Fall 2004

Corrosion of Cement Paste Coated Steel Bars in Marine Concrete

Md. Abdullah-Al-Mamun
Shilpi Banik

The performance against corrosion of cement paste coated steel bars in concrete was investigated under marine accelerated tidal exposure. Cement paste coats were applied over the steel bars before casting concrete. Cement paste coats were made with ordinary portland cement (OPC), slag cement of Types A and B (SCA and SCB), fly ash cement of Type B (FACB), alumina cement, ordinary portland cement with silica fume, and ordinary portand cement with metakaoline. W/C ratios of cement paste coat were 0.3, 0.5, 0.7 and 1.0. Concrete specimens of size 100 mm in diameter and 200 mm in length were made with cement paste coated steel bars. W/C ratio of concrete was 0.5. The specimens were exposed to an accelerated tidal environment, where the specimens were submerged into 60oC seawater for 3.5 days and dried in ambient exposure for 3.5 days. Electrochemical and physical investigations on corrosion of steel bars in concrete were carried out periodically. The results showed that application of a cement-paste coat with a low W/C over the steel bars before casting concrete is a very effective way to improve chloride threshold against corrosion of steel bars in concrete. Poor performance for coats with alumina cement was found due to the conversion of cement reactions of hydration products of alumina cement at high temperature.