ABSTRACT
Stray current causing increased rates of corrosion is a significant problem for steel structures in the ground or water. Carbonation may occur when carbon dioxide gas from the atmosphere dissolves in concrete pore water and penetrates inwards or when the concrete surface is exposed to water or soil containing dissolved carbon dioxide. The attack of buried concrete by carbon dioxide dissolved in the groundwater is a two-stage process. Natural waters may be classified as ‘hard’ or ‘soft’ usually dependent upon the concentration of calcium bicarbonate that they contain. Since the stability of the calcium silicates, aluminates and ferrites that constitute the hardened cement gel requires a certain concentration of calcium hydroxide in the pore water, leaching by soft water can result in decomposition of these hydration products. The presence of chloride at the steel reinforcement surface massively reduces the amount of stray corrosion current required to initiate corrosion.
