All liquid retaining structures, design and construction shall comply with this Specification and IS 3370.
Where concrete is designated on the drawings as liquid retaining, the finished structures shall be free from penetration of dampness .
The method proposed for dealing with shrinkage cracks, leaks, dampness or other defective work shall be approved prior to commencement of the work
. Special attention shall be directed during the construction phase for the elimination of cracking.
In this connection consideration should be given to the following :-
Concrete Mix Quality:
- Concrete mix shall be homogeneous, pump able grade as specified in the relevant codes.
- Integral water proofing compound viz, Conplast WL of fosroc or equivalent, dosage as specified by the vendor shall be added to concrete while mixing at concrete batching plant.
- Recommend use of Recron 3S fibres concrete which helps to reduce segregation and increase the homogeneity of mix & to improve the permeability of concrete.
- Use of Self compacting concrete (SCC) is most preferable and effective for construction of water retaining structure. It will give uniform placement with self-consolidation which will highly reduce the probability of leakage.
- Concrete shall be placed within 60 minutes after mixing of it. Strictly prohibit addition of extra water at batching plant, during transit or at site.
- Mix without proper slump or cohesion shall not be used.
- Concrete shall not be placed from a height more than 2.0 m for pump able mix.
- Ensure uninterrupted supply of the concrete and pouring sequence such that placement of top layer took place when the bottom layer has not set.
- Ensure proper & uniform compaction with striking of external faces using wooden mallet as well as with immersion type vibrators ( not applicable for SCC)
- Avoid formation of cold joint.
- Use only prefabricated PVC cover blocks.
- Form work should be properly engineered and designed to specific requirement.
- Forms shall have uniform, smooth face. It shall maintain rigidity throughout the placing, ramming, vibration, and setting of the concrete.
- All joints shall be sufficiently tight to prevent leakage of cement slurry. 2 to 3 mm thick foam strips shall be placed in the sandwich form between two shuttering plates to avoid slurry leakage.
- The form work from manufacturer’s like L&T DoKa or equivalent type are recommended with necessary form work design.
- Supports shall be designed to withstand the worst combinations of self-weight, reinforcement and wet concrete weight, concrete pressure, construction and wind loads.
- Care shall be taken to the type of mix when considering the design pressure on the form work & supporting.
- Use of any ties or wires projecting out of concrete face shall be strictly prohibited.
Tie-rod Procedure :-
- NOTE : In Water retaining structure use of through tie rod shall not be used.
- Threaded tie rod with cone arrangement as shown in the sketch given here-in shall be used.
- Cone can be metallic or PVC type with dimension to suit the site requirement. Space of the cone portion after removal of the cone shall be filled with non-shrink type of grout, immediately after the form work is struck out.