Corrosion evaluation of steel bars in steam-cured concrete under chloride attack and alkali–silica reaction

One of the challenges to reinforced concrete slabs in bridges is deterioration due to rebar corrosion by deicing salts. In order to simulate a concrete slab subjected to deicing salt penetration from the top surface of the bridge slab during winter, high-strength steam-cured concrete with double-layer reinforcements was exposed to 10% sodium chloride solution to investigate rebar corrosion. Five concrete mix proportions were prepared, including high early strength concrete and concrete containing fly ash and blast furnace slag as supplementary cementitious materials (SCMs). For both the high early strength and fly ash concretes, alkali active andesite in the pessimum proportion was mixed with coarse aggregates to investigate the effect of alkali–silica reaction (ASR) on rebar corrosion. It was found that the combined effects of chloride attack and ASR adversely affected the corrosion resistance of high early strength concrete. Fly ash concrete had excellent performance as to corrosion resistance and ASR mitigation. Results also showed that a widely used electrochemical technique known as the half-cell potential test can satisfactorily diagnose corrosion of double-layer reinforced concrete. Concrete specimens containing SCMs with no ASR threat showed no signs of steel bar corrosion and significantly low chloride diffusion coefficients after 3 years.