Amorphous calcium carbonate formation from carbonated recycled cement powder: A novel carbonation-activated cementitious material

Research on recycled cement powder (RCP) has shown great potential for carbon sequestration, however understanding of calcium carbonate polymorphs evolution in carbonated recycled cement powder (C-RCP) remains limited, especially concerning the formation of amorphous calcium carbonate (ACC) and its impact on the development of concrete strength. In this study, ACC is produced from C-RCP using poly-aspartic acid (pAsp) to control the crystallization of CaCO 3 , aiming to create a highly reactive cementitious material. The research systematically investigates the effects of various processing parameters, specifically pAsp concentration, ethanol concentration, temperature, and carbonation duration on ACC formation, microstructure of carbonation products , and the chemical environment. Additionally, the compressive strength of C-RCP as supplementary cementitious materials (SCMs) is also evaluated. The results indicate that higher concentrations of pAsp (10–15 %) and ethanol (50–70 %) enhance the stabilization of ACC formation. The decrease in carbonation degree correlates with the increase in the formation of metastable calcium carbonate (mCC), including ACC and vaterite within C-RCP. Furthermore, elevated temperature and extended carbonation duration promote the formation of vaterite due to an increased carbonation degree. The incorporation of novel C-RCP, characterized by a maximum relative content of mCC, significantly enhances the strength of cement paste, attributed to the transformation and crystallization of ACC. This method utilizes pAsp to control the crystallization of calcium carbonate in C-RCP, effectively activating the reactivity of the calcium carbonate phase. This approach significantly enhances the potential of C-RCP as a novel cement-based material by optimizing its hydration reactivity, making it particularly well-suited for application in carbonated cement composites.