN
OTHER C ON SIDERATIONS:W ith the joint spacing determ ined by the ab ove factors,joint layout becom es a m atter of finding the m ost suitable p attern of rectan gu lar or squ are panels to fit the geom etry of the particular pavem en t. A joint layout for a typical jointed unreinforced pavem en t is show n in Figu re 1.9.
W herever po ssible,structures such as drainage p its, access holes,colum ns bases,service p its,m achine footings, etc sho uld be located in the corners or at the ed ges o f pan els,an d separated from the pavem en t by an isolation joint. Irrespective of the pavem en t typ e, it is essen tial that the plan s show joint location s and types,an d reinforcem en t details.Joints m ay be d etailed to have an orthogo nal or skew ed layou t,or the d esign er m ay w ish to chevron the joint layout in traffic aisles to red uce the load across the joint (Figu re 1.10).C onstruction o f pavem en ts w ithout properly estab lished joint locations an d details is likely to result in uncon trolled cracking o f the concrete. Fo r the reinforced strip m ethod the bay sizes in Figu re 1.9 w ou ld typically be L /W = 1.8 m ax,i.e.8m x 4.5m . Fo r the open screed ing the induced tie joints w ou ld create bay sizes 8m x 8m as a m axim um .
2.1.4 Joint se a lants
FIGURE 1.9
Joint layo ut for a typical jointed unreinforced internal pavement
Column
External wall
5m typical
Direction
4m typical
of placing
Joint spacing to suit paving equipment and pavement geometry
Isolation jo in t ar ou nd columns Isolation joint around services and blockouts
Longitudinal construction joints
Isolation jo in t ar ou nd perimeter
Edge strips reinforced if L:W > 1.3 :1
Transverse contraction j oints
FIGURE 1.10
The m ovem ents w hich occur at contraction joints in a properly d esign ed con crete p avem en t are gen erally very sm all,m aking n arrow joints (w hich are m ore durable under the p assage of w heel load s) adequ ate. For m ost indu strial pavem ents,sealing is recom m en ded to p reven t dirt or other incom pressible m aterials from en tering the joints.In w et con ditions,w here there are special hygien e or dust-con trol requirem en ts,or w here sm allsolid-w heeled vehicles are used,joint sealing is essen tial.In som e instan ces, an d especially after m ost of the shrinkag e effects have o ccurred in the con crete p avem en t, som e d esigners prefer to specify solid sealan ts for internal pavem ents. There are several catego ries o f joint sealan ts: • Field-moulded sealants w hich are po ured or gun ned into the joint; • Factory-moulded sealants w hich are preform ed an d inserted,gen erally in a com pressed condition,into either the plastic con crete (eg self-expan ding cork) or a recess saw n in the h ardened con crete (eg cellular neoprene);and • Epoxy-filled joint system s Strictly speaking these are not sealan ts.These sho uld bon d to o nly one side of the joint.The joint m ay req uire refilling if filled im m ed iately after con struction of the p avem en t,as n oted previously,as shrinkag e takes place an d the joint open s. Field-m ou lded sealants range from the cheaper m astics and rub ber bitum inou s to the m ore expen sive an d du rable polysulphide,silicon ,urethan e an d epoxy-based m aterials. The u se of a ‘ gu n grade’ m aterial w ill be fou nd m ore con ven -
The designer should gi ve careful attention to t he joint l ayout
ien t for use in narrow grooves.A backing rod is used in the joint to en sure that the size o f the sealan t (ie w idth versus dep th) m eets the m anufacturer’ s recom m endation s. It is im portan t that the sealan t typ e b e selected specifically for the exp ected service conditions of the p avem en t, that it be ap propriate to the typ e of load ing and en vironm en tal factors w ith special atten tion being p aid to chem icalresistan ce requirem en ts.The m an ufacturer’ s recom m en dations regarding selection an d ap plication should be carefully follow ed. Sealan ts ten d to failat the interface w ith the concrete. R egular inspection and m aintenance of joint sealants is essentialto m axim ise the perform an ce ofthe joint.
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DESIGN
2.1.5 Joint Protection
2. 2 CONCRETE PROP ERTIES
A C I 302 1 R recom m en ds that joints in industrial floo rs subject to sm all hard-w heeled traffic be filled w ith a m aterial such as epoxy that gives ad equate support to the top surface of the joint an d has sufficien t resistan ce to w ear. Th ese joint m aterials sho uld have a m inim um Sh ore hardn ess of 50 an d elon gation of 6% .
2.2.1 General
Note: These joint nosings should be applied w here o nly m inim al further (shrinkage) m ovem en t is expected.3 to 6 m on ths after the slab placem en t w ou ld be ideal.In practical term s ho w ever this is not usually p ossible d ue to the n eed to m eet construction program m es.
To keep joint gap s to a m inim um at least tw o factors sho uld be con trolled: •the slab m ix in w hich the w ater con ten t is kept to a m inim um con sisten t w ith placing w orkability; an d •the spacing of con traction joints w hich sho uld be cho sen to red uce the im pact of the estim ated ‘ in tim e’ shrinkage m ovem ent. Joints m ay also b e p rotected by steelflats or an gle iron. This provides go od protection althou gh at a h igh er cost. Field m oulded or preform ed elastic joint sealan ts should be u sed only w here they w ill not be subject to the traffic of sm allhard w heels.C are sho uld b e taken to en sure that the seal is a tight interference fit,otherw ise subsequen t open ing of the joint w ill allow the sealan t to escap e.
The m ajor du rability consideration for an industrial pavem en t is abrasion resistan ce.H ow ever,depen ding on the environ m en t of the pavem en t,corrosion of reinforcem en t, freeze thaw ,and chem icalattack m ay also n eed to be con sidered.A ll of these ten d to be con trolled by specifying concrete of an ap propriate ch aracteristic stren gth,f’ c. U sually the f’ red for du rability w ill be h igher than crequi that required for structural purposes and w ould therefore govern the d esign . The gen eral properties of concrete in its plastic an d hardened state are w ell do cum ented in Gui de to Concrete 4 Construction . The m ix characteristic having the greatestinfluen ce on the drying shrinkage ofcon crete is the w ater content.Shrinkage of a cem en t paste,typically over 2,000 m icrostrains takes place as the evap orable w ater is rem oved on drying.In concrete, how ever,the coarse aggregate plays an im portan t role in restraining shrinkage to less than a third ofthe equivalen t paste value.C oncrete shrinkage w illtherefore be reduced if the coarse aggregate quan tity and size is m axim ised.The stiffness of the aggregate w illalso influen ce the restraint that can be provided. Therefore in develop ing a concrete m ix d esign prim arily targeting a low shrinkage,the follow ing factors sho uld be con sidered: Low water dem and , through:
•U se of air entraining, w ater reducing adm ixtures or sup erplasticisers to reduce w ater dem an d for a given w orkab ility. •L ow est w orkability con sisten t w ith p lacem en t an d com paction techniqu es being used.A vibrating screed ,for instan ce,can utilise a low er slum p con crete.A pum p m ix w illgenerally h ave a h igh er sand con ten t resulting in a higher w ater dem and . •L argestm axim um aggregate size w hich redu ces both cem ent paste volum e and w ater dem and .l9m m is the m axim um aggregate size routinely available.L arger sizes m ay b e availab le for special contracts. •U se of natural rou nded river run agg regates and san ds if available. Maximum restraint by coarse aggregate,throu gh :
•M axim ising coarse aggregate volum e throu gh specially design ed m ixes requiring m ore com pactive effort by utilising vibrating screeds for instan ce.Vacuum dew atering w illalso allow the use of m ore coarsely graded m ixes. •U se ofaggregates w ith high m odulus of elasticity.G en erally there is not a ch oice ofaggregate type available. There are region al variation s in the m inim um con crete shrinkage values w hich can practically be targeted ,an d
16
DESIGN
these are prim arily influen ced b y local w ater dem an d an d aggregate stiffness.Som e of the ab ove factors are in conflict w ith other design criteria such as the targeting of m axim um com pressive or ten sile stren gth for exam ple. In generalfor a given w orkability shrinkage is not sign ifican tly effected by an increase of cem en t conten t. C uring of con crete d oes n ot have a sign ifican t effect on shrinkag e,how ever it does op tim ise hydration an d early developm en t of ten sile stren gth w illlessen the risk o f cracking before a bo nd can develop w ith any reinforcem ent. Shrinkag e of a slab w ill not com m en ce un til w et curing ceases an d the slab starts to dry o ut.
TABLE 1. 5
Minimum charact eristic concrete s trength (f’ c ), for abrasion resista nce, curing period a nd cover required for corrosion protection Minimum Minimum characteristic strength, f’ c (MPa)
Curing period* (days)
Cover (mm)
A2
25
3
35
B1
30
7
35
Exposure classification
* Initial continuous curing under ambient conditions. Other combinations of concrete q uality and cover are included in S ect ion 5, NZS 3101.
2.2.2 Abras Abras ion res ista resis ta nce A brasion (w ear) resistan ce is ach ieved by con trolling a w hole series o f factors.It is not sufficien t to specify just an appropriate concrete strength.Th is m ust be com plem ented by proper construction practices,eg p lacing com paction, finishing and curing.W here very high abrasion resistan ce is required,special agg regates or dry shake m ay be need ed, either add ed to the surface or as a top ping. The relative effect of the various factors on ab rasion resistan ce is discussed in A ppen dix E. N ZS 31017set s out requ irem ents for the m inim um f’ c dep end ing on m em ber and type o f traffic.Th ese are sum m arised in Table 1.4. It m ust be em phasised that these are m inim um streng ths and serve as a guide on ly. TABLE 1. 4
2.2.4 Freeze-tha w resista nce U sually,internal industrial pavem en ts w ill not be subject to freeze-thaw condition s,thou gh som e pavem ents for coo l room s or in very cold clim atic con ditions,w illbe.W here this is the case, the requ irem en ts for air en trainm en t an d f’ c given in N Z S 3101 and setou t in Table 1.6 sho uld be follow ed .N ote that for freezing cham bers,not only is it im portan t that the freeze-thaw resistan ce of the concrete be con sidered but the design er also take into accou nt the im plication of freezing tem peratures below the slab an d on ad joining structures1. TABLE 1. 6
Freeze-tha w resistance
Minimum concrete strength for abrasion resistance
Member an andd type of tra traffic ffic
Minimum chara cha racteristic cteristic strength, f’ c (MPa)
Floors in commercial a reas s ubject only to ped estria n a nd /or light trolley tra ffic
25
Floors s ubject only to light pneuma tic-tyred tra ffic (vehicles <3t gross) Floors in warehouses and factories subject to medium or heavy: • p neuma tic-tyred tra ffic (>3t gross) • non-pneuma tic-tyred tra ffic • steel-wheeled traffic
25
30 40 ≥40 (to be assessed)
2.2.3 Corros ion resis resista Corrosion ta nce M inim um requ irem ents for prevention of corrosion of reinforcem en t are set ou t in N Z S 3101,Section 5.A ssum ing the p avem en t is in an internal environm en t,not protected by a dam p-proof m em brane an d n ot in contact w ith an aggressive soil,then the exposure classification w ill be either A 2 or B1 dep end ing on w hether or not the p avem ent w illbe sub ject to rep eated w etting or drying. O n this basis,the requirem en ts for f’ c,an d curing p eriod an d cover are set ou t in Tab le 1.5.
Min. characteristic strength, f’ c
Entrained air for nominal aaggregate ggregate size (mm)
Exposure con condition dition
(MPa)
10–20
40
25 - 49 cycles per a nnum
20
8–4%
6–3%
≥ 50 cycles per a nnum
30
8–4%
6–3%
Refer to part 2, NZS 3101 for more detailed information.
2.2.5 Resista nce to chemical a tta ck ttack For m ost industrial operations,the specification of an ap propriate con crete stren gth (f’ c),the utilisation of prop er con struction techniques and atten tion to com paction an d curing w ill provide a pavem en t surface that has an adequate resistan ce to attack by alkalis,an d reason ab le resistan ce to attack by m ineralan d veg etable oils (although oils do cause som e staining).
C hem icalattack of con crete is no t covered by N Z S 3101 an d N Z S 3102.The effect of variou s chem icals on con crete an d protective b arrier system s are d iscussed in A ppen dix C .
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DESIGN
w areh ou ses use forklift trucks an d require a sm oo th surface for ease of clean ing, som e p ow er-floated surfaces com bined w ith curing com po un ds m ay m ake the surface too slipp ery for areas also u sed by ped estrian s (eg load ing d ocks).
2. 3 S URFACE FINIS HES
2.3.1 General The selection of an ap propriate finish is an essen tial part of pavem en t design w hich can m aterially affect bo th the perform an ce an d overall cost-effectiven ess.The type o f finish should be d eterm ined in relation to the anticipated service conditions,w ith particular referen ce to the typ e and freq uen cy of load ing,im pact,ab rasion,chem ical resistan ce, an d in som e circum stan ces,other factors such as hyg ien e, dust prevention,skid resistan ce an d aesthetics.W hen the pavem ent is exposed to som e form s of aggressive agen ts, special surface treatm en ts or coatings m ay be required . N Z S 3114, Specification for C oncrete Surface Finishes8, as w ell as Inform ation Bulletin 339of the C & C A N Z ,provide inform ation relevant to surface finishes. Table 1.7 provides general recom m en dation s on surface finish/finishing tech niques o n the basis of typ ical ap plications,an ticipated traffic and exp osure conditions. Skid resistan ce of pavem en ts is provided by bo th the m icrotexture an d m acrotexture of the surface. M icrotexture is that part of the surface related to the san d conten t in the m ortar,w hile m acrotexture consists of striations or grooves form ed in the plastic con crete.Investigations by the R TA on rubber-tyred traffic10i ndicate that a sand w ith about 40% siliceous conten t provides the pavem en t w ith a suitable skid-resistan t surface. In 1993,a joint A ustralian and N ew Z ealand Standard set out m inim um requirem en ts for the skid resistan ce of pedestrian surfaces in w et an d dry areas (A S 3661.111). These m inim um requ irem en ts are based on specific test proced ures using a p en dulum friction tester.W hilst m any
2.3.2 Single-course versus two-course pa vements A single-cou rse pavem ent is a pavem ent in w hich each pan el is laid in one operation an d then finished to provide a durable su rface. In N ew Z ealan d,this is typically the m ost econ om ical pavem en t typ e an d w illprovide satisfactory p erform an ce if it has been properly constructed from correctly specified high quality con crete,as d iscussed previously,an d is recom m ended in p reference to tw o-course pavem ents.H ow ever,it m ust be em ph asised that w orkm anship of surfaces has to b e of the h igh est quality,w hich m ean s longer w aiting tim e before the co ncrete is ready for finishing. Tw o-course pavem en ts should b e con structed o nly w here really n ecessary,since they com m only suffer from on e or m ore of the follow ing p rob lem s: •lack of bo nd to the slab (in bo nded top pings); •curling of thin toppings; •low er con crete stren gth due to lack of com paction in thin, dry top ping m ixes;and •cracking (especially reflective cracking from the bottom slab). Th e m argin betw een success and failure in tw o-course con struction is a n arrow on e.This approach requires detailed specification an d a h igh stan dard of w orkm an ship to avoid the problem s noted ab ove.
TABLE 1.7
Recommended s urface finishes Typical aa pplicatio pplicat ions ns
Anticipa ted t raffic
Exposure/service ccond onditio itions ns
Finish
Office a nd a dminis tra tion a rea s, la bora tories
Ped es tria n or light trolleys
Pa vements to receive ca rpet, tiles, pa rq uetry, etc
Steel floa t
Pavements with skid-resistant req uirements
Wooden float or Broomed/tyned (light texture)
Smooth pa vements
Steel trowel
Dry pa vements with skidresista nt req uirements
Steel trowel (ca rborundum dus t or silicon ca rbide incorporated into concrete surface)
We t a n d ext ern a l p a ve me nt a rea s
B ro ome d /t yn ed he ss ia n d ra g (light to medium texture)
Light to medium industria l premises, light engineering workshops, s tores , wa rehouses, ga ra ges
Light to hea vy forklift trucks or other industrial vehicles with pneuma tic tyres
Sloping pa vements or ra mps or high-speed-tra ffic a rea s He a vy in du st ria l p re mis es , hea vy engineering works, repa ir work-shops, stores and wa rehouses
18
Broomed/tyned (coa rse texture) or grooved He a vy s o lid -w he ele d ve hic le s or steel-wheeled trolleys
P a ve me nt s su bje ct to s eve re a bra sion
S te el t ro we l/ b urn is he d fin is h (use of specia l a ggrega te monolithic toppings)
DESIGN
2.3.3 Surface finish
2.3.5 Surface treatments a nd coa tings coatings
Pavem en ts are norm ally specified to h ave one of the follow ing finishes:
A large variety of surface treatm en ts an d coatings is available.H ow ever,the com plex subject of their selection an d application is not con sidered in this m an ual.
• Trowelled finish Finishing by po w er or han d trow elling to provide a den se,hard-w earing surface. • Burn ished finish This finish is produced by a final trow elling w hen the concrete is alm ost set using a rotary disc com pactor,an d this results in a very h ard an d glassy surface.This typ e of finish requires a concrete stren gth grade in excess of 30 M Pa. • Wear-resistan t finish The spread ing, com pacting in,an d sub sequen t trow elling of specially prep ared m etallic agg regate into the w et con crete surface can give enhan ced w ear characteristics.Suitab le for trow elled or burnished surfaces.
A s a g en eral gu ide,design ers sho uld establish the n eed for such treatm en ts based on an ticipated in-service con ditions,evaluate all the alternative m aterials,an d select the ones likely to be the m ost cost-effective.The p erform an ce history of specific coatings under particular service condition s often provides the m ost suitable m ean s of assessm en t. FIG 1.9
• Skid-resistan t finish The skid resistan ce of a sm oo th pavem ent can b e increased by trow elling carbo rundu m dust,silicon carbide o r other prop rietary top pings into the plastic surface. U sed w here ligh t broom ing o f the surface is not satisfactory due to a requ irem en t for cleaning. • Hessian-dra g finish A w et hessian cloth is dragged horizontally over the surface im m ed iately after the con crete h as been finished to the final level an d before bleed w ater ap pears.Figu re 1.9. • Broomed or tyned finish The concrete surface is textured by dragging a broom or tyn e over it to provide a non-slip surface Figure 1.10.C oarse textures,suitab le for steep slopes or heavily trafficked areas,are produced by stiff-bristled broom s or tyn ed rakes,w hile m ed ium to fine textures are obtained w ith soft-bristled broom s.
Typical hessian-drag finish FIG1. 10
• Coloured finish W hile colou red con crete can be ob tained by u sing a p igm en t in the m ix,con crete can also be colou red by trow elling a d ry shake con taining p igm en t,cem en t an d fine aggregate into the p lastic surface. • Patterned finish A patterned finish m ay be created by using a sten cil or pressing a m ou ld on to the w et con crete surface.Th ese w ou ld be used in external pavem ents or w here there is a d esire to d em arcate specific areas.
2.3.4 Top pings H igh-stren gth ‘ gran olithic’ toppings have been used for m any years to provide an abrasion -resistan t,hard-w earing surface to con crete pavem ents for a w ide range of com m ercial an d industrial uses.They m ay b e ap plied either m onolithically w ith the slab or as a fully-bonded topping.
Typical hessian-drag and tyned fini sh
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DESIGN
2. 4 S URFACE TOLERANCE N Z S 3114, Specification for C oncrete Surface Finishes, m akes provision for un form ed surfaces w hich are gen erally laid horizontally,an d incorpo rate screeding,floating or trow elling during their prod uction.Such surfaces are described in Section 3 of the specification an d are classified “ U ”finishes.These surfaces rem ain exposed w hen con crete casting is com pleted.The surface results from screed,float or trow el action ,an d texture som etim es provided by addition al m easures such as broo m ing, raking, grinding o r scabbling. Tolerances are defined in term s of abrupt deviations w hich are to b e less than 3m m in all finishes,an d gradu al deviation s w hich are w ithin 5m m over 3m for m ost classes of finish. H ow ever the typicallim it used is 3m m over 3m for a h igh class sm oo th finish. Pavem en t flatness has becom e increasingly im portan t in recent years.Som e w areh ou se operation s involve the m ovem en t of loosely stacked item s on forklift pallets. Spillages during tran sit resulting from pavem en t uneven ness are costly bo th in term s of dam aged good s and loss of productivity.O perator perform an ce can also be influen ced by unacceptable flatness or poor joint detailing,especially w here veh icles have solid,sm all-diam eter w heels.This is now recognised as an occup ation alhealth and safety con cern.
FIGURE 1.13
Floor f latness is critical when t he aisle width is narrow and racks are high
20
In w areh ou ses w ith high -racking b ays (Figu re 1.13), pavem en t flatness is essential as forklifts often have to m ove an d lift to high reach es sim ultan eously to en sure productive outputs. The ch aracteristics of surface flatness are: •slop e an d direction; •m inor ho les and rises; an d •the w aviness of the surface in one direction. The surface flatness also h as to be w ithin verticalposition tolerances to en sure satisfactory equipm en t installation. Shrinkage o f the con crete,curling of pan el ed ges and pavem en t deflection affect the pavem en t levelness.Since shrinkag e and curling w ill vary w ith tim e,the m easurem en t of the surface is generally carried out w ithin 72 hours of placem en t an d after saw cutting. Surface tolerance as specified by the design er w ill depend on con crete p lacem ent,com paction ,and finishing techniqu es. N Z S 3109 C on crete C on struction12refers to N Z S 3114 C on crete Surface Finishes w here abrup t and gradual deviations are specified . W hile it is recogn ised that the 3m straigh ted ge techniqu e h as been used for m any years,an d it is sim ple to u se
FIGURE 1.14
The ARRB TR Walki ng Profi ler
DESIGN
an d inexp en sive, the follow ing deficien cies are n oted13: •D ifficulty in testing large pavem en t areas •D ifficulty of ran dom sam pling pan els •A n inability to reproduce test results •Failure o f the m etho d to pred ict acceptability o f irregularities or surface rou gh ness •Inability of the u nleveled straighted ge to evaluate the ‘ levelness’ of the floor. It has also b een recogn ised that the straigh ted ge technique m ay be inad equate for‘ sup erflat’ pavem en ts an d those pavem en ts that require to b e w ithin the specified design level. In A C I 3026a m ethod of specifying pavem en t flatness an d levelness is detailed an d con sists of tw o Face floorprofile num bers,called F-n um bers. The F-num ber system provides the specifier,con tractor and ow ner w ith a convenient and precise m ethod of com m un ication ,m easurem ent and d eterm ination o f com plian ce of floor surfaces required an d achieved . The firstF-num ber is related to the m axim um allow able floor curvature over 600m m com pu ted on the basis of successive 300-m m elevation differentials14.This lim it is referred to as the flatness F-n um ber (FF) The other Fnum ber is related to the relative conform ity of the p avem en t surface to a h orizon tal plan e as m easured over a 3.05m len gth.This lim it is referred to as the levelness F-n um ber (FL ).G en erally,the tw o F-n um bers are exp ressed as FF/FL . A s a com parison, FF 22.0 is ap proxim ately equivalen t to 3m m o ver 3m .
profiler’ as show n in Figu re 1.14.The d evice w as produced for the road pavem en t industry to m easure the lon gitudinal profile o f both new an d existing roads.The d evice is pushed alon g the pavem ent surface and op erated by a notebook com puter w hich electronically stores the d ata d irectly o nto a spread sheet.Its accuracy is no ted as 0.02m m heigh t per m etre travel an d is therefore suitab le for determ ining the elevation of industrial pavem en ts.Som e calibration of the softw are is required if the d esign er inten ds to use the d evice to calculate the F-nu m bers. Flatness and levelness versus slope,are m easu rable an d can be related to a specific pavem en t functionality.W here forklift trucks are used,the w aviness of the pavem en t can be a critical param eter (Figure 1.15).Forklift truck s u sually travel at less than 25 km /h an d their vertical acceleration is greatest w hen the forklift travels over pavem en t w avelen gths (ie the distan ce betw een tw o adjacent peaks or valleys) from 0.5 to 2.0 tim es the forklift’ s w heelbase. FIGURE 1.15
Som e lim itation s to the m easuring system are suggested in A C I 302.Th e A C I C om m ittee R eport 117-90 (and C om m en tary),Standard Specifi cati ons for Tolerances for Concrete Constr uction and M ateri als ,provides an in-dep th discussion on the F-num ber system . It is im portan t to reco gnise that specifications for floor tolerances need to be m atched w ith the intended use of the floors. A floor specified as FF 100/FL 50 cou ld cost 3 to 4 tim es as m uch to place an d finish as a FF 25/F L 20 floor. The techniqu es for m easuring the surface vary from using an op ticallevel or a m ore refined m ethod using a floo r profilograph .A R R B Transpo rt R esearch (A R R B TR ) has developed a h eigh t m easu ring device,called a ‘ w alking
A
0.5 x wheelbase
B
1 x wheelbase
C
1.5 x wheelbase
D
2 x wheelbase
Forkli ft behaviour on p avements with wavelengths equal to 0 .5, 1.0, 1.5 and 2.0 times the for klift’ s wheelbase (after Ytterberg)
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DESIGN
2. 5 GRADIENTS AND S URFACE DRAINAGE Surface grad ien ts are essen tial for the d rainage o f liquids an d,in particular,storm w ater.Surface drainage is im portan t for external pavem en ts an d in areas w here veh icles traverse from external to internalpavem en ts.It is alw ays m ore econ om icaland less risky to constructa pavem ent w ith grade than to use a topping to create the n ecessary falls to drains. Inad equate provision for drainage presen ts the follow ing prob lem s: •Ponding of w ater on the surface lead ing to excessive spray an d splash gen eration •L oss of friction •Poten tial aquaplan ing o f m oving veh icles •L oss of visibility o f lan e/route m arkings,an d of reflectivity •W ater entering the bu ilding an d the subgrade below the internal pavem en ts. D esign ers shou ld u nderstan d that a few m illim etres of w ater on a con crete pavem ent w ill be seen by a b uilding ow ner as a ‘ pool of w ater’ .The grad e for internal and external runoff w ill dep en d on the surface texture.Internal pavem ents are generally sm oo th to ensure ease of clean ing. H ow ever,w hen these surfaces becom e w et,they m ay becom e slipp ery an d the d esign er needs to b alance grades w ith safety.
22
A quap lan ing is generally the result oflight vehicles losing con trol at high speed s on very w et surfaces w ith som e levelof pon ding.It m ay also result from sm oo th tyres on very sm oo th surfaces at low speeds w ith thin w ater film s on the surface. O ther factors relating to p oten tial aquaplan ing are high tyre pressure,grades and veh icle loading.D iscussions w ith forklift m anufacturers and operators w illprovide som e guidance on w hen a surface is likely to cause aquaplan ing. A t the p erim eter of the b uilding, all areas sh ould be graded aw ay from the building to reduce w ater en tering the subg rade n ear the internal pavem ent and other fou ndation s. Excessive w ater in the sub grade m ay lead to pum ping of undow eled joints and a resulting step ping at the joints. The guidelines in Table 1.8 are given relating to surface drainage: TABLE 1. 8
Recommended Grad ients Minimum slope for isola ted spilla ge and clea ning down of smooth surfaces
1: 80
Preferred slope for isola ted spilla ge a nd cleaning down of smooth surfaces
1:60
Minimum crossfall slope for surface water drainange
1:50
Ma ximum slope for rough surfa ces a nd greater spillage or corrosive use
1: 40
DESIGN
3. DES IG N FOR S TRENGTH 3. 1 OB JECTIVES
3. 2 SUBGRADE S UBG RADE AND AND SSUBBASE UBB AS E
A n indu strial and com m ercial pavem ent m ay be sub jected to variou s types of load ing ranging from dyn am ic w heel load s through post load s to d istributed load ing from stacked m aterial.
3.2.1 Site conditions
The o bjective of thickn ess design is to en sure satisfactory perform an ce of the pavem en t under allthe applied loads,by preven ting the o ccurren ce of: •excessive flexuralstresses,resulting in cracking of the con crete; •excessive bearing stresses on the concrete surface; •excessive punching shear stresses due to concentrated load s; •differen tial deflections at joints;and •excessive d eflections du e to settlem en t of the subgrade. The con trolling design con sideration varies according to the load typ es/con tact areas,as sho w n in Figu re 1.16.Fo r m ost pavem en ts,the governing d esign con sideration w ill be the flexural ten sile stress induced in the concrete by w heel or po st load s.If a slab plate of ad equate size is not provided under the leg or post of a storage rack sub ject to heavy load s,excessive bearing stresses or punching shear m ay occur. Fo r distributed load s exten ding over large areas,such as in stacked storage bays,flexu ral ten sile stresses u nder the load s m ay n ot be as critical as stresses du e to the n egative m om en ts in the aisles betw een stacks.Excessive p ressures due to heavy distribu ted loads m ay cau se faulted joints du e to differen tial settlem en t of the su bgrade, or resu lt in unaccep table total settlem en ts in som e situations. It should be n oted that the data in Figu re 1.16 provides an approxim ate guide on ly.Bou ndaries betw een differen t con trolling design con siderations are n ot exact an d w ill vary depen ding on m any factors,including sub grade stren gth an d the thickn ess and stren gth of the con crete slab.
Site con dition s w hich m ay influence the p avem ent design include: •those resulting from the clim atic con ditions in the region, particularly rainfall an d tem perature; •the slope an d generallevel of the existing g round w ithin an d surrou nding the site; •the grou ndw ater level an d the exten t to w hich it is influen ced by seasonal,flood or tidal conditions;an d •the so il profile, the n ature of the insitu m aterial an d the layer thickness. The first three factors w ill largely d eterm ine d rainage requirem en ts and establish the d esign pavem en t level.This in turn w ill dictate on-site earthw ork requirem en ts,i.e. cut to spoil,cu t to fill,or borrow to fill. FIGURE 1.16
Controlling des ign considerat ions for various load types /conta ct-areas TYPE OF LOAD
Concentrated
Distributed
Posts of storage racks
Special loads
Without base plates
(eg rolls or coils)
With base plates
Storage areas
Vehicle wheels Solid tyres
Pneumatic Special tyres tyres
CONTROLLING DESIGN CONSIDERATIONS
Concrete bearing punching shear
Negative moment (in un loaded area) jo in t f aul ti ng settlement
Flexural stress under load 1 2 4 10 20 40 100 200 400 2 4 (m m x 1 0 )
1 2 (m 2)
4
10 20 40
LOAD CONTACT AREA (for each tyre, post or singl e load)
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DESIGN
3.2.2 Site investigation A n investigation of the soil con ditions on the site sh ould be con ducted to d eterm ine the prop erties of the subgrade an d w hether there are adverse soilcon ditions w hich w illrequire special pavem en t design ,details or con struction procedures. The investigation should also p rovide estim ates of the expected surface m ovem en t (settlem en t or sw ell) an d the allow ab le soil bearing capacity if heavy load s are to be applied to the pavem ent.
3.2.3 Subgrade s trength The calculation of con crete pavem en t thickn ess requires an assessm ent of the subgrade strength.The m easure of sub grade streng th m ost com m on ly used in concrete pavem en t design is the C alifornia B earing R atio (C BR ). Typically,specific engineering d esign m etho ds rely on the develop m en t of an equivalen t uniform soil layer w hose beh aviour rep resen ts that of the actual soil layer. M odels using linear an alysis based on elastic soil beh aviour use equivalen tYoung’ s m odulus (Es) of the soil an d an assessm en t of Poisson ratio ( ν). A lthou gh the em piricaldesign m ethod used in this part of the m an ual does not require such a levelof sop histication, the theory regarding the assessm ent of the above-m entioned key param eters is given to provide d esign ers w ith a useful referen ce in A ppen dix F.
3.2.4 Subgra de uniformity Because of the rigidity of the concrete p avem en ts concentrated load s are distributed over a w ide area. Thus con crete pavem en ts do not necessarily require stron g support.H ow ever they do requ ire the m aterial to b e of a u niform nature that w ill not be altered b y,for exam ple, the ph enom enon of pum ping o r problem s from an expansive soil.These m atters are d iscussed in m ore d etailin A ppen dix F, as are issues of stabilising the su bgrade.
3.2.5 Subbas e materials a nd thickness For con crete pavem en ts,it is seldom necessary or econom ical to b uild up the supporting cap acity of the subgrade w ith a thick subbase.This is because increasing the subbase thickn ess results in only m inor increases in sub grade sup port values,an d h en ce on ly m inor reductions in pavem en t thickn ess for given loading con dition s.
24
N evertheless,a sub base is frequen tly provided under a con crete pavem ent to: •provide a stable ‘ w orking platform ’ on w hich to operate construction equ ipm ent; •facilitate the provision of a u niform bearing surface under the p avem ent; •red uce d eflection at joints,thus en suring effective longterm load tran sfer across joints by aggregate interlock (especially if no other load -tran sfer devices are p rovided ); •assist in the co ntrol of excessive shrinking an d sw elling of expan sive subgrade soils;an d •preven t‘ pum ping’ at joints an d pavem en t edges. U nbo un d granular m aterials for use as a sub base m ay be com posed of san d gravels,crushed rock,crushed slag,or a m ixture of these m aterials.U nder m ost con ditions,a subb ase 100 to 150m m thick w ill be ad equ ate to con trol pum ping, provided that it is a d en se,w ell-graded,stable m aterial con form ing w ith the follow ing: •A m oun t by w eight passing 75-m icron sieve:15% m axim um •P lasticity index:6 m axim um •L iqu id lim it:25 m axim um . The m aterial sho uld be suitably graded to p erm it com paction to a d ensity w hich w illm inim ise any con solidation after the p avem en t is in service. Since the inclusion of an u nbo und granular subb ase provides on ly a m arginal increase in sup port for the p avem ent,no adjustm ent to the sub grade strength value should be assum ed for design pu rpo ses. Bou nd subb ases are generally cem ent-treated rock and gravelor lean m ix.These are d escribed in A ppen dix F. Typicalthicknesses of un bo und subb ases are sho w n in Tab le 1.9. TABLE 1.9
Recommended nominal subba se th ickness Subgrade rating
Typica l CBR (%)
Recommended nominal subba se thickness (mm)
Poor
2 or less
200
Medium
3 to 10
150
Good
10 or more
100
DESIGN
3. 3 S IMPLIFIED THICKNES S DESIG N
3.3.1 Genera l For ligh tly-loaded com m ercial an d industrial pavem en ts, m inim um thickn esses based o n p reviou s satisfactory perform ance m ay be selected from Table 1.10. Thickn ess design of a floo r slab is dep en den t upon the follow ing:
Table 1.11 is based on studies done in the U K and pub lished by the C & C A (U K ) by D eacon in Concrete Ground 15 Floors: their design, constr uction and f in ish . Fu rther w ork IT N w as do ne on the classification of loading by the B C A ( 11 - The Design of Gr ound Support ed Concrete Indu stri al Floor 16 Slabs ). This study h as resulted in gu idelines w hich sim plify the definition of load ing categories. B ased on this inform ation, the follow ing g uidelines are u sed:
•type an d m agn itud e of load ing ap plied TABLE 1. 11
•grade o f con crete used •supportoffered by the sub base an d/or sub grade
Loading Definition
W here floors are su bjected to cyclic load ing,i.e. traffic (fork lift trucks) it is n ecessary to lim it the m axim um ten sile stresses in the concrete. Ideally a value of 50% of the ultim ate flexu ral ten sile stren gth of the concrete should be used. L oad ing p atterns or cycles for floors are not easily predicted an d this m akes estim ating the slab thickn ess difficu lt.
Loading
Class
Limits of loa loadding ing
Lig ht
p a lle t ra c kin g
4 le ve ls (o ne o n f lo o r) o f 0 .75 t on ne unit loa ds, 4.5 tonnes end frame
mezzanine floor design load 3.5 kN/m2 shelving
end fra me of 4.0 tonnes
forklift
ca pa city 2.0 tonnes
Medium pallet racking TABLE 1. 10
mezzanine floor design load 5.0 kN/m2
Guide to slab th ickness
Typical aapplica appplication plication tion
Light (loading class)** Offices, s hops, clas srooms, garages mainly for private ca rs, light industria l premis es Loa ding up to 3.5 kPa forklift ca pa city <2 to nnes Medium (loa ding cla ss)** Garages mainly for commercial vehicles, industrial premises, wa rehouse Loa ding up to 5 kPa Fo rklift ca pa city <3 to nnes
4 levels (one on floor) of 1.0 tonne unit loads 6, tonne end frame
Ra ting of Rating subgrade*
Minimum Minimum thickness of pavement (mm)
Poor Medium to Good
Poor
150 125
175-200
Med ium to Go od 150-175
* Refer to Tab le 1.9 for s ubgrad e ra tings ** Refer to Tab le 1.11 for de finition of eq uivalent load ings
3.3.2 Loading In general,a slab w ill be subject to a com bination of the follow ing types of load ing: a) W heelload s,i.e. forklift trucks,trolleys an d other vehicles. Trucks w ith ratings u p to 2 ton nes have negligible effect on the slabs. b) L eg load s from w areho use racking system s. c) U niform ly d istributed loads placed directly o n the floor slab.
shelving
end fra me of 5.4 tonnes
forklift
ca pa city 3.0 tonnes
The study show ed that for exam ple,a 3 tonne forklift generated com parable stress levels to tho se of a 6-tonne racking en d fram e. Importan t Note: If the d esign criteria fall outside the sco pe of the load ing defined above, a specific en gineering design proced ure m ust be undertaken ,as outlined in Part2. H ow ever,the follow ing referen ces provide u seful inform ation and gu idance:
•C on crete S ociety (U K ) R epo rt N o 34:Concrete In dustr ial Ground Floors –A Gu ide to Their Design & Construction.
17
•C em ent an d C on crete A ssociation of A ustralia T48: In dustr ial Floors and Pavements –Gui deli nes for Design, 18
Constr uction and Specifi cati on.
•The Institution of C ivil Engineers D esign an d P ractice G uides: Concrete Industr ial Ground Floors.19 •Th e A berdeen G roup: D esigning Floor Slabs on Grade.20 • ACI Practiti oner’s Gui de to Slabs on the Ground.21 •M arais,L .R .an d Perrie, B.D :Concrete In dustrial Floors on .P C I,M idran d,South A frica.22 the Ground
Concrete Ground Floors and Pa vements : Pa rt 1
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25
DESIGN
3.3.3 Designing for shrinkage movements A llstan dard concretes shrink d uring their drying o ut phase. Basically this shrinkage starts at the end of the cu ring period an d w ill continue until the m oisture conten t stab ilises w ith the am bient cond ition s,w hich m ay take m any m on ths. C racks observed w ithin o ne to tw o d ays are N O T caused by the lon g-term drying of harden ed concrete. They are cau sed by p rem ature drying of plastic concrete or by ‘ early age’ therm al m ovem en ts. These are p rim arily issues that need con trol during the production and construction phase. W hen shrinkage strain causes stresses to exceed the ten sile stren gth of the co ncrete slab,then the slab w ill crack. In practice this is likely to be a com bination of linear shrinkag e an d w arping effects.W arping is caused by the differen tial shrinkag e w ithin the d ep th of the slab,i.e. the top dries ou t faster than the bottom of slab. W ith the top shorten ing m ore than the bottom ,the slab w ill try to cu rl upw ards,particularly at any edges or joints. The classic design for shrinkage in a con crete ground slab relates to allow ing the shrinkage m ovem en ts to take place and controlling the position s of w here the m ovem ent is allow ed to o ccur. This process is influen ced an d in som e cases totally controlled by the follow ing. a) Groun d friction :If the interface b etw een the concrete slab w ere friction less,then the p hen om en on of the con crete shrinkage w ou ld not cause stress build up. b) Construction features that cause a constraint to movement :Fo r exam ple,slabs tied to foundations internal or external,step s in floor etc. W hile the k ey elem en ts that determ ine the potential am ou nt of shrinkage are the typ e an d quan tities of m aterials used in the con crete m ix,particularly w ater conten t,cem en t con ten t an d aggregate type/con ten t,it is not possible to d esign a con crete m ix that w illavoid d im en sion changes. W hile carefulm ix proportioning an d selection w ill red uce m ovem ents taking place w hich m ay be of advantage in relation to the w idth of active m ovem en t at a joint,it D O ES N O T obviate the need to design for m ovem ent control joints.
Th e leng th o f slab betw een FR EE JO IN TS determ ines the slab reinforcem en t,see Table 1-12 or use the follow ing equation : Steel area/m width = weight of slab/m x
values). Table 1-12 h as used “ µ”1.5. Fu rther inform ation is con tained in A ppen dix D . TABLE 1. 12
Ma ximum Spacing of Free Joints (m) Steel
2
Steel mm Area
200
26
21
17
15
13
664
186
33
27
22
19
17
663
205
37
30
25
21
18
662
260
37
31
27
23
661
290
35
30
26
661/0
330
34
30
H12 dia m a t 250mm
452
41
36
H12 dia m a t 225mm
503
40
For mes h Fy = 485 mPa; for H12 Fy = 430 mPa
FIGURE 1.17
TYPICAL VALUES FOR “ µ” COEFFICIENTOF FRICTION Va lues of t he coe fficient frictio n for a 215-mm-thick slab on different bases a nd subbases 19. More information on t he five selected subba ses (a to e) is in Appendix D.
First movement Average subsequent movement Plastic soil (a) Blended washed sand and gravel (b)
Sand layer (d)
26
175
145
Using reinforcemen t (no construction method determined –assum e continuous p our)
ii)The floor plan m ust be studied an d the p osition of‘ free en ds’ of the slab determ ined . Th is is absolutely essential and the actual construction of w ork on the job M U ST follow this decision.C han ging the p ositions of these joints alters the design concep ts for reinforcing steelan d joint patterns.
Sla b Thicknes s (mm) 100 125 150
665
Granular subbase (c)
Th ickn ess = _____ m m
xµ
2/3 yield stress of steel
µi s the frictional coefficien t (see F igure 1.17 for typical
3.3.3.1 Design process for linear movement
i) T he thickn ess of the slab is determ ined from load ing con siderations by referring to Table 1-10 or by using Part 2 w here special an alysis w ill be required :
1/2 spacing of free joints
Polythene sheeting (e) 0 0.5 1.0 Coefficient of friction, µ
1.5
2.0
Th e recom m ended m axim um length betw een FRE E joints is 32–40m . R einforcem ent = _____m m 2/m (fr om Table 1-12) For practical purpo ses for industrial floors,it is n ot recom m ended that m esh w ith a steel content of less than 145m m 2/m ,i.e.m inim um stand ard m esh w ou ld be 665.
DESIGN
P rovided slabs are 150m m m inim um thickness equ ivalen t,steel bar substitutions are p erm itted ,provided bar spacing d oes no t exceed 400m m .Figure 1-18 diagram m atically sh ow s the stress levels.
1. Get thickness from Table 1.10 2. Is s la b fr e e to m o ve ?
If Y ES:use Table 1.12 an d calculate am ou nt of reinforcem en t; If N O : if fixed one en d,double the steel requirem en t (see Table 1.12) or halve span ; if fixed both ends,use 0.9% reinforcem en t (see Part 2).
FIGURE 1-18
FREE-ENDED SLAB Steel Free Joint
Tied Joint
Tied Joint
Tied Joint
Free Joint
3.3.3.2 Design process for wa rping movement
L = Tie slab l ength between free joints T Maximum tension T =
µ x weight of slab x L
2
W hile there has been significant research on this issue,the decision on w arping is very m uch related to a rule-of-thum b recom m endation w hich is as follow s (see Figu re 1.21): Take the distan ce betw een free joints and divide into u p to fou r bays,provided that this do es N O T:
iii) M odified ‘ Free End’ C onditions a) If,for exam ple,on e en d is tied an d o ne free the am ount of reinforcem en t calculated in (ii) should be d oubled or the span halved.
a) give a len gth lon ger than 10m
R einforcem ent 1 Free En d 1 Fixed = 2 x _____m m 2/m (see Figure 1.19)
1. Determine the spacing of joints for warping:
FIGU RE 1-19
FIXED S LAB ONE END FREE Fixed end
Tied Joint
Tied Joint
Tied Joint
Free Joint
b)create a bay w idth-to-len gth ratio greater than 1.8.
Sp acin g = _____m 2. D r aw o u t th e p a t t e rn o f jo in t s This establishes the position of all the joints required on the slab. A t this stage there are n o m odifications of tie joint positions associated w ith con struction m ethods,e.g. bay w idths to suit fixed screed ing m ethods.
Steel
FIGURE 1.2 1
L = Tie slab length between free joints
DECIDING JOINTPOSITIONS: T
Free Joint Maximum tension T = µ x weight of slab x L
b)If,for exam ple,the slab is tied betw een tw o foundation ed ges. See Figu re 1.20,i.e.no free en d the reinforcem en t requirem en t is ...
t n i o J e e r F
2
s t n i o J d e i T
F r e e
No more than four bays 40m max
J o i n t
N o Free En ds:R einforcem ent = 0.9% m m or see Part 2.
Free Joint FIGURE 1-20
M aximum bay size 10m
FIXED S LAB BOTH ENDS Fixed end
Fixed end
Tied Joints Steel There is no movement, hence full shri nkage stress must be carried by steel. 2 Use 0.9% mm m for steel or specific design Part 2.
SUMMARY: This section has provided the m inim um am ount of slab reinforcem en t interrelated to the d istan ce betw een free joints. It is possible to h ave d ifferent am ounts of steel in differen t directions w here the free joint distan ces are also differen t.
s t n i o J e e r F
W
s ) y d a o b h t r e u m o f p n i r a t s h t n i e r t o p m e c o x e N (
W = M aximum bay size 10m
Concrete Ground Floors and Pa vements : Pa rt 1
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27
DESIGN
FIGURE 1.22
FREE JOINTS: SELECTION CHART There a re two prima ry joint t ypes : • Permitting shrinka ge/contra ction movement • Permitting expansion and s hrinka ge/contra ction movement
FREE JOINTTYPE FJ
TYPI CAL APP LICATION
FJ1a
All of thes e joints will a lso a llow s ome expans ion Sealant Filler
D
FJ1b
Abutting pavement or other structure
Adjoining wa lls, columns e tc where no load transfer is req uired across joint.
20mm wi de joint sealer 20mm compressible filler board
FJ1c
Longitudinal joint Isolation joi nt
Tied control joint
FJ2
0.25D D
Sealant reservoir and sealant with bond-breaking backing tape Induced crack
UNDOWELLED JOINT – jointed unreinforced pavements
28
This joint can b e us ed where limited loa d t ra nsfer is req uired where unreinforced s labs a re used with restricted ba y sizes.
DESIGN
FIGURE 1. 22: S ELECTION CHART(CONT CHART( CONT) FREE JOINTTYPE FJ
TYPI CAL APP LICATION
FJ3
Bond-breaking compound
0.5D D Dowel (length, L)
0.5L
0.5L + 25 DOWELLED JOINT – jointed unreinforced pavements 75
Loa d trans fer is req uired principally for wheel loa ds but a lso sta ck load ing over the joint. The joints as illustra ted a re formed a fter construction. They ca n a lso b e formed up joints. Using do wels for slab s b elow 150mm thickness is not recommended. For dow el size a nd s pa cing s ee Ta ble 1.13
75
50 minimum 0.5D D Dowel (length, L)
Bond-breaking compound
0.5L 0.5L + 25 DOWELLED JOINT – jointed reinforced pavements
FJ4
Dowel bar size: see Table 1.2 20mm wi de joint sealer
Half bar coated with bondbreaking compound or use sleeve
0.5D D
20mm wide compressible filler board
Loa d transfer required with full expansion movement option. Using do wels for slab s b elow 150mm thickness is not recommended. For dow el size a nd s pa cing s ee Ta ble 1.13
100mm 20mm
Dowel cap, end filled with compressible material
FJ5 0.5D D
Plastic sleeve Rectangular shape permitting lateral movement
FJ6
5-10mm wide sawn or moulded groove sealed as required
D
2m m
0.3D
Where the free joint is required t o a ccommodate both wheel loading and sepa ration from a n a djacent bay s hrinking parallel to the o riginal free joint direction, a specia l dowel syste m is required. Using dow els for sla bs b elow 150mm not recommended . For dow el size a nd s pa cing s ee Ta ble 1.13
Tongue a nd groove joint not recommend ed fo r hea vy wheel load transfer but us eful for slabs under 150mm where dowels are not recommended. Limited d ra w on the g roove is need ed. Recommended maximum joint spacing is 5m.
0.3D FREE KEYED JOINT
D/6 but ≥ 20mm
Concrete Ground Floors and Pa vements : Pa rt 1
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29
DESIGN
FIGURE 1.2 3
TIED JOINTS: SELECT SELECTION CHART
The principa l concern relates to the suita bility of construction (i.e. formed o r induced) a nd th e level of load transfer – pa rticularly with wheel loads required. TIED JOINTS (TJ)
TYPI CAL APP LICATION 5-10mm wide sawn or moulded groove sealed
TJ1a
≥D/ 4
Mesh
Induced cra ck by sa wing the concrete. Reinforcement pa ss es through joint.
D Induced crack
TJ1b
50 minimum 0.5D D Deformed tie bar (length, L)
0.5L
Alternat ive d eta il using ba rs. Illustrated as formed deta il but can be created as an induced crack/sa wn method . Steel ba r same a rea as reinforcing mesh. Roughen interface with surface retarder on formwork.
TIED JOINT ( NOT USED AT A CONTRACTION JOINT LOCATION ) reinforced and unreinforced pavements
TJ2
50mm min.
R
0.5D
4
0.4D 1 0.2D
D Deformed tie bar (length, L)
Tongue a nd g roove free joint modified a s a tied joint. Steel ba r size/spa cing to give s ome a rea a s reinforcing mesh.
0.4D
0.1D
0.5L
3.3.3.3 Design proces s for selection of joint joint types FREE END JOINTS OR ISOLATION JOINTS (see Section 2.1.2.1 for more inf ormati on) :A s this nam e im plies there m ust be n o
restraint in linear m ovem en t. C hoose the follow ing from Fig 1.22 Free Joints Selection C hart: a) W here there are lim ited load tran sfers use FJ1 b) W here w heel load transfers use: •FJ6 K eyw ay Joint •FJ3 D ow el Bar w ith sliding free en d c) A s (b) bu t w here ad joining slab is to be castseveral w eeks after the firstslab or w here the slab has significan tly different overallfree joint dim en sions use: •FJ5 D ow el Bar w ith sliding free en d in sleeve providing lateral horizon tal m ovem en t
TIED JOINTS (see Secti on 2.1.2.2 for more infor mati on):
There are a variety of tied joints to prim arily su it the m ethod s of con struction . H ow ever,as the nam e im plies, there is alw ays som e reinforcem en t passing throu gh the joint: a) W here there are no w heelload transfers use TJ1 Figu re 1.23. Th e grooves to a d epth of D /4 m ay be form ed d uring construction or cut gen erally w ithin 24 hours ofcasting. R ecom m end ed for slabs no t thickerthan 150m m . Th e reinforcem ent is w hat w as determ ined in the calculation from Table 1.12. Th e load tran sfer on these joints relies on aggregate interlock. A variation of this joint that can be used w here thicker slabs than 125m m are used or w here fixed form s and a strip m ethod of con struction applies is show n as TJ2 Figure 1.23. The m esh reinforcem ent is stop ped and a tie bar is used. b)W here there are sign ificant w heel load m an oeuvres,it is recom m en ded that a tied keyw ay jointTJ2 is used –see Figu re 1.23.
30
DESIGN
c) A n alternative joint for heavy w heel loads is to u se 1620m m do w els. Th ere are som e risks associated w ith this detail because the reinforcem en t area at the joint is high er than that provided in the slab,so the shrinkage m ovem ent can form at the w eakest po int i.e.near the en d of the d ow el (see Figu re 1.23 T J2). A lso,w hen the d ow elling techn iqu e is used in tw o directions at righ t an gles to the bay,the bay becom es locked in position w ith an inevitable 45°crack develop ing w ith shrink age m ovem ent.
3.3.3.4 Design Des ign process proces s for spe special cial cond itions It is im portan t to rem em ber that the d esign all relates to allow ing the slab to be free to slide. In construction there are often a num ber of features that can cause the slab to ‘ lock up. A typ icallist is: 1. Casting intern al foun dations with the slab: A lw ays cast separately an d debond the surface of the fou ndation by bitum inou s painting, polythen e sand layer. M ake sure the fou ndation top surface is flush w ith underside o f the slab (see F igu re 1.25). 2. C o lu m n s :A lw ays form a isolation/free joint around a colum n (see Figu re 1.26).
Summary M ark o n the con struction draw ings the type of joint/s selected for each m ovem en t position (see Figu re 1.24).
3. Pits and ducts:Treat these as thou gh they n eed a free joint detail. If this is not possible, then they b eco m e a fixed ed ge requiring red uction of joint spacing or an increase in reinforcem en t in the slab.
FIGURE 1. 124
FIGURE 1.26
DECIDING JOINTTYPE:
IS OLATION JOINTATCOLUMN
FJ Type X, eg FJ1
X e p y T J T
Longitudinal joint s ) y d a o h b t r e u m o f p n i r a t s h t n e i r t o p m e c o x e N (
3 J F g e , X e p y T J F
TJ Type X, eg TJ1
Isolation joint Tied control joint
FIGURE 1.2 5
IS OLATION JOINTATS TANCHION
100mm minim um cover Concrete pad to stanchion cast after m ain base
Compressible fill (20mm thick) Joint sealant (where required)
Slip membrane
Subbase
Do not concrete the subbase in with the floor slab. If the foundation concrete is at the underside of floor slab, debond it from the slab by carrying the slip m embrane through.
Concrete Ground Floors and Pa vements : Pa rt 1
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31
DESIGN
4) Re-entrant angles A ll re-en tran t an gles n eed to have ad ditional steel provided in the form of bars set at 45º across the angle (see Figu re 1.27). FIGURE 1.2 7
REENTRANTANGLES REQUIRING ADDITIONAL STEEL
3.3.3.6 Influence of fixing ssla labb to founda tion If in the preceding exam ple the en d fou ndation w as cou pled into the floor slab,then ,for instan ce, an ad ditional free joint w ou ld be needed (see Figu re 1.29). If the slab ed ges are all built into the foundations then a cen tral free joint w ould need to be created (see Figu re 1.30). U nfortunately,in the corner there w ill be a serious risk o f diagonal cracking since the slab is held in tw o directions. If the centralfree joint is not accep tab le then a fully reinforced con tinuous slab cou ld be used,but the steel content w ou ld be approxim ately 1350m m 2/m w idth for a 150m m slab. Th is has to be com pared to 186m m 2/m for a 22m distan ce betw een free joints.
Two 1.2m D12s for each angle FIGURE 1.29
3.3.3.5 Design and const ruction proces s for des ign
Free Joint
If the consultan t an d con tractor h ave determ ined that the long strip m ethod of con struction w ill be used (see Figu re 1.7) then w hile the p rocess of determ ining the reinforcem en t requirem en ts is un chan ged ,the bay patterns w ill be influenced by the w idth of the screed op eration s and m any of the joints w ill be form ed contraction joints rather than induced contraction joints.
n o i t a d n u o f h t i w d e x i F
8m
8m Extra free joint
Typically the w idth of the strip w ill be 4.5m an d,using the W /L ratio o f 1.8, w ill give b ays of 8m .
Free Joint FIGURE 1.30
The free joint position need s to b e 4x the bay m od ule, i.e. 32m (see Figure 1.28).
Fixed End
It can b e seen that chan ging the con struction m ethod can alter the original concept an d m ay alter free joint spacing. FIGURE 1.2 8
Free Joint 8m
8m
32 m FJ 4.5m
Serious risk of cracks developing
4.5m FJ
4.5m
8m
4.5m 4.5m FJ
32
m 5 . 7 2
FJ
Additional FJ
DESIGN
3.3.4 Design process for linea linearr movement for unreinforced pa nel cons truction W hile this m ethod uses the sam e p rinciples as free joints, the slab s stillrely o n an ability to m ove w ithout raising ten sile stresses that w ill cau se cracks to occur,but totally relian t on the co ncrete; i.e. no steel.Because o f this,the relative size of bays is restricted gen erally to 25 to 30 tim es the slab thickn ess. Typically,for a 150m m slab,the m axim um bay d im ension is app rox 4m . Bays shou ld be n om inally square,not exceeding a W /L ratio of 1.3. Each joint m ust be free to m ove,therefore joint selection is restricted . a) P lan free joint c) W here sign ifican t w heel tran sfers are expected a free do w el joint can be used TABLE 1-13
TIE BARS* BARS*
Spacing Diameter mm mm
Length mm
Spacing mm
100
not recommended
10
800
300
125
not recommended
10
800
300
150
20
400
300
12
800
300
175
20
400
300
12
800
300
200
25
450
300
16
1000
350
A com bination of a keyw ay on tw o op po site edges and do w els on tw o o pp osite edges is an acceptable com bination .
3.3.5 Design proces processs for linear linea r movement for reinforced pa nel cons consttruction ruction
For exam ple,665 m esh,w hich is the low est practical m esh recom m end ed, w ill easily m eet the 8-10m bay requirem en t for allslab thickn esses. H ow ever,the system req uires sim ilar joint details for the unreinforced slab s,i.e. dow elled or keyw ay joints.W here dow els are required in tw o directions it w ill be n ecessary to use special dow els,as illustrated in Figure 1.31.
Guide to specifying dowels and tie bars
Slab Diameter Length Thickne hicknessss mm mm
It is essential that dow els are set exactly at right an gles to avo id b inding during m ovem en t. A s stated b efore,if dow els are used in tw o direction s then the special dow els that allow sidew ays m ovem en t are likely to be required (see Figure 1.22).
In this situation,the u nreinforced slabs described in the previous section are reinforced according to the sam e theory as the reinforced system ,bu t each pan el edge is seen as being a free joint or partially free. This allow s the bay size to be increased to the sugg ested m axim um of 8-10m and yet use m uch less steel per square m etre.
b) A keyw ay joint betw een adjacent slabs
DOWELS
It should be n oted that slabs used in road ing, veh icular park o r access ten d to use this m ethod of con struction . Because dow els are the u sual m ethod of tran sfer at the joint po sition ,slabs tend to be 180 to 200m m thick.For dow el spacing, see Table 1-13.
The ad vantage ofthis type of design is that the actualjoint m ovem ents are equalised on alljoints rather than the original reinforced slab m ethod w here there can be approxim ately 20m m of m ovem ent at the free joint extrem es of the slab. Fu rther inform ation on this m ethod is contained in Part2 o f this m an ual.
* To b e checked with the requirements of Tab le 1.12
FIGURE 1.31
Seal sleeve to concrete face to prevent ingress of grout
Seal sleeve to concrete face to prevent ingress of grout 20 x 20m m square steel dowel in sl eeve
20 x 20mm square steel dowel in concrete slab poured first
Plastic sl eeve to pass through sl ab edge form
Plastic sl eeve and cap
Plastic cap FULLY SLEEVED D OWEL AT CONSTRUCTION J OINTS This arrangement can be used at sawn control joi nts
PARTIALLY SLEEVED DOWEL AT CONSTRUCTION JOINTS Plastic sleeve 20mm
SLEEVE SECTION
Plastic locating tips Steel dowel 32mm approx
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NOTES
34
CONSTRUCTION
Cha pter 2: Construction 1. S CO P E
36
7. CU RI N G
47
7.1 Purpose ................................................................. 47
2 . I N TRO D U CTI O N
36
3 . S I TE P REPARATI O N
37
3.1 General ................................................................. 37 3.2 Subgrade Preparation ........................................... 37 3.3 Subbase Construction ........................................... 37
7.2 Ponding ................................................................ 47 7.3 Sprinkling ............................................................. 47 7.5 Impermeable Coverings ......................................... 47 7.6 Curing Compounds ............................................... 48
8 . JO I N TS
49
3.4 Backfilling of Service &Drainage Trenches ....... ...... 38
8.1 General .................................................................49
3.5 Vapour Barrier ....................................................... 38
8.2 Contraction Joints ..................................................49
4 . FO RM W O RK
39
4.1 Forms .................................................................... 39 4.2 Form Setting .......................................................... 39 4.3 Subbase Between Forms .......................................39 4.4 Form Removal ........................................................ 40
8.2.1 Trans verse contraction joints ......... ........ ....... 49 8.2.2 Longitudinal contraction joints ........ ........ ..... 50 8.3 Construction Joints ................................................50
8.3.1 Trans verse construction joints ........ ......... ..... 50 8.3.2 Longitudinal construction joints ......... ........ .. 50 8.4 Isolation Joints ...................................................... 50
4.5 Temporary Forms ...................................................40
5
REI N FO RCEM EN T
9 . PRO TECTI O N O F CO N CRETE PAVEM EN T
51
10 . AD VERS E W EATH ER CO N D I TI O N S
51
40
5.1 Placing Methods ................................................... 40 5.2 Preset Reinforcement on Bar Chairs ....... ....... ...... ..... 40
10.1 General ................................................................. 51
5.3 Strike-off Method ....... ....... ...... ....... ....... ....... ...... ..... 40
10.2 Concreting in Hot Weather ....... ....... ...... ....... ....... ... 51 10.3 Concreting in Cold Weather ....... ....... ....... ...... ....... .. 51
6 . P L A C I N G , C O M P A CT I N G , FI N I S H I N G A N D TEXTU RI N G
42
6.1 Placing .................................................................. 42
11. CON STRUCTION TOLERANCES FOR PAVEM ENT S U RFACES
52
6.2 Compacting ........................................................... 42
11.1 Typical Concrete Pavements ....... ....... ....... ...... ....... 52
6.3 Finishing ............................................................... 44
11.2 ‘Superflat’ Pavements ........................................... 52
6.3.1 General ........................................................44
11.3 Measuring Equipment ........................................... 52
6.3.2 Levelling ........ ......... ......... ......... ......... ........ .. 44 6.3.3 Floating a nd trowelling ........ ......... ......... ....... 45 6.4 Weath er Conditions ...... ....... ...... ....... ....... ....... ...... ... 46 6.5 Texturing ....... ....... ....... ...... ....... ....... ....... ...... ....... .... 46
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CONSTRUCTION
1. S COPE This C hapter provides a guide to the construction of con crete industrial pavem en ts on the grou nd an d finishing by m ethod s such as trow elling o r broom ing.It do es not cover the construction of suspen ded floo rs or those incorporating a w earing layer provided either as an integral finish or as a bon ded top ping . The con struction proced ures covered are: •Site prep aration •Form w ork erection •R einforcem ent placing •C oncrete placing, com paction an d finishing •C uring •Jointing •P rotection •P recaution s for adverse w eather •C onstruction toleran ces.
36
2. I NTRODUCTION The three b asic con struction m ethods (long-strip, con tinuou s-po ur and cheq uerboard) and the u se of top pings (i.e. tw o-course construction) are discussed in detail in Section 2.1.3 in Cha pte r 1: Design .Th e recom m end ation s to adop t either the lon g-strip or continuou s-pou r m ethod an d to avoid tw o-course con struction cann ot be over em phasised. The elem en ts of con crete industrial pavem en ts are defined in the introduction in this m an ual (page 4).
CONSTRUCTION
3. S ITE P REPARATION FIGURE 2.1
3. 1 GENERAL Before constructing the p avem en t,a n um ber of site activities m ust be un dertaken ,includ ing: •preparation of the sub grade; •con struction of the sub base; •installation of services an d drainage pipes an d fittings;an d •installation of vapour barrier (if required).
3. 2 S UB GRADE P REPARATION Fo r m ost projects,earthw orks com prising either excavation or filling,or a com bination of both these o perations,w illbe necessary to b ring the sub grade to the required shape an d level. The gen eralfinished surface levelw ill norm ally b e determ ined by drainage requ irem ents and con sideration of such factors as: •the clim atic conditions of the region,particularly rainfall;
Subbase being compacted wi th a pedestrian-operated vibrating roller
FIGURE 2. 2
•the slope and generallevel of the existing grou nd relative to its surroundings; •the grou ndw ater level an d the exten t to w hich it is influen ced by seasonal,flood or tidal conditions;an d •the soil profile, the n ature of the insitu m aterial an d the layer thickness. The subgrade w ill gen erally be con structed to the sam e shap e as the finished surface of the slab.Thus,at any p oint, the su bgrad e level is equal to the finished level of the slab m inus the total pavem en t thickn ess (w ithin the specified toleran ce). W hen im ported fillis required ,a selected granular m aterial sho uld be u sed, placed in uniform layers and com pacted at or near op tim um m oisture con tent to achieve the specified den sity.Suitable eq uipm en t for com pacting granular fill includes p late type vibrators,ped estrian operated vibrating rollers an d sm all tan dem rollers (typ ical exam ples of w hich are illustrated in Figu res 2.1 and 2.2). L ayer thicknesses shou ld be chosen such that com paction occurs over the full layer,an d not exceed 150m m ,unless heavier com paction equ ipm ent than that noted above is used. Four to eigh t passes of the eq uipm ent w illnorm ally be required .Trucks and tracked or w heeled con struction veh icles that have low con tact pressures w ith the grou nd are not suitable for com pacting fill. The stren gth of the su bgrad e is not critical,since applied load s are dispersed o ver large areas by the concrete pavem en t an d b earing p ressures tran sm itted to the subgrade are relatively low .H ow ever,it is essen tial that the upper portion of the subgrade is of uniform m aterial an d den sity,an d provides uniform sup port.In order to achieve the desired uniform ity,alltop soil should be rem oved ,an d soft areas iden tified an d replaced.
Subbase being compacted with a tandem roller
3. 3 SUB CONSTRUCTION S UB B AS E CONSTRUCT In som e circum stan ces,eg o n go od qu ality natural sand s or gravels,it m ay b e p ossible to build a satisfactory p avem en t directly on the subgrade,but a subbase is frequen tly used as a levelling course,or as a m eans of providing a ‘ w orking platform ’ .Fine-grained subgrad e soils in the p resence of free w ater m ay b e ‘ pum ped’ throu gh joints and cracks under the action of frequen t heavy w heel loads.In this case a nonpu m ping subb ase m ust be provided . In con structing the subbase,it is im portan t that the specified density be achieved to avoid any subsequent prob lem s associated w ith consolidation and n on -un iform support. Subb ases should b e placed in uniform layers,generally not exceeding 150m m thick,and com pacted at or near optim um m oisture content using approp riate equ ipm ent.
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CONSTRUCTION
T h e subb sub b ase shou sho u ld be fin ishe shed d w ith in th e req requ u ired to leran erances ces to to th e speci sp ecified grad grade e an a n d leve evel l.In th e ab a b sen sence ce of of speci spe cified val valu u es,a to to leran erance ce of o f + 0, -10 -10m m m is con sid ered d esirab abl le an a n d ach achi ievab evabl le w ith in reason ab abl le stan stan d ar ard d s of con stru ct cti io n .Fi Fin n ish shed ed sub b ase pr p ro files can b e ach ieve eved d by u sin g a sc scr rat atch ch tem p lat ate e w h ich op er erat ates es from th e top top ed edge ge o f th e lev level ell led sid e fo fo rm s (see (see S ectio n 4. 4.3). 3). A ccuracy of o f sub b ase p ro file w illh el elp p en sure th th at a un u n ifo rm con co n cr crete ete laye ayer r of th e sp eci ecif fied th ick ckn n ess is pl p lace aced d. T h e use u se of o f a bl b lin d in g laye layer r o f fin e gr g ran u lar m ater ateri ial al, ,eg sand san d ,m ay ass a ssi ist in grad gradi in g to th e requ ired leve evel l,an d w ill red u ce th th e risk of o f p erfo ratio n o r tea eari rin g o f th e vap va p o u r b arr arri ier (if u sed ).
3. 4 B ACKFILL CKFILLING ING OF SERV S ERVIC ICE E AND AND DRAINAG DRAINAG E TRENCHES E xcavat xcavati io n s fo fo r fo o tin gs,d rain ag age e an d ser servi vice ce tren ch ches es sho u ld be ba backf ckfi illed in such a m an n er th at th e rep repl laced m at ateri erial exh ib its a sim ilar resp espo o n se to to b o th lo ad in g an a n d th e envi en viron m en ent t as th e ad jacent sub sub gr grad ade e m at ater eri ial.M any speci sp ecif ficatio n s req u ire tren ch ex excav cavati atio n s to b e back b ackf filled w ith granu lar m at ater eri ial to sub subgrade grade level level in u n iform com p acted layer layers s not no t exceedin g 150m 15 0m m .H ow ever ever, ,in such lim ited w o rki kin n g areas,p o o r com p act acti io n o f th e back b ackf fill m at ateri erial is com m o n ,resu esul ltin g in in surface d ep ressio n s fro m sub seq sequ u en t con sol soli id at ati io n o f m at ateri erial w ith in th e tr tren ch ch. .A s a m ean eans s of over overcom com in g th th is probl problem em ,cem en ent ted m at ater eri ials (such as cem en t-stab abi ilised san d ,cr cru u sh shed ed ro ck, lean -m ix con cr cret ete e or o r con tro lled lo w -stren gth m at ateri erial23),w h ich are less dep en d en t o n com p act acti io n fo r stren gth an d stab stabi ility, sh ou ld b e used.
3. 5 V VAPOUR AP OUR B BARRIER ARRIER C on cret ete e slabs over 100m m in th ickn ckness ess an and d con const stru cted u sin g goo g oo d q u ality con cr cret ete e th th at h as been w ell com p act acted ed an d cured ar are e resi resistan t to th e p ass assag age e of o f w at ater er from th e gro u n d .H o w ev ever, er,co con n cr crete ete slab s,irresp especti ective o f th ei eir r th ickn ess ess, ,ar are e not n ot im p er erm m eab eabl le to to th th e slow p ass assag age e of w at ater er vapou vap ou r from th e soil soilben eat eath h. It is fo r th is rea reaso son n th at a vap o u r b arr arri ier sho sh o u ld b e p laced u n d er allin ter eri ior concr con cret ete e pavem p avem en ts on th e groun grou n d , p articu cul larly if if th ey are likel ely y to receive receive an im p erm ea eab b le flo o r coverin g, or are are to to b e used u sed for for any p u rp ose w h er ere e th th e p ass assage age o f w at ater er vap ou r th ro u gh th e pavem p avem en t is in tol oler erable. Th e m ost com m on form of vapo ur barr barrier is plastic shee sh eet tin g (p o lythe ythen n e).In o rd er to to resist d eter eteri io ratio n an d p u n ctu res fr from sub subsequ sequ en t con stru ction o p er erat ati ion s,th e po lyt ythen hen e sho sho ul uld d h ave a m ini nim m um thi hicknes ckness s of 0.25m m and b e m an u fact actu u red from virgi gin n p lastic (n (n ot from reclaim ed scr sc rap p ol olyt yth h en e) e). . A vap o u r b arr arri ier placed placed d irect ectl ly u n d er th e con co n cr cret ete e also also fu n ct cti io n s as a slip layer an d red u ces sub grad grade e d rag frict cti io n . W ith less rest restr rain t to slab m ov ovem em en t,th e extent exten t o f cr crack acki in g d ue to vol volum um et etr ric chan ges of th e con cret ete e m ay w ell be reduced. T h e use u se of o f a vap va p o u r b arr arri ier also p reve even n ts th e lo ss o f m ixin g w at ater er from th e concr con cret ete e do w n in in to to th th e su su bb ase or subgrade. T h e vap va p o u r b arrier is placed placed d irect ectl ly on o n th e sub su b b ase (o (o r sub grad grade e if if n o sub b ase cou co u rse is pr p rov ovi id ed ),b u t if th e sur su rface is ro ro u gh an d likel ely y to p erfo rate th th e p last asti ic shee sh eet tin g,a b lin d in g layer of o f fin e m at ateri erial sh sho o u ld b e ap a p p lied .T h e sheeti sheet in g shou sh ou ld be con tin u ou s un d er th e sid e form form s and lapp ed at a t all joi oin n ts by a m in im um of 150m m .Th er ere e is no n eed to seal th ese jo in ts w ith ad adh h esive tape fo r vap o u rp ro o fin g p u rp o ses as vap va p o u r ri rises verti vertically.Fu rth erm o re, tap in g can ca n cau cause se pr p ro b lem s by n o t al all lo w in g the p last asti ic to to sli slip as th th e co n cr cret ete e is is pl p laced . Sp ecial care sho ul uld d be taken to avoi avoid d d am age to th e vap o u r b arrier p rio r to an a n d d u rin g con co n cr cret eti in g, an d an any y tears tears o r perforatio n s sho u ld be p at atche ched d im m ed edi iat atel ely.P lacin g th e sheeti sh eetin g as lat ate e as a s po p o ssib le w ill assist in avo avoi id in g d am ag age. e.
38
CONSTRUCTION
4. FORMWORK
4. 1 FORMS
4. 2 FORM S ETTIING NG
T h e fi fin al surface accuracy accuracy of a con cr cret ete e pavem p avem en t d ep epen en d s largel argely y o n th e con co n d itio n an d rigi gid d ity o f th e fo fo rm s,an d th e care car e w ith w h ich th ey ar a re set to leve evel l an d fixed xed. .
Form s sh ou ld b e conti contin uo usly bedded bed ded on the subbase sub base and firm ly pi p in n ed to avo id vibration an and d m ovem en ent t d urin g con cr cret ete e pl p lacin g, com p act acti in g an a n d fin ish shi in g o p eratio n s.T h e subb ase m ay be fin ished sligh tly h igh an and d th en trim m ed to th e req equ u ired leve evel lu n d er th th e fo rm s.A lterna ernat tivel vely, y,th e fo rm s m ay be b e seated seated on steel shi shim m s or other su su itab abl le packi p ackin n g.
S tee eel lfo rm s are are m o st su sui itab le beca b ecau u se of o f th ei eir r rigid con stru ction an d d u rab abi ility.H ow ever ever, ,tim b er form s m ay be be u sed if th ey are are un da dam m aged an and d in in go good od con cond d ition .Ti Tim m ber form s m ay be b e given given an ext exten en d ed life by p rotec otect tin g th th e to to p edge ed ge w ith m et etal al an gl gles es or chan n els (see (see Figu Figu re 2. 2 .3) 3). . Irresp ective o f th e type typ e o f m aterial u sed ,it is essen essen tial th at th e top o f th e fo fo rm is flat and an d lev evel el. .In m o st cases it it shou sho u ld also form form a squar squ are e ed ge w ith th e surf surface to to com co m pl ply y w ith th e jo in t d etailin g for th e in ten d ed traffic lo ad s. Fo rm s sh For sh ou ld be coat coated ed w ith oi oil l or an app roved release agen age n t an d clean clean ed an d o iled be bef fore reu reuse. se. FIGURE 2.3
TYP YPIICAL FORM DETAILS
NOTE: NOTE: All forms to have adequate means of maintaining line and level at joins
Metal edge-protector
STEEL
T h e fo fo rm s sh sh o u ld b e set to the fin ish shed ed surface level level w ith in th e sp eci ecif fied to leran erances. ces.A to leran erance ce o f± 3m m in lev level el is deem ed to be bo th de desi sirabl able e an d achi achievabl evable e w ith go good od q u al ali ity w o rkm an sh shi ip, bu t fo r speci sp ecial al‘ sup su p erflat’ p av avem em en ts, th e side form s m ay h ave to to be seteven m ore accur accurat atel ely to to achi ach ieve th e n ecessar ecessary y pave p avem m en t surface regu larity (see (see C h ap apt ter 2:S ect ecti io n 11 11. .2).T h e ju n ctio n o f ad jacen t fo rm s sho sh o u ld b e check ch ecked ed to en sure con tin u ity of o f surface leve level l. Fo rm s shou sho u ld b e set suf suff ficien tly in ad advan van ce of o f con cr cret ete e p lacin g to perm p erm it p ro gress gressi ive ch eck ecki in g o f h o rizo zon n tal an d verticalalign m en t,an d con cr cret ete e shou sh ou ld n ot be p laced in an any y area ar ea u n til th e form form s have b een checked .
4. 3 S UB B AS E B ETWEEN FORMS FORMS FORMS Fo llow in g settin g ofth e fo Fol form s,th e shap sh ape e an an d level ofth e sub base betw betw een th e for form m s sh sh ou ld be checked ch ecked usin g a sc scr ratch tem p lat ate e or or sim ilar d evice.T h e scrat atch ch tem p lat ate, e,w h ich m ay be be op erated eith er from th e sid e form form s or from con cret ete e pr p reviou sly p lac aced ed in ad jac acen en t p ou rs,in co corp rpo orat rates es ‘ tee eet th ’ set to th e requ req u ired sub base p rofile (see Fi Fig gu re 2.4).A s it trave avel ls alon g th e form s, any hi h igh or low sub ubbase base areas ar are e m ar arked ked and then trim m ed or or filled an d com co m p act acted ed as app ap p rop riat ate. e. Fo llow in g checki Fol checkin n g,th e sub base sho ul uld d be m ain tain ed in a sm oo th ,com p act acted ed con d ition an d ke kep p t free of o f fo reign m at att ter er, ,w ast aste e con co n cr cret ete e an a n d o th er deb de b ris at all tim es. FIGURE 2. 4
Metal edge-protector COMPOSITE
TIMBER
Subbase being trim med to correct level level wi th a scra scratch tch template – the type shown can be made from scrap timb er
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CONSTRUCTION
4. 4 FORM REMOVAL Fo rm s sh sh ou ld rem ain in p lace for for at least eigh t h ou rs fro m th e ti tim e of o f con cr cret eti in g, an d fo r a lo n ge ger r p erio d if con d ition s are are such su ch th at early str stren gt gth h ga gai in s m ay b e d elayed, eg w h en th e am bi bien ent t tem pe per rat ature ure falls below 10°C . Th e for form m s sho sho ul uld d be ca car reful ull ly rem rem oved to avoi avo id dam agin g the con co n cr cret ete, e,an d ba bar rs sh sh ou ld n ot be u sed as a s a lever agai ag ain n st th e con cr cret ete e to assist w ith fo rm strip p in g.
4. 5 TEMP OR ORA ARY FORMS In som e situ at ati io n s,it m ay b e d esirab abl le or o r exp ed ien t to p lace lar arge ge ar a reas of a pavem p avem en t in a con tin u ou s pou po u r rat ath h er th an in strip s betw betw een form s.If such a m et eth h od is to b e
5
Tem p o rar ary y fo fo rm s,eith er tim b er or p ro p riet etary ary typ e screed gu id es or o r rai ail ls,are set se t to lev evel el as for no n o rm al fixe xed d fo rm s an d u sed fo r in itial leve evel llin g an d screed in g p u rp o ses. T h e tem tem po rar ary y form form s sh sh ou ld b e w ell sec secu u red to to th th e subb ase an d m ay d em an d p rior in stallat ati ion o f fitm en ts to to allow qu ick and an d easy rem rem oval of th e tem tem p orary form form s dur du rin g th th e p laci acin n g an d fin ish shi in g o f th e co n cr crete. ete.T h e vo v o id s lef eft t af aft ter rem ova val l o f th e fo fo rm s,if sign ifican t,sh sho o u ld b e fi filled im m ed iatel at ely w ith con cr cret ete e as th th e pr p ro cess co co n tin u es.
REIN RE INF FORCEME MEN NT
5. 1 P LA LACI CING NG MET METHODS HODS HOD S To m ai ain n tai ain n th e cor co rrect p o sitio n o f th e rei rein n fo rcem en t (m ost com m on ly in th e form form of w eld ed w ire fabri fabric) in p avem en ent ts,cor corr rect h ar ardw dw ar are e sup po rt sho shoul uld d be used used. . W h en acces access s to to th e str strip of con con cr cret ete e u n d er con con stru ction is no n o t lim ited an d tran sit m ixers o r d u m p ers can d istrib u te th e con co n cr cret ete e even eve n ly over o ver th e fu fu ll p lacin g w id th fro m o u tsid e th e form form s,p reset rein forc orcem em en t on ba bar r ch ch airs shou sho u ld be u sed sed. .In o th er si situ atio n s,th e con co n tractor sh sh o u ld co con n sid er th e p lacin g of o f con concr cret ete e by p um p in g. T h e pr p ractices of o f lay ayi in g rein fo rcin g fabric on th e sub su b b ase b efore con co n cret crete e is is pl p lace aced d an d liftin g it it in to p o sitio n after p laci acin n g,o r placi placin n g it o n th e fin ish shed ed su sur rface o f th e co n cr crete ete an d ‘ w al alk kin g it in ’ ,sh sho o u ld n o t b e p erm itted as th th ese m ethod s give n o ass assu u ran ce th th at th e rein forc orcem em en t w ill en d u p in a tr tru e p lan e at th e req requ u ired d ep ept th be bel low th e sur su rface.
5. 2 P RESET RESETREIN RESETREINFORCEME RESETREINF REINF FORCEME ORCEMENTON NTON BA B AR CHAIRS CHAIRS Fo llo w in g com p let eti io n o f th e sub su b b ase,in stal all lat ati io n o f th e vap va p o u r bar ba rrier (i (if req u ired ) and an d fo rm set sett tin g,th e rein fo rcem en t can be p laced in th e req requ u ired lo cat cati ion an d at th e speci spe cified d ep th sup p o rted o n b ar ch ch airs Figu re 2.5. 2.5. B ar chai cha irs o f sui suit tab abl le hei h eigh t an d spaced sp aced on a 1m grid sh ou ld be sufficien t to sup p o rt th e rein fo rcem en t,w o rke ker rs and an d th e im p act o f th e con co n cr crete ete as it is pl p lace aced d .W h ere fab abri ric rei rein n fo rce-
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em p loyed ,m uch gr great eater er car care e and an d a h igh er stan and d ar ard d of w orkm an shi ship p w ill be n ecess ecessar ary y to to achi a chieve eve th th e req requ u ired surf su rface lev evel els s an d to leran ces.To assi assist st in lev evel ell lin g th e flo o r, tem po rar ary y for form m w or ork k shou ld be u sed.
m en t ligh ter th an 663 is used ,it sho u ld be sup p o rted o n rei ein n fo rcin g b ars or clo ser-spa -spaced ced b ar chai cha irs.In d ep en d en t sup p orts no t restin g on th e rein forcem en t or sid e fo fo rm s sho u ld be u sed to car carr ry ot o th er con con stru ctio n loa oad d in gs such as p lan ant t or equ ip m en t. O n sof soft t sub subgrades grades o r w h en a vap va p o u r barr barrier is in stalled ed, , th e bar b ar ch ch ai air rs sh sh o u ld b e fi fitted w ith a pl p lat ate e sup p o rt u n d er th e leg egs s to p reven t th em sin ki kin n g in in to the subg su bg rad ade e or or p u n ct ctu u rin g th th e vap o u r b arrier er. .
5. 3 S TRIKE-OFF METHOD In th is m et eth h o d ,con cr cret ete e is placed placed be bet tw een th e fo fo rm s to a leve level l sligh tly ab a b ove th e requ req u ired rei ein n fo rcem en t lev evel el to give gi ve a u n ifo rm surcha surchar rge ge, ,ov over er a len len gth to sui suit t th e fabric sheet she et be bei in g u sed.A n otc otch h ed tem p lat ate e is is used to strike of off f th e co con n cr crete ete at th th is sur su rch charge arge lev evel el –see Figu re 2. 2.6. 6. P rel eli im in ary com p act acti io n o f th is lo w er layer of o f con cr cret ete e to rein fo rcem en ent t level is th en un de der rtaken an and d can b e achieved achieved b y th th e u se of a n ot otched ched tim ber han ha n d tam p er –see Figu re 2.7. 2.7.Th e fab abr ric is th en p laced o n th e com co m p act acted ed layer of con cr cret ete e– see Fi F igu re 2. 2 .8 –w ith th e speci sp ecified lap s,an d th e rem ain in g u p p er layer of o f con cr cret ete e is is th en spread to surcha surchar rge leve evel l an d fu lly com p act acted ed w ith a vibrat vibratin g-b g-beam eam .T h e up u p p er layer sho sh o u ld b e p lace aced d w h ile the th e lo lo w er laye ayer r is sti still in th e p last asti ic state.
DESIGN
FIGURE 2.5
FIGURE 2.7
RECOMMENDED PRESET-REINFORCEMENTSUPPORTDETAILS Bar or fabric reinforcement Vapour barrier
Support plate
Bar chairs
1000 BAR OR FABRIC REINFORC EMENT GENERALLY
Fabric reinforcement lighter than 663 16-mm -dia. bars at 800- to1000- mm centres
A notched tamper being used to compact the l ower layer of concrete to reinfor cement level
Bar chairs Support plate
300-mm overlap
Vapour barrier
FIGURE 2.8
1000 to 1200 LIGHT FABRIC REINFORCEMENT FIGURE 2.6
DETAILS OF NOTCHED TEMP LATE
Notched template used to spread con crete to a uniform su rcharge above Side form reinforcement l evel Notched template Required surcharge
Reinforcement level
Fabric sheets being laid on concrete already compacted t o reinfo rcement level
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CONSTRUCTION
6. P LACING, COMP ACTING, FINIS HING AND TEXTURING
6.1 P PLACING LACING
6 . 2 COMP COMP ACTING
There are m any w ays of transporting and placing con crete. W hichever m ethod of tran spo rt is used ,it is im portan t to place the co ncrete as close as possible to its final position. This w ill avo id ad ditional han dling and increased risk of segregation.U niform spreading d irectly from the tran spo rting equipm en t w ill reduce the p hysical effort required in distributing the concrete24.H ow ever,if con crete h as to be m oved b y m anu alm ethod s,it shou ld b e done w ith sho vels. Poker vibrators should not be u sed to m ove concrete. M ostconcrete is placed either directly from the chute ofthe supply truck (tran sit m ixer,agitator truck,etc) or by pum p.
The reason for com pacting concrete is to rem ove the air entrapped w hen it is m ixed and placed,thus en suring m axim um den sity,stren gth an d d urability.O f the different m ethod s available,the m ost suitable for pavem en ts up to 200m m thick is to use a vibrating beam .This is gen erally o f steel or alum inium and m ay be either a single or dou ble beam w ith a p urpose-m ade vibrator m oun ted on top.D ue to the better finish ach ieved,double beam s are gen erally preferred.For pavem ents m ore than 200m m thick,additional com paction by the u se of internal poker vibrators is required to ensure com paction throu gh ou t the full depth.
To perm it supply trucks to discharge their load s directly into the final position,the site should be w ell plan ned ,an d obstacles such as excavated soil,building m aterials,set-out pegs and co nstruction huts located to p erm it truck access.
Th e com paction produ ced by pow er floats and trow els is lim ited to the surface of the concrete on ly,so that the use of vibrating beam s and poker vibrators (especially ad jacen t to side form s)is essentialto provide strong,durable p avem ents.
D im en sion s of a typical6-m 3-capacity transit m ixer are show n in Figu re 2.9.
W hilst w etter con crete is easier to com pact,it w ill generally take longer to finish an d w ill be w eak er,particularly at the surface.U nder no circum stan ces shou ld w ater be added to the con crete on site to assistplacing an d com pacting o peration s.Th e optim um slum p for con crete to be placed u sing the eq uipm ent and techn iqu es discussed herein is w ithin the range 40 to 80m m .
FIGURE 2.9
3
TYPICAL 6-M TRANSITMIXER
7200
4000
0 0 8 1
0 0 7 3
A fully loaded tran sit m ixer w ith a cap acity of 6 m 3can w eigh up to 24 tonnes an d it is essential that allroads and access points on the site can sup portthis load,even in w et conditions. In addition to the m ore u sual fixed-form paving m ethod , the u se of slipform pavers can assist in rapid an d econ om ical construction of industrial concrete pavem en ts,particularly for industrial drivew ays an d externalhardstan dings.
A s entrapped air in the concrete is rem oved by vibration , the co ncrete su rface level w ill drop.The initial level to w hich the concrete is spread sho uld therefore b e h igh er than the side form s.The h eigh t of this surcharge w ill vary according to the concrete m ix and m ethod of placing,bu t m ay be 10% or m ore of the com pacted concrete thickness. A recom m ended m ethod of produ cing an even surcharge of con crete is to use a tim ber tem plate (fitted w ith packers of the required depth) draw n along the side form s over the p an el area that has previously b een sligh tly overfilled w ith concrete (see Figure 2.10). FIGURE 2.10
Slipform pavers have b een used to pave external industrial pavem en ts in A ustralia in thickn esses from 150 to 400m m .Paving w idths in the rang e 2 to abo ut 10m can be slipform ed by specialist com pan ies in this field.C onstruction efficiency can be enhanced by design ing the pavem ent to m axim ise the n um ber of equ al-w idth paving run s,ie the locations of longitudinal construction joints. A s the p aved edge m uststand un sup ported w itho ut un du e edge-slum p,the consisten cy of concrete used for slipform paving is less than 50m m and typically in the range 40 - 45m m . In plan ning a slipform paving o peration,note that there is a side clearance requirem en t of 1.0 to 1.5m for the paver betw een the paved edg e of concrete an d any o bstruction , such as a w all,light stan chion or other sim ilar feature.
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Timber template wit h packers being used to produce a uniform surcharge of concrete prior to fin al compaction of slab
CONSTRUCTION
G enerally,tw o p asses of the vibrating-beam are m ade over each section of the pavem ent at a rate of betw een 0.5 an d 1.0 m /m inute.D uring the firstpass,a u niform ridge of concrete abou t 50m m deep should be m aintained ahead of the screed over its entire len gth (see Figures 2.11 to 2.13).O n the second finishing pass,only a slight rollofconcrete sho uld be m aintained alon g the screed .A ny addition alpasses of the screed w ill not ach ieve significan t increases in den sity but w illresult in excessive m ortar being brough t to the surface.The beam should be draw n even ly forw ard from the tim e vibration starts and the vibrating action should be stop ped w henever the screed is stationary and in contact w ith the concrete. W here vibrating beam s are used to com pact slabs up to 200m m thick, it is necessary that a poker vibrator be used adjacent to the side form s (an d next to existing p avem en t edges w hen com pleting infill bays) because vibrating beam s are least effective near their en ds (see Figure 2.14).
FIGURE 2. 12
Slab being compacted with a double vibrati ng beam FIGURE 2 . 13
To ensure com paction an d accurate surface levels,the top edge o f the side form s should b e kept clean an d free from con crete,m ortar an d aggregates. V ibrating screed s available in N ew Z ealan d can 22m and have hyd raulic w inches to p rop elthe m achine forw ard. A djustable truss design m akes it possible for the screed to be kept straigh t over lon g span s or have a cam ber or dish set into the screed . R oller screed s are also available in a n um ber of form s; single or triple roller design s being the m ost com m on . These screed s have the ability to strike off large volum es of con crete q uickly and accurately. Self-propelled laser-gu ided screed s are becom ing pop ular. Th ese m achines are essentially ride-on an d have the ability to d isperse concrete by auger and then vibrate an d com pact the con crete. Th e grade is established by laser. The screed w hich is typ ically 4m w ide and self-levelling is m ou nted on a p ow erful telescopic boom w ith a reach o f 6m . In this case it is possible to level 24m 2of floor w ith every pass in less than 1 m inute. Th is equipm en t has obviou s advan tages,such as increased pour sizes,go od floor tolerances and hand ling low slum p concrete.
Slab being compacted with a doubl e vibrating beam (note that the height of concrete is no more th an 50mm above finished level) FIGURE 2.14
FIGURE 2.11
FUNCTION OF A DOUB LE VIB RATING BEAM
Direction o f travel Double vibratingbeams
Rear beam screeds surface
Concrete surcharge Front beam maintains roll o f concrete ahead
-
Final pavement thickness
Poker vibrator being used to compact concrete near slab edges, ahead of vibrati ng beam
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CONSTRUCTION
6.3 6 . 3 FINISHING FINISHING
FIGURE 2.15
6.3.1 G e n e r a l This section describes d irect finishing tech niques for concrete pavem en t com prising levelling,floating,trow elling an d texturing (if req uired ).Special finishing tech niques (including the use of vacuum dew atering, K elly com pactors, etc) an d ap plied surface treatm en ts (including d ry shakes) or coatings are not w ithin the scop e of this m an ual. M any o f the problem s associated w ith the perform ance of con crete pavem en ts are caused by poo r finishing p rocedures.D uring the com pacting, levelling an d p ow er floating of a p avem en t,a layer of cem en t-rich m ortar is inevitably brough t to the surface.This surface laitan ce should not be allow ed to b ecom e too thick by excessive w orking of overw et con crete.A slab w ith a thick layer of surface laitan ce w ill w ear rap idly,possibly craze, an d dust bad ly.The u se of fully com pacted,low -slum p con crete follow ed by the floating and trow elling operations at the correct tim es w ill avo id the production of an excessively thick layer of laitan ce, an d result in a d urable p avem en t surface.
Pavement surface being levelled with a ‘skip’ (or ‘bull ’) float – on the forward stroke, the float i s pushed, with h andle lowered. FIGURE 2 . 16
It is essential in the d irect finishing of concrete p avem en ts that no floating o r trow elling o peration s be com m enced w hile bleed w ater continues to rise or rem ains on the surface.The incorporation of bleed w ater into the surface layer w ill significan tly increase the w ater-cem en t ratio of the co ncrete in that surface layer,resulting in a w eaken ed surface prone to dusting.The u se of a m ixture of cem ent and ston e dust(kn ow n as driers) to absorb bleed w ater w ill also p rod uce a very p oo r w earing surface,an d this practice sho uld be banned for industrial pavem en ts.
6.3.2 Levelling It is im portan t that the concrete surface b e b rough t to the final specified level prior to the com m en cem en t of any finishing o perations,an d this w ill gen erally be ach ieved by on e or tw o passes of the vibrating b eam .Floating and trow elling sh ou ld not be con sidered as m ethod s of correcting inaccuracies in level or profile. W here a p avem ent is to be finished by p ow er floating an d trow elling, the surface left by the d ouble-beam vibrating screed w ill be level en ough to be follow ed by initial pow er floating after a su itab le d elay (see Section 6.3.3). If pow er floating an d trow elling are not used,the surface of the con crete m ay be im proved b y the use of a straighted ge fitted w ith a long han dle referred to as a ‘ skip’ or‘ bull’ float.The b ull float should be d raw n tran sversely across the pavem en t soon after com paction to correct sm all surface irregularities.It should be p ushed forw ard across the pavem ent w ith the h andle low ered (see Figu re 2.15) and draw n back w ith the han dle raised (see Figu re 2.16).M ost of the bleed w ater should have left the concrete before the float is first used or grooves m ay be left by its ed ges.
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On the return stroke, the float is pulled with th e handle raised
A second use of the bull float m ay be required before the con crete h arden s to correct any sligh t undulations in the pavem ent surface.O nly the m inim um am oun t of w orking of the p avem ent surface shou ld be allow ed so that an excessively thick layer of laitan ce is not produced .To m inim ise the num ber of ridge m arks left at the ed ge of the blade, the m axim um overlap o f float passes shou ld b e abou t 50m m .A sm aller trow el fitted w ith a long h an dle m ay be used at a later stage of con crete stiffen ing to sm ooth dow n these ridge m arks. A larger lightw eight float fitted w ith a sm all vibrator can be u sed to ach ieve accu rate levelling;firstly w ithout the vibrator running (w hile the co ncrete is stillplastic) an d later (w hen the w ater sheen has just left the con crete surface) w ith the vibrator running.
CONSTRUCTION
6.3.3 Float ing a nd trowelling
FIGURE 2 . 17
G en eralfloating and trow elling for large pavem en t areas is norm ally un dertaken u sing p ow ered equ ipm ent.Pow er floating and trow elling w ill not necessarily achieve a better quality of surface finish than go od han d floating and trow elling, bu t w illbe m ore econ om ical. A pow er-trow elled pavem ent finish is obtained in tw o stages: STAGE 1: Power-floatingt he stiffen ed concrete to even out any slight irregularities leftby the vibrating beam . A pow er float is a m achine w ith large horizon tal steel rotating blad es, used for the initial floating operations only.
close the surface, STAGE 2: Final power- trowe llingto m aking it sm ooth and den se.A po w er trow elis the sam e or sim ilar m ach ine to a pow er float,but fitted w ith sm all individual steel trow el blad es that can be p rogressively tilted during the trow elling o perations.The pow er-trow el should be u sed only for the final trow elling operation.
Slab surface being p ower floated
FIGURE 2.18
Power-floating: It is im portan t that pow er-floating is not begun until the co ncrete has stiffen ed sufficien tly.The tim e intervalbefore the initial pow er floating can com m en ce depends on the con crete m ix and the tem perature.In cold w eather it m ay be three h ou rs or m ore after the con crete is placed .In hot w eather the concrete m ay stiffen rap idly,an d it is then im portan t that con crete is not placed faster than it can be prop erly pow er-floated an d trow elled w ith the available resources.
A s a generalguide, w hen an average-w eigh t m an can stan d on the surface an d leave foo tprints no t m ore than abo ut 3m m deep, the surface is ready to pow er float. The p ow er-float sho uld be system atically operated over the concrete in a regular pattern leaving a m attfinish (see Figure 2.17). C oncrete close to obstructions or in pan el corners that cann ot be reached w ith a p ow er-float m ust be m anually floated before an y pow er-floating starts.
Finish near slab edge being imp roved with a steel hand trowel
FIGURE 2.19
A steelhand -trow elm ay be u sed to g ive an im proved finish near the p an el edges (see Figu re 2.18).The concrete m ust alw ays be kept level w ith the side form s. Power-trowelling If pow er-trow elling is started too early, the trow el blad es w illleave ridges.Po w er-trow elling should be com m enced w hen m ostof the m oisture brou gh t to the surface by the initial pow er-floating h as disappeared an d the concrete h as lost its stickiness.W hilst high concrete stren gth assists in providing su rface abrasion,resistan ce pow er trow elling also increases surface abrasion.
A practical test to check the read iness for each trow elling op eration is to press the palm of the h an d on to the con crete surface.If m ortar sticks to the p alm w hen the h an d is taken aw ay from the surface,the pavem en t is no t yet ready for trow elling.
Close-up view of trowel blade ti lted dur ing fi nal stages of power trowellin g
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CONSTRUCTION
FIGURE 2.20
6 . 4 WEATHER CONDITIONS In cold w eather con ditions,con crete setting can be accelerated by increasing the cem ent content and/or using Type H E (high -early stren gth) cem en t or heating the m ixing w ater. In hot conditions it is ab solutely vital to take precautions against prem ature drying out and early age therm al m ovem ents.Th ese factors can gen erate cracks w ithin hou rs of placing the con crete.Those cracks form a perm an en t w eakness w hich is often m ade w orse by d rying shrink age taking place at these points,rather than joint positions (refer to Section 10).
6 . 5 TEXTURING Three-head power trowellers are now being used in major warehouse proj ects.
Pow er-trow elling o f the full pavem en t bay is un dertaken in a system atic pattern w ith the trow el blad es set at a sligh t an gle; the an gle d epen ds on the concrete stiffness but should be as steep as possible for the p articular surface (see Figure 2.19).If the tilt on the b lad es is too great,the co ncrete surface w ill be m arked . W here a second pow er-trow elling is specified ,it should not be com m enced until the excess m oisture broug ht to the surface d uring the initial trow elling h as disappeared .A gain, the p ractical test described above m ay b e u sed.The tilt of the trow el blade shou ld be gradu ally increased to m atch the concrete stiffness. For som e heavy-duty pavem ents,three stages of pow ertrow ellings m ay b e specified (see Figure 2.20).The third trow elling should be u ndertaken after a sim ilar w aiting period,w ith the blad e tilt again increased as the concrete hardens. A lim iting factor in the construction of a p ow er-trow elled pavem en t is the w aiting tim e required betw een successive trow ellings w hile the concrete is harden ing. These delays often m ean that con crete placem ent m uststop for the d ay in the early afterno on to allow tim e for the finishing operation s to be com pleted w ithin n orm al w orking hou rs.Th is can be an even greater problem in cold w eather or w here a pavem ent m ust be con structed in the o pen or on sites expo sed to w inds.To m inim ise these prob lem s in interior pavem en ts,the construction of a building sh ould be prog ram m ed,w here p ossible,so that at least the roof and preferably the w alls are com pleted before the p avem en t is placed ,as seen in Figu re 2.20.
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The texture to be im parted to a d irect-finished con crete pavem ent should b e chosen w ith reference to the type of traffic an d load ing,poten tial w ear an d slipperiness,an d ease of clean ing. In m an y light to heavy industrial situations,a structuralslab m ay be d irectly finished by pow er or han d-trow elling to give a den se,hard-w earing surface.This finish w ill provide a lim ited degree o f protection against the pen etration of oil, but m ay n ot provide ad equate skid resistan ce if sub jected to frequen t traffic,especially w hen dam p. W hen a greater degree of skid resistan ce is desired,the finished surface of the pavem ent can b e broom ed.C oarse textures,suitab le for steep slopes o r heavy-traffic areas are produced by stiff-bristled broom s,w hilst m ed ium to fine textures are obtained w ith soft-bristled broom s.The finish is achieved by pu lling a dam p broo m across the freshly trow elled surface,preferably in a d irection perpen dicular to the traffic. A lternative form s of texturing m ay be p rod uced u sing a dam pen ed hessian drag o r grooving o f the plastic concrete using a steel-tyn ed com b.
CONSTRUCTION
7. CURING
7. 1 PURPOSE The curing o f con crete h as a m ajor influen ce on the stren gth, w ear resistan ce,final quality an d perform an ce o f the w earing su rface. P roper curing reduces the risk of cracking, crazing, curling and dusting o f the pavem en t. C uring shou ld com m ence im m ediately after finishing. The purpose of curing is to m aintain w arm ,m oist con dition s un der w hich the con crete can continue to harden an d gain its fullstren gth an d w ear-resistan ce properties. A pavem en t has a large surface area exposed to d rying in relation to the volum e of con crete.P rom pt an d adequate curing is therefore essential an d for best results the p avem en t surface should be continuously cured for at least seven days.
should be taken to cover the en tire surface, including any exposed edges of slabs.The coverings should b e kep t con tinuously m oist so that a film of w ater rem ains on the con crete surface throu gh out the cu ring period . W et coverings o f sand are effective for curing but in recen t years have been largely discon tinued due to their high cost an d the p ossible d iscolouration of the concrete. M oist sand sho uld be even ly d istribu ted over the surface of the con crete in a layer abo ut 50m m thick an d kep t continuou sly w et.This m ethod is often usefulon sm all job s. W et coverings w hich are allow ed to d ry ou t can h ave a detrim en tal effect on the concrete by sucking m oisture from it.If con tinuous w etting can not be guaranteed ,eg by the use of soaker hoses,this form of curing sh ou ld not be u sed.
C uring m ethod s fallinto tw o catego ries: •Those w hich supply addition al m oisture to the con crete during the cu ring p eriod –these include p onding, sprinkling, an d w et covering (such as hessian or sand). •Those w hich prevent loss of m oisture from the con crete by sealing the surface –this m ay be d on e by m eans of w aterproof pap er,plastic sheets,or sprayed liquid m em brane-form ing com poun ds.
7. 2 PONDING O n flat surfaces of pavem ents,earth or clay m ou nds can be built around the p erim eter of the concrete surface to retain a pon d of w ater w ithin the en closed area.Ponding is also effective in m aintaining a u niform tem perature in the slab.It gen erally requ ires a considerable am ou nt of labour and sup ervision,causes site obstructions and m ay be im practical on larger jobs.
7. 5 IMP IMPERMEABLE ERMEAB LE COVERINGS A m ost reliable an d efficien t w ay to cu re concrete pavem en ts is by fully covering the surface w ith plastic sheeting or w aterproo f building p aper as soo n as the con crete has harden ed sufficien tly to avoid m arking (see Figu re 2.21). P lastic sheets shou ld be lapped an d w ell fixed dow n at the edges to avoid any w ind blow ing betw een the sheets and the con crete. This typ e of covering also provides som e protection to the concrete againstdam age from subsequ ent con struction activity. U neven colou ration of the concrete surface,w hich som etim es occurs w hen plastic sheeting is used, m ay be m inim ised by floo ding the surface b efore the sh eeting is laid,an d en suring u niform con tact is m aintained betw een the sheeting and the con crete. FIGURE 2. 21
7. 3 S P RINKLING C ontinuous sprinkling w ith w ater is also an excellen t m ethod of curing.A fine spray of w ater app lied con tinuou sly through a system of nozzles provides a con stan t sup ply of m oisture.This preven ts the p ossibility o f crazing or cracking caused by alternate cycles of w etting an d d rying. D isadvan tages o f sprinkling include its cost,the n ecessity for a drainage system ,an d the possibility of uncom fortable w orking con dition s.The m ethod requ ires an ad equ ate sup ply of w ater and careful sup ervision.
7. 4 WETCOVERINGS W et coverings such as hessian or other m oisture-retaining fabrics are exten sively u sed for curing concrete.Such coverings should b e placed as soo n as the con crete has harden ed sufficien tly to p revent surface dam age.C are
Placing pl astic sheeting on a p avement whi ch is to b e cured by this meth od – sheets must be lapped and weigh ed down at edges.
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CONSTRUCTION
7. 6 CURING COMPOUNDS
FIGURE 2.2 2
L iqu id m em brane-form ing curing com pou nd s can also b e used to lim it evap oration of m oisture from the concrete. They are an effective m ean s of curing w hen applied correctly.They are suitable for curing not only fresh concrete but m ay also be used for further curing o f con crete after rem oval of form s or after initial m oist curing. C lear or translucent com pou nds are available.M any contain a fugitive dye w hich facilitates even coverage of the concrete surface.D uring hot w eather,w hite p igm ented com pounds are m osteffective,since they reflect the sun ’ s rays and thereby m inim ise the tem perature rise in the concrete. C uring com po un ds are applied by h and -operated or pow er-driven spray equipm en t (see Figu re 2.22).The con crete surface to be cured should be m oistw hen the coating is ap plied.N orm ally,only o ne co at is ap plied in a sm ooth even texture,bu t tw o coats som etim es m ay be necessary to ensure com plete coverage.A secon d coat,w hen used,should be applied at righ t an gles to the first. A n ad vantage of a liqu id m em brane-form ing curing com pound is that it can be applied to fresh con crete earlier than sheet m aterials –an im portan t con sideration in hot w eather. C are m ustbe taken to check that the use of the com pound w ill not affect the adhesion of any later surface treatm en ts.W ax em ulsion an d ch lorinated rubb er curing com pou nds shou ld n ot be applied to surfaces that are to receive toppings or tiles,etc as they m ay im pair the bond betw een them and the slab.
48
Liquid membrane-forming curing compound being appli ed wit h back-pack spray. Note use of hoo d over nozzle to avoid loss of spray.
Sim ilarly,certain curing com pounds m ay affect the ad hesion of flooring m aterials such as vinyl tiles or parqu etry.C laim s that som e curing com po un ds break do w n after a tim e, an d do not affect subsequ en t adhesion of other m aterials to the concrete surface,should be verified by testing b efore the com pou nd is used.For all curing com pou nds,m inim um occup ation al health and safety gu idelines should be follow ed.
CONSTRUCTION
8. JOINTS
8 . 1 GENERAL Joints are p rovided in concrete p avem ents as a m eans of con trolling cracking resulting from drying shrinkage an d therm al expan sion an d con traction of the concrete.There are four different types of joints,an d these sh ould be co nstructed in accordan ce w ith the details,an d at the locations sho w n on the contract draw ings.Typicaldetails are show n in C hapter 1 D esign of this m anual.
SAWN JOIN TS: are con structed by saw ing a n arrow groove (generally 3 to 5m m w ide) in the concrete after it has harden ed (see Figu re 2.24). FIGURE 2.2 4
8 . 2 CONTRACTION JOINTS
8.2.1 Trans verse co ntra ction joints These joints are provided tran sversely to the direction of placing at pred eterm ined locations to con trol cracking by creating a p lan e o f w eakness at w hich the crack w ill occur. They m ay be con structed either by form ing a groo ve in the plastic con crete (Fo rm ed Joint) or by saw ing a groove in the harden ed concrete (Saw n Joint). FORMED JOIN TS: are con structed by inserting a steel strip,T-section,or back-to-b ack an gle iron cutter into the plastic concrete directly follow ing norm al finishing o perations (see F igure 2.23).The cu tter m ay b e leftin place until the concrete stiffen s and then rem oved;alternatively,the cutter m ay be rem oved im m ed iately an d a joint filler,eg fibreboard or self-exp an ding co rk,or proprietary typ e crack inducer,inserted into the groove.In the latter case,the con crete on both sides of the joint should be re-levelled an d re-com pacted using a vibrating float.If req uired ,the joint can be sealed by rem oving the filler m aterial to the required depth at a later stage. In the case of som e m aterials such as self-exp an ding cork,the filler m aterial m ay also fun ction as the joint sealer an d can be left in position. FIGURE 2. 23
Concrete saw being used to cut sawn joint in h ardened concrete.
The tim ing of saw ing is critical,an d sh ou ld com m en ce as early as possible before random cracking can occur,but after the con crete has h arden ed sufficien tly to prevent ravelling or tearing o f the surface u nder the action of the saw .The app rop riate tim e can vary betw een 4 and 48 hou rs,dep ending o n the factors that influen ce the setting and early rate of stren gth d evelopm en t of the concrete. G en erally,the clim atic conditions have the greatest effect.The appropriate tim e for saw ing can be assessed by casting test pan els adjacent to the w orks and con ducting saw ing trials at various intervals after placing the concrete.A s a gen eral gu ide,depen ding o n tem perature the joints shou ld be saw n before the tim es show n in Table 2.1. TAB LE 2. 1
Lat est t ime for sawing de pending on ambient temperature
Steel T-section cutter being used to make a formed joi nt in pla stic concrete.
Daily Da ily maximum ma ximum temperature tempera ture (°C)
Lat Latest est time awing ing La test time for for ssaaw a wing (hours)
<10
48
10– 20
36
20–30
24
>30
12
In hot con dition s w hen concrete is placed in the m orning, saw ing ou tside n orm al w orking hou rs,requiring special ligh ting an d sup ervision,m ay be n eed ed.In som e instan ces, w hen the joint is to b e sub sequ en tly w iden ed to receive a joint sealer,early saw ing leaving a slightly ragged joint edge Concrete Ground Floors and Pa vements : Pa rt 1
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CONSTRUCTION
m ay be acceptable.W here dow elled tran sverse contraction joints are specified ,the d ow els should be p refab ricated in assem blies and securely fixed to the sub grade or subbase prior to con crete p lacing to resist displacem en t w hen con crete is placed over them (see Figu re 2.25). The dow els should be align ed parallel to b oth the direction of m ovem ent and the surface of the pavem ent to w ithin close toleran ces to prevent‘ locking-up’ of the joint.To perm it m ovem en t,the dow els m ust be perfectly straigh t,w ith cleanly saw n ends an d m ust be provided w ith a ‘ bo ndbreaker’ on one side o f the joint. FIGURE 2.2 5
TYPICAL DOWEL-SUP PORTASS EMBLY (the bot tom supporting wire must be cut once the cage is fixed to subb as e and b efore concrete placing)
Line of transverse joint L/ 2
L/ 2
Tack w elds
Tie wire Dowel (debonded for L/2 + 25 mm)
t
Subbase fixing
t/ 2
Fabric bent into shape shown and tack welded to give correct location to dowel
Fabric must be cut once cage is fixed to subbase and before placing concrete
8.2.2 Longitudinal contraction joints W hen concrete is placed in w idths exceeding ab ou t 5m ,it m ay b e n ecessary to p rovide a cen tral longitudinal joint to controlcracking in this direction.The joint m ay either be saw n or form ed as discussed in Section 8.2.1 of this chapter. These joints are som etim es referred to as hinge or w arping joints.The joint,if form ed ,should be at least 1/3 o f the depth of the slab.
50
8 . 3 CONS TRUCTION JOINTS
8.3.1 Trans verse co nst ruction joints ns truction These joints are provided tran sversely to the direction of placing. Joints installed at the en d of each day’ s placing operations are norm ally constructed at a location that relates to the spacing of the tran sverse con traction joints.They should be form ed by a steel or tim ber head er board firm ly staked to the subbase,and som e m ean s of load transfer (such as dow els or tie bars) sho uld be provided. Joints required at any location w ithin a p avem en t slab w hen con crete p lacing is interrupted by an em ergen cy such as plan t failure,a break dow n in con crete supply,or by adverse w eather con dition s,sho uld be con structed using the follow ing principles. If the interruption occurs near the end of a p an el,at or very close to a tran sverse contraction joint,a d ow elled or tied joint as ap propriate sh ould be p rovided sim ilar to that described abo ve. O therw ise,the joint sho uld be located w ithin the m iddle third of the len gth of a pan el,a key sho uld be form ed an d deform ed tie b ars inserted in place of dow els.In reinforced slabs,the reinforcem en t sho uld be con tinued throu gh the joint to p reven t m ovem en t an d to ensure that the slab acts m onolithically.
8.3.2 Longitudinal construction joints L ongitudinal con struction joints are constructed betw een ad jacen t paving lan es at the location of the side form s.To provide for load transfer,these joints are n orm ally fitted w ith dow els or tie bars.In reinforced slab construction,the reinforcem ent m ay be con tinuou s throu gh the side form s.
8 . 4 IS OLATION JOI NTS Isolation joints are full-dep th joints w hich allow indepen den t m ovem en t of the slab on each side of the joint.They are used to isolate the p avem en t slab from perim eter w alls, m achinery an d colum n bases,and any other fixed o bstructions in the p avem en t.This typ e o f joint is con structed by providing a com pressible filler m aterial (such as selfexp an ding co rk) over the fulldep th of the slab.
CONSTRUCTION
9. P ROTECTION OF CONCRETE P AVEMENT W here con crete pavem en ts are con structed at an early stage of a project,they sho uld b e protected from dam age by follow ing trad es.Fo ot traffic should be kep t off new lycom pleted surfaces for on e or tw o days an d ligh t pn eum atic-tyred traffic for about seven days.This tim ing w ill of course depen d on the strength develop m ent of the con crete; in cold w eather,surfaces w ill harden m ore slow ly. If early load ing o r trafficking o f the pavem en t is un a-
voidable,the stren gth develop m en t at early ages sho uld be m on itored by cylinder testing an d the structural adequacy of the slab checked for these early stren gths. Po lythene sh eeting u sed for curing w ill assist to a lim ited degree in protecting the co ncrete surface from deterioration. H ardbo ard sheets or tim ber bearers laid on con centrated traffic rou tes w ill assist in protecting the su rface w here early use of the pavem en t is necessary.
10. ADVERS E WEATHER CONDI TIONS
10.1 10. 1 GENERAL GENERAL A dverse w eather con dition s are d efined as any com bination of clim atic con ditions that m ay im pair the q uality o f the plastic or harden ed con crete.
10. 2 CONCRETING IN HOTWEATHER The effects of high tem peratures can b e sum m arised as follow s: •Shorter setting tim es an d early stiffen ing •Increased rates of harden ing •Po ssible stren gth loss
plastic shrinkage cracking (this sho uld be repeated as necessary during an y sub sequ en t op eration s up to final finishing) •Im m ed iate cu ring after final finishing is com plete •M oist curing to con trolcon crete tem perature •R estricting placing to nigh t tim e w hen am bient tem peratures are generally low er.
10. 10. 3 CONCRETING IN COLD COLD W EATHER WEAT The p rim e effects of low tem perature o n freshly p laced con crete are:
•D ifficulties in placing an d finishing
•a d ecrease in the rate at w hich the con crete sets and gains stren gth,w ith a resultan t increase in the tim e taken to finish the co ncrete;
•D an ger of cold joints –a cold joint is form ed w hen plastic con crete is placed against con crete that has set an d com m enced h ardening.
•(at tem peratures below freezing) physicaldam age to the con crete in the form of surface scaling or bu rsting, an d the cessation of hyd ration.
P recaution s for hot-w eather con creting shou ld be initiated w hen the am bien t tem perature is expected to exceed 30 to 35°C .Th ese precaution s m ay con sistof one or m ore of the follow ing p ractices:
P recaution s w hich m ay be taken to p rotect the con crete in cold w eather m ay con sist of on e or m ore of the follow ing practices:
•Increased ten den cy for preharden ing cracking
•D am pen ing form s,reinforcem ent and subbase •Erecting w ind breaks and sunshad es to p rotect expo sed concrete surfaces •C ooling con crete ingredien ts •(D uring tran sport) cooling containers,pipelines,chutes, etc •C om pleting the tran sporting, placing an d finishing of concrete as rap idly as is practicab le •Inform ed usage o f set-retarding adm ixtures (to cou nter prem ature stiffen ing of the fresh m ix) •Im m ed iately follow ing the initial finishing operation, spraying a fine film of aliphatic alcoholover the exposed con crete surface –to lim it evap oration an d help con trol
•P roviding h eaters,insulating m aterials,an d en closures if sub-zero tem peratures are exp ected •U sing h igh -early-strength cem ent •H eating the m aterials (the tem perature o f the concrete w hen it is placed in the form s shou ld be abo ve 5°C ) •N ot placing con crete on frozen grou nd •Ensuring m ean s of m aintaining suitable curing tem peratures (w hen using Type G P (gen eral purpose portland) cem ent the tem perature of the con crete sho uld be m aintained at 20°C or above for 3 days,or 10°C or above for 5 d ays) •Insulating the co ncrete (a thick insulating blan ket is often sufficien t protection for pavem en ts).
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CONSTRUCTION
11. CONS TRUCTION TOLERANCES FOR P AVEMENTS URFACES
11.1 TYPICAL CONCRETE P AVEMENTS
11.3 MEA MEAS S URING EQUIP EQUIP MENT
The tolerances specified for surface regularity of concrete industrial pavem en ts should b e ap propriate to the function of the p avem en t an d the surfacing m aterial to be used, if any.
For sm aller pavem ent areas,surface regularity m ay be assessed using a m etalstraigh tedge w ith shim s and spacers (or rollers) placed progressively along the surface (see Figure 2.26).
Fo r application s w here pavem en t flatness is no t a p rim e consideration,such as areas w ith ped estrian traffic,or light pneu m atic-tyred vehicles only,it is sug gested that,using average standards o f w orkm anship and supervision ,the follow ing toleran ces should be achieved : •The d eviation of any p oint on the p avem ent surface from a straigh t line joining any tw o points on the surface 3m apart sho uld n ot exceed 10m m . •Th e levelof any p oint on the pavem ent shou ld not deviate by m ore than 15m m from the specified d esign level. C loser surface toleran ces m ay be required for pavem en ts subject to heavy vehicular traffic or w ith special operational needs. The follow ing tolerances are regarded as achievable w ith accu rate placem en t of screed rails an d carefully controlled levelling,floating an d trow elling operations:
For larger areas,it m ay be m ore con ven ien t to use a m obile straigh ted ge, com prising a series of light trusses m ou nted on w heels w ith a sm all sensing-w heel located at m idspan.A s the straigh tedge is m oved over the pavem ent, the m ovem en t of the sensing w heel op erates preset lim it sw itches connected to a w arning d evice to d etect ou t-oftolerance areas. A ccurate m easurem en t of the flatness of‘ superflat’ pavem ents m ay be carried ou t w ith convention al surveying equ ipm ent or by u sing the W alking P rofilom eter. FIGURE 2.25
STRAIGHTEDGE TESTING OF SURFACE REGULARITY
3-metre-long metal straightedge 6-mm -dia. roller should be able to pass under straightedge for its full length
•The deviation from a straigh t line sho uld n ot exceed 5m m over a 3m leng th.
12-mm-dia. roller should NOT be able to pass anywhere under straightedge
•Th e levelof any p oint shou ld no t be m ore than 10 m m from the specified design level. 6 dia.
11.2 ‘ S UP ERFLAT’ P AVEMENTS H igh -den sity industrial w areh ouses introd uced in recent years use n arrow aisle, turret typ e stacking veh icles that require especially flat pavem en t surfaces for their efficien t operation.‘ Superflat’ pavem en ts are d iscussed in m ore detail in Section 2.4 in C hapter 1 D esign . Since con struction of such close-toleran ce pavem en t surfaces can be exp en sive, the exact requirem en ts for a project an d the p avem en t areas over w hich these toleran ces ap ply,should b e established beforeh an d b y con sultation betw een the h andling-equ ipm ent m anufacturers,the client an d the contractor. M easurem ents of flatness should be m ade frequ ently during construction,an d any out-of-tolerance high areas grou nd to level w ith a p ow ered grinding m achine.
52
M ethod of determining if a surface meets a tolerance of ± 3 mm as measured beneath a 3-m etre straightedge
12 dia.
9 9-mm shims each end
GUI DE TO SPECIFICATION S
Cha pter 3: Guide to Specifica tions I N TRO D U CTI O N
55
1. G EN ERA L
56
7.5 Compacting ........................................................... 63 7.6 Finishing ............................................................... 63 7.7 Levelling ............................................................... 64
1.1 Referenced Documents ..........................................56
7.8 Floating ................................................................. 64
1.1.1 New Zealand Standards ................................. 56
7.9 Trowelling ............................................................. 64
1.1.2 American Society for Testing &Mat erials ....... 56
7.10 Surface texturing ................................................... 65
2 . M ATERI ALS
56
8 . CU RI N G
66
2.1 Concrete ................................................................ 56
8.1 General ................................................................ 66
2.2 Cement ................................................................. 57
8.2 Initial curing ......................................................... 66
2.3 Aggregate ............................................................. 57
8.3 Moist curing ......................................................... 66
2.4 Water .................................................................... 57
8.4 Sprayed membrane curing .................................... 66
2.5 chemical admixtures ............................................. 57
8.5 Impermeable-sheet curing..................................... 67
2.6 Fly ash, slag and silica fume .................................. 57 2.7 Reinforcement, dowels and Tiebears ..................... 57
9 . JO I N TS
67
2.8 Curing materials .................................................... 57
9.1 General ................................................................. 67
2.9 Underlay membrane ..............................................58
9.2 Construction joints (tied or free) ............................ 67 9.3 Contraction joints (free joints) .............................. 68
3 . EQ U I PM EN T
58
9.4 Isolation joints ..................................................... 69
3.1 General .................................................................58
9.5 Dowels and tiebars ............................................... 69
3.2 Maintenance ......................................................... 58
9.6 Joint sealing ......................................................... 69
4 . FO RM W O RK
59
10 . PRO TECTI O N O F CO NCRETE P AVEM EN TS
70
4.1 Forms .................................................................... 59
10.1 General ................................................................. 70
4.2 Form setting .......................................................... 59
10.2 Construction traffic................................................ 70
4.3 Scratch template ................................................... 59
10.3 Access for concrete placing ....... ....... ....... ....... ....... . 70
4.4 Subbase ............................................................... 60
10.4 Unhardened concrete ............................................ 70
4.5 Form removal ....................................................... 60
11. AD VERS E W EATH ER CO N D I TI O N S 5 . U N D ERLAY M EM B RA N E
61
71
11.1 Definition .............................................................. 71
5.1 Storage ................................................................. 61
11.2 Concreting in hot weather...................................... 71
5.2 Laying ................................................................... 61
11.3 Concreting in cold weather .................................... 71
5.3 Repairing of membrane ......................................... 61
11.4 Protection against rain .......................................... 71
6 . P LACI N G A N D FI XI N G REI N FO RCEM EN T
61
12 . TES TI N G & A CCEPTA N CE O F CO N CRETE
72
6.1 General ................................................................. 61
12.1 Code requirements ................................................ 72
6.2 Pre-set method...................................................... 61
12.2 Other requirements ............................................... 72
6.3 Strike-off method .................................................. 61
12.3 Acceptance criteria ................................................ 72
6.4 Placing tolerances ................................................. 61
12.4 Rejection criteria ................................................... 72
7. PLACI N G AN D FI N I S H I N G
62
13 . CO N S TRU CTI O N TO LERA N CES
73
7.1 Approval .............................................................. 62
13.1 General ................................................................. 73
7.2 Delivery ................................................................ 62
13.2 Standards to be achieved ...................................... 73
7.3 Placing restrictions............................................... 62
13.3 Testing procedures ....... ...... ....... ....... ....... ...... ....... . 73
7.4 Placing ................................................................. 62
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GUI DE TO SPECIFICATIO NS
SCOPE
INTRODUCTION
This C hapter has been develop ed to show how specification m atters m igh t be d ealt w ith.
The specification for a p avem en t project w ould typ ically be divided into the follow ing parts:
Th e N Z Stand ard N Z S 3109 C on crete C on struction in con jun ction w ith S tandards N Z S3104 C on crete Production H igh & Sp ecialG rade25and N Z S 3114 S pecification of C oncrete S urface Finishes are the p rim ary stan dards for com plian ce,particularly w here construction is deem ed to 26 fall w ithin the requirem en ts of the N Z Building A ct .
•Site w orks
The use of these do cum en ts require the defining o f the term ‘ C onstruction R eview er’ in N Z S 3109 in term s of respo nsibility of the d esign er on the one h an d an d con structor on the other.
The p urpose of this ou tline guide specification is to provide typical clau ses for those p arts of the sp ecification dealing either w ith the construction of the concrete slab,or the parts w hich affect this construction.It is not ap propriate to include a cop y o f this docum en t in a p roject specification, nor to refer to it as a stan dard specification,since each clau se w ill have to be review ed as to its relevan ce.A bracketed space (…) has been left w herever it is necessary for users to provide inform ation ap propriate for a p articular project.
The other issue is that w hile gen eric aspects of w orkm an ship are covered in N Z S 3109, the specifics relating to slab or pavem en t con struction are no t included . It is suggested that m uch o f w hat is included in this chapter should form the p art of a m ethod statem ent requ ired from the contractor to dem onstrate that app ropriate m atters have been con sidered prior to the com m encem ent of w ork and m aintained during the con struction of the slab or pavem en t. In Part1 of this m an ual,the design has been assum ed to be the responsibility o f the engineer,w ith the u sual con tractural relationship w ith the contractor an d sub con tractors. In the u se of special floor ap plications.an alternative approach is for the engineer to provide o utline requ irem en ts for the p erform an ce of the floor,but the actual design , detailed specification an d construction is passed to the specialist flooring co ntractor. M ore specific details of this con tractural arran gem en t is con tained in Part 2 w hich d eals w ith specific engineering design .
•D rainage •Sub grade preparation •Subb ase con struction •C on crete pavem ent construction .
This outline gu ide specification does n ot include clau ses related to gen eral requirem en ts such as order of w orks, setting out,records,inspections,etc,nor do es it cover requirem en ts for clau ses of the w ork not directly related to con crete. In using N Z S 3109 it is considered that using the follow ing sp ecification clau se contained in the project docum ent: “The constru ctor shall requ ire the concrete sup plier to subm it to the designer a relevant produ cer statemen t with current inde pen den t certification records to indicate that the plant, concrete production and concrete testing a re in full comp liance with N ZS 3104 an d clau se s 6.10 an d 6.11 of NZ S 3109.”
This w ill effectively p lace the responsibility of m eeting the requ irem ents of N Z S 3109 C lause 6.10 an d 6.11 in the han ds of the con crete prod ucer. H ow ever,it still requires the designer to specify the perform an ce requirem en ts needed for the con crete prior to establishing this agreem en t. It is also strongly suggested that the follow ing specification clause should be included in the p roject docu m en tation : “The constructor shall prod uce a method statem ent for placing, finishing and protecting the fresh concrete giving the p recautions that will be taken to prevent the influences of the weathe r causing prem ature cracking of the concrete elemen t.”
C han ging clim atic con dition s an d the u se of differen t types of con crete can con tribu te to prem ature cracking of concrete elem en ts,particularly concrete floors.
54
GUI DE TO SPECIFICATION S
1. GENERAL
1.1
2. MATERIALS
REFERENCED DOCUMENTS
1.1.1 New Zea land Zeala nd Sta nda rds The follow ing S tan dards are referred to and form a part of this specification to the extent indicated in the ap propriate clause:
2. 1
CONCRETE CONCRETE
2.1.1 Th e concrete for the variou s elem en ts of the p avem en t shall contain the specific typ es of m aterials listed in Table 1,an d these m aterials shallsatisfy the requirem en ts detailed in C lau ses 2.2 to 2.6.
N Z S 3104 C oncrete Produ ction H igh and SpecialG rade N Z S 3109 C oncrete C onstruction N Z S 3122 Portland and Blended C em ents27 N Z S 3402 SteelR einforcing B ars for C on crete N Z S 3421 SteelR einforcing W ire for C on crete28 N Z S 3422 W elded W ire Reinforcing Fabric for C on crete29 30
TABLE 1
Concrete materials a nd so me properties req uirements PAVEMENTELEMENT Element 1 Element 2
MATERIAL MATERIAL
Cement t ype Min. ce ment co ntent (kg/m3)
A S 1478/N Z S 3113 C hem icalA dm ixtures for C on crete
Maximum supplementary cementitious materials 1
A S 3582
Ad mixt ure s
A S 3799
Su pp lem entary C em entitiou s M aterials for use w ith Portland C em ent Part 1 Fly A sh Part 2 S lag –G rou nd G ran ulated Iron BlastFurnace Part 3 S ilica Fu m e31 Liquid M em brane-Form ing C uring C om pounds for C on crete32
1.1.2 America n S ociety for Tes ting &Ma terials (AST (ASTM) C 171–97 Stan dard S pecification for Sheet M aterials for C uring C on crete33i s referred to,an d form s part of this specification to the extent indicated in the ap propriate clau se.
Ma x. w/c ratio Strength
– Compres sive – Flexural – Indirect Tens ile
Slump (mm) Max. nominal coarse aggregate size (mm) 1 S upplementary cementitious materials, s uch as fly as h, expresse d as a percentage of cement content.
2.1.2
W here specific types of m aterials are n ot required by Tab le 1 for a particular elem en t then a selection shall be m ade from the gen eral types listed in C lauses 2.2 to 2.6 an d approval shall be ob tained for the u se of these m aterials prior to the com m encem ent of the w ork.
2.1.3
C hem icaladm ixtures m ay be u sed on ly if app roved as d etailed in Tab le 1.
2.1.4
The con crete for the variou s elem en ts of the p avem ent shall be so d esign ed and p rod uced that the properties listed in Tab le 1 are ach ieved .
2.1.5
The selection ,proportion ing an d m ixing of the con crete m aterials shall be such as to prod uce a m ix w hich w orks read ily into corners an d an gles of the form s and arou nd reinforcem ent w ith the m etho d o f placem ent em ployed on the w ork,bu t w ithou t perm itting the m aterial to segregate or excess free w ater to collect on the surface.The resultan t concrete shall be sou nd an d have the other qualities specified .
2.1.6
P rem ixed con crete shall be m anufactured an d sup plied in accordan ce w ith the requirem en ts of N ZS 3104.
Commentary A l ist may be necessary and should be checked to ensure th at onl y t hose documents referr ed to are included. W here more recent Standards have been publ ished, these should replace th ose li sted. There is only one Table in this Chapt er and i t does not have a prefi x number in order for C lauses to refer to
– Ma n d a t ory – Permitted – Banned
Table 1 in t hi s gui de specifi cati on.
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Commentary: Table 1 should be completed to show mandatory requi rements in terms of m ateri als and properti es for each element of th e pavement .
2. 6
FLY AS H, S LAG AND S ILICA FUME Fly ash ,slag an d silica fum e shallcom ply w ith the requ irem ents of A S 3582.1,A S 3582.2 an d A S 3582.3 respectively.
only w ith t he Clauses 2.2 to 2.6 as appropr iate.
2. 7
REINFORCEMENT, DOW ELS AND TIEB EARS EARS DOWELS
CEMENT
2.7.1
R einforcem ent shall com ply w ith the requ irem ents of N Z S 3402,N Z S 3421 and N Z S 3422,as appropriate.
2.7.2
R einforcem en t (im m ediately p rior to con crete placing) shallbe free from loose m illscale, loose rust, m ud,oil,grease an d o ther non-m etallic coatings w hich w ou ld redu ce the bon d betw een the con crete an d the reinforcem en t.N evertheless,deform ed bars an d w elded w ire fabric having m ill scale o r rust shall be d eem ed to com ply w ith this section if a sam ple of such reinforcem en t,after w ire brushing b y h an d,has dim en sion s of cross-section an d a m ass not less than those required by N Z S 3402 and N Z S 3422.
W here specifi c requi rements for materi als are not detai led in Table 1, then th e materials have to comply
2. 2
2.2.1 Portland an d b lended cem ent shall com ply w ith the requ irem ents of N Z S 312234.Type G P –G eneral P urpose Portlan d cem en t –shall be u sed u nless otherw ise approved. Commentary: This section shoul d be amended if another ty pe of cement is preferr ed. For example, the use of Type 34 SR (sulphat e resisti ng) cement may be advant ageous for pavement s subject t o some for ms of mi ld chemi cal att ack. For more detai l on the use of shr in kage-li mi ted cement r efer t o D rying Sh rinkage o f C em ent and 35 C on crete .
2. 3
Commentary: The bond properti es of reinfor cing bars and ti ebars are not affected by li ght surf ace rusting wh ich for ms on steel after nor mal exposure to the atm osphere, and th is need not be removed.
AGGREG AGG REG AT ATE A ggregates shall com ply gen erally w ith N Z S 3121. Commentary: This section shoul d specify th e test procedur e and the associated li mi ts where alternat ives are provi ded i n N ZS 3121. The test procedur e to be in cluded should be that most suit able for t he part icular project.
2.7.3
D ow els shall be one-p iece,straight,plain,round steel bars com plying w ith the requ irem ents of N Z S 3402,and of the sizes show n in the d raw ings.They shall be saw cut to len gth prior to delivery to the site an d the en ds shall be square and free from bu rrs. D ow els shall be clean an d free from m ill scale or loose rust.
2.7.4
Tie b ars shall be deform ed bars com plying w ith the requ irem ents of N Z S 3402, and o f the size show n in the draw ings.
2. 8
CURING MATERIALS
A Cement & Concrete Associati on of New Z ealand publication A lkaliA ggregate R eaction –G uidelines on
M inim ising the R isk of D am age to C on crete TR 336 wi ll help specifi ers to understand t he practi cal i ssues rai sed by this phenomenon.
2. 4
WATER W ater shall be free from m atter w hich in kind and quan tity is harm fulto concrete or steel reinforcem en t. W ater shall m eet the requ irem ents of N Z S 3121. Commentary: If there is any doubt about t he quali ty of wat er li kely to be used, eg in a r emote locati on, it may be desirable to specify that a sample be submi tt ed for analy sis and appr oval pr ior to the commencement of the project.
2. 5
CHEMICAL ADMIXT ADMI XTURES
2.5.1
C hem ical ad m ixtures,w here specified in Table 1,or if approved for use,shall com ply w ith the requirem en ts of N Z S 3113 or A S 1478.
2.8.1 L iqu id m em brane-form ing curing com po un ds shall com ply w ith the requ irem ents ofA S 3799 o r A S TM C 30937. Commentary: Of the many dif ferent forms of liqui d membrane-forming cur in g compounds available, the wax- based emul sions and chlor inated ru bber types are preferr ed an d r ecommended. Recent research has shown th at special safety precauti ons are necessary for t he use of chlori nated ru bber compounds. A wh it e pigmented dye is sui table to vi sually check that the pavement has been sprayed. Wax- based curi ng compounds are generall y effi cient in
Commentary: In cold areas, air- entrai ni ng agents are recommended to i ncrease fr eeze-th aw resistance.
terms of moistur e retenti on, but can pr ovide a sli ppery
The use of admixtur es that w il l result in high slumps or
be used w hen th e pavement i s to be subject to earl y f oot
‘f low able’ concrete is not r ecommended in pav ements
or vehicular t raffi c.
wi th crossfalls or gradi ents of 3% or more.
If pavement coati ngs are specifi ed, the designer should
surface. For this reason, i t is recommended that they not
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GUI DE TO SPECIFICATION S
2.8.2 Im perm eable sheet m aterials shall com ply w ith the requirem ents ofA STM C 171. 2.8.3 W here curing com po unds perm itted by the specification are used they shall be ap plied in accordan ce w ith the m an ufacturer's instructions and shall not be used on any surface u ntilthe successful com pletion of the follow ing: • Tests to prove that no discolouration of off-form or other special surfaces w ill occur due to the com pou nd o r interaction betw een it and an y add itive,form coatings or release agen ts. • Tests to show that the adhesion of any applied concrete or other finish or covering w ill not be adversely affected by the com pou nd. C ertified existing test results w hich satisfy the ab ove requirem en ts shall obviate the n eed for these special tests.
3. EQUIPMENT
3. 1
GENERAL D epen dable and sufficien t equipm en t that is appropriate and ad equ ate to m eet the app roved plan and schedule for the w ork sp ecified shall be furnished by the contractor an d assem bled at the site of the w ork in sufficien t tim e before the start of paving to perm it thorough inspection,calibration,ad justm en t of parts, and the m aking o f any repairs that m ay be requ ired. Commentary: The range of equi pment sui table for use in constructing pavements is wi de and var ied. Thi s section has been w ri tt en i n thi s form so as not to r estr ict t he use of equipment wh ich the contractor owns, nor w it h w hich the contractor is famil iar ; or to restr ict i nnovation. The onus is on the supervi sor t o reject equipment w hi ch wi ll not enable the requir ements of the specifi cation t o be 24 achieved .
Commentary: Discolour ati on of the pavement sur face may or may not be a major concern . It is import ant t o check the effect of any curi ng compound on the adhesion of any appli ed coatin g, includi ng paints.
The condit ions of tenderi ng should i nclude the requi re- ment that detai ls of th e intended equi pment to be used are to be provi ded.
2. 9
UNDERLAY MEMB RANE The underlay m em brane shall be flexible,polym eric film ,nom inally 0.25m m thick and m anufactured from suitable h igh-quality ingred ien ts satisfying the 38 requ irem ents of the N ew Z ealand Building C od e. Commentary: Some manuf actur ers of impermeable sheets use (par ti all y or total ly ) recycled materi als in producti on. It i s suggested that the specifi er in qui res about the pr operti es of the sheet wh ere recycled materi als are used.
3. 2
MAINTENANCE The app roved equ ipm ent shallbe m aintained in go od w orking condition.It shallbe checked regularly for w ear,setting an d calibration.If not up to the required stan dard,the equ ipm en t shall be repaired or rep laced prior to its con tinued use on the p roject.
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4. FORMWORK
4. 1
FORMS
4.1.1
Form s shall be of steel or season ed,dressed tim ber plan ks fitted w ith a m etal an gle or chan nel section con structed to finish flush w ith the face of the form , covering the full w idth of the top of the form ,an d full dep th of slab. Commentary: It is desirable to prot ect t he top sur face of ti mber f orms to provi de a smooth and dur able datum for screeding by i ncorporati ng a steel angle or channel. H owever, for small er projects or w here the forms are not to be re-used, thi s requi rement may be wai ved and unpr otected timber forms permi tt ed. The condit ions of tenderi ng should i nclude the requir e- ment that detail s of t he type and quantit y of forms int ended to be used are to be provi ded.
4.1.2
4.1.3
4.1.4
4.1.5
4.1.6
Form s shall be free o f w arps,bends or kinks,an d the top surface of the form shallnot vary from a 3m straigh tedge placed alon g the top edge by m ore than 3m m .
4.2.1 The subg rade or sub base under the form s shall be firm an d cut true to level so that each form section w hen placed w illbe firm ly in contact for its en tire len gth an d slab w idth.A lternatively the form s m ay be seated on : • approved hardw oo d o r steel shim s or plates of w idth equ al to the slab w idth of the form s,and not less than 200m m long, installed at intervals not exceeding 1.5m an d in con tact over their fullarea w ith b oth the form and the subb ase;or • a cem ent/sand m ortar bed of proportion s 1 cem ent:3 sand. 4.2.2 The form s shall be staked into p osition w ith steel stakes,not m ore than 1.5m apart,so that the top of the form do es no t deviate by m ore than 3m m from the required level. Commentary: It i s import ant that the forms are adequately staked to prevent movement dur in g placing. The figure of 1.5m n eed not be mandat ory. It is r ecom- mended as being appropri ate fr om experience. The form sett in g tolerances of 3mm in level (Cl ause 4.2.2) and 6mm in ali gnment (Clause 4.2.3) may al so be
Fo rm s shall be of such cross-section an d stren gth an d so secu red as to resist the p ressure of the con crete w hen placed,an d the im pact an d vibration of any equ ipm en t they support,w ithou t springing or settlem en t.
Tighter t olerances are requir ed for superfl at fl oors.
Th e m ethod of conn ection betw een form section s shallbe such that the joints do not m ove in any direction,an d continuity of line, level an d grad ien t across the joint is m aintained . Fo rm ing strips for the keyw ay o f con struction joints, w here req uired ,shall be securely fasten ed flush against the face o f the form s so that the cen tre o f the key is at the m id-dep th of the slab,w ithin the toleran ces show n in the d raw ings.
W here dow els or tiebars are required in con struction joints,the form s shallallow for their insertion an d for rigidly supporting them in the correct align m en t.
4.1.8
Form s shall be cleaned an d coated w ith an ap proved oil or release agen t each tim e b efore co ncrete is placed.
4.1.9
A ll form s shall be ap proved prior to com m encem ent of con creting operations.
58
FORM S ETTING ING
The slab w idth of the form shallbe su fficien t to prevent any o verturning or rocking w hen the form s have been pinned an d are in use.
Commentary: This section may be deleted if there are no keyed join ts in the part icular pr oject. 4.1.7
4. 2
var ied i f deemed appr opri ate. These val ues have been established as being represent ati ve of what can be achi eved wi th good-qual it y w orkmanshi p in t he fi eld.
It is suggested that for pr ojects requir in g str ict control of pavement level and smoothn ess, the contr actor shoul d employ a sur veyor for sett in g out and checking the forms.
4.2.3 The form face shall be verticalan d not vary m ore than 6m m from the requ ired align m ent. 4.2.4 The stakes shall be of sufficien t len gth to hold the form s securely in position during the concrete placing an d finishing operations. 4.2.5 Fo rm sections shall be tightly locked together.A ll w edg es,keys and form locks on the form s shall be m aintained tigh t during placing, spreading an d finishing of the concrete. 4.2.6 Form w ork shall be set and checked at least on e day prior to placing the co ncrete and the setting of the form s shall be approved by the sup ervisor before any con crete is placed . Commentary: The supervisor shoul d check the forms for ali gnment, continu it y and r igidi ty. Any problems should be recti fi ed and approved before approval is given t o place concrete.
GUI DE TO SPECIFICATION S
4. 3
S CRATCH TEMP LATE D etails regarding the con struction an d o peration of scratch tem plates are contained in C hapter 2 C on struction.
4.3.1
A scratch tem plate shall be used for checking the shap e an d level of the subb ase.The tem plate shall be design ed to o perate from the side form s or the concrete in ad jacent pan el strips,an d shall be of such stren gth an d rigidity that the d eflection at the centre of the tem plate is not m ore than 3m m .
4.3.2
4. 4
The tem plate shall be provided w ith teeth projecting do w nw ard to the subbase at no t m ore that 300m m intervals,an d set to the required profile o f the subbase surface.
4.5.2
W hen con dition s on the w ork are such that the early stren gth d evelopm en t of the con crete is delayed ,the form s shall rem ain in place for a longer period as directed. Commentary: The conditi on most l ikely to contri bute to delayed earl y strength development i s cold w eather. The use of blended cements may al so in fl uence form str ippi ng times.
4.5.3
Form s shall be rem oved w itho ut dam aging the concrete,dow el bars or tieb ars.Bars or other tools shall not be u sed as a lever against the concrete in rem oving the form s.
4.5.4
A ny dam age to the con crete occurring d uring form rem oval shall be repaired prom ptly by an approved m ethod.
SUBBASE
4.4.1 The subbase shall be free o f foreign m atter,w aste concrete and other debris at all tim es,an d (after setting of the form s) shall be finished to the required profile of the bottom of the pavem ent as show n in the draw ings. 4.4.2 Th e sub base shallbe tested w ith an approved tem plate as detailed in C lause 4.3 an d trim m ed as necessary. 4.4.3 Th e subb ase shallbe m aintained in a sm ooth, com pacted con dition in con form ity w ith the required profile and level,untilthe concrete is in place. 4.4.4 Th e subb ase shallbe d am pened (bu t not saturated) and kep t dam p prior to placing concrete. Commentary: Thi s secti on is not appli cable when concrete is pl aced di rectl y over an imperm eable materi al (eg polyt hene vapour barr ier) or a material of relativ ely low perm eabil ity (eg bit umi nous sealed sur face or l ean- mi x concrete).
4. 5
FORM REMOVAL
4.5.1
Fo rm s shall rem ain in place at least (…) ho urs after the con crete h as been placed. Commentary: The appropriate time for the str ippi ng of forms wil l var y according to the envi ronment and t he type of concrete used. An absolut e mini mum period of eight hours is recommended. A peri od of 48 hour s should be specified; however, common pav ing practice is to place concrete in one day and to stri p the form s on the foll owi ng day. Some contr actors have found t hat t ooli ng th e surface of the concrete adjacent to the form enhances th e strength of t he concrete edge, reducin g the risk of damage dur in g form removal and subsequent construc- ti on wor ks. Thi s requi rement may be specifi ed i n Cl ause 7.6.
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5. UNDERLAY MEMBRANE Note: If no underlay membrane is requir ed, these clauses wi ll not be requi red.
5. 1
6. P LACING AND FIXING REINFORCEMENT
6.1
S TORAGE The u nderlay sh all be d elivered to the site in suitab le protective packag ing.The p ackaging, han dling an d storing of the u nderlay shall en sure that it is not pu nctured,torn,or otherw ise dam aged at any tim e. The u nderlay m aterial shallhave sufficien t resistan ce to sunlight and associated rad iation,so that its specified properties are unaffected by its exp osure.
5. 2
LAYING The u nderlay sh all be laid over the levelled an d com pacted subbase.Sh eets of m axim um practical w idth to suit the layout shall be used an d shall be arran ged such that overlaps face aw ay from the direction of con crete p lacem en t.The sh eets shall be lapp ed as recom m end ed by the m anu facturer,bu t no t less than 150m m .
5. 3
REPAIRING OF MEMBRANE MEMBRANE REPAIRING OF Th e m em brane shall be inspected after laying and before the concrete is placed .A ny p unctures or tears shallbe patched an d sealed.
GENERAL R einforcem en t shall be provided in the locations show n in the draw ings and shall be p laced by the m ethod described either in C lause 6.2 or C lause 6.3. L aps and other details shallcom ply w ith N Z S 3101 and N ZS 3109. Commentary: Generally, reinforcement w il l be placed and fixed prior to concreting as detailed in Clause 6.2. However, in some circumstances, eg areas of limited access, it may be necessary to traffi c the area being paved and the presetting of r einforcement may not be possible. In these cases, the method detailed in Clause 6.3 may be used. If only one method is to be permitted (either by pr eference or circumstance), the sections relat ing to t he excluded method should be deleted. The practices of laying reinforcing fabric on the subbase and hooking int o posit ion after concrete is placed, or walking the fabric in from the surface of the concrete, are not acceptable as these methods provide no assurance that the reinforce- ment w il l end up in a true plane at the required level.
6.2
P RE-SETMETHOD
6.2.1 R einforcem en t shall be placed an d securely h eld in its correct position by the u se of approved sup ports. C hairs,spacers and stools used as sup ports for reinforcem ent shall be purpose-m ade of m etal, con crete o r plastic.Scrap pieces of w ood,aggregate, brick or the like shall not be u sed. 6.2.2 The sup po rts shall be adequ ate to w ithstand con struction traffic an d shallbe sufficien t in num ber an d spacing to m aintain the reinforcem en t in its correct position during the con crete p lacing o peration.
6.3
S TRIKE-OFF METHOD METHOD
6.3.1 The concrete shall be placed,struck-off an d com pacted to the level of the reinforcem en t as sho w n in the d raw ings.The reinforcem en t shall be laid upon the com pacted surface,an d the rem aining con crete shallthen be p laced,com pacted an d finished in the requ ired m ann er. 6.3.2 A ny p ortions of the low er layer of con crete w hich have develop ed initial set,or w hich have been placed for m ore than 30 m inutes w ithou t being covered by the upper layer,shall be rem oved an d replaced w ith new ly m ixed con crete.
6.4
P LACING TOLERANCES U nless show n otherw ise in the d raw ings,the reinforcem en t shallbe fixed and m aintained in its correct position w ithin the toleran ces specified in N Z S 3109.
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7. P LACING AND FINIS HING
7. 1
7. 2
DELIVERY
7.2.1
The concrete shall be tran spo rted from the delivery vehicle to its final position as rap idly as possible by a m ean s w hich w ill preven t segregation or loss of m aterials or con tam ination ,an d in such a w ay that prop er placing an d com paction of the con crete w ill not be adversely affected.
7.2.2
P um ped concrete shallbe used only if approved .Th e ap proval of pum ping sh allnot relieve the con tractor of their ob ligation to satisfy the requirem en ts for the con crete as set ou t in C lause 2.1 an d Tab le 1.The con tractor is required to n otify the concrete m an ufacturer w hen a concrete m ix is required to be p laced by pum ping.
7. 3
P LACING RES TRICTIONS
7.3.1
C on crete shall be placed w ithin 90 m inutes from the tim e of batching,or before if the consisten cy of the con crete is such that it cannot be p roperly placed an d com pacted w ithou t the add ition of any m ore w ater to the m ix.Th e tim e lim itation m ay be w aived by agreem ent. Commentary: N ZS 3109 requir es that concrete be discharged fr om tru ck mixers wit hin 90 min utes of the commencement of mixi ng. It al so stat es that th is li mi ta- ti on may be wai ved by th e pur chaser if t he concrete is of such consistency, after 90 mi nutes has elapsed, that i t can be placed wi thout th e additi on of water. In h ot weather or under conditi ons contri butin g to earl y stif feni ng of t he concrete, a time less than 90 mi nutes may be specifi ed by the pur chaser. Conversely in cold condit ions, the lim it may be extended.
The tem perature o f the con crete as p laced shall be not less than 5°C nor m ore than 30°C unless special precaution s are taken in accordan ce w ith C lause 11 . Commentary: The li mit s shown are those given i n N ZS 3109. A lso, refer to the G uide to C on crete C on struction .
The con crete shall not be placed if the slum p is outside the specified lim its. Commentary: N ZS 3109 states that t he concrete shall be deemed to comply w it h t he specifi ed slump, if the measured slump is wi thin th e tolerance for slump given in Table 9.1 in that Standard.
AP P ROVAL ROVAL The co ntractor shallgive at least 24 hours notice o f inten tion to place con crete in any area, to en able the area to b e inspected,checked an d approved prior to com m encem ent of placing. U nless app roval is given no concrete shall be placed in that section of the w orks.A ny concrete placed w ithou t app roval shallbe d ug up an d rem oved from the w orks at the con tractor's expense.
7.3.2
7.3.3
7.3.4
There shall be no addition of w ater or any other m aterial to the concrete by the contractor at the site w ithou t approval,except as provided for by C lause 6.8.2 of N Z S 3109.
7.3.5
Concrete s hall not be placed when hea t, wind, rain, low humidity, or pla nt and eq uipment defect de fectss will prevent the req uirements o f this spe cifica tion being met. Commentary: This is a vital section that requir es full understandi ng of the contr actor because fai lure to consider these issues wi ll guarantee a failed pavement or slab.
7.3.6
P lacing at each location shall be at a rate o f not less than 20 m 3per hou r and the plant,equ ipm ent and labour force shallbe cap able of m aintaining this rate. Commentary: The int ent of thi s clause is to ensure that placing proceeds at a reasonable rate and t hat no ' cold 3 joints' are formed. A fi gure of 20m per hour is consid- ered a reasonable rat e for manual placing methods wit h one crew, but t hi s figur e may be adjusted to t ake into account t he anti cipated envi ronmental condi ti ons and supply ar rangements.
7.3.7
If an interval of m ore than 30 m inutes betw een placing of any tw o consecutive load s of con crete should o ccur,paving operations shall cease an d a tran sverse construction joint (in accordan ce w ith C lau ses 9.2.3 an d 9.2.5) shall be installed .
7. 4
P PLACING LACING
7.4.1
C on crete shallbe dep osited in such a m anner as to requ ire a m inim um of rehandling an d sh all be distribu ted so that w hen con solidated an d finished , the slab thickn ess,surface shap e an d level show n in the draw ings w illbe obtained.
7.4.2
The concrete shall be p laced so that its w orking face is generally vertical,an d norm al to the d irection of placing. It shall be p laced uniform ly o ver the w idth of the slab an d in such a m anner as to m inim ise segregation.
7.4.3
W orkers shall not be perm itted to w alk in the con crete d uring placing w ith bo ots coated w ith soil or other deleterious sub stan ces. Commentary: In some instances, specifiers do not permi t eati ng, dri nki ng or smoking n ear concrete placement and/ or in in ternal areas to min im ise concrete contami nati on.
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7.4.4
w orking o rder shall be not less than on e per 7m 3of con crete placed per hour,an d the con tractor shall en sure that at least one vibrator in w orking order is held in reserve at all tim es.
H and spreading o f concrete shall be don e w ith shovels,not rakes. Commentary: Vibr ators should not be used to spread concrete as it causes segregati on of the concrete mi x.
7.4.5
C oncrete p lacing shall be carried out con tinuously betw een form s and/or con struction joints and in such a m an ner that a p lastic con crete face is m aintained.W here their location is show n in the draw ings,construction joints shall neither be relocated nor elim inated w ithou t app roval.W here no con struction joints are show n in the d raw ings,the location of any w hich m ay be required shall be approved before w ork starts. Commentary: The proper locati on of constr uction joint s is cri ti cal t o the functioni ng of the pavement. The Supervi sor should consult the designer before givi ng any approval to t he relocation of constr uction join ts or t he in clusion of n ew ones.
7. 5
7.5.5
The vibrators shallbe inserted into the concrete to such dep th as w illprovide full com paction,but no deep er than 50m m above the surface of the subbase. The vibrators shallbe o perated by quickly inserting and slow ly w ithdraw ing them in a u niform pattern at a spacing to en sure full com paction over the en tire slab.V ibrators shall be inserted an d w ithdraw n vertically.The duration of vibration shall be sufficien t to p roduce satisfactory com paction,but not longer than 30 secon ds in any one location.V ibrators shall not be u sed for tran sporting and spreading concrete.
7.5.6
Particular atten tion shall be paid to the vibration of con crete ad jacen t to side form s and con struction joints.A ny h on eycom bing w illbe grou nds for rejection of the p laced con crete in accordan ce w ith C lau se 12.4.1 .
7.5.7
V ibrating beam s shall incorporate d ou ble b eam s m ade of extruded alum inium or steel,or m etal-shod tim ber section s w ith edges at least 75m m w ide.They shall be at least 300m m lon ger than the w idth of the strip being com pacted, and equ ipped w ith handles to allow the assem bly to be draw n over the con crete surface from ou tside the form s.
7.5.8
Tw o p asses shall be m ade w ith the b eam over each section of the slab at a rate o f betw een 0.5 to 1.0m per m inute. D uring the firstpass of the b eam ,a uniform ridge of con crete abo ut 50m m deep shall be m aintained ah ead of the beam over its entire len gth. O n the second pass on ly a sligh t roll of con crete shall be m aintained alon g the beam .
COMP COMP ACTING Commentary: The method of compacti on to be empl oyed is dependent on the pavement thickness. The relevant clauses fr om the opti ons 7.5.2, 7.5.3 or 7.5.4 appr opri ate to t he specifi c project shoul d be selected. A guide to th e most appropr iat e method can be summa- rised as foll ows: •In ternal (i mmersion) vi brator s are not suit able for compacti ng fl oors and pavements less than 150mm t hi ck. •For pavements over 200mm t hi ck, sur face vi bration may n ot be suff icient to compact th e concrete over i ts ful l depth, and int ern al vi brati on is requir ed. •In ternal vi brati on should be used adjacent to all construction joint s and edges. The designer and specifi er shoul d also refer t o Chapter 8 of th e G uide to C on crete C on struction4.
7.5.1
A ll con crete, including that adjacen t to form s or existing concrete,shall be com pacted by m echan ical vibration through the u se of internal vibrators an d/or vibrating-beam screed s as detailed herein.
7.5.2
Pavem ents up to 200m m thick shall be com pacted an d screed ed to the requ ired surface p rofile u sing a vibrating b eam .Internal vibrators shall be u sed to supplem ent the com paction adjacent to the side form s and at con struction joints in accordance w ith C lau ses 7.5.4 to 7.5.6.
7.5.3
Pavem ents greater than 200m m thick shall be initially com pacted using internal vibrators.The con crete shall then be screed ed to the requ ired surface p rofile u sing a vibrating beam .
7.5.4
The internal vibrators shall be operated so as to prod uce n oticeable vibrations at a distan ce of 300m m from the h ead .The n um ber of vibrators on site in full
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Commentary: The fir st pass is the most effi cient f or compacti ng th e slab, so it should be as slow as possible and the beam must r emain i n contact w ith t he concrete over i ts enti re width . Hence, the requir ement f or th e maintenance of a r idge of concrete for t hi s fir st pass. The second pass is to screed the sur face and giv e as unifor m a fi ni sh as possibl e. 7.5.9
The vibrating action of the beam shall be stop ped w henever the beam is station ary.
7. 6
FINIS HING
7.6.1 Finishing operations com prising levelling,floating, trow elling an d texturing, shall com m en ce follow ing com paction of the con crete,an d shall be com pleted as soon as possible w ith due d iligen ce. Commentary: The sequence of fini shin g operati ons may be vari ed to suit the parti cular pavement application. Generall y, for pavements to be tr affi cked by pneumat ic-
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dep ressions shall have all stones larger than nom inal 20m m rem oved .P rojection s above the requ ired level shall also be struck-off an d refinished .
tyred vehi cles, power floati ng and tr owell ing are not used, and t he concrete sur face is textur ed follow in g the levell ing operat ions. For many fl oors, the concrete wi ll be levell ed, fl oated and tr owell ed but surf ace textur ing may not be requi red.
7.6.2 The ad dition of w ater to the surface of the concrete to assist in finishing operations shallnot be p erm itted.H ow ever,in hot w eather or dry,w indy con ditions the ap plication of w ater to the surface in the form of a fog, or fine m ist spray,or the spraying of the surface w ith an approved aliphatic alcoh ol m ay be perm itted. Commentary: Sprayi ng wi th aliphat ic alcohol immedi- ately after ini ti al fini shing wi ll li mit evaporation of wat er and r educe plasti c shr in kage crackin g in hot weather condit ions. Refer t o H ot W eather C on creting39 (Chapt er 2 Cl ause 10). 7.6.3 N o m aterial shall be applied to the surface o f the slab to soak u p surface m oisture. Commentary: Thi s applies to cement, stone-dust or a combinati on of these materi als. Dr y- shake materi als in corporati ng special aggregates whi ch are util ised to im prove the abrasion r esistance of fl oors or for decorat ive effect do not fal l i nto thi s category as they form part of the construction process and must be appli ed at the time recommended by the product suppl ier.
7.7.5
The straigh ted ge testing an d finishing shallcon tinue until the entire su rface of the co ncrete is free from observab le dep arture from the straigh ted ge,con form s to the requ ired grade an d shap e,and,w hen harden ed,w ill satisfy the surface requirem en ts specified in C lau se 13.
7. 8
FLOATING
7.8.1 Floating shall be undertaken using ap proved po w ered m echan ical equipm ent. Commentary: The power float should be used for t he in it ial power-f loating operati ons only. The subsequent operat ion of tr owelli ng should be carr ied out wit h a power tr owel. Refer t o Clause 7.9.
7.8.2 Floating sh all not com m en ce until all surplus m oisture has been rem oved or has evapo rated from the surface o f the concrete,an d the surface is sufficien tly h ard to resist displacem en t under the action of the float. Commentary: It i s import ant that power-f loatin g is not commenced un ti l the concrete has sti ffened suffi ciently. The time int erv al before the init ial power-f loating can commence depends on t he concrete mi x and th e weather. In cold w eather, it may be three hours or more after t he concrete is placed. In hot w eath er, the concrete may sti ffen rapidl y and i t i s import ant t hat concrete is not placed at a greater rate than i t can be properly power-f loated and trowelled.
7. 7 LEVELLING 7.7.1
Follow ing the secon d p ass of the vibrating beam , m inor irregularities an d score m arks in the su rface shallbe elim inated by m eans of a h and-operated, long-h an dled float. Commentary: It is import ant th at the concrete surf ace be brought t o the fi nal specifi ed level pr ior to the commencement of any fi ni shing operat ions, and this wi ll generall y be achi eved by the vibr ati ng beam. Floatin g must n ot be considered as a meth od of correcting gross in accur acies in level or profi le.
7.7.2
7.7.3
7.7.4
7.8.3 Floating sh all be u ndertaken in a regular pattern o ver the entire surface o f the concrete to p roduce a closed an d level surface.
7. 9
TROWELLING
7.9.1
Trow elling shall be undertaken using ap proved po w ered m echan ical equipm ent.
W hen necessary,the float shallbe used to sm ooth an d fill in op en -textured areas in the p avem en t surface. The su rface shall also be tested for truen ess w ith a 3m straigh ted ge held in successive positions parallel an d at righ t an gles to the cen treline of the p avem en t an d in con tact w ith the surface,an d the w hole area covered as n ecessary to detect variations.The straigh tedge shall be advanced alon g the pavem ent in successive stages of not m ore than on e h alf the len gth of the straigh ted ge. A ny depression s fou nd d uring straigh tedge checking shallbe filled w ith freshly-m ixed concrete, struck-off, consolidated an d refinished .C oncrete used for filling
Commentary: A power t rowel is simi lar t o a power-f loat but fi tted wi th small i ndiv idual steel t rowel blades. The small blades can be sli ghtly ti lt ed dur in g trowelli ng operat ions. Thi s clause shall not pr event t he use of hand- tr owell in g to fini sh the surface of small areas unable to be covered by mechani cal equipment an d al ong edges. 7.9.2
Trow elling shall com m en ce after the surface has been po w er-floated.Trow elling shall not com m ence until the su rface is sufficien tly h ard to resist displacem ent un der the action of the trow el. Commentary: The power-t row ell ing is commenced wh en the excess moistur e brought to the sur face by i ni ti al power-f loati ng has lar gely evaporat ed and the concrete
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has lost it s sti ckiness. The wai ti ng ti me before power- tr owelli ng also depends on both t he concrete mix and the weath er. A pr acti cal test to check the readin ess for each tr owelli ng operat ion i s to place the palm of t he hand on the concrete sur face. If mort ar sti cks to th e palm w hen the hand is taken aw ay f rom the sur face, the concrete is not ready for t rowelli ng. If tr owell in g is star ted too earl y, the tr owel blades wi ll leave ridges.
7.9.3 The b lades of the trow el shall be tilted such that m axim um pressure is app lied w ithou t leaving ridg es on the surface of the concrete. Commentary: The fi rst power-t rowelli ng of the ful l pavement bay is undertaken in a systemati c pattern wi th the trowel blades set at a slight an gle (the angle depends on the concrete sti ffness but as large a ti lt as possible to suit the surface shoul d be used). I f t he til t on t he blades is too great, the concrete sur face will be mar ked. 7.9.4 Su bsequ ent trow elling shall not com m ence until the provisions of C lau ses 7.9.2 and 7.9.3 are com plied w ith. Commentary: W here a second power-tr owelli ng is specified, it should not be commenced un ti l t he excess moistur e brought t o the surface dur ing the fi rst power- tr owelli ng has evaporated. Again, th e practi cal t est descri bed above may be used. The ti lt of the tr owel blade should be graduall y i ncreased t o match t he concrete stiffness. Some heavy- duty fl oors may requir e three power-t rowelli ngs to be made. In many l ight t o heavy in dustr ial sit uati ons, the slab may be dir ectl y fi ni shed by power or hand t rowelli ng to give a dense, hard- weari ng sur face. Thi s finish may provi de a li mi ted degree of protecti on again st the penetrat ion of oil , but may not pr ovide adequate skid resistance if subject to f requent tr affi c, especiall y w hen damp.
7.10
S URFACE TEXTURING
7.10.1 Fo llow ing finishing o f the concrete,the surface sh all be p rovided w ith a (…) texture. Commentary: Clauses 7.10.3, 7.10.4 and 7.10.5 are alt ernati ve clauses, only one should be used for any section of t he pavement 7.10.2 Texturing shall not com m en ce w hilst the con dition of the concrete is such that the surface co uld be torn an d co arse agg regate particles displaced,or w hilst there is free w ater on the su rface. 7.10.3 Broom texturing:Th e w hole surface of the slab shall be broom ed in a direction perpen dicular to the direction of placing or as show n in the d raw ings. Broo m s shallbe at least500m m w ide w ith bristles of natural m aterial,nylon or flexible w ire.The b room shallbe d raw n across the full w idth of the slab in a
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series of overlap ping strokes.The m arks in the slab surface shall be uniform in appearan ce and approxim ately (…)m m in depth w ithou t disfigu ring m arks. Commentary: For most pavements, no additi onal force other t han t he self weight of the broom need be appli ed to the sur face. To impr ove tr acti on in r amped or i nclined areas, a coarser t exture can be achieved by apply ing extr a for ce to the broom. 7.10.4 Hessian-dra g Texturing:Th e surface sh all be textured by dragging hessian longitudinally over the fullw idth of the slab to p roduce a u niform ,gritty texture.The drag shall com prise a seam less,tw olayer strip of dam p hessian w hich is in con tinuou s con tact w ith the slab over its full w idth an d over a len gth o f at least 1 m .D rags shall be kep t clean an d free from en crusted m ortar. 7.10.5 Grooved Texturin g:Th e surface sh all be textured by m eans of a m echanicaltyning d evice w hich p rod uces grooves in the plastic con crete.The tyn es shall be rectangular shaped an d of flat spring steel,ap proxim ately 0.6m m thick and of a uniform leng th betw een 100 an d 150m m .Th e w idth o f the tynes shall be no t less than 2m m no r greater than 3m m and they shall be spaced betw een 8 and 21m m apart in an approved ran dom pattern.D etails of this proposed device shall be subm itted for approval an d,if required,the prop osed m ethod o f achieving the required texture sh all be d em onstrated .The texture depth shall be n ot less than (…)m m nor m ore than (…)m m . Commentary: Grooved textur ing is necessary only for pavements where tr affic speeds in excess of 80 km /h are anti cipated or for ramped areas. Where surfaces are li kely to experience soil or other w aste materi al deposits, a grooved sur face may assist i n improvin g tracti on for vehicles.
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curing h as been ap plied ,the surface of the concrete shall be kept continuo usly dam p by m eans of a w ater fog or m ist app lied w ith app roved equ ipm ent
8. CURING
8.1
GENERAL
8.1.1
C oncrete shall be cured by protection against loss of m oisture an d rapid tem perature chan ges for a period of not less than 7 d ays from the com pletion of the finishing operations.C uring shall com prise initial curing follow ed by either m em brane curing,im perm eable sheet curing, or m oist curing. Commentary: Properties of concrete such as str ength and wear r esistance improve with age as long as condi ti ons are favourable for conti nued hydrat ion of the cement. The improvement is rapid at an earl y age, but conti nues more slowl y thereafter. The requir ed conditions are: • the presence of moisture • a favourable temperatur e.
Commentary: The use of a spray ed film of ali phati c alcohol i s not a part of the cur in g process, it is simply a temporary moisture-r etention facil it y for use dur ing placing and fi ni shing operat ions, as noted in Cl ause 11.2.5.
8.3
MOISTCURING
8.3.1
A s soon as possible after the finishing operations have been com pleted and the concrete h as setsufficiently to preven t m arring the surface,the form s and entire surface ofthe new ly-laid concrete shallbe covered w ith w et hessian m ats,or other approved m aterial.
8.3.2
H essian m ats shallhave sufficien t w idth,after shrinkage,to cover the entire w idth and faces ofthe concrete slab.Provision shallbe m ade to securely an chor the m ats to ensure that they rem ain in place in w indy con ditions.The m ats shalloverlap each other at least 150m m .The m ats shallbe saturated before placing an d shallbe kept con tinuously w et an d in intim ate con tact w ith the slab edges and surface for the duration ofthe required curing period.
8.4
S P RAYED MEMBRANE CURING
Evaporati on of wat er fr om newl y- placed concrete can cause the hydrati on pr ocess to stop. Loss of w ater also causes concrete to shr ink, thus creati ng tensil e str esses at th e sur face. If tensil e str esses develop befor e the concrete has att ained adequate str ength, sur face crackin g may result. H ydr ati on proceeds at a much slower rat e wh en tempera- tures are low; t here is practi call y no chemical acti on betw een cement and w ater w hen the concrete temperatur e is near fr eezing point . It foll ows that concrete should be protected so that moistur e is not lost dur ing t he earl y har denin g peri od, and t hat concrete shoul d be kept above fr eezing point .
8.1.2
Before con crete placing com m ences,all equ ipm ent need ed for adequate curing of the concrete shall be on hand and checked to b e ready for use.
8.1.3
Failure to com ply w ith the specified curing requirem ents shall be cau se for im m ediate suspen sion of con creting o perations.
8.1.4
Th e sides of panels exposed by the rem oval of form s shallbe cured by one of the m ethod s detailed herein. Th is shall com m ence w ithin on e h ou r of rem ovalof form s.
8.1.5
The u se of covering m aterial that con tains or becom es contam inated w ith sug ar in any form , tan nic acid,or any other substan ce considered detrim en tal to Portlan d cem en t con crete sh all not be perm itted. Commentary: Contami nated cur ing covers generall y affect th e surf ace of th e concrete, commonl y as a retar da- ti on of sett in g and hardening characteristi cs.
8.2
INITIAL CURING Im m ed iately after the finishing operations have been com pleted and un til the m em brane, sheet or m oist
8.4.1 O n com pletion of initial curing and for the rem ainder of the cu ring period,the entire exposed surface of the con crete including edges shallbe uniform ly coated w ith an ap proved m em brane curing com pou nd.The con crete shall not be allow ed to dry out before the ap plication of the m em bran e.If any initial drying has occurred ,the surface o f the concrete sh all be m oisten ed w ith a spray of w ater.The curing com pou nd shall be applied to the finished surfaces by m eans of an app roved m echanicalspraying device. Commentary: Wax- based cur ing compounds are generall y effi cient i n terms of moisture retention but can provide a slippery sur face. For t hi s reason, it i s recom- mended that th ey not be used wh en the pavement i s to be subject to earl y foot or vehicular tr affi c. The likeli hood of satisfactory bondi ng of any toppin g, surface tr eatment or coati ng wh ich i s to be subsequently appli ed should be checked (see Cl ause 2.8.3 ). 8.4.2
The spraying d evice shallbe equipped w ith a spraying nozzle or nozzles that can be so controlled and op erated as to com pletely an d uniform ly cover the surface w ith the requ ired am ou nt of curing com po un d. Spraying pressure shallbe sufficien t to produce a fine spray an d cover the surface thorough ly an d com pletely w ith a uniform film .The spray n ozzle shallbe provided w ith a suitable w ind gu ard.
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8.4.3 Th e curing com po un d should b e sprayed un iform ly at the rate recom m ended by the m anufacturer to achieve com pliance w ith A S 3799. Commentary: W here chemi call y compatible wi th in di vi dual cur ing compounds, the use of whi te pigments or coloured fugit ive dyes are effecti ve in r educing temperat ur e var iati ons near t he slab surf ace, and in provi ding for a vi sual check of uni form coverage. 8.4.4 Th e com po un d shallform a un iform ,continuo us, cohesive film that w ill not check,crack or peel,an d that w ill be free from pin holes an d other im perfections.If discontinuities, pin holes or abrasions exist, an ad ditional coat shall be applied to the affected areas w ithin 30 m inutes. 8.4.5 C oncrete surfaces that are sub jected to heavy rainfall w ithin 3 hou rs after the curing com po und h as been applied,shall be resprayed by the m ethod an d at the coverage specified above. 8.4.6 In the even t of failure to ach ieve the required coverage, either m oist curing b lan kets or im perm eable sheet curing sh all be im m ediately u sed.
8.5
IMP ERMEAB LE-S HEETCURING
9. JOINTS
9. 1
GENERAL
9.1.1
A ll joints shallconform to the d etails,an d shallbe con structed in the location s show n in the draw ings. Commentary: Typical joint detail s are provi ded in Chapter 1 D esign.
9.1.2
Transverse and longitudinal joints shallbe straight, and continuo us from edge to edge of the pavem ent through out allpaving strips that are con nected in a single slab area, except w here show n otherw ise in the draw ings.
9.1.3
Joints shallbe plum b and w hen tested w ith a 3m straighted ge p laced at right an gles across the joint, the surfaces of adjacent pan els shall not vary from the straigh tedge by m ore than the toleran ces specified in C lau se 13.
9. 2
CONS TRUCTION JOINTS (TIED OR FREE)
9.2.1 L ongitudinal construction joints shall be constructed betw een all slab strips.
8.5.1 O n com pletion of initial curing an d for the rem ainder of the cu ring period ,the m oisten ed con crete surfaces shall be covered w ith approved im perm eable cu ring sheets.
9.2.2 D ow els or tieb ars shall be installed in longitudinal con struction joints as required by, an d in accordance w ith the details sho w n in the draw ings,an d C lause 9.5.
Commentary: The most commonl y used impermeable covering i s waterproof pl asti c sheeti ng, such as clear polyethyl ene, or it s equi valent. The sheeti ng should be placed as soon as th e condi ti on of t he concrete is such that the sur face wi ll not be marked or damaged.
9.2.3 Transverse co nstruction joints shall be installed at the en d of each d ay's placing o peration s and at any other points w ithin a pavem en t strip w hen placing is interrupted for 30 m inutes or longer.
8.5.2 The curing sheets shallbe in pieces large en ough to cover the en tire w idth an d edges o f the slab.A djacent sheets shalloverlap not less than 500m m and the lapped edg es securely tied or w eigh ted dow n along their full len gth to p revent displacem en t or billow ing by w ind. Sh eets shall be folded dow n over the side of the pavem en t edges,con tinuou sly w eigh ted,an d secured.Tears and holes appearing in sheets du ring the cu ring period shall be repaired im m ediately. 8.5.3 The sh eets shall rem ain in place for the entire rem ainder of the specified curing p eriod.A ny dam age that m igh t reduce the serviceability and effectiven ess of the sheets as a curing m edium shall be preven ted.C uring sheets that do n ot provide a con tinuous cover as required for effective cu ring m ay be rejected at an y tim e.
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9.2.4 Tran sverse co nstruction joints at the end of each day’ s placing operation shall be installed at the location of a p lan ned tran sverse contraction or isolation joint. Commentary: In joi nted pavement construction, 'end- of- day' joints shoul d be constr ucted at t he planned locati on of contraction or i solation j oints. In continu ously reinforced pavements, 'end-of-day' joint s should be constructed by usin g header boards wi th the reinforcement contin ued through the joint.
9.2.5 W hen con crete placem en t is interrupted for 30 m inutes or lon ger,or can not be continued due to equipm en t failure or adverse w eather con ditions,a tran sverse construction joint m ay be installed w ithin the slab (but only w ithin the m iddle third of its len gth betw een plan ned joints),an d excess con crete rem oved .W hen a construction joint is installed w ithin a pan el and betw een m ovem ent joints it shall be con structed so as not to p erm it m ovem ent in accordan ce w ith the details show n in the draw ings.A
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tran sverse construction joint w ithin a concrete slab shallnot be p rovided w ith a groo ve at the surface of the con crete.W hen con crete p lacing is resum ed,the plan ned joint spacing shall be m aintained,beginning w ith the first regularly sched uled tran sverse joint. Commentary: Thi s is an 'emergency' join t whi ch can be constructed mid- panel and i t i s a ti ed join t designed not to permi t movement. For external pavements, joint seali ng i s recommended. 9.2.6 O ne com plete set of form w ork stakes,do w els and /or ties an d other equ ipm en t necessary to con struct a tran sverse co nstruction joint shall be ready at the site of placing at all tim es.
9. 3
CONTRACTION JOINT JOI NTS (FREE JOINTS )
9.3.1 Tran sverse contraction joints shallbe o f the w eak en ed-plan e type,an d shall be con structed in accordance w ith the d etails show n in the d raw ings. 9.3.2 Transverse contraction joints shall be constructed as either form ed joints,w herein a groove is form ed in the p lastic concrete,or saw n joints,w herein a g roove is saw n in the h arden ed con crete,or an ap proved regu lar com bination of the tw o. Saw n con traction joints w ill be perm itted w here sufficien t stan d-by m achines are available an d saw ing o peration s are carried ou t as required during the d ay o r nigh t regardless of w eather con ditions. Commentary: The advant ages and di sadvant ages of sawn and for med contracti on join ts are discussed i n detai l i n Chapt er 1 D esign. Thi s clause assumes that t he contr actor wi ll decide whi ch t ype to use. If, however, onl y one type of contr acti on joint is to be permi tt ed for a specifi c project, thi s clause must be rewri tt en and either Clauses 9.3.4 and 9.3.5, or 9.3 .6 thr ough 9.3.10 omi tt ed. 9.3.3 Irrespective o f w hether or no t form ed con traction joints are u sed,the co ntractor shall have access to on e ap proved con crete saw in w orking o rder at all tim es for saw ing of con traction joints in the even t of delays in finishing p recluding the construction of a form ed joint in the plastic con crete. 9.3.4 Form ed joints shallbe con structed by form ing a vertical groove in the p lastic concrete to provide a w eaken ed-plane joint of the dim ension s show n in the draw ings.The groove shall be cut by inserting an ap proved steel cutting d evice into the plastic con crete at the prescribed joint location im m ed iately follow ing finishing operations. 9.3.5 A fter rem oval of the cutting d evice,an ap proved joint filler shallbe installed in the p lastic concrete to form a joint,m eeting the follow ing requ irem en ts: • A djacent sections of the joint filler w ithin each slab shall be securely joined together by su itab le
fasten ers or other approved m ean s so that the filler is continuous for the full len gth of the joint. • The con crete shall be thorou gh ly con solidated against the filler for its dep th.A n ap proved vibrating-p late float shallbe u sed to com pact the concrete about the filler. • The filler shall be n orm al to the finished surface o f the slab an d shall be straigh t an d not vary m ore than 15m m from true joint align m en t at the prescribed joint location sho w n in the d raw ings.The top of the filler shall be flush w ith the slab surface. • The slab surface adjacen t to the joint shall con form in surface sm oo thness to the requ irem ents of C lause 13 and shall con form in texture w ith the ad jacent slab areas. Commentary: Thi s clause is appli cable only when a preformed join t seali ng materi al, eg self -expandin g cork, is to be insert ed i n t he plastic concrete. 9.3.6 Saw n joints shallbe con structed by saw ing a g roo ve not less than 3m m and n ot m ore than 5m m in w idth for the entire d ep th of the cu t as indicated . 9.3.7 The tim e of saw ing shall be varied,depen ding on w eather con dition s,an d shallbe such as to p reven t uncontrolled cracking of the p avem ent.Saw ing of the joints shall com m en ce as early as p ossible an d be com m ensurate w ith the concrete h aving h arden ed sufficien tly to perm it cutting w ithout excessive chipping,spalling o r tearing.The saw n faces of joints shall be inspected for undercutting o r w ashing o f the concrete d ue to early saw ing.If this action is sufficien tly deep to cause structural w eak ness or clean ing difficulty,the saw ing operation shall be d elayed,an d resum ed as soon as the saw ing can b e continued w ithou t dam aging the concrete pan el.A dequ ate provision shall be m ade to perm it saw ing overnigh t if con crete h as been placed during the day. Commentary: The appropr iat e ti me for sawi ng is best assessed by casti ng test panels adjacent to t he wor ks and conducti ng tr ials to evaluate the extent of chi pping, spall ing or teari ng. The actual t ime wi ll be dependent on the characteri sti cs of the mi x and th e envi ronmental conditi ons prevaili ng after placing. 9.3.8 The joints shall be saw n in the sequ en ce of the con crete placem ent. 9.3.9 A chalk line or other suitable guide shall be u sed to m ark the align m en t of the joint.The saw cut shall be straigh t from edge to edge o f the pan els and shall not vary m ore than 15m m from the true joint align m ent. 9.3.10 Before saw ing a joint,the concrete shall be exam ined closely for cracks,the joint shall not be saw n if a crack h as occurred near the location cho sen for a joint.In these instan ces the p roposed joint shall be
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relocated aw ay from the crack an d rem edial treatm ent m ay be requ ired. Saw ing shall be discon tinued w hen a crack develop s ahead of the saw cut. Commentary: W here a crack occurs ahead of th e sawi ng, usuall y as a result of sawi ng too late, remedial measur es may be required – dependi ng on the length, directi on and li nearit y of th e crack. W here the crack closely f ollow s the int ended joint l in e, it may be suitable to r out t he crack to r eceiv e a fi eld- moulded sealant . W here the crack is considerably skewed in relation t o the in tended joi nt li ne, it may be necessary to i nject the crack wi th a sui table penetrat ion epoxy compound and then complete the ini ti al saw cut lat er. Each crack of t hi s type should be considered indi vi dually before deciding whether or n ot remedial t reatment i s necessar y, and i f so, what t ype.
9. 9. 4
9.4.2 Isolation joints shall be form ed about structures an d features that project through,into or against the slab, using joint filler of the type, thickn ess an d w idth as indicated,an d installed in such a m an ner as to form a com plete,uniform separation betw een the structure and the panel.
DOW ELS AND TIEB ARS DOWELS
9.5.1 D ow els and tiebars shallbe prepared and placed across joints w here indicated in the d raw ings.The correct dow el bar type sh all be p recisely align ed an d securely held parallel to the surface of the finished slab during placing an d finishing o perations. Commentary: Dow els permi t hori zontal movement of panels at joi nts and tiebars hold panels together w it hout movement at t he joint . Some dowels permi t t wo di rec- ti onal h orizontal movements. 9.5.2 D ow els and tiebars shallbe p laced by the bo ndedin-place m ethod .Installation by rem oving an d replacing d ow els and tiebars in preform ed holes, including their w ithdraw al to assist in form stripping, shallnot be perm itted . Commentary: It is poor pr acti ce for dowels or t iebars to be hamm ered i nto the wet concrete. 9.5.3 The spacing an d verticallocation of dow els and tieb ars shall be as specified in the d raw ings.The
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9.5.4 The spacing of dow els and tiebars in lon gitudinal construction joints shall be as indicated,except that w here the plann ed spacing cannot be m aintained becau se of form len gth or interference w ith form braces,closer spacing w ith ad ditional dow els or tieb ars shall be u sed. 9.5.5 D ow els an d tiebars in longitudinal joints shall be om itted w hen the centre of the dow el or tiebar w ou ld be occurring w ithin 200m m (horizon tally) of a transverse joint. Commentary: Dowels and ti ebars located close to a tr ansverse joint may r estr ict fu ncti oning of the joint, and may cause a corner crack to be developed due to th e restr ain t unless the special dowels whi ch all ow hori zontal movement s are used.
IS OLATION JOI NTS
9.4.1 Isolation joints shall be form ed by m ean s of an ap proved preform ed filler m aterial w hich sh all be installed only after the co ncrete o n one face of the joint has harden ed .The filler sh all be fitted tightly together,attach ed to the h arden ed con crete w ith approved adhesive,an d held in line to ensure con tinuity an d preven t any concrete from en tering the joint.
9. 5
follow ing tolerances shall not be exceeded : • H orizontal location –half the d iam eter of the dow el or tiebar • Vertical location –dow els:half the diam eter of the dow el;tieb ars:± 10m m .
9.5.6 The m ethod used to h old do w els in position shall be sufficien tly rigid to en sure that individual dow els do not deviate by m ore than 3m m in 300m m from their specified align m en t. 9.5.7 A ll dow els an d tiebars shallbe clean an d free of oil, grease,loose rust an d other foreign m aterial w hen the concrete is placed to perm it m axim um bo nd ing w ith the co ncrete.A t construction joints,the uncoated en ds of dow els shall be installed in the first-placed p an el. 9.5.8 Th e p ortion of each do w elintend ed to m ove in the con crete, including the d ow el en d,shall be clean an d free of oil,grease, loose rust an d other foreign m aterial and shall be coated w ith an approved bo ndbreaking com po und prior to placing con crete.
9. 6
JOINTS EALING N ote: Omi t these clauses if: • formed joint s wh ich are sealed as part of the joint in g operati on are specified exclusively; or •join t seali ng is not requi red.
9.6.1 Widen ing of sawn joints: A fter exp iration of the curing p eriod an d im m ed iately p rior to joint sealing operations,a groove for the joint sealer shallbe saw n as specified hereinafter in the top of saw n joints. W here m ultiple cuts are n ecessary to saw the groo ve to the specified dim en sions,the groove sh allbe w ashed ou t betw een successive saw cuts so that a check can be m ade of the align m ent over the joint ed ge.The sides of the saw n groove sh all be parallel.
GUI DE TO SPECIFICATION S
9.6.2 Sea lant Insta llation: Im m ediately before the installation of the sealer,the joints shallbe thorou gh ly clean ed using com pressed air or high pressure w ater jet until alllaitan ce, curing com pound,filler and protrusions of harden ed con crete are rem oved from the sides and up per edges so that the entire joint space is free from concrete, dirt,dust an d o ther m aterials.C on struction an d saw n con traction joints w ithin the various con creted areas shall be sealed using an approved joint sealing m aterial an d backing tape in accordan ce w ith the m an ufacturer's recom m en dations.The joint sealer shall be set flush or not m ore than 5m m below the slab surface. Commentary: Joint sealant s are usually div ided int o tw o categori es: • Field-moulded sealant s wh ich are poured or gunned int o the joint . • Preformed sealant s, such as cell ular r ubber str ips which are inserted int o the joint in a compressed condition.
10. P ROTECTION OF CONCRETE PAVEMENTS
10.1 GENERAL C on crete p avem en ts shallbe p rotected against all dam age prior to final acceptance of the w ork. Traffic shall be excluded from the slab by erecting an d m aintaining barricades an d sign s until the concrete is at least (…) days old,or for a longer period if so directed. Commentary: The peri od for protecti on from traffi c should be based on practical considerations associated wi th each parti cular project. M ini mum peri ods of 7 days (i .e. the min imu m curi ng peri od) for l ight t raffi c, and 14 days for heavy tr affi c are suggested. Fast- tr ack pavi ng by utili sing high- strength concrete mi xes can all ow earl y tr affi cking of th e pavement 39.
10.2 CONS TRUCTION TRAFFIC Irrespective of age, trafficking of pavem en ts by tracked or solid-w heeled construction equipm en t shall be p erm itted only if protective m atting,steel plates,or tim bers are placed under their w heels or tracks. 10.3 ACCES ACCES S FOR CONCRETE PPLACING LACING A s a con struction exp ed ien t,in con creting interm ed iate strips betw een previously com pleted strips, operation of con crete tran spo rt veh icles or other equipm en t w ill be p erm itted on the previou sly con structed pavem en ts after the con crete h as been cured for (…) days,provided : • the joints have b een sealed or otherw ise protected; an d • all foreign m atter including agg regates an d con crete are progressively an d con tinuou sly rem oved from the area over w hich traffic is m oving. U po n com pletion of the new strip o f con crete and o n the sam e day,the surface of con crete on w hich equ ipm ent has op erated,shallbe clean ed and the barricades rep laced . 10.4 UNHARDENED CONCRETE U nharden ed con crete shall be p rotected from rain and flow ing w ater.
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• Sp rayed m em brane curing in accordan ce w ith C lau se 8.4 • Im perm eable-sheet curing in accordance w ith C lause 8.5.
11. ADVERS E WEATHER CONDI TIONS
11.1
11.2
DEFINITION Fo r the p urposes of this specification,ad verse w eather m eans any com bination of clim atic con ditions that m ay im pair the quality of plastic or hardened concrete. CONCRET ING IN IN HOTWEATHER HOT WEATHER CONCRETING
11.2.1 W hen the shade tem perature is likely to exceed 30°C or clim atic or other conditions are likely to result in the tem perature of the con crete exceed ing 30°C , w hen placed,som e or allof the follow ing p recautions shallbe taken in placing,curing and protecting the con crete as necessary an d as directed . Commentary: H ot W eather C on creting, G uide to C on crete C on struction 4. 11.2.2 The form s,reinforcem ent and subbase shallbe sprinkled w ith w ater im m ediately before placing the concrete. 11.2.3 Such of the follow ing precaution s shall be taken as are necessary to en sure that the concrete is placed at the low est tem perature practicable,an d in no case exceeding 30°C : • A ggregates shall be shad ed from the sun. • M ixing w ater shall be cooled. • M ixing an d placing o f concrete shall be do ne during the coolest period of the day. 11.2.4 C oncrete shall be tran spo rted,placed an d finished con tinuously,an d as rapidly as p ossible. Commentary: The rate shoul d be adequate to ensure conti nuous placing and that no 'cold joint s' are form ed. 11.2.5 D uring the p lacing an d finishing operations,a fine film of ap proved aliphatic alcohol shall be sprayed over the exp osed surfaces to lim it evap oration of w ater.This procedure m ay be carried ou t w henever there is a break in the sequen ce of placing an d finishing o perations.Its rep eated use does n ot affect the properties of the finished concrete. 11.2.6 A s soon as possible after final finishing o perations have been com pleted,m oistcuring in accordan ce w ith C lause 8.3 shallbe com m enced. Commentary: M oist cur in g is recommended as a means of contr olli ng the temperat ur e of t he concrete, as well as preventi ng the surface fr om dryi ng out. 11.2.7 Final curing shall then proceed an d be undertaken until the end of the specified curing period.This shall con sist of one o f the follow ing: • C on tinuation of m oist curing in accordan ce w ith C lause 8.3
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11.3
CONCRETING IN COLD W EATHER WEAT
11.3.1 If it is necessary to place concrete w hen the tem perature of the air,aggregates or w ater is below 5°C ,or w hen the concrete is likely to be subjected to freezing co nditions before the expiration of the specified curing p eriod,placing sh all proceed only upon full com plian ce w ith the follow ing provisions. Commentary: C old W eather C on creting,G uide to C oncrete C on struction 4. 11.3.2 The subbase shallbe p repared and protected and shall be entirely free of frostw hen the concrete is deposited. 11.3.3 The tem perature of the con crete w hen placed in the slab shall be n ot less than 5°C nor m ore than 30°C . H eating of the m ixing w ater an d/or aggregates shall be undertaken as necessary to m aintain the m inim um tem perature of 10°C .A ll m etho ds and equ ipm en t for heating sh all be subject to approval. 11.3.4 The agg regates shall be free of ice,snow ,an d frozen lum ps before entering the m ixer. 11.3.5 M em brane curing in accordan ce w ith C lause 8.4 shall be com m enced as soon as possible after finishing, follow ed by im perm eable sheet curing in accordance w ith C lause 8.5.The sheets shallbe applied as early as practicable w ithout m arring ofthe surface ofthe con crete an d shallrem ain in place u ntilthe en d of the specified 7-d ay cu ring p eriod,in lieu ofnorm al curing procedures as detailed in C lause 8.1. 11.3.6 Suitable covering an d other m ean s shall be provided for m aintaining the concrete at a tem perature o f at least 10°C ,for no t less than 72 hours after placing, an d at a tem perature above freezing for the rem ainder of the cu ring period.Salt,chem icals,ad ditives or other foreign m aterial shall not be m ixed w ith the con crete to p revent freezing. 11.3.7 A ny concrete d am aged by freezing shallbe rem oved to the full dep th an d rep laced .
11.4
P ROTECTION AGAINS TRAIN
11.4.1 N o con crete shallbe p laced during rain,an d unharden ed con crete shallbe protected from rain and flow ing w ater. 11.4.2 W hen rain app ears im m inent,paving op eration s shall cease an d allconcrete less than 24 hours’ old shallbe protected.W aterproof covers for the protection ofthe surface of such concrete shallbe available on site at all tim es,an d paving shallnot begin untilthis provision is com plied w ith.
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12. TES TING & ACCEPTANCE OF CONCRETE
12.1 CODE REQUIREMENT REQUIREMENTS The con crete shallbe sam pled an d tested for stren gth in accordan ce w ith the requirem en ts of N ZS 3109.
12.3 ACCEP TANCE CRIT CRITERIA ERIA 12.3.1 Strength: The criteria for com plian ce w ith an y of the ch aracteristic strength requirem en ts of this specification shall be in accordance w ith N Z S 3109. 12.3.2 Slump: The slum p shallbe ‘ deem ed to com ply’ if the approp riate requ irem en ts of N Z S 3109 are satisfied. Commentary: Refer to comments at the end of Clause 7.3.3.
12.2 OTHER REQU IREMENTS REQUIREMENT (…) Commentary: Any other r equir ements regardi ng the sampli ng and testi ng of concrete over and above that contai ned in N ZS 3109, should be specifi ed. The clause should contai n detail s of sampling and testi ng frequency. For example, shr inkage testing could be requi red:
Shrinkage testing: The standard shr in kage test t o AS 1012 Part 13 i s a means of evaluati ng the dryi ng shri nkage potential of a concrete mix. The test i s based on making up 7 5mm square by 285mm long concrete beams which are fir st condit ioned, and th en pl aced i n acceler- ated dryi ng condit ions and the length r educti on meas- ur ed for t he standard d ry in g period of 8 w eeks. The beams are condit ioned to age 7 days underw ater t o stabilise are measur ed, and t hen placed i n a 23 C 50% RH dry ing envi ronment. The test i s a useful way of comparing the concrete shri nkage potential for mi x development pur poses, and also can be used as a qual ity control measur e for specifyi ng li mi ts on shri nkage. W hen it come to relati ng standard test valu es to actual concrete slab shr inkage in th e fi eld, other factor s need to be considered, such as slab thickness and t he exposure envi ronment, whether the slab is int eri or (and air conditi oned) or exteri or. 41 The Austral ian Concrete Structures Standard A S 3600 recommends a defaul t basic shri nkage strai n of 700 mi crostr ain (7mm per 10m slab length). Factors are given (A S 3600 secti on 6) to be appli ed to th is to determi ne typical design shr in kage strai ns in th e fi eld. For a 100mm t hi ck floor slab in doors for i nstance, the total design shr inkage strai n is 550 mi crostr ain af ter 30 years. Considerat ion needs to be given to shr inkage strai ns to opti mise joint spacing and join t w idt h w here there is the potential for j oint wear by hard w heeled traffi c, for instance. The lar ger concrete producers should be able to pr ovide standard shr inkage data on their concrete mixes. Withi n test var iat ion is typi cally u p to 40 microstr ain and for th e same concrete produced over say a th ree mont h peri od, the coeffi cient of var iat ion i n dr yi ng shr inkage is around 15% i n t he field. Therefore design valu es whi ch are based on the standard shri nkage test values should be conservat ive. W here shr inkage val ues are specified, a single test al lowable upper li mit of 100 mi crostr ain should be allowed above the tar get average shri nkage. °
12.4 REJECTION CRITERIA CRITERIA 12.4.1 H arden ed concrete shall be liab le to rejection if an y of the follow ing defects occur: • It is porous,segregated or honeycom bed . • The reinforcing steel has been displaced from its correct location. • Inserts and o ther item s em bed ded in concrete have been displaced from their specified position. • Th e concrete w ork can b e sho w n to b e otherw ise defective. 12.4.2 C oncrete that is liable to rejection m ay be p erm itted to be retained on the basis of satisfactory results being o btained from on e or m ore of the follow ing: • A n ap praisal of the statistical inform ation related to the concrete stren gth • A structural investigation • A dditional tests (such as outlined in N Z S 3109) • A pproved rem edialw ork. 12.4.3 W here concrete w ork h as been finally rejected it shall be rem oved to the exten t determ ined,an d replaced in accordan ce w ith C lause 14.
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13. CONS TRUCTION TOLERANCES
13.1 GENERAL 13.1.1 Fo llow ing com pletion,the finished surfaces of the various sections of the pavem en t shall be tested for con form an ce to the grades,lines and levels show n in the draw ings,an d for surface sm oo thness by the m ethod s detailed h ereunder. 13.1.2 A dditionally,determ ination of the slab thickn ess m ay be carried out as d etailed in C lau se 13.3.4. 13.1.3 C on struction w ith intent to u se m axim um tolerances shallnot be perm itted . Commentary: The tolerances permi tt ed in level, smoothness and t hi ckness are the normal devi ati ons that may occur i n pavement constr uction under good wor k- manship and supervi sion. An example of t he int enti onal use of maximum tolerances woul d be the subbase being deli berat ely fi ni shed high all over, to effect an overall r educti on in concrete thi ckness (but wi thi n the thickness variat ion detailed in Clause 13.2.4). Tolerances included w it hi n t hi s section shoul d be relat ed to the size and standar d of the part icular pr oject. A discussion on appropri ate values is contain ed i n Chapt er 2 Constr uction.
13.2 S TANDARDS TO B E ACHI EVED EVED 13.2.1 Surface levels: The finished surface o f the slab shall con form to the levels,grades an d cross sections show n in the d raw ings to the extent that any point on the finished surface shall not vary b y m ore than (…)m m above or below the level indicated.R efer to N ZS 3109. 13.2.2 The finished surfaces of abutting pan els shall coincide at their junction. 13.2.3 Surface smoothn ess: The finished surfaces of the various sections of the pavem en t shall not deviate from the testing ed ge o f an approved 3m straigh tedge by m ore than (…)m m .R efer to N Z S 3114. Commentary: W here more than one pavement element is i nvolved, the relevant tolerances can be li sted i n an extended version of Table 1. In t hi s case, Clauses 13.2.1 and 13.2.3 should be amended to r efer t o that Table. 13.2.4 Thickness:W here the average thickn ess of the slab, as determ ined in accordan ce w ith C lause 13.3.4,is w ithin (…)m m of the thickn ess specified,the pavem en t shall be con sidered w ithin the lim it of perm issible thickness variation an d satisfactory in thickn ess.
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13.3 TES TING P ROCEDURES 13.3.1 Surface levels: Follow ing cu ring,or earlier if practicable,each section of the p avem en t shall be tested for con form an ce w ith C lause 13.2.1 by determ ining the finished surface levels of a grid of points spaced not greater than (…)m in each direction. 13.3.2 Surface smoothn ess: Fo llow ing final curing,or earlier if practicable, each section of the p avem en t shall be tested for con form an ce w ith C lau se 13.2.3 using a 3m straigh tedge o perated over a grid o f points spaced not greater than 3m in each direction , or at an y other locations as directed. 13.3.3 Fo r this testing,a 3m -long straighted ge (con sisting of an alum inium box-section of sufficien t rigidity to m aintain its accuracy) or a m obile straigh ted ge of approved design shall be used. 13.3.4 Thickness determ ination: The thickn ess of the slab shall be determ ined on the basis of the average o f slab-thickness m easurem ents m ade on cores not less than 100m m in d iam eter taken from selected p oints. In calculating the average slab thickness,individual cores m easuring in excess of the thickness show n on the d raw ings shall be con sidered as being o f the specified thickn ess.The len gth an d w idth of any deficien t section shall be the distan ce betw een the nearest points from w hich cores of satisfactory thickn ess are taken .
13.4
DEFICIENCIES A ND CORRECT CORRECTIONS AND
13.4.1 Surface level and smooth ness: A ll areas of the pavem en t that are defective w ith respect to surface levelan d/or surface sm oothness as hereinafter specified shall be rem oved an d replaced. 13.4.2 H igh areas of un satisfactory sm oo thness m ay be reduced by g rinding w ith an approved surface grinding m etho d. 13.4.3 If the area to b e corrected by grinding exceed s 10% of the area of an y integral slab or exceed s 3% of the total area of pavem en t,specified areas that exceed the requ ired surface toleran ces m ay b e requ ired to be rem oved an d replaced. 13.4.4 A ll areas that have been surface grou nd m ay be requ ired to b e re-textured by an approved m ethod . 13.4.5 Thickness:W hen the m easurem ent of any core indicates that the slab is deficien t in thickness by (…)m m or m ore,ad ditional cores shall be d rilled on a grid at 3m intervals,until tw o consecutive co res indicate that the d eficien cy in thickness is less than (…)m m .A llpavem en t areas deficien t in slab thick-
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ness by (…)m m or m ore shallbe con sidered defective slab areas an d shall be rem oved an d replaced w ith pan els of the sp ecified thickness.If the co ntractor believes that the cores an d m easurem en ts taken are not sufficien t to indicate fairly the actual thickness of the p avem ent,addition al cores and m easurem en ts m ay be taken if the con tractor so requests.A ll core h oles shallbe repaired by an approved m ethod .
14. REMOVAL AND REP LACEMENT OF DEFECTIVE AREAS
14.1 DEFECTIVE PP AVEMENTS 14.1.1 Pavem en t areas of unsatisfactory sm oo thness an d/or of unsatisfactory level that have n ot been corrected in accordan ce w ith C lau se 13.4.1; areas that are deficien t in slab thickn ess as defined in C lau se 13.4.5; an d areas rejected in accordan ce w ith C lau se 12.4 shall be con sidered as defective pavem en t areas. 14.1.2 D efective pavem ent areas shall be rem oved and replaced as specified herein w ith pavem en ts of the thickness an d quality required by this specification. 14.1.3 Jointing of the rep lacem en t concrete to the existing con crete shall be by an approved m ethod .
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APPENDICES
Appendix A: Glossa ry of Terms The follow ing term s are typically used in the description of industrial pavem en ts and m any h ave been used in C hapters 1 to 3 42 of the m anual.For further inform ation or other term s,refer to A C I 116 C em ent and C on crete Term inology or Barker,JA 43 D ictionary of C oncrete . Bleeding The rising to the free su rface o f m ixing w ater w ithin new ly-placed concrete caused by the settlem en t of the solid m aterials w ithin the m ass. Bond The ad hesion of con crete to the surface of harden ed con crete or other m aterials such as reinforcem en t. Bonding agen t A proprietary m aterial used either as an adm ixture in a b on ding layer m ortar or grou t to im prove its bonding properties,or as the b onding layer itself. Bond ing layer A layer of grou t,m ortar or other m aterial applied to a h arden ed con crete pavem en t,before a top ping is placed,to im prove the bon d betw een the pavem ent and the topp ing . Bull float A flat,broad -blad ed steel han d toolused in the final stages of finishing operations to im part a sm ooth surface to con crete pavem ents and other un form ed concrete surfaces. Chatter marks M arks on the surface of con crete caused by a trow el or other finishing tool bouncing off coarse aggregate particles lying just below the surface. Compaction The p rocess of inducing a closer packing of the solid particles in fresh ly-m ixed concrete du ring p lacing b y the reduction of the volum e of voids. Construction joint The location w here tw o successive placem ents of concrete m eet. Con traction joint (Free joint) A form ed, saw n or tooled joint provided to relieve ten sile stress in the p avem en t due to contraction. Con trol joint A joint provided in a con crete pavem en t to prevent stress due to expan sion,con traction or w arping. Controlled low-strength ma terial (CLSM) A cem entitiou s backfill m aterial that flow s like a liquid,self-levels and sup ports like a solid w ithout com paction . Crack ind ucer A strip of m aterial placed w ithin the pavem en t so as to induce a crack at a d esired location. Crazing Fine,ran dom cracks on the con crete surface. Curing M ainten ance of hum idity an d tem perature of freshly placed con crete during som e definite period follow ing placing,casting or finishing,to en sure satisfactory hydration of the cem en titiou s m aterials and prop er harden ing o f the con crete. Curing mem brane A proprietary coating applied to the surface of a concrete p avem en t to reduce loss of m oisture and prom ote curing . Curling W arping of a concrete p avem ent,top ping or screed w hereby the ed ges curl up becau se of differential shrinkage or therm al m ovem ents throu gh its depth.
Dowel bar A sm oo th steel bar,coated w ith a debo nding agen t over half its len gth,placed horizontally across a joint to tran sfer vertical load s from one slab to the n ext w hile perm itting differen tial horizontal m ovem en t betw een the p anels. Dusting D evelop m en t of po w dered m aterial at the surface of hardened con crete. Edging tool A tool sim ilar to a float,but having a form suitable for rounding the edge of freshly p laced con crete. Expa nsion joint A joint,norm ally filled w ith a resilien t m aterial,provided to separate a p an el from ad joining pan els or structures to prevent stress due to expan sion. Finish The texture an d sm oo thness of a surface. Finished paveme nt level The level of the w earing surface of the pavem ent. Finishing L evelling, sm oothing, or otherw ise treating surfaces of fresh ly- or recently-p laced concrete to p roduce the d esired ap pearance and characteristics. Fixed end The co ncrete slab is cast integrally w ith foundation. Float (see also Power f l oat) A flat-faced w oo d o r m etal hand tool,for evening or flatten ing concrete. Float finish A rather rough surface texture o btained by finishing w ith a float. Floating The u se of a float du ring finishing operations to im part a relatively even (but not sm ooth) texture to an unform ed fresh con crete surface. Free joint (see Contr acti on j oint ) Granolithic concrete C oncrete –suitable for use as a w earing surface to p avem en ts –m ade w ith specially selected aggregate of suitab le h ardn ess,surface texture an d p article shape. Granolithic topp ing A layer of granolithic concrete laid over a fresh,green or harden ed con crete slab. Grinding R em ovalof parts of the surface of harden ed con crete by m ean s of an abrasive w heel,disc or grindstone. Grout A m ixture of cem en t an d w ater,of fluid con sisten ce, w hich m ay or m ay not con tain other finely divided, insoluble m aterial. Hardened concrete C on crete w hich h as attained an ap preciable stren gth. In-fill In alternate b ay or lan e co nstruction,the b ays o r lan es cast betw een the previou sly laid and h arden ed bays or lanes to com plete the pavem ent.
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APPENDICES
Isolation joint A joint betw een a panel and other parts of the structure to prevent stress du e to expan sion or con traction or other structural m ovem en ts.
Screed A layer of m ortar or other plastic m aterial laid over a pavem ent and broug ht to a defined level.
Joint filler A strip of com pressible and/or elastic m aterial used to fill an exp an sion or isolation joints.
Screed board A straigh tedge o f w ood o r m etalm oved o ver guides to strike off or finish the surface of a screed.
Joint sealan t A m aterial used to preven t ingress of w ater or solid foreign m aterials into a joint.
Seal The p revention of ingress of w ater or foreign solid m aterial into a joint or crack.
Key (keywa y) A recess in the surface of a m aterial w hich facilitates the tran sfer of vertical load betw een ad jacent panels.
Sealant A m aterial used to form a seal in a joint or crack.
Laitance A thin-layer com po sed of w ater,cem ent and fine agg regate w hich form s on the surface of over-w et or overw orked concrete. Lean-mix concrete C on crete w hich h as a low strength. Levelling comp ound A sem i-fluid m aterial ap plied to a pavem en t before the installation of a dry-laid surfacing, so as to im prove its surface regularity. Longitud inal joint The joint betw een bays and lanes parallel to the d irection in w hich casting proceed ed . No-fines concrete C oncrete w hich con tains little o r no fine aggregate. Panel A unit of con crete pavem en t laid in on e piece and bounded on all sides by free edges or joints. Placing The d eposition and com paction of freshly m ixed m ortar or concrete in the p lace w here it is to harden . Power float A m otor-driven revolving disc that flatten s and com pacts the surface of con crete p avem ents. Power tr owel A m otor-driven device w hich operates orbiting steel trow els on rad ial arm s from a vertical shaft. Rotary discompactor A m otor-driven rotary disc used after final trow elling to b urnish the pavem en t surface an d provide a h ighly ab rasion-resistan t surface. Sawn joint A tran sverse groove,cut by a special circular saw to b etw een on e quarter and on e third of the d epth of the harden ed con crete p avem en t,so as to create a con traction joint w hen shrinkage restraint forces cause a crack betw een
76
the bo ttom of the groove an d the bo ttom of the slab.
Set (initial) The con dition of cem ent paste or con crete w hen it can n o lon ger be m ou lded bu t has not attained any ap preciable stren gth. Shrinkage Th e reduction in volum e caused by drying, therm aland chem icalchanges. Side form A form used alon g one side o f a pavem ent to retain the concrete an d act as a datum for finishing the surface. Slab The m ain structuralelem ent of the con crete pavem ent. Subbase A layer of select m aterial betw een the subg rade an d the slab. Subgrade The n aturalor prepared form ation on w hich the pavem en t is con structed. Surface h ardener A chem icalapplied to a concrete pavem ent to redu ce w ear and du sting. Toggle joint –see Keyway. Tie ba r A steel bar (usually a d eform ed bar) used across longitudinal joints and prim arily d esign ed to prevent open ing of the joint,rather than as a m ean s of vertical load tran sfer (as does a dow el bar). Tied joint A joint w hich h as bon ded reinforcem ent passing through the joint. Topping A n integral or app lied layer used to increase abrasion (w ear) resistan ce an d/or chem ical resistan ce of the slab. Trowel A tool(usually of high ly tem pered steel) w ith a w oo den h and grip an d m ade in a variety of patterns. Wearing sur face Th e surface w hich com es in con tact w ith traffic using the p avem en t
APPENDICES
Append ix B: Des ign exa mple EXAMPLE:
METHOD 1 S TRIP METHOD (A)
•M an ufacturing p lan t w ith a principal factory area 50m x 30m an d a poten tial exten sion of the factory area eastw ards.
Step 5: Design for linea r movement
•Special construction for the gab le w all requires the w allto be h orizontally tied to grou nd floor at w est en d.
Establish positions of free joints,note in this exam ple there can be n o free end on the w est gable.M axim um leng th betw een free joints is recom m end ed in the rang e 32-40m .
•Factory u ses forklifts < 3000kg load . FIG B2 FIG B1
POS ITION OF FREE JOINTS:
N
50 m
Manufacturing Plant Floor
W
E
Future Extension
Free Joint t n i o J e e r F
t n i o J d e x i F
t n i o J e e r F
Free Joint Site boundary
Step 1: Concrete properties So m e m echanicalabrasion dam age p ossible,bu t not extrem e. fc = 30M Pa
Step 2: S urfa ce texture urface P rocess is dry so a pow er trow elled finish of the concrete w ill be satisfactory.
18m
32m
Select from Table 1.12 the reinforcem en t for 150m m thick slab an d spacing o f 32m . For 31m :reinforcem ent = 662 m esh is acceptable N ote the rules for m od ified en ds w hich d ou bles the am ou nt of steel determ ined from Table 1.12 for the 18m spacing (or you can dou ble the span) 150m m slab w ith 18 x 2m . R einforcem ent = 661 m esh FIG B3
From N Z S 3114 cho ose U 3 finish
REINFORCEMENTREQUIRED:
Step 3: Site subgra de A n assessm ent of the subgrade is requ ired to be m ade.A trial pit is useful rem em bering that the subgrad e w ill,on m any level sites,be the m aterial im m ediately b elow the top soil.A ssum e a m edium class in Table 1.9. Su bbase thickness 150m m
6 6 1 M e s h
6 6 2 M e s h
Step 4: Thickness of concrete pa vement sla b From Table 1.10 choose appropriate thickn ess.In this case use indu strial prem ises w ith m edium load ing/m edium subgrade. C on crete thickness 150m m Beyond this po int there are three sep arate design alternatives in Part 1 and a fourth in Part 2 o f the m an ual. Concrete Ground Floors and Pa vements : Pa rt 1
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APPENDICES
FIG B6
Step 6: Design Des ign for for wa warping rping joints In strip con struction one d im en sion of the bay sizes is determ ined by the w idth of the screeding eq uipm ent –say 4.5m .
FREE JOINTTYPES
FJ1b
FJ1b
FIG B4
FORMED JOINTS WITH S TRIP METHOD
FJ4 18 m
FJ4*
32 m
6 bays of 4.5m 2 edge strips of 1.5m
FJ1b
FJ1b
* A modification for t he east end would be to fit sleeves to allow dowels in the new phase of construction to be i nserted later.
FIG B7
TIED JOINTTYPES
FIG B5
TJ1b
COMP LETED JOINT/BAY PATTERN
3 bays of 6m
4 bays of 8m
TJ1a 6 bays of 4.5m 2 edge strips of 1.5m
L en gth to w idth of strip sho uld not exceed 1.8 preferably less,i.e.square is the ideal. M axim um bay length = 4.5 x 1.8 = 8.1 For w arping, joints spacing shou ld be kep t under 10m .
A ll other joints are tied joints selected from Fig.1.23.The longitudinal joints w ill be TJ1b w hich are form ed during construction.The tran sverse joint w ould be saw n later,i.e. use TJ1a o r if con cem ed abou t w heel load tran sfers,then providing the slab is greater than 150m m thick, the tied keyw ay cou ld b e used. N ote 1: The slab must be free to move and w hi le not considered
i.e. C hoose 8m
in this example, the positi on of stanchions/ colu mns, etc, wi ll
For the w estern end using 2 bays of 9m exceeds the W /L lim its.Therefore u se 3 bays of 6m .
also infl uence the posit ion of j oint s. N ote 2: If t he external wal ls are constr ucted before the slab, it is
necessary t o bri ng the longitudi nal join t i n fr om the wall to
Step 7: Select joint types The free joints on the north an d south w alls do not have load ing tran sfers.Select FJ1b from Fig.1.22. The east an d interm ediate FJ w ill have w heel loads crossing the joint,therefore ch oose FJ4 dow elled form ed joint.
78
create constr uction space for t he str ip method.
APPENDICES
FIG B8
Step 7: S Seelect lect joint types
EDGE STRIP FOR CONSTRUCTION US ING S TRIP METHOD
Free joints as for M ethod 1. The tied joints are all induced type created usually by saw ing using detailTJ1a.
600mm minimum edge strip to allow for construction equipment
N ote 1: The slab must be fr ee to move and w hi le not considered
in this example, the positi ons of stanchions/columns etc wi ll
TJ1b
in fl uence the posit ion of joi nts.
FJ1b
FIG B10
JOINT-TYPE P OS ITIONS
FJ4
FJ1b
TJ1a FJ4 METHOD 2: CONTINUOUS P OUR
Step 5: Design for linea r movement A s for M ethod 1.
TJ1a
Step 6: Design Des ign for for wa warping rping joints In con tinuous paving m ethod s there are no restriction s on the bay d im en sion s resulting from con struction equipm en t. The restriction s becom e o nes associated w ith con crete m ovem ents. The recom m en dation in this m ethod is that overall spacing should be divided to create ap proxim ate squ are p attem s no t exceeding 8m . FIG B9
METHOD 3: S TRIP METHOD (B) (B )
Step 5: Design for linea r movement The system is described on page 31.Essentially L ,the distan ce betw een the perim eter free joints in M ethod s 1 and 2 is applied to the len gth of the actual bay,i.e.L = 8 -10m . R eference to Table 1.12 show s that for 150m m slab using a 665 m esh the free spacing w ou ld b e 19m .H ow ever,the 665 m esh is considered the p racticalm inim um size to handle an d fix in position.
BAY PATTERN - CONTINUOUS POURING
3 bays of 6m*
FJ1b
4 bays of 8m
R einforcem ent = 665 m esh
Step 6: Design for wa rping warping
4 bays of 7.5m
The bay size restrictions are sim ilar to the lim its in Step 5, i.e. joint spacing 8 -10m . H ow ever,in the strip construction m ethod the spacing of longitudinal joints is often governed by construction m ethod ,i.e.4.5m assum ed for norm alcon struction m ethods. Th e L /W ratio still applies and therefore the m axim um bay size becom es 4.5m x 8m .
* 2 bays of 9m could b e considered
Th e bay p attem is show n in B11.In this m ethod there is no need to con sider the 32m /18m split of the 50m .
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APPENDICES
Step 7 Select joint joint types types
METHOD 4: P ANEL CONTINUOUS P OUR
Perim eter-free joints as for other m etho ds.The tied joints of the p revious strip joint now becom e free joints requiring selection from Fig.1.22
Fo llow s the sam e principles of M ethod 3, but ap plies it to con tinuou s paving con struction .This develop m en t is discussed in Part2 o f the m an ual.
In this case,becau se w heel load s are to be d esign ed for,the FJ joints selected m ust be capable of tran sm itting w heel load s,i.e.FJ4.If it w ere assum ed that m ost traffic m ovem en t is E-W then FJ6 cou ld b e used for the longitudinal joints. H ow ever for industrial floor slabs,unlike high w ay p avem en ts,w heel traffic can be in any d irection,hen ce the n eed to con sider dow els to tran sfer w heel load s over allthe joints. FIG B11
BAY PATTERN AND JOINTS
FJ1b
6 bays of 7m
1 of 8m 6 bays of 4.5m 2 edge strips of 1.5m FJ4
FJ1b
FJ5 or 6 In this special case the restraint provi ded by on e bay needs to be checked – ie, design for 2 x 7m= 14m < 19m, therefore 665 mesh is OK Note: This method reduces the general level of r einforcement
provi ded i n t he slab, but i ncreases the sophisti cati on requir e- ments of joint ing w here it is recommended that if dowell in g is requir ed in tw o dir ections, one di recti on must use dowels that have the abil ity t o absorb l ateral movements.
80
APPENDICES
Appendix C: The effect of chemica ls on concrete pa vements M any substan ces w ill attack con crete,lead ing to deterioration of the b on d of the m atrix causing loss of stren gth an d/ or the ab ility of the concrete to protect the reinforcem en t from corrosion.In m ost cases,the aggressive agent has to b e in liquid form to pen etrate the con crete and attack it.Thus con crete pavem en ts no t in con tact w ith liqu ids are n ot usually subject to ch em ical attack. The effect of various chem icals on con crete is given in 44 the Concrete Design Handbook .In m ost cases, the rate of attack can be slow ed b y using an im perm eable,dense concrete.In the case of interm itten t or low -level concen tration of an aggressive agen t,the specification of a suitable con crete can m inim ise the effect of attack.W here continuous expo sure and/or a high levelof con cen tration of the aggressive ag en t cannot be avo ided ,then a protective coating is necessary.The properties of various generic typ es of coatings to protect con crete are sum m arised in Tab le C 1. Table C 2 (overleaf) gives a typ ical list of substan ces en countered in N ew Z ealand .
Cleaning and d ra rainage inage The service life o f a co ncrete floor in poten tially co rrosive environ m en ts is influen ced not on ly by factors such as the choice of concrete an d surface finishes,but also b y atten tion to rou tine care through clean ing and drainage.
A level floor w ill alw ays p uddle d ue to surface level toleran ces. Typ ical surface d eviations for a high-class sm oo th finish w ou ld be 3m m in 3m (N Z S 3114). It is therefore im portan t that floors w hich w illbe in con tact w ith corrosive m aterials sho uld be slop ed tow ards a d rainage system . Transferring liquid into longitudinal chan nels red uces the n eed for exp en sive floor coatings,particularly w here clean ing ou t processing equipm en t results in a d ischarge of corrosive liquid onto o ne part of the floor. L ining the drainage chan nel w ith a corrosion -resistan ce m aterial w ould then be the first line o f defen ce. G reater slop es shou ld b e avoided because pedestrian use becom es difficult. TABLE C3
Recommended drainage s lopes Smooth surfaces surfa ces
Minimum: 1 in 80 Recommended: 1 in 60
Rough surfaces surfaces // Heavy spillage
Recommended: 1 in 40
Note: Vehicle traffic should move a cross the slope – rather than up and down
TABLE C1
PROTECTIVE BARRIER SYSTEMS (a fter ACI 201.2R-92
45
)
Severity of chemical environment
nomin a l Tota l nomina thickness range of coating
Typica l prot proteective ctive barrier systems
Typical bbut ut not eexclusive use uses xclusive us ess ooff protective systems in order of severity
Mild
Under 1 mm
Polyvinyl butyra l, polyuretha ne, epoxy, a crylic, chlorinate d rubber styrene-acrylic copolymer, aspha lt, coa l tar, chlorinated rubber, epoxy, polyurethane, vinyl, neoprene, coa l-tar e poxy, coal-tar uretha ne
•
Improve freeze-thaw resistance
•
Prevent staining of concrete
•
Protect concrete in contact with chemical solutions having a pH as low a s 4, depending on the chemical
Intermediate Intermedia te
3–9 mm
Sa nd-filled epoxy, sa nd-filled polyester, sand-filled polyurethane, bituminous materials
•
Protect concrete from abrasion and intermittent exposure to dilute acids in chemical, da iry, and food processing plants.
Severe
0.5–6 mm
Gla ss-reinforced epoxy, gla ss-reinforced polyester, precured neoprene she et, plasticised PVC sheet
•
Protect concrete tanks and pavements during continuous exposure to dilute mineral, (pH is below 3) organ ic acids , sa lt solutions, s trong alkalies.
Severe
0.5–7 mm
Composite s ystems : • Sa nd-filled epoxy system top coated with a pigmented but unfilled epoxy • Aspha lt membrane covered with a cid-proof brick using a chemical-resista nt mortar
•
Protect concrete tanks during continuous or intermittent immersion, exposure to wat er, dilute acids, strong alkalies, and sa lt solutions
•
Protect concrete from concentrated acids or combinations of a cids and s olvents
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APPENDICES
TABLE C2
EFFECTOF VARIOUS SUBSTANCES ON CONCRETE FLOORS
Acids
MATERIALS
CONCRETE EFFECTON CONCRETE
P ROT ECTIVE SYSTEM ROTECT
Acetic <10%
Slow disintegra tion
AB
Acetic >10%, Ca rbolic, ca rbon ic, cit ric, la ctic 5% phos phoric 10%, ta nnic, ta rtaric Acid wa ters
Slow disintegra tion of surfa ce morta r but a ction usually not prolonged
AB
Humic
Slow disintegra tion possible depending upon humous material
AB
Hydrochloric, nitric, sulphuric
Ra pid disintegra tion
C
Ca rbona tes of a mmonium, pota ssium a nd sodium, silicates, hydroxides of alkali materials
None
Ch lo rid es o f p ot a ss iu m, ca l ciu m a n d s od ium
No ne , un le ss t he co nc re te is a l te rn a te ly wet a nd dry
A
Chlo rid es o f a mmo nium, co ppe r, iro n, magnesium, zinc
S lo w d is integra tio n
AB
Chloride of a luminium
Ra pid disintegra tion.
C
Nitra te – ca lcium, ferric, zinc
None
Nitrate – lead, magnesium, potassium, sodium
Slow disintegration.
BC
Nitra te – a mmonium
Disintegra tion.
C
Nitrite – sodium
Slow disintegra tion
AB
S ulphid e – co pper, ferric, po ta ss ium
No ne unle ss sulpha te s a re pres ent
Sulphide – sodium
Slow disintegra tion.
Sulphite – sodium
None unless sulpha tes a re pres ent.
Sulphite – a mmonium
Disintegra tion
C
S ulp ha t es w it h e xc ep tio n o f a m mo niu m
*Dis in te gra t io n un le ss co nc re te is s ulphate-resista nt
AB
Sulpha te of a mmonium
Disintegra tion
C
Petroleum P etro leum oils o ils
Hea vy o ils below 35° B a ume gra vity
None
Man y lubrica ting oils contain some vegetable oil. Concrete exposed to such oil should be protected a s for vegetable oils
Light oils a bove 35° Ba ume gra vity – b enzine, ga soline, keros ene, na ptha , high octa ne ga soline
None, but to prevent sta ining a nd loss from penetra tion, impervious co ncrete is req uired a nd surfa ce trea tments are genera lly used
Coal Coa l ta r
Aliza rin, a nthra cene
None
Distiliates Distilia tes
Benzol, cumol, pa ra ffin, pitch, toluol, xyiol, creosote, cresol, phenol
Disintegra tes slowly
Vegetable Vegeta ble oils
Cottonseed
No a ction if a ir is excluded, slight disintegrat ion if exposed t o a ir
Rosin
None
Some sa salts lts and a nd alkali solutions so lutions (Dry ma terials g en era lly ha v e no effect)
82
C
AB
AB
AB
APPENDICES
TABLE C2 (c ont inue d): EFFECTOF VARIOUS SUBSTANCES ON CONCRETE FLOORS MATERIALS
Vegetable Ve ge ta b le oils o ils (cont) (co nt) Almo nd , ca sto r, co co nut , o live , peanut, poppy seed, rape seed, walnut
Dis inte gra tes surfa ce s lo wly
Ch in a wo od , lins ee d, s oyb ea n, tun g
Dis int eg ra t es s urfa ce slo wly b ut if a pp lie d in thin coats , the material q uickly oxidises and ha s no effect
Turpentine
None, but to prevent penetra tion a surfa ce treatment is generally used
Fat Fats nd fa fatty Fa tss aand tty Acids Fish oil (animal)
Miscellaneous Miscella neous
EFFECTON CONCRET E CONCRETE
P ROT ROTECT ECTIVE SYSTEM SYSTEM
AB
Most fish oils a tta ck concrete slightly
AB
Foot oil, la rd and la rd oil, ta llow and tallow oil
Disintegra tes surfa ce slowly
AB
Alcohol
None
Ammonia
None
Ba king soda
None
Beer
Slight surfa ce deteriora tion only
Blea ching powder
None
Blea ching solution
Usua lly no effect – where subject to freq uent wetting a nd drying with solutions conta ining calcium chloride some surface treatment should be provided
Bora cic
None
Bora x
None
Brine (sa lt)
Usua lly no effect on impervious concrete. Where subject to freq uent wet ting an d drying some s urface treatment s hould be provided
Butter milk
Sa me a s milk
Ca ustic soda
None
Cha rged wa ter
Sa me a s ca rbonic a cid – disintegra tes slowly
Coa l
The grea t ma jority of floors show no deteriora tion. Exceptional cas es ha ve been coa l high in pyrites (sulphide o f iron) and moisture showing some a ction but the rate is greatly retarded by deposit o f a n insoluble film. Action may be stopped by surface treatment
AB
Cya nide solutions
Disintegra tes slowly
C
Electrolyte
Depends on liq uid. For lea d a nd zinc refining and chrome plating some surface treatment is necess a ry. For nickel an d coppe r pla ting no treatment is required
AB
Forma ldehyde, forma lin
Aq ueous solutions disintegra te concrete
C
Fruit a nd vegeta ble juices
Most fruit juices ha ve s ome sma ll effect a s tarta ric a cid and citric acid marginally affect concrete. Floors under raisin seeding machines have show n some effect, proba bly due to poor concrete. sugar solutions mixed with juices will atta ck concrete
AB
Glucose
Disintegra tes slowly
AB
AB
AB
AB
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APPENDICES
TABLE C2 (c ontin ue d): EFFECTOF VARIOUS SUBSTANCES ON CONCRETE FLOORS MATERIALS
Miscella neous (cont) Glycerine
EFFECTON CONCRETE
P ROT ECTIVE SYSTEM ROTECT
Disintegra tes slowly
AB
Honey
None
Milk
Fres h milk ha s no effect but if a llowed to sour, the lactic acid will at tack
AB
Mola ss es
Does not effect impervious, thoroughly cured concrete. Dark, partly-refined molasses may atta ck concrete tha t is not thoroughly cured. Such concrete sho uld be protected
AB
Sila ge
Atta cks concrete slowly
AB
Soda
Sa me a s sodium ca rbona te. None
Suga r
Dry suga r ha s no effect on concrete tha t is thoroughly cured. Sugar s olutions at tack concrete
AB
Ta nning liq uor
Depends on liq uid. Most of them ha ve no effect. Ta nneries using chromium report no effects . If liquor is acid s ome treatment is necessa ry
AB
Urine
Disintegra tes slowly
AB
Vinega r
Disintegra tes (see a cetic a cid)
AB
Wa s hing s oda
None
Wa ter (a cidified na tura l)
Surfa ce morta r ma y b e erod ed but us ua lly action then stops
AB
Whey
The la ctic a cid will a tta ck concrete
AB
Wine
None
Wood pulp
None
NOTATION OF PROTECTIVE S YSTEMS A. Production of a high-qua lity power-compacted, trowelled concrete surface. The use o f vacuum dewate ring methods in the process produces a finish of improved q uality A+ . B. Having produced a surface to A or A+ the surface is treated with sod ium silicate or fluosilicates of magnesium or zinc. C. A chemical resista nt membrane ha s to be used to isolate the concrete from chemical atta ck. NOTES The nota tion indicates the minimum precautions tha t should be ta ken to protect the concrete floor. In many cas es it may be necessa ry to use chemically-resista nt membrane coatings in order to comply with various hea lth regulations. Other surfa ce sea lers in the resin field a re also a vailable but before use the ir chemical resistance to the pa rticular range of materials to be placed on the floor should be checked with the manufacturer. * Precautions should follow the relevant NZ Sta nda rd requirements for minimum cement contents a nd wa ter cement rat ios. Concrete products which have been stea m cured show a high resista nce to sulphate a ttack.
Concrete surface s
S P ECIAL S URFACE TREATMENTS
P roducing a low -perm eability concrete is the first step in red ucing corrosive attack. C areful specification and good w orkm an ship are vital in en suring a corrosive-resistan t con crete floor. Incorrect tim ing or un satisfactory m ethods of surface finishing w ill seriously affect the p erform an ces of the floo r.R ecom m en ded prod uction specification s are: •low w ater/cem en t ratio (low perm eability) •placing m ethod suitable for low slum p con crete •vibrating screed com paction •correct finishing an d trow elling tech niques •w et curing for at least 7 d ays
This section does not include the u se of toppings, bu t high ligh ts a num ber of treatm ents w hich can im prove the corrosive resistan ce o f the slab of floor.
84
Va cuum dewa tering This process com prises the ap plication of a vacuum to the surface o f the concrete im m ed iately after laying. T he process rem oves surplus w ater from the slab to enable easy trow elling w hich im proves productivity in floor con struction. It has been found that the process also im proves
APPENDICES
ab rasion an d resistan ce to co rrosion of the concrete floor. Vacuu m dew atering is an alternative to the u se of w aterred ucing agen ts,perm itting concrete w ith g ood w orkability to h ave sup erior lon g-term prop erties throu gh the rem oval of excess w ater. W hen correctly executed,vacuum treatm en t can reduce the w ater content of the con crete by 15-30% , w ith the am ou nt of extracted w ater reducing w ith an increase in fines or w hen using air-en training agents. The w ater/cem en t (w /c) ratio is equally reduced ,resulting in high er stren gth an d im proved durability due to the redu ced w ater con ten t. O ne aspect of vacuum -treated concrete m eriting special note is show n in Figu re C 1.In non -vacuum -treated concrete the w /c ratio is typ ically greatest near the u pper surface of the con crete due to the influence of segregation and bleeding. The resulting stren gth gradien t is show n by the d ashed line betw een A and B. U sing vacuum treatm ent it is the up per section of the concrete that has the low est w /c ratio,resulting in the strength gradient betw een C and D (see Figu re C 2). The gain in surface strength,an d sim ilarly durab ility,is then m easured betw een A and D . Figure C 2 show s that there is not only im proved stren gth, but also faster stren gth develop m ent. A nother im po rtant advantage of vacuu m FIGURE C1 ) e u l a v s y a d 8 2 f o % ( H T G N E R T S E V I S S E R P M O C
130%
dew atering is its ap plicability in cold an d w et w eather, w here the p roject can be finished an d covered faster. Th is is also u seful w hen there is the possibility of frost,perm itting w ork to be planned w ith greater confidence. D ue to rem oval of the extracted w ater,the volum e of concrete red uces. For typ ical thicknesses,concrete floors w ill sink abou t 1m m per 100m m of floo r thickness. To com pen sate for possible h eigh t differen ces w hen casting against previously p laced con crete,it m ay b e n ecessary to use a spacer at the edges of a beam screed . If m ajor un evenness in the concrete surface is detected after vacuum treatm en t,it m ust be corrected before the finishing process. W hen dew atering,care m ust be taken to sealjoints and ducts so that they d o not preven t the establishm en t of a vacuum . Sim ilarly,it m ay be necessary to seal the low er surface o f elevated concrete floors to en sure that air does not pass directly through the floor. Severalvacuum dew atering processes are available,bu t all involve the use o f a filter to en sure that on ly w ater is extracted ,not cem en t slurry. Th e filter should be sufficien tly effective to en sure that only p ure w ater can pass through , but it should not be so den se as to o ffer excessive resistan ce. A bo ve the filter there is a m em brane p erm itting the vacuum to be established . The m ost com m on process is the use of suction m ats,having a w idth of abou t 1.5 m an d b eing laid ou t over the en tire project w ith overlapping b etw een m ats of 30-50m m . The dew atering p rocess is com plete w hen a sufficien t volum e of w ater has been extracted. Th is is difficult to accurately con trol,but a generalrule is ab out 1-1.5 m inutes for every 10m m of floor thickn ess. Insufficien t vacu um tim e, vacuu m leakage,clogged filters,gap s betw een m ats,an d too-fine co ncrete m ay allresult in insufficien t w ater being extracted from the project.
100%
50%
5
10
15
20
25
30
AGE (days)
Th e tim e saving in using vacuum dew atering results from the fact that im m ediately after the m ats are rem oved the surface is hard en ou gh to w alk o n and pow er floating an d finishing m ust start im m ediately.
NON-VACUUM TREATED CONCRETE VACUUM TREATED CONCRETE
Sprinkle or ssha surfa ces ha ke surfaces
FIGURE C2
Incorporation of various m aterials into the w et surface o f con crete can achieve a n um ber of ben efits.
Surface A
m o t t o b d l u o m m o r f T H G I E H
1. Improved abrasion resistance: D
The spread ing an d subsequ en t trow elling of specially prepared m etallic aggregate into the surface can en han ce the w earing ability. R ecom m end ed rates of spread rang e from 5kg/m 2≤to 9kg/m 2≤dependi ng o n the surface up grading required.
Bottom
B
2. Skid resistance:
C
Increase of compressive strength
STRENGTH
Increase of surface strength NON-VACUUM TREATED CONCRETE VACUUM TREATED CONCRETE
W hen ligh t broom ing o f the surface is no t suitable becau se of clean ing requirem en ts,the skid resistan ce of a sm oo th floo r can be increased by incorporating carborundum dust,silicon carbide o r crushed flints into the surface.
Concrete Ground Floors and Pa vements : Pa rt 1
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85
APPENDICES
3. Colour:
W hile colou red con crete can b e ob tained by ad ding a pigm en t to the m ix,con crete can also be colou red using a surface-ap plied dry sh ake m aterial.The action of trow elling and the m aterial itself prod uce a h arder and m ore du rable surface.R ecom m ended rates of spread are provided by sup pliers. Surface treatm en t of the w et concrete in a structural slab has the advan tage o f avoiding the need for a top ping. H ow ever,the d epth of treatm en t is lim ited,so in very h eavy w ear situation s the u se of a top ping shou ld be con sidered. W hile a top ping can be constructed at a con venien t tim e w ithin an overall construction sched ule, the surface treatm ents described abo ve m ustbe do ne at the tim e of finishing of the structural slab w here this is p ossible.Treated surfaces then w ill need p rotection from dam age from sub sequ ent con struction operations.
Surface hardeners A num ber of floor harden ers are available.The m ajority rely on form ulas that includ e sodium silicate an d m agn esium , sod ium an d zinc silicofluorides. The action of these chem icals on the concrete surface is a‘ case harden ing’ effect,im proving resistan ce to m ild chem icalattack, w ear and dusting.
86
Recommen ded process: Tw o or three ap plications at intervals of 24 hours are norm ally required using either a spray,brush or m op. U nabsorbed liqu id shou ld b e rem oved w ith w ater after the last ap plication.The best results are obtained w hen the h arden er is applied to co ncrete that has dried out for about 14 days after curing. The com m on form ulas,their app lication an d effects,are: 1. Comm ercial grade sodium silicate: (not suitabl e for very dense, closed impermeable sur faces) Application: Th e concrete shou ld be ab ou t fou r w eeks old w hen the solution is applied .It should be d iluted w ith w ater and ap plied in three coats.The first coat is often 1 p art sod ium silicate to 4 parts w ater,w ith the tw o succeeding coats sligh tly m ore con centrated . Effects: The sodium silicate reacts w ith free lim e in the surface layers of the co ncrete to form calcium silicate. 2. Silicofluoride compou nd s: P rob ably the b etter choice of surface sealan t.M agnesium , sod ium an d zinc silicofluorides are used either singly o r in com bination . Effects: Form inert calcium fluoride,providing som e protection against chem ical attack.M ost con tain surface w etting agen ts to assist pen etration into the surface layers of the concrete. 3. Organic compound s: M ainly low -viscosity ep oxy resins.C ostly,but provide a significan t degree of chem ical resistan ce.
APPENDICES
Appendix D: Determina tion of a mount of shrinka ge reinforcement For design purposes it is assum ed that w here a crack occurs, the stress in the concrete h as dim inished to zero an d that the entire stress m ust be taken up by the steel reinforcem ent.
conservative allow able stress of 0.67 yi s recom m ended. The m ost con ven ien t type of reinforcem en t for jointed con crete pavem en ts is w elded w ire fabric,rather than plain or deform ed b ars or cold w orked bars.
C on sider a base of length L (m ) betw een joints w here the base (slab) can m ove due to shrinkag e con traction or therm al expan sion ;w idth B(m ) of the panel (som etim es taken as 1 m for ease of calculations);thickn ess D (m m ) of base,an d den sity of con crete base W g(kN /m 3) (see Figure D 1).If the coefficien t of friction betw een the base and the sub base is µ,then the force F (kN ) required to prevent a crack open ing at m idspan (i.e.to hold a p oten tial crack closed) is:
A ssum ing w elded w ire fabric is used, then :
F = W gL / 2 BD µ
Equati on D1
Substituting W g= 24 kN /m
3
,µ= 1.5 and B = 1m ,then :
F = 0.018D L kN per m etre w idth o f base A ssum ing that the ten sile stren gth of the concrete is zero,then steelreinforcem en t m ust resist the force. If s (M Pa) is the allow ab le steel stress in ten sion,then the required area of steel,A s (m m 2),per m etre w idth of base is: A s= 1 8D L / s(m m 2/m )
Equation D2
FIGURE D 1
FORCES DEVELOPED IN A BASE DUE TO SHRINKAGE t n i o j l o r t n o C e e r F
Control joint spacing, L L/ 2
Longitudinal steel area, A s
t n i o j l o r t n o C e e r F
fs Base weight Potential crack Friction, µ
Induced crack
The allow able steelstress, s,should not exceed the yield stress of the reinforcem en t, y.W elded w ire fabric com plying w ith N ZS 3422 has a m inim um yof 485M Pa and m anufacturers are n ow prod ucing 500 M Pa steel bars and fabric.The m inim um perm issible stresses for reinforcem en t in pavem en ts varies for each au thority,an d the A C I 360 D esign of Slabs on G rade46sugg ests that fs is taken in the range of 0.67 to 0.75 y.W hilst such a reduction in the factor of safety seem s reasonable for concrete pavem ents given the assum ption that no ten sile stress in the concrete is allow ed ,a
s= 0.67
y= 0.67 x 485 = 325 M Pa
Substituting into Equati on D2 : A s = 18D L / 325 = 0.0554D L(m m 2/m )
Equati on D3
Example: A ssum ing a base thickness of 200m m (D = 200) an d a con trol joint spacing o f 16m (L = 16),then :
A s = 0.0554 x 200 x 16 = 177m m 2/m Note 1: The length L is the distance betw een joints or base edges w hich are free to m ove.Thus,for the longitudinal reinforcem ent in a road pavem ent,L is the distance betw een tran sverse contraction joints. The sam e theory applies to the transverse reinforcem ent. Thus,L is the w idth of the road pavem ent (ie say,7.4 m for a tw o-lane carriagew ay or 14.8 m for a four-lane carriagew ay). Note 2: The am ou nt ofsteel required to keep a potentialcrack tigh tly closed is a m axim um at m id p anel,and d im inishes linearly to zero at the p an elen d.In practice,the sam e am ount ofsteel required at m idspan is usually carried through the len gth ofthe pan el.In this w ay it can be seen that reinforcem en t design for jointed reinforced pavem ents is conservative and has an adequate factor ofsafety. Not e 3: A s m en tioned previously,the term coefficien t of friction ap plied to the d esign of steel reinforcem en t in pavem en ts is partly m ade u p of friction an d shear at the base/subbase interface.The coefficien t of friction at this interface is generally co nsidered to be b etw een 1.0 (for a very sm oo th subb ase) and 2.0 (for a very rou gh subb ase). W hether ofa bou nd or un bou nd type,the subb ase rou gh ness w ill usually be som ew here b etw een these tw o lim its.A coefficien t of friction of 1.5 has b een ad opted . Not e 4: In Figu re 1.17 a b rief description w as given of the subbase types and m ore inform ation is listed below :
(a) The plastic soil w as a m icaceou s clay loam . (b) G ranular subb ase con sisted o f a m aterial m eeting the U S Bureau of Pu blic R oad s grading and plasticity requirem en ts for Federalhigh w ay p rojects. (c) G ranu lar sub base con sisting of a blend of w ashed sand and gravel. (d) Sim ilar to (b) w ith a 25m m sand layer covered w ith on e-ply building p aper. (e) Sim ilar to (b) w ith a thin levelling cou rse of sheet asphalt covered by a double layer of polyethylen e sheeting containing a sp ecial friction-red ucing ad ditive.
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APPENDICES
Appendix E: Effect of va rious fa ctors on a bra sion resista nce The abrasion resistan ce of concrete is directly related to its stren gth an d the increase in resistan ce is principally d ue to an increase in cem ent content and redu ction of w ater con ten t. Th e quality of the m ortar is im portan t –the hardness of the coarse agg regate only becom es sign ificant under exceptionally abrasive con ditions i.e.w hen the surface m atrix has been w orn aw ay. Th e goo d w earresistan ce properties o f gran olithic concrete arise m ainly from its being a very rich con crete an d less from the aggregate it con tains. In general,w ell-graded natural sands free from soft m aterials shou ld be used, w ith coarse aggregates w hich need only b e especially selected for con ditions of excep tionally h eavy w ear. C oarse aggregates shou ld be free from soft sand ston e o r soft lim eston e. A part from the direct relationship b etw een abrasion resistan ce and con crete co m pressive stren gth, other factors also h ave a m ajor effect on abrasion resistan ce. M ethod s of con struction such as the finishing p rocess can have an influen ce. C uring an d the type of surface treatm en t are other im portan t factors. The relative effect of each of these variab les is illustrated in Figures E 1 to E 5. This data is based on w ork carried ou t by the U niversity of A ston47and the 48 C em ent & C on crete A ssociation of N ew Z ealand . The accelerated abrasion testm ethod adop ted in the research project allow ed a reliable d eterm ination ofsurface w ear againsttim e.The extent of abrasion w as m easured by a m icrom eter at intervals of 5,10,15 an d 30 m inutes oftest,an d these are plotted in Figures E1 to E 5 for various test conditions. The results sho w that the finishing technique, especially the use of rep eated p ow er trow elling, has the greatest influen ce on abrasion resistan ce,follow ed by curing,then con crete m ix prop ortion s.The study also fou nd that:
The repeated p ow er trow elling using a solid d isc pow er float m ach ine con sisted of three p eriods of pow er trow elling separated to allow the b leed w ater to reach the surface an d evaporate. FIGURE E1
0.0
e c n -0.8 a t s i s e r
•
88
surface harden ers seem ed to provide initial im provem en t bu t on ce the h arden er layer w as penetrated,the ab rasion resistan ce reverted to that of an untreated concrete.
W/C = 0.52 W/C = 0.65
float finish ing and polyth ene sheet curing.
FIGURE E2
0.0
-0.4
failure to cure the slab com pared to covering w ith polythen e sheeting can result in m ore than dou bling the w ear;and
30
Water-cement ration’ s effect on abrasion resistance - power
not using the appropriate finishing techn ique can increase the w ear by 3 to 4 tim es;
•
25
W/C = 0.44
n -1.0 o i s a r b A -1.2
•
the use of surface treatm en ts,such as po lyu rethan e or epoxy,w ere found to sign ifican tly en han ce the abrasion resistan ce;
20
) -0.6 m m (
-0.2
•
15
-0.4
a change from G rade 40 to G rade 25 concrete w illresult in an increase in w ear of abo ut 20% ;
rep eated pow er trow elling is an effective finishing technique to im prove abrasion resistan ce;
10
-0.2
•
•
Time (minutes) 0 5
Time (minutes) 0 5
10
15
) -0.6 m m ( e c n -0.8 a t s i s e r n -1.0 o i s a r b A -1.2
20
25
30
Repeated power float Power float and vacuum dewatering
Power float Hand float
Finishi ng metho d’s effect on abrasion resistance - w/ c ratio of 0.65 and polyth ene sheet curing .
APPENDICES
FIGURE E3
0. 0
Time (minutes) 0 5
10
FIGURE E5
15
20
25
30
0.0
-0.2
-0.2
-0.4
-0.4
90% efficient resin membrane
) -0.6 m m (
10
15
20
25
30
Metallic Natural No shake
-0.6
) m m ( e c n a t s i s e r n o i s a r b A
Polythene sheet Wet hessian
e c n -0.8 a t s i s e r n -1.0 o i s a r b A -1.2
Time (minutes) 0 5
-0.8
Air curing
-1.0 -1.2
Curing method’ s effect on abrasion resistance - w/ c ration of
Dryshake treatment’s effect on abrasion r esistance - w/ c
0.65 and repeated power float finishing .
ratio of 0.65, repeated power float finishi ng, and 90% efficiency resin membrane curing.
FIGURE E4
0.0
Time (minutes) 0 5
10
15
20
25
30
-0.2 -0.4 -0.6
) m m ( e c n a t s i s e r
Epoxy coating Polythene coating Acrylic coating Sodium silicate No treatment
-0.8
n o i s a r b A
-1.0 -1.2
Liquid treatment’s effect on abrasion resistance - w/c ratio o f 0.65, repeated power float fini shing, and p olythene sheet curing.
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APPENDICES
AP P ENDIX F: S UB GRADE AND S UB BAS E EVALUATIONS
F1 S UB GRADE S TRENGTH The calculation of con crete perm an en t thickn ess requires an assessm ent of the subgrade strength.The m easure of subg rade strength m ost com m on ly used is the C alifornia Bearing R atio (C BR ). L inear an alysis u tilising elastic so il beh aviour is often incorporated in design m od els and the key p aram eters w hich m ust be assessed for each soil layer are the eq uivalen t Young’ s m odulus (Es) of the soil an d an assessm en t of Poisso n’ s ratio ( ν). It is im portan t to recognise that different values of Young’ s m odulus an d Po isson ’ s ratio w ill be ap plicable to short-term (or rap id) loading co nditions and to long-term (or sustained ) load ing conditions.Fo r san dy o r gravelly soils, there is little d ifferen ce b etw een the values for short-term an d long-term load ing. H ow ever,for clay and silty soils there m ay be a sign ificant difference,w ith Young’ s m odulus for long-term load ing being less than for short-term loading. In the case of design for w heel loading w here the loads are ‘ transien t’ ,short-term values ofYoung’ s m odulus and Po isson ’ s ratio are likely to b e relevant an d should be u sed, w hile for distributed or post load ing, long-term values shou ld b e used. The relation ship b etw een sho rt-term an d lon g-term values of Escan be expressed as: E ss (short-term) = Esl (l on g - te r m ) / ß
Typicalvalues of ß are show n in Tab le F1.
Equation F1
Typ ical values of Esf or various soil typ es are given in Table F2.H ow ever,it is recom m en ded that,w here possible, actual values based on soil data for the site b e u sed for design . TABLE F2
Typica l values of Young’ s modulus, Es for various subgrades Typica ypic a l Youn g’s modulus, Es Description of subgrade
Short-term Long-term
Clay, plastic Cla y, highly pla stic (CH) well-dra ined poorly-dra ined
52.5
21 9–15
Silt (ML)
well-dra ined poorly-d ra ined
30 13– 21
21 9– 15
Silty cla clayy (CL)
well-dra ined
33–36
23–25
Sandy Sa ndy clay cla y (SC)
poorly-dra ined
26–30
18–21
Sand Sa nd (SW,-SP)
both
44–46
35–37
The correlation ofYoung’ s m odulus w ith the follow ing geotechnicaldata can be ob tained from : • C alifornia Bearing R atio (C BR ) Figu re F1; • Standard penetration test(SP T) data Figu re F2;and • Static cone p enetration test (C P T) data. The correlation betw een the short-term Young’ s m od ulus an d the static cone p en etration resistan ce, qc,is given by: Es = α q c
TABLE F1
Correlation Fact or, ß, for various soil types Soil type
Th e recom m end ed values forαare sho w n in Table F3 for various soil typ es. TABLE F3
Correlation Correla tion fa ctor, ß
Gra vels
0.9
Sa nds
0.8
Silts, silty cla ys
0.7
Stiff cla ys
0.6
Soft cla ys
0.4
Equation F2
Correlation Factor, α, for various soil types So il Type
Sand Sa nd
Correlation factor, α
loose medium dense dense
5 8 10
Silt
12
Silty clayy Silty cla
15
Clay Cla y
highly pla stic
20
Typical values of Poisson’ s ratio, ν,for various soil typ es are show n in Table F4.
90
APPENDICES
FIGURE F1
TABLE F4
ν, for various soil Typical values of Po isson’s ratio, ν
10 0
types
90 Poisson’s ratio, ν
80
Soil type
Short-term loa ding
Long-term loa ding
Gra vel
0.30
0.30
Sa nd
0.35
0.30
Silt, silty cla y
0.45
0.35
Stiff cla y
0.45
0.25
Soft cla y
0.50
0.40
Compa cted cla y
0.45
0.30
F1.2 S ubg ubgra raddee uniformity Becau se of the rigidity o f con crete p avem en ts,ap plied concen trated load s are distributed over w ide areas, resulting in relatively low bearing pressures being ap plied to the subgrade.Thus,con crete pavem en ts do not necessarily require strong support from the subgrade; how ever,it is im portan t that the sup port provided by the subg rade is reasonably un iform . W here subgrade con dition s are not reasonably uniform , this should be corrected by sub grade p rep aration practices such as selective grad ing,m ixing of soil at abrup t tran sitions an d m oisture/den sity con trolof subgrade com paction .
70 60 50
) a P M (
40
l s
E , s u l u d o m s ' g n u o Y
30 20
m r e t g n o L
10 0 0 2 CBR (%)
4
6
8 10
20
40
60 80 100
Correlation between long-term Young’s m odulus, E sl , and CBR
FIGURE F2
A loss of uniform sup port after con struction m ay occur w here pavem en ts are con structed on either expan sive soils or fine-g rained soils prone to ‘ pum ping’ .
4. 0
3. 5
NOTE: Not to be used for soft clays. For sands, gravels and other cohesionless soils use PI = 0%
F1.3 Construction procedures on expansive soils 3. 0
E xcessive differential shrinking and sw elling o f exp an sive soils can cause con crete pavem en ts to b ecom e sufficien tly distorted as to im pair their riding qualities.
2. 5
M ost soils w arran ting special consideration,classified by the A STM Soil C lassification System (see Table F5),are:
2. 0
•M H (inorganic silts). 1. 5
•C H (inorgan ic clays of high plasticity). •O H (organ ic clays of m edium to h igh plasticity). There are m any other tests w hich can be used to classify expan sive soils,but using sim ple tests com m on ly applied to soils,an approxim ate relationship has been established betw een exp an sion cap acity (soil classification) an d the percen tag e sw ell/plasticity index characteristics. Th e am ou nt of volum e chan ge occurring dep end s on several factors: •The m agn itude of m oisture variation s w hich m ay take place over a long p eriod of tim e,because of w et an d dry seasons,trees,lack of surface d rainage or a leaking w ater pipe.
1. 0 ) a P M (
0. 5
N / s s
E
0 0 10 20 Plasticity index (%)
30
40
50
60
70
80
Correlation between short-term Young’ s modulus, E , N from s standard penetration test and plasticity index
•Surcharge effect of pavem en t con struction above an exp an sive soil.
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APPENDICES
TABLE F5
Classification and rating of subgrade soils 46 MAJOR DIVISIONS
GROUP SYMBOLS
TYPICAL NAMES NAMES
SUBGRADE RATING
Coarse-grained Soils Gra vel a nd gra vely soils
GW GP GM GC
Well-gra ded gra vels a nd gra vel/sa nd mixtures, little or no fines Po orly-gra d ed gra vels a nd gra ve l/s a nd mixture s, little or no fines Silty gra vels, gra vel/sa nd/silt mixture Cla yey gra vels, gra vel/sa nd/cla y mixtures
Good Go od Good Good
Sa nd a nd sa ndy soils
SW SP SM SC
Well-gra ded sa nds a nd gra velly sa nds, little or no fines Poorly-gra ded sa nds a nd gra velly sa nds , little or no fines Silty sa nds, sa nd/silt mixtures Cla yey sa nds, sa nd/cla y mixtures
Good Good Medium Medium
ML CL
Inorga nic silts, very fine sa nds, rock flour, silty or cla yey fines Ino rga nic cla ys o f lo w to me dium pla sticity, gra velly cla ys , s a nd clays, silty clays, lean clays Orga nic silts a nd orga nic silty cla ys of low pla sticity
Medium Me dium
Fine-grained soils Silts and clays, liquid limit ≤ 50
OL Silts a nd cla ys , liq uid limit > 50
Highly organ organic ic ssoils oils orga nic
MH
Poor
CH OH
Inorga nic silts , mica ceo us or dia toma ceous a nd fine s ands or silts, elast ic silts Inorga nic cla ys of high pla sticity, fa t cla ys Orga nic cla ys of medium to high pla sticity
Medium Poor
PT
Pea t a nd other highly orga nic s oils
Poor
•Subg rade con dition at the tim e of con struction. •Site con dition s w hich m ay lead to distortion of pavem ent pan els include: •E xpan sive soils that have been com pacted w hen too dry,or allow ed to dry out before p aving,resulting in expan sion w ith any subsequ ent m oisture increase. •Subgrades w ith w idely varying m oisture con ten ts,w ith subsequen t differential sw elling. •A brup t chan ges in soil types. •A t cut-and-fill tran sitions. Tests indicate that soil sw elling can be reduced by surcharge load s and therefore can be con trolled by p lacing the m ore expan sive soils at relatively low er levels during subgrad e prep aration.In areas invo lving cu tting,the rem oval of surcharge m ay lead to d elayed sw elling an d this factor need s to b e closely m onitored . Sw elling and shrinkage can be reduced by adequ ate m oisture an d d en sity con trols during com paction .L aboratory research h as show n that expan sive soils com pacted at m oisture con ten ts sligh tly above the optim um for stan dard com paction (A S 1289,Part E)49,expan d less and absorb less m oisture. W here high ly-expan sive subgrades occur in sem i-arid areas subject to p rolonged periods of dry w eather,a cover layer of non -expan sive soilsho uld be placed over the w hole of the subgrad e.A lternatively,a layer of the existing soil m ay be stabilised w ith cem en t,or a com bination of cem en t an d lim e. The function of the cover layer is to m inim ise changes in
Medium
m oisture con tent and hence volum e chan ges in the un derlying expan sive soil,as w ell as providing som e surcharge effect.The n on -expan sive cover shou ld have a low to m od erate perm eability. The ch oice of thickn ess for a n on -expansive cover layer w ill dep en d on site conditions at the tim e of con struction an d the expected service conditions after con struction.It sho uld b e based on local experien ce.
F1.4 Proced ures for preventio n of pumping of finegrained soils P um ping is defined as the ejection of w ater and subg rade or subbase m aterial throu gh joints and cracks,or at pavem en t edges.P um ping can occur w hen a concrete pavem ent is placed directly on a fine-g rained plastic soil,there is free w ater present in the subgrade or sub base,and the pavem ent is subjected to rep etitive heavy load s over an exten ded period .C on tinued and un controlled pu m ping even tually lead s to the d isplacem en t of eno ugh soil for un iform ity o f sup port to be lost,an d for sections of pavem en t to be left unsupported. The initial reason for the onset of pum ping is the creation of a void u nder the pavem ent w here w ater can accum ulate.Tw o factors contribute to this: •L oads of sufficien t m agnitude to cause plastic deform ation of the subgrade. •W arping due to tem perature or m oisture chan ges w ithin the con crete pavem ent. A fter the void is created ,w ater is ab le to infiltrate.If the
92
APPENDICES
soil is w ell-drained ,the w ater w ill not rem ain.But if the so il is poorly drained ,sub sequ en t pavem en t deflections w ill cause a m ixture of w ater and fine-grained soil to be ejected . The ten den cy of a soil to pum p w ill gen erally vary w ith its plasticity. A ll three o f the follow ing conditions m ust be presen t for pum ping to o ccur50: •A subg rade that w ill go into suspen sion –pum ping w ill generally not occur on natural sub grades w ith less than abo ut 45% of the soil passing a 75-m icron sieve an d w hich have a p lasticity index of 6 or less. •Frequen t passage of heavy axle load s (typ ically greater than 100 passes per day). •Free w ater betw een the con crete pavem ent and sub grade, or sub grade saturation.
teristic 28-day co m pressive stren gths (f’ c) of 5 to 8 M Pa. C em ent contents are com m only about 6% . In addition to p reven ting sub grade p um ping, the follow ing b enefits can be ob tained from a bou nd subb ase: •G ranu lar m aterials used in a bo un d sub base need not have all the qualities requ ired for those used in an un boun d subbase –optim um use can be m ade of low cost or m arginal quality m aterials,particularly w here high -qu ality m aterials are scarce o r expen sive. •P rovision of a firm an d uniform sup port for the concrete pavem ent. •P rovision of firm sup port for paving equipm en t an d/or form s. •P rovision of a stable w orking platform w hich facilitates construction,particularly in w et con ditions.
P rob lem s caused by pu m ping of fine-grained soils can be p revented by:
•M inim ised subbase con solidation under traffic.
•provision of a suitable bo un d o r un bo und subb ase as specified in C lau se 3.2.5 an d Figu re 1.6; an d/or
•A ssistan ce in controlling expan sive so ils.
•provision of adequate drainage of the sub grade.
F1.5 Sta bilised bilised gradeess bilise d ssub ubgrad In som e circum stan ces,con siderable benefits can be derived from stab ilisation of exp an sive subgrad e soils (the addition of sm allam ou nts of cem ent,lim e or a com bination of these m aterials),particularly w here h igh m oisture levels are found. Stabilising a m aterial of this typ e im proves its physical properties by reducing its plasticity and perm eability (and so reducing its ten den cy to erod e) and im proves its com pressive stren gth.The stab ilisation of clay subgrad es w ill also en han ce their un iform ity of sup port under con dition s of seasonal m oisture variation.The cost of such sub grade im provem en t w ill usually b e o nly a sm all part of the total construction cost. In som e cases involving ligh tly-loaded pavem en ts, subg rade stabilisation m ay p rovide a m ore econom ical solution than the provision of an im ported subbase.
F1.6 Bound subbase Bou nd subbases are generally cem en t-treated gravel, cem en t-treated crushed rock,or lean -m ix con crete.The m ain difference betw een the typ es is that aggregate p articles in cem en t-treated sub bases are on ly p artially coated w ith cem en t;w hereas in lean -m ix con crete,aggregate particles are fully coated w ith cem en t,m aking the m aterial m ore erosion resistan t. For cem en t-treated subb ases,and w here acceptable m aterials are availab le, a typical req uirem en t is for the sub base to achieve a m inim um 7-day un confined com pressive strength of 2 M Pa.Th e cem ent con tent w ill vary according to individual m aterial properties and is best determ ined by laboratory testing.
•Im proved load tran sfer at pavem en t joints. •P revention of sub grade infiltration into the subbase an d the intrusion of hard gran ular m aterial into pavem en t joints. W hen a b ou nd sub base is provided, the assessed subgrade stren gth for that layer of subgrade m ay be increased for thickn ess design purposes as indicated in Figu re F3. FIGURE F3
Effective increase in s ubgrade s trength with use of bound subbas e Recommended maximum value for design purposes 35 ) % ( R B C , n g i s e d s s e n k c i h t e t e r c n o c r o f h t g n e r t s e d a r g b u s e v i t c e f f E
30
25 20 15 12 10 8 7 6 5 4
15 0
12 5 100 = thickness of bound subbase (mm)
3 1 2 3 4 5 Assessed subgrade strength, CBR (%)
6
7
8
10 12
L ean -m ix concretes are typ ically specified w ith charac-
Concrete Ground Floors and Pa vements : Pa rt 1
/
93
APPENDICES
F1.7
Subba Subbase se thickness
Becau se the effect of sub grade/sub base stren gth o n stresses in the pavem en t is sm all,subgrades can be rated sim ply as ‘ poor’ ,‘ m edium ’ or‘ good’ (see Table F5) an d a subbase thickn ess nom inated for each (Table F 6).These thickn esses m ay be redu ced w hen construction occurs in the dry season or under roof cover,or if construction traffic on the subbase is only light. TABLE F6
Recommended nominal subba se th ickness Subgrade rating
Poor Medium Good
Typica ypic a l CBR (%)
Recommended nominal subbase thickness (mm)
2 or less
200
3 to 10
150
10 or more
100
F 1.8 La bora tory tes testing ting L aboratory testing usually involves the determ ination of the C BR of sam ples of either the existing subg rade (taken at or just below the d esign sub grade level),or of m aterial proposed for use as com pacted fill.M ost C BR testing is carried ou t on bu lk sam ples of m aterial that are recom pacted prior to testing (testing can also be carried out on undisturbed sam ples).
94
A s far as po ssible, C BR testing should be carried out on sam ples that are in a sim ilar state of den sity,etc as the m aterial that the sam ple is m ean t to represen t w ill eventually be. H en ce, req uests for lab oratory C BR testing require the follow ing aspects of sam ple prep aration to be specified : •Sam ple den sity •Sam ple m oisture con tent •Surcharge load ing applied to the sam ple (to m od el the w eigh t of the overlying p avem en t),an d •D uration of sam ple soaking,if an y,prior to testing (to m od el adverse grou nd m oisture con dition s). Fo r exam ple,the C BR testing o f a clay m aterial prop osed for use as com pacted fill,m ay specify sam ple prep aration to include: •a dry density ratio of 100% of m axim um dry den sity as determ ined by S tand ard C om paction ; •a m oisture content equ alto the O ptim um M oisture C on tent as determ ined by Stand ard C om paction ; •a surcharge loading of 6.75k g; an d •four days soak ing prior to testing. L aboratory C BR testing (refer to N Z S 4402) is therefore usually accom panied by labo ratory Standard C om paction . In som e instan ces,an insitu falling-w eigh tpen etrom eter test is used an d calibrated for the know n soil type to give an estim ate of the C BR .
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