Performance of limestone calcined clay blended cement-based concrete against carbonation

The aim of this work is to investigate the carbonation resistance of limestone and calcined clay blended cement-based concrete. Two limestone and calcined clay concretes with an average 28 d compressive strength of about 36 MPa were considered. Limestone and calcined clay (with a ratio of 2 : 1) were blended with a general purpose (GP) cement. The GP cement substitution rates considered were 30% and 45%.A low-grade calcined clay was used with about 50% amorphous phase. Accelerated and natural carbonation tests were performed. Mercury intrusion porosimetry and X-ray diffraction were carried out, to assist in the analysis of the experimental results. Results show that the early-age compressive strength is only marginally affected by the limestone and calcined clay substitution up to 45% and a significant refinement of the pore structure was observed compared to the reference GP cement concrete. The resistance of concrete against carbonation reduces with increase in the GP cement substitution rate. Overall, this study shows that a limestone and calcined clay blend used as a simple substitution for GP cement in concrete can provide adequate protection against carbonation-induced steel reinforcement corrosion if the ordinary Portland cement content in the mix is at least 60%.