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Footings
1) PCC should be done in level as per given size in drawing with Dobra marking.
2) Demarkation of foundation should be done with correct orientation of column as per centre line plan.
3) All footings shall rest on PCC of M15/M10 Grade concrete, having minimum thickness of 150mm / 75mm or as per drawing.
4) Concrete shall be cast in max 450mm layers and vibrated by 60mm vibrating needle.
Columns and Shear walls
1) Platform erected for labour for concreting shall be independent of column shuttering.
2) If required, Grade of concrete for column starters shall be one grade higher than that of column concrete.
3) Minimum height of starters shall be 6” to 9” and shuttering shall be of fabricated steel / steel channels or plywood. (Planks or fali should not be used in sides of starters.) Concrete within shall be suitably vibrated and cured.
1) Platform erected for labour for concreting shall be independent of column shuttering.
2) If required, Grade of concrete for column starters shall be one grade higher than that of column concrete.
3) Minimum height of starters shall be 6” to 9” and shuttering shall be of fabricated steel / steel channels or plywood. (Planks or fali should not be used in sides of starters.) Concrete within shall be suitably vibrated and cured.
4) Formwork for starters of column / shear walls when erected shall be checked using theodolite / linedori for
the correctness of dimensions and orientation (including offsets if any).
5) Thick Mortar slurry of 1:1 cement sand mix shall be poured at base of columns to prevent honeycombing. This mortar slurry shall have water cement ratio 0.05 less than that recommended for concrete mix.
6) Concrete for columns shall be cast and vibrated in layers of 450mm.
7) Column concreting shall be done up to lowest level of beam bottom at the junction.
8) Concrete key shall be made at top surface of column for better bond with next pour/ 20mm metal packing shall be done on top of concrete surface for proper bonding with next pour / chipping of top surface for removal of laitance.
9) If reinforcing bars are congested at the junction of column and beam, a special concrete mix of higher grade using 10mm Aggregates may be used therein.
Slab and Beams
1) Concrete from hoist shall be unloaded on MS tray
2) Walking platforms shall be provided for easy movement of labour without disturbing the reinforcement.
3) Level marking / ghodi having height equal to thickness of slab shall be used while slab concreting is in progress.
4) Concreting area for the day shall be well demarcated and concreting shall commence from the farthest end and proceed towards direction of hoist. In case of pumping, proper planning should be done for placing of concrete.
5) Slab top levels shall be checked during and after finishing with leveling instrument for controlling the thickness of slab.
6) Beams and slabs having depth more than 150 mm shall be vibrated by 25/40/60 mm needle depending on size of beams and spacing of reinforcement, whereas slabs having thickness of less than 150 mm shall preferably be vibrated by surface vibrator. The spacing of inserting the vibrating needle in concrete shall be as follows:
a) 25mm needle – 150mm c/c
b) 40mm needle – 300mm c/c
c) 60mm needle – 450mm c/c
5) Thick Mortar slurry of 1:1 cement sand mix shall be poured at base of columns to prevent honeycombing. This mortar slurry shall have water cement ratio 0.05 less than that recommended for concrete mix.
6) Concrete for columns shall be cast and vibrated in layers of 450mm.
7) Column concreting shall be done up to lowest level of beam bottom at the junction.
8) Concrete key shall be made at top surface of column for better bond with next pour/ 20mm metal packing shall be done on top of concrete surface for proper bonding with next pour / chipping of top surface for removal of laitance.
9) If reinforcing bars are congested at the junction of column and beam, a special concrete mix of higher grade using 10mm Aggregates may be used therein.
Slab and Beams
1) Concrete from hoist shall be unloaded on MS tray
2) Walking platforms shall be provided for easy movement of labour without disturbing the reinforcement.
3) Level marking / ghodi having height equal to thickness of slab shall be used while slab concreting is in progress.
4) Concreting area for the day shall be well demarcated and concreting shall commence from the farthest end and proceed towards direction of hoist. In case of pumping, proper planning should be done for placing of concrete.
5) Slab top levels shall be checked during and after finishing with leveling instrument for controlling the thickness of slab.
6) Beams and slabs having depth more than 150 mm shall be vibrated by 25/40/60 mm needle depending on size of beams and spacing of reinforcement, whereas slabs having thickness of less than 150 mm shall preferably be vibrated by surface vibrator. The spacing of inserting the vibrating needle in concrete shall be as follows:
a) 25mm needle – 150mm c/c
b) 40mm needle – 300mm c/c
c) 60mm needle – 450mm c/c
7) Care shall be taken not to over/under vibrate the concrete. While withdrawing vibrator needle no holes
shall be visible in concrete.
8) Concrete shall be placed in layers not exceeding 450mm deep in deep beams and placed to the full depth in slabs and small beams. Each layer shall be placed and well compacted before the preceding layer has taken its initial set and in a manner that will entirely prevent any cold joint forming between the layers.
9) If concrete is being placed by pump or crane bucket, concrete should not be poured directly in to the beams.
10) If grade of concrete for slab and columns is different, column portion shall be cast first before slab concreting starts. Care shall be taken to prevent formation of cold joint at junction i.e. portion adjoining columns shall be cast before initial setting starts in columns. Welded wire mesh or equivalent shall be used as stoppers to prevent excess concrete from columns to flow into beams.
11) Construction joint in beams shall be provided as per drawings or in absence of such drawings, where shear force is zero. Cement sand slurry of 1:1 with bonding agent shall be used at construction joints to create better bonding between old and new concrete. At construction joints, new concrete shall be over-vibrated for proper bonding with old. Wooden stoppers with step shall be provided at construction joints in such a way so as to facilitate their easy removal.
12) Slab panels shall be covered with wet Hessian cloth, tarpaulin or plastic sheets immediate after concreting, after initial set occurs, to prevent formation of shrinkage cracks.
8) Concrete shall be placed in layers not exceeding 450mm deep in deep beams and placed to the full depth in slabs and small beams. Each layer shall be placed and well compacted before the preceding layer has taken its initial set and in a manner that will entirely prevent any cold joint forming between the layers.
9) If concrete is being placed by pump or crane bucket, concrete should not be poured directly in to the beams.
10) If grade of concrete for slab and columns is different, column portion shall be cast first before slab concreting starts. Care shall be taken to prevent formation of cold joint at junction i.e. portion adjoining columns shall be cast before initial setting starts in columns. Welded wire mesh or equivalent shall be used as stoppers to prevent excess concrete from columns to flow into beams.
11) Construction joint in beams shall be provided as per drawings or in absence of such drawings, where shear force is zero. Cement sand slurry of 1:1 with bonding agent shall be used at construction joints to create better bonding between old and new concrete. At construction joints, new concrete shall be over-vibrated for proper bonding with old. Wooden stoppers with step shall be provided at construction joints in such a way so as to facilitate their easy removal.
12) Slab panels shall be covered with wet Hessian cloth, tarpaulin or plastic sheets immediate after concreting, after initial set occurs, to prevent formation of shrinkage cracks.
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