POLYPROPYLENE FIBRE REINFORCED SHOTCRETE
ABSTRACT: The 1020 MW Tala Hydroelectric Project in Bhutan is a run-of-the-river scheme being constructed on river Wa Wangchu ngchu in Bhutan The total estimated !uantity of concrete and shotcrete for the construction of different com"onents of the "roject is #or$ed out as 11%00%000 m& and 1%'0%000 m&%res"ectively (n innovative a""lication of "oly"ro"ylene fibre reinforced shotcrete )P*+, #as underta$en for right ban$ slo"e "rotection #or$ on the d.s of the concrete gravity dam The mi/ design trials #ere carried out in THP( laboratory and site trials #ere also carried out before ado"tion of final mi/ The details of mi/ design and features of site a""lication including difficulties encountered in P*+, a""lication have bee n brought out in this "a"er 1.0
INTRODUCTION
(s "er the re"ort of ( ommittee '0-1+ fibre reinforced concrete.shotcrete is defined as mortar or concrete containing discontinuous discrete fibre that is "neumatically "rojected at a high velocity on to the roc$ surface *ibres for shortcrete can be made of steel% glass% synthetic and natura naturall mater material ials s When When the fibre fibress are made made of synth syntheti eticc materi material% al% "oly"r "oly"ro"y o"ylene lene%% the material may be called "oly"ro"ylene fibre reinforced shotcrete )P*+, P*+, is thus essentially a conventional shortcrete to #hich "oly"ro"ylene fibres are added The P*+,.shotcrete may also contain "o33olana and other admi/tures used #ith conventional concrete n case of river valley "rojects under construction.contem"lated in the Himalayan region% various structures li$e head race tunnels% "o#er house% desilting chambers etc are generally designed as under ground structures ,ince the roc$ moss formations in the Himalayas are very young besides heterogeneous and fractured #ith shear 3ones% etc% #henever o"enings are made in such roc$ roc$ form format atio ions ns%% imme immedi diat atee su""o su""ort rtss are are re!u re!uir ired ed so as to contr control ol the the defo deform rmat atio ions ns of underground o"enings steel fibre reinforced shotcrete ),*+, is very commonly used to arrest or minimi3e the movement of the roc$ mass in the underground o"enings (t Tala Hydroelectric Project in Bhutan "lain shotcrete and ,*+, #ere used for tem"orary and "ermanent su""ort of roc$ mass along #ith other su""orting system such as roc$ bolts% anchors% steel ribs% + etc This This a""lica a""licati tion on of P*+, P*+, #as limited limited to slo"e slo"e "rotec "rotecti tion on #or$ #or$ Ho#eve Ho#ever% r% its use may be e/tended to other a""lications #hen sufficient e/"erience about its usage is gained 2.0
TALA PROJECT
Tala Hydroelectric Project is a run-of-the-river scheme% located & $m do#nstream of the e/isting && MW hu$ha Hydroelectric Project on river Wangchu in ,outh West Bhutan in 4astern Himalay Himalayas as The "rojec "rojectt envisa envisages ges constru constructi ction on of a 52m high high concret concretee gravit gravity y dam6 dam6 three three desilting chambers each of 2'0m / 1&50m / 17'm si3e for removal of sus"ended sediments of 02mm and above si3e coming #ith the river #ater diverted through the inta$e structure6 a modi modifi fied ed hors horsee shoe shoe tunn tunnel el of 7m 7m diam diamet eter er and and 2&$m 2&$m in leng length th to carr carry y the the #ate #aterr to underground "o#erhouse )20m / 20m / 88'm for utili3ing a gross fall of 71'm ( tail race tunnel of &1 $m length and 99'm diameter #ill discharge the #ater bac$ into river Wangchu
55
The installed ca"acity of "o#erhouse is 1020MW ) / 190MW The "roject has been ta$en u" for e/ecution from 1st :ctober 1559 and is scheduled to be commissioned by 200' The "roject is being e/ecuted by the Tala Tala Hydroelectric Project (uthority )THP( )THP( #hich is a joint venture of the ;ovt of ndia and the +oyal ;ovt of Bhutan 21 Slope Protecto! "or# The concrete gravity dam sho#n in *ig1 has five sluice s"ill#ays and one overflo# s"ill#ay The dam orientation #ith res"ect to river gorge is such that the #ater trajectory from t#o s"ill#ays on e/treme right of dam% im"inges on the roc$ slo"e at d.s of the dam Therefore e/tensive roc$ cutting #as underta$en to clear the #ater "assage on right ban$ The su""ort system for slo"e "rotection #or$ consisted of &2mm diameter% 10 m long roc$ bolts s"aced at 10' m both #ays and 100 mm thic$ shotcrete layer Based on various considerations% it #as decided to use "oly"ro"ylene fibre reinforced shotcrete )P*+, in "lace of #ire mesh or steel fibres as reinforcing shotcrete
*ig 1< ="stream face of the dam 211 Roc# Bolt$ The &2 mm diameter diameter and 10 m long roc$ bolts s"aced at 10' m both #ays #ere installed installed in '1 mm dia holes The end anchorage #as achieved by fast set resin ca"sules #ith minimum com"ressive strength of resin of 0 MPa at 1 hour The end anchorage of 1' m #as achieved by 1' resin ca"sules of si3e 27 mm dia and 200 mm length The roc$ bolt #as "retensioned u"to 10 ton load The remaining length of roc$ bolt #as grouted #ith cement mortar after "retensioning The roc$ bolts #ere designed for 20 ton load (s the slo"e almost vertical #ith dee" gorge% roc$ bolting machine could not be em"loyed and the installation of roc$ bolts #as carried out manually >ifferent combinations of anchorage such as mechanical anchorage% cement ca"sules% raisin ca"sules etc and installation methods #ere tried and their efficacy tests #ere conducted The "ull out tests u"to 20 tons #ere conducted in each case The load deformation characteristics
100
of one raisin grouted roc$ bolt are "lotted in *ig2(fter "re tensioning u" to 10 ton load% the unanchored "ortion of roc$ bolts #as grouted #ith cement grout Then a 100 mm thic$ layer of P*+, #as laid on the roc$ surface
*ig 2< ?oad >eformation urve of +esin ;routed +oc$ Bolt %.0
FIBRE RE REINFORCE RCED SH SHOTCRETE
=nreinforced shotcrete has a lo# tensile strength and lo# strain ca"acity at fracture These shortcomings are traditionally overcome by adding reinforcing bars or "restressing steel *ibres are discontinuous and unli$e conventional reinforcement% they are distributed randomly through out the concrete concrete matri/ matri/ There are numerous numerous fibre ty"es ty"es available available for use in concrete.sh concrete.shotcret otcrete e The basic fibre categories are steel% glass synthetic and natural fibres =se of steel fibres has gro#n over the last three decades into a matured industry but the technology of using synthetic fibres in concrete and shotcrete is ne# and gro#ing ra"idly due to the availability of #ide s"ectrum of fibre ty"es urrently the largest use of synthetic fibres is aimed at controlling "lastics shrin$age crac$ing This a""lication generally g enerally uses 01@ by volume of synthetic fibres High volume )08 - 09@ of fibres significantly increases toughness and reduces crac$ #idth
%.1
Steel F&re$
;enerally% the ultimate tensile strength of steel fibres varies from &8' to 2090 MPa (,TM ( 720 )& s"ecifies a bending re!uirement ,teel fibres shall #ithstand bending of around &17 mm
101
inside diameter to an angle of 500 at tem"eratures not less that 1 0 #ithout brea$ing This bending re!uirement "rovides a general indication of fibre ductility% ductility% as may be im"ortant in resisting brea$agae during handling A mi/ing o"erations n most a""lications% the uncoated steel steel fibres fibres are used used n s"ecia s"eciall cases% cases% #here #here aesthe aestheti tics cs is im"or im"ortant tant or e/trem e/tremee corros corrosive ive environment is involved% the galvani3ed fibres are used (s "er (%)1% fibre si3es range from 1&/ 02' mm to 8 / 09mm% #ith "o"ular fibre si3e range for shotcrete being 2' to &0 / 080 mm This si3e range is easily handled ,horter fibres are easier to mi/ A shoot at lo# rebound loss% but the shotcrete "ro"erties% "articularly toughness and "ostcrac$ resistance% are lo#er ?onger fibres% although su"erior in "roducing high strength and toughness "ro"erties% "ro"erties% usually result in more "lugging "lugging and have a higher fibre rebound rate ,ome of the "roblems #ith shorter fibres have been over come #ith the introduction of fibres having deformations or end anchorage "rovisions ,teel fibres #ith bent or deformed ends have a high "ullout resistance and may be used in smaller !uantities than straight fibres to achieve the same "ro"erties The as"ect ratio% #hich is defined as the length.)e!uivalent diameter% ranges bet#een '0 to 9' ?oose steel fibres #ith a high lengh.e!uivalent diameter ratio% #hich is essential for good reinforcement% are difficults to add to the concrete and to s"read evenly in the mi/ture )(,TM 18&-97 Bundling of fibres into units of &0-'0 is a sim"le and efficient method to mi/ easily and homogeneously The bundling of fibres is done #ith a #ater soluble glue These bundles can be added to the dry aggregates as #ell as to the already mi/ed concrete To allo# the fibre bundles to be used also in the dry mi/ "rocess% s"ecial glue has been develo"ed in order to ma$e it dissolve by the aggregate moisture content )&-@
%.2
S'!t(etc )&re$
,ynthetic fibres are derived from organic "olymers *ibre ty"es that have been used in concrete are acryl acrylic% ic% aramid aramid%% carbon carbon%% nylon% nylon% "olyes "olyester ter%% "olyet "olyethyl hylene ene and "oly"r "oly"ro"y o"ylen lene e m"or m"ortant tant "hysical "ro"erties of some commercially available fibres are are given in Table Table 1
Table Table 1< Pro"erties of ,ome ommon ,ynthetic *ibre Ty"es Ty"es )( '881+-5
*ibre Ty"e
>iamer 4!uivalent
,"ecific gravity
Tensile strength
102
4lastic modulus% MPa
=ltimate elongation%
(crylic (ramid (ramid Cylon Polyester Polyethylene Poly"ro"ylene %.%
diameter% mm / 10-& 129 1081 12 101 225 157 2'8 101 -
11 117 188 188 118 1&8 1&5 052 05 050 051
MP M Pa
25 1000 25&0 2&88 5' 227 110& 9 '7 1&7 50
"ercent 1&950 15&0 9' '00 20'' 8 8 11921' 2 ' '191 20 192&9 12 1'0 '000 & 70 &887 872 1'
Pol'prop'le!e )&re$
The monofilament form of these fibres are "roduced in an e/trusion "rocess in #hich the material is hot dra#n through a die of circular cross section generating a number of continuous filaments at one time called a to# *ibrillated "oly"ro"ylene fibres are "roduced in an e/trusion "rocess #here die is rectangular The resulting film sheets of "oly"ro"ylene are slit longitudinally into e!ual #idth ta"es Poly"ro"ylene fibres are not bonded chemically in a concrete matri/% but bonding is "resent due to mechanical interaction %.*
PFRS
The concrete com"osites containing "oly"ro"ylene fibres ranging from 01 100@ by volume have been re"orted in literature High volume of fibres results in considerable loss of #or$ability #hich is "artly com"ensated by use of a""ro"riate !uantity of su"er "lastici3ers ( '88% addition of fibres does not affect the com"ressive strength of concrete Ho#ever a slight increase in fle/ural strength )09 2@ at 01@ fibre by volume and a slight decrease at 02 0&@ by volume of fibres is re"orted The main advantage of adding fibres is in terms of achieving im"roved toughness% im"act and fatigue strengths etc and reduction in crac$ #idth *.0
+I, DESI-N OF PFRS
*.1
+terl$
The Portland slag cement )P, #ith microsilica #as used in in first fe# laboratory trials but after#ards the re!uired mi/ture #as achieved #ith P, alone ,and grading conforming to ,< &7&<1590 #as used in P*+, a""lications ,u"er"lastici3er% lignosulfonate based at the rate of about 1'@ by #eight of cement #as added for increasing the #or$ability of the fresh mi/ (ccelerator% sodium silicate based #as used at site and not in laboratory trials The dosage of accelerators #as fi/ed at 8 @ by #eight of cement for increasing the early strength of shotcrete. ,*+, There is a normal tendency to use higher dosage of accelerator to reduce the rebound% but higher dosage results in lo#er 27 days strength The rebound should be reduced by "ro"er mi/ design and $ee"ing the o"timum #or$ability Poly"ro"ylene *obre ) *ibrecon-* #ith the engineering "ro"erties mentioned in Table Table 2 #as used Table Table 2< Pro"erties of Poly"ro"ylene *obre ) *ibrecon-*
10&
,l Co 1 2 & 8 ' 9 *.2
Pro"erty
Dalue
Tensile strength% MPa 4longation at "ea$ load% @ Modulus% ;Pa Melting "oint% degree (l$ali resistance *ineness% denier ?ength% mm
'02 2898 '2' 1&7'-190& 4/cellent 8' &2-80
L&ortor' Tr Trl$ l$
The mi/ design of P*+, consists of designing a basic shotcrete matri/ ando"timising dosage of fibres fibres Pro"or Pro"orti tioni oning ng basic basic matri/ matri/ is no diffe differen rentt than than convent convention ional al shotcr shotcrete ete *or slo"e slo"e "rotection #or$ at Tala Tala "roject% P*+, #as designed first as dry shotcrete and then as #et shotcrete ,ite trials of dry shotcrete sho#ed that the fibres #ere flying a#ay in the air due to air "ressure of dry shotcreting Moreover% there #as no control of #ater !uantity at no33le in the absence of a trained no33le man Therefore% the idea of dry shotcrete #as dro""ed and #et shotcreting method #as ado"ted Wet shotcrete trials #ere carried out in laboratory ;enerally :P is used in shotcrete% but in this Wet a""lic a""licati ation% on% P, #as used used due to its resistan resistance ce against against al$ali al$ali silica silica reacti reaction on and overal overalll durability durability Previous Previous steel fibre reinforced reinforced shotcrete shotcrete a""lication a""licationss for underground underground su""orts invariably consisted of microsilica for good dis"ersability of fibres and strength But% an attem"t #as made to use P, alone in the "resent a""lication The first fe# trials #ere made #ith a tentative mi/ containing microsilica to srudy the effect of fibre dosage t #as observed that increase in fibre dosage reduced slum" considerably even after increasing #ater content as sho#n in Table & (lso due to increase in #ater demand% the com"ressive strength got reduced #ith increase in fibre dosage (t fibre content beyond & $g.m &% e/cessive balling #as observed The entire "aste #as entra""ed #ithin fibres leading to segregation and the dis"ersion of fibres #as inade!uate (fter (fter these trials% trials% the matri/ matri/ design design #as im"roved to accommodate accommodate ma/imum & fibre content u" to & $g.m #ithout causing attendant "roblems as described above Ce/t trials #ere carried out #ithout microsilica to reduce ultrahigh fines content ement )P, #as increased and coarse aggregate #as reduced ( satisfactory mi/ at cement content of '00 $g.m& #as obtained at fibre content of 2 to & $g.m &
Table Table &< Mi/ Pro"ortion #ith Dary Darying ing *ibre >osage ,l Co 1
Material. Pro"erty &
ement% $g $g. m
0 89'
Poly"ro"ylene *ibre >osage% $g. m& 1 ' 2 ' & 0 89' 89' 89'
108
0 89'
2 & 8 ' 9 7 5
10
*.%
Microsilica% $g. m& Water% $g. m& * (% $g. m& ()10-89' mm mm% $g $g. & m *ibres% $g. m& ,u" ,u"er"lastici3e ci3err% $g. $g. & m ,lum"% mm om"ressive st strength% MPa 9 days 27 days *le *le/ural strengt ngth% MPa 9 days 27 days
2' 210 589 &1
2' 210 589 &1
2' 210 589 &1
2' 21' 589 &1
2' 22' 589 &1
0 9 '
1 ' 9 '
2 ' 9 '
& 0 9 '
0 9 '
2'0
1'0
12'
11'
8'
1822 2775
175 &075
1'22 &015
1275 288
11'' 2'&&
27 0
27 7
&0 7
2 '2
28 87
E))ect o) F&re T'pe$ T'pe$
T#o diff differ eren entt ty"e ty"ess of synt synthet hetic ic fibr fibres es%% Poly" Poly"ro ro"y "yle lene ne )*B )*B+4 +4: :CC-* * and and Poly Polyes este ter r )+4+:C &, #ere available +4+:C &, Polyester fibre #as 1' mm long and adosage of 1' $g.m& #as recommended by the manufacturer Therefore trials #ere made #ith both fibres as "er manufacturerEs recommendations ( control mi/ #ithout fibres and one #ith steel fibres #ere also made for a com"arison The details are given in Table 8 Co substantial difference in fle/ur fle/ural al strengt strength h #as obtain obtained ed Ho#eve Ho#ever% r% the ma/imu ma/imum m fle/ur fle/ural al strengt strength h of 9 MPa #as obtained #ith Poly"ro"ylene fibre )*B+4:C-* The dis"ersion of "olyester fibres #hich #ere #ere short shorter er in length length #as e/cell e/cellent ent The slum" slum" reduct reduction ion #ith #ith steel steel and "olyes "olyester ter fibre fibre com"ared to control mi/ #as minimal )20 to &0 mm but "oly"ro"ylene fibres reduced slum" by 120 mm ,ince the durability of "oly"ro"ylene fibres is #ell established% these fibres #ere ado"ted instead of "olyester fibres
Table 8 < 4ffect of *ibre Ty"es Material. Pro"erty
*ibre ty"e and dosage% $g. m&
10'
,l Co 1 2 & 8 ' 9 7 10
*.*
0
&
ement% $g $g. m Microsilica% $g. m& Water% $g. m& * (% $g. m& ()10-89' mm mm% $g $g. & m *ibres% $g. m& ,u" ,u"er"lastici3e ci3err% $g. $g. & m ,lum"% mm *le *le/ural strengt ngth% MPa 9 days 27 days
Polyester )+4+:C &,% 1' '00 2' 20& 109& 80
,teel%
'00 2' 17' 109& 80
Poly"ro"yle ne)*B+4 :C% 2' '00 2' 21' 109& 80
0 9 5
2 ' 9 5
1 ' 9 5
80 9 5
200
70
150
170
&& 0
'1 9
&& 0
8' 2
80 '00 2' 17' 109& 80
A/opte/ +
Based on observations observations of laboratory laboratory trials the shotcrete shotcrete matri/ matri/ #as further further revised revised and after observing its satisfactory "erformance% the same #as ado"ted as given in Table ' ( se"arate study on slum" loss using ado"ted mi/es #ith varying "oly"ro"ylene and steel fibre dosage #as conducted and the results are "lotted in *ig & Poly"ro"ylene fibres have sho#n high slum" loss Table'< Table'< (do"ted Mi/ Pro"ortions ,l Co 1 2 & 8 ' 9 7 5
10
Material. Pro"erty ement% $g $g. m& Water% $g. m& (ccelerator% $g $g. m& * (% $g. m& ()10-89' mm% $g. m& *ibres% $g. m& ,u" ,u"er"lastici3e ci3err% $g. $g. m& ,l ,lum"% mm om"re "ressive strength% MPa 9 days 27 days *le/ *le/ur ural al str strengt ength% h% MPa 9 days 27 days
Poly"ro"ylene *ibre >osage% $g. m& 2 ' & 0 ''0 '00 157 200 22 20 1011 1089 '88 '8 2 ' & 0 72' 9 ' 12' 12' 150' &9&&
&1'' &79
87 9'
' 72'
10
*ig & ,lum" ?oss #ith Darying Darying >osage of Poly"ro"ylene and ,teel *ibre
*.
Lo/ De)orto! C3r4e
?oad deformation curves obtained for P*+, and ,*+, using ?oad controlled machine are "lotted in *fs 8 and ' res"ectively res"ectively
*ig 8 ?oad >eformation urve in om"ression for P*+,
109
*ig ' ?oad >eformation urve in om"ression for ,*+,
.0 .0 CONC CONCLU LUSI SION ONS S
1 2
&
8 '
+esi +esin n grout grouted ed roc$ roc$ bolt bolt 10 10 mm mm lon long% g% &2 &2 mm mm dia dia #it #ith h 1' 1' m anch anchor orag agee leng length th #ere #ere successfully installed manually as a "art of su""ort system #ith P*+, Poly Poly"r "ro" o"y ylene lene fibr fibres es )&7 )&7 mm mmlo long ng #ith #ith 2' 2' to to &0 &0 $g.m $g.m& doses #ere used The com"ressive strength in the range of &9 to &7 MPa and fle/ural strength from 9' to 72' MPa #as achieved (ddi (dditi tion on of Poly" Poly"ro ro"y "yle lene ne fibr fibres es red reduce uce slum slum" " consi conside dera rabl bly y The The "ro "ro"e "err mi/ mi/ "ro"ortioning is re!uired to com"ensate for slum" loss and to ma$e ma$e a smooth and #or$able mi/ >ry >ry mis mis P*+, P*+, coul could d not not be ada"t ada"ted ed in in vie# vie# of of los losss of fibr fibres es due due to to thei theirr fly flying ing a#ay a#ay in the air and im"ro"er dis"ersion of fibres High dose of fibres beyond & $g.m& cost difficulty difficulty in handling and "um"ing of P*+, Therefore more study is re!uired on utilising higher doses of fibres
107
REFERNCES
1 2 & 8 ' 9 7 5 10 10 11 11 12
( ( '0% '0% 1+7 1+78 8 )155 )1555 5 sta state te of of the the (rt (rt re" re"or ortt on +ei +einf nfor orce ced d shotc shotcre rete te%% +e"or +e"orts ts of of ( ( committee '0% ( Manual of concrete Practice% Part-'% 1555 "" '0 1+ -1 to 14-11 (,TM ( 72020-50 50 F,t F,tandard ,"ec "ecification for ,te ,teel *ib *ibers for *iber +einforced oncreteG :? :?> > Bul Bulle leti tin n -80 -80 F*ib F*ibre re +ein +einfo forc rced ed onc oncre rete teG% G% 1572 1572 ,<1 ,<115 1555-15 155 5%% Fnd Fndia ian n ,tan ,tanda dard rd Meth Method od of ,am"l ,am"lin ing g A (nal (naly ysis sis of oncr oncret eteG eG%% ,i/t ,i/th h +e"rint% uly 1570 (,TM (,TM -10 -1017 17--75 F,t F,tanda andarrd Test Test Met Metho hod d for for *le/ *le/ur ural al To Toughn ughnes esss A *ir *irst ra rac$ c$ ,trength of *ibre +einforced oncrete )using Beam #ith third "oint loadingG ( ( < &17 &17 + )1555 )1555% % FBu FBuil ildi ding ng ode ode +e! +e!ui uire reme ment ntss for for ,tru ,truct ctur ural al onc oncre rete teG% G% ( ( Man Manua uall of oncrete Practice% Part % (merican oncrete nstitute , &7& &7& < 1590% 1590% F ,"e ,"eci cifi fica cati tion on of of oar oarse se and and *in *inee (ggr (ggreg egat ates es fro from m Catu Catura rall ,our ,ource cess for for oncreteG% Bureau of ndian ,tandard% Ce# >elhi , 8'' 8'' < 1575 1575%% F,"ec F,"ecif ific icat atio ion n for Port Portla land nd ,lag ,lag em ementG entG%% Burea Bureau u of ndia ndian n ,tand ,tandar ards ds%% Ce# >elhi , 8' 8' < 2000 2000%% F Plai Plain n and +ei +einfor nforce ced d onc oncrrete ete od odee of Prac PractticeG% ceG% Bur Bureau eau of ndi ndiaa ,tandards% Ce# >elhi , 1875 1875 < 1551 1551 )Par )Partt % F,"e F,"eci cifi fica cati tion on for Port Portla land nd Po33ol Po33olan anaa ement ement )*lya )*lyash sh based basedG% G% Bureau of ndian ,tandards% Ce# >elhi , 711 7112 2 < 1575% 1575% F8& ;rad ;radee :rdin :rdinary ary Portl Portland and eme ement nt ,"ecifi ,"ecificat cation ionG% G% Burea Bureau u of ndian ndian ,tandards% Ce# >elhi , 510& 510& < 1555% 1555% Foncre Foncrete te (dmi (dmi/tu /tures res ,"ecif ,"ecifica icatio tionG nG Burea Bureau u of ndi ndian an ,tanda ,tandards rds%% Ce# >elhi
105
