Corrosion of Steel in Concrete under the Influence of Chloride

Abstract

The Japan Society of Civil Engineers has recommended the allowable chloride content of fine aggregate in RC and pretensioned PC member to be 0.1% and 0.03% by weight, respectively. In Kyushu about 90% of the fine aggregates used for concrete works are sea sand. However, the relationship between the salt content of concrete and corrosion of reinforcing bar and PC wire has not been clearly known and the basic concept for the recommended salt content is not firmly established yet. Under these circumstances, the authors have made experimental studies on rusting of reinforcing bar and PC wire in concretes.
Although the experiments are still being conducted, the results up to date are as follows.
(1) The measured values of salt contant in the specimens placed on land were found to be reduced to about one half of the designed amount, but in other cases in sea and on coast reached up to 1-2% near the surface. It is thought that the phenomenon for the latter cases was caused by infiltration of chloride ions.
(2) Though the PC wires were covered with rich mix concrete, their rusting was remarkable as compared with that of reinforcing bars. In the case when the salt content of concrete was 0.2-2.0%, the pitting due to rust began influencing upon the ultimate tensile strength of PC wires.
(3) When the salt content of concrete was 0.5-1.0%, the percentage of rusting weight of steel became remarkable. Every effort should be made to keep the salt content as low as possible when placing concrete.