Effects of sufficient carbonation on the strength and microstructure of CO2-cured concrete

To maximize its potential in capturing CO2, concretes with various water-to-binder (w/b) ratios underwent a sufficient carbonation through CO2 curing in this study. The variations in the compressive strength and microstructure of concrete were examined. Thermogravimetric analysis (TGA), scanning electron microscopy (SEM) with backscatter electrons (BSE), and mercury injection porosimeter (MIP) were employed to investigate the amount of CO2 captured by concrete, the changes in the microstructure of cement hydrates and interface transition zone (ITZ), and the pore structure, respectively. The results indicate that the amount of CO2 captured by concrete can be increased through two aspects: (1) an increase in carbonation depth, and (2) an increase in the CO2 uptake per unit mass of cement paste. Additionally, the compressive strengths of concrete at the ages of 28 and 56 days show a significant improvement, and this differs from existing studies in which CO2 curing primarily improves the compressive strength at early age. The porosity deceases due to a reduction in the volume of pores with a diameter less than 50 nm. An increase in the degree of cement reaction results in a denser ITZ. The pH of concrete decreases to about 8.9, which means that CO2-cured concrete with a sufficient carbonation could be applied in moderate or low humidity environments.