Acids and concrete

Acids generally attack the surface of concrete by dissolving the matrix leading to surface disintegration.

Concrete is attacked by most acids. The table shows the rate of attack of various common acids. Acids may become more concentrated due to evaporation and this can lead to an increased rate of attack.

Rate of attack at ambient temperature	Inorganic (mineral) acids	Organic acids
Rapid	Hydrochloric	Acetic*
	Nitric	Formic*
	Sulfuric
Moderate	Phosphoric	Lactic**
		Tannic
		Humic
Slow	Carbolic
Negligible		Oxalic

* When concentrated, otherwise slow
** When concentrated, not as milk

Many acids are the products of reactions of other substances that may, in themselves, be harmless or may only be present in low concentrations in these substances. These are outlined in the section headed ‘Action of other substances’.

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