Project Abstract
Chloride-induced corrosion of reinforcing steel in concrete is a major issue for the service life and reliability of concrete structures and has been estimated to cost U.S. transportation agencies approximately five billons dollar a year. Once corrosion begins, it can propogate and deteriorate the concrete in only a few years. Therefore, to increase the durability of concrete, it is critical to prolong the initiation stage, which is a function of the chloride transport properties of concrete (usually the diffusion coefficient), the surface chloride content dictated by the environment, the concrete cover thickness, and the chloride threshold concentration determining the onset of active corrosion. State departments of transportation (DOTs) have developed concrete mixes for corrosion mitigation of bridge structures, and mineral admixtures have been used to reduce the permeability of concrete to chlorides while keeping the concrete cover requirements at reasonable thicknesses. Current test methods, however, do not provide consistent or expedient methods for evaluating different concrete mixes and admixtures. The objectives of this research are to validate chloride diffusion coefficients of mineral admixture concrete mix designs currently developed for corrosion mitigation, and to verify the adequacy of existing measures to mitigate corrosion caused by exposure to marine environments and deicing salt applications. The project will develop and establish standard, accelerated test methods to determine the chloride diffusion coefficient and chloride depassivation thresholds of conventional and mineral admixture concrete specimens, as well as a model for calculating projected service life of steel-reinforced concrete structures.