Acid Attack on Concrete

Acid Attack:

Ordinary Portland cement is alkaline in nature. When the cement paste comes into contact with the acids its components break down, this phenomenon is known as acid attack.

When acid attack concrete it dissolves both hydrated and unhydrated cement compounds as well as calcareous aggregates. In many of the cases the chemical reaction results in water soluble calcium compounds which are leached away. Concrete vulnerability to acid attack increases as the pH of the acid in contact decreases from 6.5. Degree of aggression is Slight for pH: 6.5 to 5.5, Severe for pH: 5.5 to 4.5 and Very Severe for pH less than 4.5.

Note that the aggression of the acid attack is not only because of its pH value but also due to the presence of CO₂ in relation with the hardness of water.

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