"Carbonation, Amount of Chloride Ion, and Corrosion of Steel Reinforced Concrete Buildings in HANSHIN Region"

Many reinforced buildings were damaged by the Hygoken-Nanbu Earthquake of 1995. In order to clarify the actual state of carbonation of the concrete and the chloride ion content in concrete of buildings in the Hanshin area, the depths of carbonation and the amount of chloride ion were measured in 117 concrete samples that were obtained from 97 damaged buildings. The effects of carbonation depth and chloride ion content with regard to the corrosion of steel were also investigated. The measured carbonation depths were wildly scattered, with some of the concrete being heavily carbonated. The amounts of chloride ions in old river sand concrete were small. Large amounts of chloride ion were found mixed with sand, that came not only from the ocean but also from rivers, in the buildings that were built between 1960 and 1978. This chloride ion was thought to be induced through sea sand and an admixture. The concentration of chloride ions in concrete were small for buildings that had been constructed after the regulation of the amount of chloride in concrete that was instituted in 1986. A great deal of the steel embedded in the carbonated concrete was severely corroded. The degree of steel corrosion tended to increase with an increase in the amount of chloride ion as well as carbonation depth.