Concrete is one of the major and most economical building products for its long life span and versatility. But concrete, more precisely, cement -concrete is porous in nature. The long life or durability of concrete is greatly dependent on water permeability and ingress of chemicals. In most of the cases, water acts as carriers for harmful chemicals like salts of chlorides, sulphates, alkalis, acids, etc. and these may corrode concrete and/or reinforced steel. Water may also come out from the concrete/ plaster and evaporates from the surface leaving salts and alkalis, which react with paint, and/or making patches. Therefore, waterproofing of concrete is an integral part for construction of a building.
Sometimes it is claimed by some that concrete admixtures are not necessary and are certainly no substitute for sound concrete mix design. But others argue that the addition of admixtures often offset errors at the practical stages of making concrete, so increasing the chance of producing concrete up to the specification. These statements have some justification for that group of admixtures known as integral waterproofers. However, waterproofing of concrete or cementitious substrates does not mean cent percent protection from water, rather some portion of water in liquid or vapour form is beneficial to continue hydration reaction of cement.
Theoretically, 22-25% (by weight of cement) water is needed to complete the hydration reaction of cement. But in normal conditions, concrete is prepared with extra amount (as much as 45-60% by weight of cement) of water to get desired workability. Any extra mixing water over the minimum requirement of hydration reaction is evaporated from the concrete mass leading to an increase of voids or creating more capillary pores. This is a common factor in all concretes allowing the passage of water and/or water vapour is the presence of inter-connected capillary pores without such voids and their inter connections water or vapour transfer can not take place.
Let us consider for a moment how voidage in concrete can be altered.
1. The gel pores that are formed due to hydration reaction of cement. These pores are very minute and have diameter of approx. 2 nano-meters and independent of water-cement ratio.
2. Capillary pores (0.05 to 1 micron diameter) that result from excess water being present and therefore depend upon water-cement ratio.
3. Entrapped voidage reflecting the concrete mixing, laying and finishing method.
Since the diameter of gel pores (approx. 2 nano-meters) are so small that water cannot go through it.
Categories 2 and 3 are relevant to problems of concrete waterproofing.
In category 2, capillary pores (approx. diameter 0.05-1.0 micron) are larger in diameter as compared to gel pores and water can travel through it. Controlling the w/c ratio using water-reducing admixture can reduce these capillary pores. During the hydration of cement some of the capillary pathways become progressively blocked by reaction products of calcium silicate hydrates gel. This gel has a very low hydraulic permeability, if water-cement ratio is low enough (less than 0.4), the volume of gel will be sufficient to completely block the inter connecting capillary within the cement paste. But in case of water– cement ratio is more than 0.40 the capillary pores generated in OPC, there will not be sufficient gel to block the capillary pores so resulting in inter connections. Curing of concrete is also an important factor to continue cement hydration reaction resulting reduction of capillary pores.
In category 3, entrapped voids are created due to following reasons:-
a) Poor mix design.
b) Faulty aggregates gradation.
c) Inadequate compaction.
d) Excessive bleeding and segregation.
e) Very high or very low workability than the requirement.
f) Poor workmanship.
b) Faulty aggregates gradation.
c) Inadequate compaction.
d) Excessive bleeding and segregation.
e) Very high or very low workability than the requirement.
f) Poor workmanship.
Sometimes cracks are developed in the plaster or concrete and water may travel through those cracks. There are so many factors for development of cracks through which water can travel and damage the embedded reinforced steel and/or paints.
Therefore, waterproofing or damp proofing is an essential and integral part of building construction and by doing so one can get following benefits:-
1) Life span of the building will be increased remarkably.
2) Frequent repair or maintenance of building shall be eliminated completely or reduced to a greater extent.
3) Life of paint in interior or exterior shall be extended remarkably.
4) Aesthetic look of the building shall remain for much longer duration.
5) Minimises health hazards.
2) Frequent repair or maintenance of building shall be eliminated completely or reduced to a greater extent.
3) Life of paint in interior or exterior shall be extended remarkably.
4) Aesthetic look of the building shall remain for much longer duration.
5) Minimises health hazards.
If we consider the cost of effective waterproofing, it is only 0.5 to 2% of the total cost of building, which is really negligible.
Waterproofing or damp proofing of concrete or masonry is carried out in two stages. One is during construction and another is post construction.
Most effective and economical waterproofing or damp proofing treatment is carried out during construction of a building whereas post construction treatment is very expensive, more time consuming and to some extent less effective.
Cementitious Polymer Coating:-
These products are available in three varieties.
First and most common variety is a single component polymer emulsion, which is to be mixed with cement at site to a brushable consistency.
Second variety is a two-component system, one pack is in liquid form and other pack is in cement based powder form. When these two components are mixed together a slurry mix is obtained.
Third variety is single component cement based products blended with various types of chemicals and fillers. This type of material shall be mixed with water to a brushable consistency. All these slurry are mainly applied by brush on the substrate surface at the positive side of the water pressure. These products are very good waterproof and flexible in nature which will not crack due to thermal movement of the structure.
Polymeric cement based waterproofing system has special advantages over all other system considering their versatile properties, low maintenance cost, ease of applications, moisture vapour breathability, UV rays resistance, economy and many more.
Conclusion:-
Waterproofing system is a minor part of a building from economic point of view but a great importance as durability of building is concerned. Since this system is dependent on so many factors it requires sound knowledge of engineering, material science, skilled and experience workforce and good co-ordination between house owner, material suppliers, specifier, applicator and inspector to fulfill the aim of waterproofing.
