The Effect of Wet-Dry Cycles on Carbonation Compared to the Constant Relative Humidity Conditions

Cement, as a very practical building material, is produced in large quantities every year, and in 2022, global cement production was approximately 4.5 billion tonnes. However, for every ton of cement clinker produced, approximately 1t CO2 is emitted, which seriously impacts the global environment, especially the greenhouse effect. Therefore, how to absorb CO2 has become a very important topic. Carbonation of waste concrete was found to be a great means of carbon capture in previous studies, so this study further explored the effectiveness of carbonation under differences in relative humidity and proposed the ideal relative humidity for promoting carbonation of waste concrete. FTIR and XRD measurements were conducted in this study to analyze the carbonation products. As a result, under wet-dry cycles compared to the constantly humid environment, the degree of carbonation was higher, and calcium carbonate is more likely to precipitate in different polymorphs, including vaterite and calcite. The best wet-dry cycle for carbonation is RH40–100, which is 1.55 times more efficient on carbonation than RH70 at 14 days of carbonation. The degree of carbonation was high in the order of RH40–100, RH50–90, and RH60–80 on the 28 days of carbonation. The greater the difference between the maximum and minimum humidity, the more it promoted carbonation. This shows that the amplitude difference is an important factor affecting the carbonation efficiency for wet-dry cycles.