Carbonation of concrete and corrosion of steel bars in existing reinforced concrete structures
Kitago Yukio; Miyagawa Toyoaki
Abstract:In this paper, the cause of corrosion of steel bars in concrete, particularly carbonation of concrete and the effect of repair work are discussed according to comprehensive investigation of existing reinforced concrete structures. A coefficient of carbonation rate ( = a) which is calculated from the examination exceeds the usual value. Deviations of the coefficient of carbonation rate ( = a) have a tendency to be smaller in the past few years. A depassivated critical value of the difference between cover and carbonation depth is nearly 10 mm or less. When the difference between those values is 0 mm, the steel bars are perfectly depassivated. When the half cell potential is nearly minus 120 mV vs Ag/AgCl, the depassivation begins and if the potentials is minus 230 mV vs Ag/AgCl, the steel bar is also perfectly depassivated. There is little influences of chloride on the corrosion of steel bars in existing carbonated concrete. The difference between cover and carbonation depth has the most important role in the corrosion of steel bars. Key Words:Carbonation, Corrosion of steel bars, Coefficient of carbonation rate, Difference between reinforcement cover and carbonation depth, Half cell potential, Chloride, Repair