CARBONATION
Concrete normally provides a highly alkaline environment that protects embedded steel from corrosion. Carbonation in which the alkaline components of the cement in concrete react with atmospheric carbon dioxide can cause reduction in alkalinity in the presence of moisture and oxygen; steel may corrode. The rate of carbonation depends on the permeability of concrete.
The degree of carbonation of the concrete cover is an indicator of durability of the concrete. The depth of carbonation of cover concrete is assessed by spraying phenolphthalein indicator. Formation of pink texture immediately after spraying indicates non carbonation of concrete, where as non-formation of pink texture indicates concrete is carbonated.
Carbonation tests are conducted to assess the ability of the concrete to passivate the reinforcement bars below. If the carbonation reaches the depth of the reinforced steel bars, reduced pH level would decrease passivity and increase probability of corrosion activity in the steel.