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 CO32- 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.