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.
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