Chloride Penetration and Reinforcement Corrosion in Fly Ash Concrete Exposed to a Marine Environment

Abstract

Steel reinforced concrete specimens, with nominal strength grades 25, 35 and 45 MPa and different fly ash levels (0 to 50 percent), were exposed to various curing treatments during the first 28 days prior to exposure in the tidal zone of a seawater exposure site. Chloride concentration profiles and rebar weight losses were measured for specimens after 1, 2 and 4 years exposure. Chloride profiles were also measured for specimens after 28 days immersion in seawater under laboratory conditions. Fly ash concretes showed substantially increased resistance to the penetration of chlorides compared with control specimens. The improved resistance of fly ash concrete to the penetration of chlorides resulted in reduced corrosion of steel bars imbedded in the concrete. Threshold concentration decreased with increasing fly ash content. Chloride concentration profiles after 28 days of immersion in seawater showed that considerable chloride penetration occurred during this period due to sorption (capillary suction) of the seawater into the unsaturated specimens. This results in a significant error in diffusion coefficients calculated from the concentration profile using the standard solution to Fick's second law.