Steel corrosion and critical chloride content in concrete with calcined kaolinite clay, fly ash, and limestone powder under natural and accelerated marine environments

Abstract

This study aims to investigate steel corrosion and critical chloride content in concrete with calcined kaolinite clay, fly ash, and limestone powder. The chloride diffusion coefficient and compressive strength of concrete, and weight loss of steel were measured after the specimens were exposed to the tidal zone in a real sea environment for 1 and 2 years. The depassivation time of the embedded steel and the critical chloride content of the concrete under an accelerated marine environment were investigated in the laboratory. The test results revealed that the coefficient of chloride diffusion and critical chloride content of concrete and weight loss of steel decreased with increasing calcined kaolinite clay contents. Although utilizing calcined kaolinite clay in concrete mixtures reduced critical chloride content (0.655% by wt. of binder for OPC and 0.573 to 0.427% by wt. of binder for C15 to C45) because of the lower portlandite content, it caused a longer rebar depassivation time (46 days for OPC and 63 to 237 for C15 to C45). The ternary binder systems of cement, calcined clay, and fly ash demonstrated the best overall performances, i.e., the lowest chloride diffusion coefficient (0.29 ×10−12 m2/s) and the highest compressive strength of the concrete (38.7 MPa), and no weight loss of embedded steel at 2 years of exposure.