Acids interacting with concrete dissolve the hydrated cement paste, leading to a softened and structurally weakened material.
Acidity breaks down the concrete when the water pH drops below 6.5, and the deterioration accelerates if the pH level falls below 4.5.
Water with 15 to 60 parts per million of carbon dioxide, such as melted ice water, can degrade concrete. Peaty water with over 60 parts per million of carbon dioxide is highly corrosive.
Domestic sewage, although alkaline, corrodes sewers, especially in the heat, when anaerobic bacteria turn sulfur compounds into hydrogen sulfide, which is oxidized by anaerobic bacteria into sulfuric acid.
The diffusion rate of hydrogen ions through the cement gel also influences the attack rate, especially after calcium hydroxide has been dissolved and washed away.
Calcium hydroxide attacks can be prevented by stabilizing it with diluted sodium silicate, which forms calcium silicates in the concrete pores.
Applying surface treatments like coal-tar pitch, rubber or bituminous paints, and epoxy resins has proven effective for general acid attacks.
