Carbonation of supersulfated cement concrete after 8 years of natural exposure

Supersulfated cement (SSC) has garnered attention as a potential lower-carbon alternative to traditional Portland cement, but its carbonation resistance has raised concerns about its wider implementation. This study aims to evaluate the carbonation behavior of SSC concrete after 8 years of natural exposure, examining the carbonation depths, changes in hydration products, and microstructures of SSC concrete with different water-to-cement ratios. The results showed that the carbonation rate of SSC concrete with a C30 grade was 1.02 mm/year, while the carbonation rate of SSC concrete with a C50 grade was 0.54 mm/year. During the exposure process, ettringite in the SSC concrete was found to be the first hydration product to carbonate, leading to a dense pore structure. However, once C–S–H gels began to carbonate, the pore structure rapidly coarsened, resulting in a significant increase in pore network connectivity. Carbonation in SSC concrete generated calcium carbonate with aragonite as the dominant polymorph due to the extensive carbonation of ettringite. The results of this study on the carbonation behavior of SSC concrete under natural conditions can serve as a reference for validating the results of accelerated carbonation tests and provide a foundation for developing a carbonation model for SSC concrete under complex environmental conditions.