Effect of Diethanolamine after Carbon Dioxide Absorption and Desorption on Mechanical Strength of Cement Mortar and Mechanism

Diethanolamine (DEA) can be used not only as a cement admixture but also to capture carbon dioxide (CO₂). However, the waste liquid treatment still faces the problems of high energy consumption and increasing environmental burden. The effects of DEA waste liquid (WL-DEA) with multiple cycles of CO₂ absorption and desorption on the setting time, hydration temperature, mechanical strength, and microstructure of cement-based materials were explored. It was found that adding WL-DEA could significantly reduce the setting time and enhance the mechanical strength. This improvement was mainly attributed to two aspects: on the one hand, alcoholamine itself could boost cement hydration, which could accelerate the generation of hydration products such as AFt/AFm, CH, C-A-S-H, and C-S-H, thereby improving the cement early strength and refining the microstructure of hydration products; on the other hand, WL-DEA contained little CO₃^2- and HCO₃^-, which reacted with Ca²⁺ to produce CaCO₃. The above reactions cooperated with the complexation effect of WL-DEA to further promote hydration and optimize densification of the hydration products. The application of WL-DEA in cement-based materials could not only effectively enhance their mechanical strength but also promote the recycling of waste liquid, which provided a new method for promoting the development of a circular economy.