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What is Waterproofing Admixture for Concrete?Waterproofing admixture is a type of admixture which prevents the passage of water through hardened concrete under a pressure head. It is also called as water resisting admixture or permeability reducing admixture or damp proofing admixture.
Requirement of Waterproofing Admixture for ConcreteWater is a vital part of concrete construction from the mixing of concrete to the curing of concrete. But once the concrete has gained its required strength, thereafter any moisture or water penetration in concrete can cause damage to the concrete. The damage can be due to corrosion of reinforcement or due to freeze thaw. When a concrete work has finished and curing completed, the water content evaporates and leaves voids inside the concrete. Thus for a good durable concrete construction, low water/cement ratio is recommended so that porosity of concrete can be reduced. But then also, a concrete cannot be completely made waterproof even by using the minimum water/cement ratio. Concrete is a porous material and water can penetrate through pores and micro-cracks of concrete due to capillary actions. Thus there is a need of an admixture which can control the porosity of concrete.
Functions of Waterproofing AdmixturesA permeability reducing concrete admixture or waterproofing admixtures function in following ways:
- It reduces the size of capillary pores, their numbers and continuity inside the concrete structure.
- It blocks the capillary pores of concrete, or
- It may line the capillary pores with hydrophobic materials. This prevents the absorption of water in the pores due to capillary absorption.
Materials Required to Prepare Waterproofing AdmixturesThe ACI 212.3 Rev.10 in its report states that following types of materials to be used in waterproofing admixtures:
- Hydrophobic or water-repellent chemicals such as oils, petroleum products which can block the entry of water into the pores by forming a layer along the pores in concrete. These materials do not fill the pores.
- Finely divided solid particles (powders)of inert and chemically active fillers to act as densifiers and restrict the movement of water through pores.
- Crystalline materials with hydrophilic nature which increases the density of calcium silicate hydrate and / or generate the pore-blocking deposits to resist water penetration.