MECHANISM OF WATERPROOFING

Mechanism of Waterproofing by Proper Cement Hydration

One of the products of hydration of cement is cement gel or Tobermorite, which is formed up to a water-cement ratio of 0.65 to 0.7. At a lower w/c ratio, it is formed more and more and vice versa. This hydration product has absolutely least co-efficient of permeability, i.e., 7×10-14 cm/sec and by itself blocks the pores and capillary in the concrete. This can result in good waterproof concrete of 10-10 to 10-12 cm/sec. However, actually, in practice at an average job, we end up getting the permeability anywhere between 10-6 to 10-8 cm/sec. This is mainly due to uncontrolled w/c ratio, lack of curing, and also other bad detailing.

Combination of Conventional and Non-Conventional Ways

Various ways of waterproofing the structures are recommended. However, a discerning client and the consultant need to study all the possible parameters, positive as well as negative and then come to a recommendatory conclusion. Conventional ways of waterproofing are like brickbat coba followed by IPS. Brickbat coba is generally used to provide a slope to the treatment and IPS layer works as an impermeable treatment by itself which also assumes the slope of brickbat coba. Though, otherwise found fairly successful; today due to speed of the work, quality of sand, inadequate curing to the concrete which is made from finer grade cement and many other related reasons the IPS is seen to crack and disintegrate allowing an early entry to water. The brickbat coba is not otherwise supposed to be waterproof, but on the contrary is absorbent, which accumulates the water. On saturation the brickbat coba attempts to transfer the water further, which generally penetrates into the slab, and penetrates more easily if the same is porous or full of cracks. As it is concrete is not by itself a fully impermeable material, and various compromises while construction can decrease the impermeability further. Needless to say, this causes unsightly leakages to begin with followed by corrosion of steel and finally results in structural damage.

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