Define Sulphate Attack - underwater inspection of bridge?
Cement contains a proportion of tricalcium aluminates, which takes part in the hydration process. These can react with magnesium sulphate, which is present in concentrations of about 0.5% in seawater. The reaction is expansive, but the presence of chlorides inhibits the degree of expansion. The net result is softening and disruption of the concrete in the form of crumbling.