Waterproof Concrete - Why Waterproofing is required?

Many a times, I am asked this question from customers looking for waterproofing solutions of buildings and other concrete structures. Can concrete be made waterproof? What is waterproof concrete?

Can concrete be made waterproof without use of any waterproofing chemicals, answer is yes, and correct mix design can always make the requirement of any waterproofing admixture redundant.

But at the same time it is difficult in practice during course of construction because in general practice due to various reasons which include among 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. Therefore, the addition of admixtures and surface coating materials can offset various errors,

Water penetrates concrete in two ways

• when there is hydro static pressure on one side of concrete mass, water travels through continuous channels which ultimately interconnect the two faces of concrete and 
• Water may be absorbed by capillary action and travel through the concrete to a face where it evaporates. 

The basic solution to reduce voids  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 waterproof concrete.