Shrinkage strip method method statement statement and thermal analysis analysis 1. Background:
For the execution of the King FAISAL specialist hospital and research centre. 2. Proposed Task:
Construction Construction Methodolog Methodology y for accommodat accommodating ing the shrinkage shrinkage strip strip in floor slabs and roof slab slab during the construction of King FAISAL FAISAL specialist specialist hospital and and research centre to eliminate the effect of dray shrinkage shrinkage on typical floors and reduce the effect of dry shrinkage and seasonal temperature effect on roof flat slab. 3. Overview:
A proposed construction methodology is developed to accommodate a shrinkage stress analysis of concrete slabs with shrinkage strips in buildings for long-span membrane structure. The shrinkage strip strip is proposed considering the stress states due to:
I. Temperature Temperature changes changes (thermal (thermal contract contraction ion and expansion) expansion) II. II. Conc Concre rete te shrin shrinka kage ge III. Further Further also consider considering ing the effects effects due to curling, curling, creep, creep, external external restrain restraintt and construction sequence.
4. Scope and Limitations Limitations::
This proposed method statement will illustrates the sequence of work at all stages / activities during exec executi ution on of typic typical al floors floors flat flat and and roof roof floor floor flat flat slab slab durin during g the the cons constru truct ctio ion n King King FAIS FAISAL AL spec specia ialis listt hospital and research centre. The proposed construction methodology also also considers the effects due to curling, creep, external restraint, restraint, thermal contraction and expansion, shrinkages and construction sequence by providing a shrinkage strip (tempo (temporar rary y joint) betwee between n axis axis (08-09) (08-09) and allow allowing ing it to be open open for 90 days. days. Shrinkage Strips:
Setting Setting shrinkage shrinkage strip (temporary (temporary joints) that that are left open for certain time 90 days to allow the early plastic plastic shrinkage, shrinkage, autogenously autogenously shrinkage, shrinkage, drying drying shrinkage, shrinkage, and and carbon carbon shrinkage shrinkage for concrete concrete is a well accepted accepted method to control temperature shrinking cracks.
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5. Proposed Construction Methodology: Sequence of Operations: Stage (1): Preparation of Continuous formwork, supports & reinforcement mesh:
Prepare of continuous formwork, supports & reinforcement bars for each part of floor slab and roof slab. .care shall be taken the reinforcement in the shrinkage strip location should not be continuous in shrinkage strip, (it should be preferably with the lap joints to accommodate any movements / shrinkage), its strongly recommended to arrange the reinforcement to be spliced to allow for shrinkage during the duration left open without any stresses in the steel rebar's. If required any extra reinforcement shall be placed to ensure that no cracks shall be developed o n concrete elements due to shrinkage strain. Stage (2):
Casting the floor slab of the two building parts right and left the shrinkage strip for each floor. Placing of approved grade of concrete for floor slabs and roof slab for each part at one single stretch. Stage (3):
Allowing a well-accepted method to control temperature shrinking Cracks by leaving a possible gap of strip for 2000 mm shall be left open for duration around 90 days to allow the early plastic shrinkage, autogenous shrinkage, drying shrinkage and carbonation shrinkage for each floor slab and roof slab during the construction. This is termed as a shrinkage str ip. Stage (4):
The shrinkage strip shall be completely left open for each floor slab and roof slab during the construction for a certain period. Stage (5):
Continuous support systems (such as formwork, bracing, or full support) must be used to assure the stability of structures and should intact the stability and alignment of adjoining the buildings. Columns, beams, walls or other structures and the formwork shall not be distributed and should be kept in place till the support of the casted elements and the formwork for the two adjacent pays to the shrinkage strip not to be released till the shrinkage strip is casted and attains 70 percentage of its strength. Stage (6):
The open area of the left over portion of the proposed shrinkage strip reinforcement shall be fully primed with concessive ZR (single component epoxy based zinc rich primer for steel) providing active galvanic protection steel. It is thick grey liquid of paint-like consistency, recommended for use where chloride included attack on steel and concrete is involved and also cover or wrap with Hessian cloth for the reinforcement and shall not be left exposed in any case to avoid any staining or rusting.
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Stage (7):
This operation will be executed floor by floor. Each floor will be casted in two parts with a gap (shrinkage strip). Stage (8):
The casted elements shall be prepared for the conventional rough chamfered edge and should be run during the casting of the concrete elements for the better adherence of the shrinkage strip. Proper case shall be taken to accommodate the construction joints earlier by providing the keyed or dowelled construction joints, if required a 25cm horizontal water stop shall be placed 12 cm in the previous casted elements and left open to accommodate during the casting of the shrinkage strip. Water stop will be used only for roof slab. Following rules for proper joining construction joints for shrinkage strips shall be applied:
Plan exact location of all joints, shrinkage strip, including timing of contraction joint sawing before construction. Provide isolation joints between first floor and roof floor slabs and columns, walls and at the junctions. Surface preparation on the exposed edges of the construction joints for existing elements interfacing with the shrinkage strip shall be prepared and cleaned and washed prior to applying the bonding agent. Treat the cleaned exposed edge with a bonding agent (Acrylic bonding agent and curing aid). Formwork and support shall be reconfirmed for the intactness and alignment with the other adjacent elements. Prior to casting shrinkage strip the formwork, supports, reinforcement and treated exposed surface from the approach slabs shall be inspected and approved by the consultant.
6. Recommendations: Casting shrinkage strip with proposed materials: Proposed Material (1)
Shrinkage-reducing Admixture (SRA) Area of Application:
Mixing in ordinary concrete transit mix for casting shrinkage strip of 2m Alternately Fiber Reinforcement can also be used: Proposed Material (2) Fiber mix (stealth): Description: Multifilament polypropylene fibers for secondary reinforcement of concrete to reduce
formation of plastic shrinkage and settlement cracks, produced in a range of lengths. Area of Application:
Generally used to in concrete, shotcreate, screeds render grouts etc. to avoid plastic shrinkage and settlements cracks.
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Proposed Material (3) Fibers mesh MD (Fiber Reinforcement): Description: Fibrillated multi-designed polypropylene fibers for secondary reinforcement of concrete,
engineered to reduce cracking, improve toughness and provide post-crack residual cracking. Area of Application:
Generally used for elevated slabs, pre-cast concrete, shot Crete, overlays, where the most effective fiber reinforcement and post-crack residual strength and important. For casting shrinkage strip 0.9 kg (one bag) per cubic meter of 35 Mpa grade of concrete mixes. Proposed Material (4) Material (Concrete repair): Description: shrinkage compensated used a high strength free flowing precision concrete free from segregation and bleeding for vertical or horizontal concrete repairs.
Note: This Construction Methodology shall be read in conjunction of Casting of Concrete Work (Sub Structure – Slab on Grade), (Super Structure – Columns, Beams, Flat Slab, Hollow block Slab & Solid Slab).
References: British standard B.S (8007) CIRIA C660 (Published by CIRIA, Classic House, 174–180 Old Street, London EC1V 9BP, UK.). Incorporation of (THE HIGHWAYS AGENCY, THE SCOTTISH OFFICE DEVELOPMENT DEPARTMENT, THE WELSH OFFICEY SWYDDFA GYMREIG, THE DEPARTMENT OF THE ENVIRONMENT FOR NORTHERN IRELAND) Incorporating Amendment NO. 1 (1989).
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