Preliminary exploration of the hydration-carbonation coupling mechanism of low-carbon calcined clay-carbide slag-cement composites

Abstract

To reduce the environmental impact of cement production and carbon emissions, the use of supplementary cementitious materials to replace part of the clinker and carbonation curing are two of the most effective strategies for reducing carbon dioxide emissions in the cement and concrete industry. This study mainly explores the effects of calcined clay on cement-based materials under different curing conditions (normal curing and carbonation curing), as well as the synergistic effect of calcined clay and carbide slag under different curing conditions. The results demonstrate that: (1) Calcined clays can undergo pozzolanic reactions with hydration products such as Ca(OH)₂. Additionally, the acceleration of the carbonation rate by calcined clay is comparable to that of quartz powder, yet the strength during the later stages of carbonation is slightly higher than that of the sample with added quartz, possibly due to the generation of more gel. (2) The addition of quartz helps to enhance the rate of carbonation. However, when cement is replaced by quartz and burnt clay at the same time (the dilution effect is dominant and the diffusion of CO₂ is fast), it will cause premature carbonation of the samples, resulting in the later carbonation strength being lower than the normal cured strength. (3) The dilution effect caused by the large dosage replacement of calcined clay and calcium carbide slag leads to a reduction in strength. However, the higher Ca(OH)₂ content in carbide slag and its synergistic effect with calcined clay can mitigate some of the negative effects of dilution.