Waterproofing of Concrete Structures

Dr. S. K. Manjrekar, Chairman and Managing Director, Sunanda Speciality Coatings Pvt. Ltd, Mumbai.
A conscientious good workmanship going along with correct mix design can always make the requirement of any waterproofing admixture redundant. As a matter of fact a well made concrete can have as low coefficient of hydraulic permeability (Kw) as 10-10 to 10-12 cm/sec. However, in general practice due to various reasons which include amongst them bad workmanship, incorrect design mix, lack of curing, improper compaction, excessive water: cement ratio etc., these ideal situations of permeability become very difficult to achieve. Thus the addition of admixtures and surface coating materials can offset various errors, increasing the possibility of producing concrete up to specifications.

Can Concrete be Made Waterproof?

Water penetrates concrete in two ways viz. (i) when there is hydrostatic pressure on one side of concrete mass, water travels through continuous channels which ultimately interconnect the two faces of concrete and (ii) water may be absorbed by capillary action and travel through the concrete to a face where it evaporates.

The basic solution to reduce voids, number of tunnels and capillaries in concrete, is to control water–cement ratio along with proper mechanical compaction. During hydration the capillaries can get discontinuous or partly blocked due to the formation of 3 CaO.2 Sio2.3H2O which is called as “Tobermorite” or “cement gel.” To get this formation of cement gel, water-cement ratio has to be less than 0.65 to 0.70 above which this product formation is very insufficient and below which it can be proportionately more. Besides, this cement gel itself also has very low hydraulic permeability kw = 7 x 10-14 cm/sec. Following these guidelines, to attain such conditions and when aided with adequate compaction, it should not be difficult to make a perfectly impermeable concrete.

Anticipating this need, there have been continuous efforts of researchers as well as manufacturers to provide the industry with various alternate products which have helped all of us to make a perfectly impermeable concrete and combat this menace of leakages.

From the user's point of view, most times such wide availability of products at equally wide range of prices can prove confusing when a matter of choice comes. In such cases often the scales are tipped by the price factor when the selection is to be made and this eventually leads to discontent for the user and erosion in quality performance of the concrete may be due to improper selection. Thus it is quite imperative for all of us users/contractors/architects/ consultants/engineers etc. to understand minimum basics of the admixture technology which will enable our faculty to (i) accept that there is a need for such materials (ii) what materials are available in the market-place (iii) how they function (iv) what way are they used and finally (v) if there is need for further research and developmental efforts, if the presently available products are falling short of their expectations and promises.

NBM&CW April 2008