Carbonation of concrete is associated with the corrosion of steel reinforcement and with shrinkage. However, it also increases both the compressive and tensile strength of concrete, so not all of its effects on concrete are bad.
Carbonation is the result of the dissolution of CO2 in the concrete pore fluid and this reacts with calcium from calcium hydroxide and calcium silicate hydrate to form calcite (CaCO3). Aragonite may form in hot conditions.
• This simple test allows the measurement of depth of carbonation through the surface of concrete.
• During the test, the broken or cored surface is sprayed with phenolphthalein solution to detect the loss of alkalinity associated with carbonation.