Corrosion of Steel in Portland Cement Concrete: Fundamental Studies

Abstract

Corrosion of steel in portland cement concrete occurs when the outside influences change the composition of the pore solution. This paper provides an overview of the information available from the literature and work done in the University of Oklahoma laboratories on this corrosion problem so important to the transportation system in the United States. Steel is passive in the high pH environment present in portland cement pore solution. Until recently, this pore solution was thought to be saturated calcium hydroxide, but now some work has shown it is more like potassium and sodium hydroxides. The work using presses to express pore solutions with subsequent analysis is described. Chloride ions can penetrate the passive film, cause the steel potential to shift, and result in corrosion. The nature of the chloride ion affects the severity of the corrosion problem. Chloride ion, which diffuses into hardened concrete will initiate corrosion at a smaller amount than that required to initiate corrosion with chloride ion mixed in the concrete. In addition the cation will affect the amount of chloride required for corrosion problems. Calcium chloride seems to be more aggressive than sodium chloride. These results will be compared to pore solution analyses, which indicate the chloride binding capacity of the portland cement changes with the type chloride ion also. Some data on the effect of portland cement analysis on the corrosion behavior will also be given. This paper shows that the pore solution composition can be used to explain the corrosion behavior of steel in concrete. Better understanding of these facts can lead to development of better corrosion control measures for this very costly problem.