Technical Guide
Protection Of Foundations
Foundations , part of which is generally below the ground level, also need to be protected whenever they are likely to come in contact with harmful chemical ingredients. Such an exposure could be as a result of contact with the soil or sub-soil water (or both) containing sulphates or chlorides (or both). Sulphates could cause the expansion of concrete conditions for corrosion like cracking. Chlorides would create conditions for corrosion of the reinforcements. Suitable protective measures are always desirable in cases where any chemicals are suspected to be present.
PROTECTION TO REINFORCEMENT STEEL
Case I
When foundation is exposed to ground water in which sulfates and chlorides are absent or within permissible limits:-
The reinforcement steel will need protection from any possible corrosion due to the ingress of ground water. The steel reinforcement in the piles (either precast or cast-in-situ) should be given a protective coating.
Method:
a) Clean the steel as much as possible with stiff wire brush.
b) Apply chemical derusting agent Rust Remover which will turn the steel into grayish black colour in 24 hours. Remove the freed loose rust particles by simple dusting with brush etc.
c) Apply a slurry consisting of 1 kg. Polymer based chemicals and 1.5 kgs. fresh ordinary Portland cement to the chemically derusted surface by brush ensuring that all area is covered and no pinholes exit.
d) Allow the coating to set for 48 hours.
e) Accidental puncture or damage to the coating, if any, must be retouched by slurry (as in 'c' above).
Case II
When foundation is exposed to ground water or soil in which sulfates and chlorides are in excess of permissible limits Table as per IS 456 (in chemical zone):
Method:
a) Provide anticorrosion treatment to steel as described in case (I).
b) Lay concrete as required, cure as per norms and allow to dry.
c) Apply approved chemicals (ready to use pack) to all the surfaces of the foundation concrete up to the plinth level ensuring that all area is covered.
d) Apply a second coat after 24 hours.
e) Back filling of the excavation with earth should be taken up after atleast 48 hours of applying the second coat.
Note:-
In effluent sumps, water reservoirs, water treatment plants etc. corrosion prevention treatment to steel should not be overlooked and similar procedure as above should be followed.