Development of Carbonated Waste-Enhanced Calcined Clay Cement (CWC 3 ) via Activated Carboaluminate Reaction: A Strategy toward Sustainable Engineering Materials

Limestone calcined clay cement (LC3) is widely recognized as a sustainable cementitious material. However, the low reactivity of natural limestone often limits the early carbon aluminate reaction and compromises the early compressive strength of LC3. This study proposes the preparation of highly active CaCO3 by carbonating SS, RCP, MS, and CS. The resulting product is then used to replace limestone and activate early carbon aluminate reactions in LC3. This strategy aims to develop a sustainable engineering material with high compressive strength and low CO2 emissions, referred to as carbonated waste calcined clay cement (CWC3). The results showed that compared with LC3, the compressive strength of CWC3 at 3 and 28 days increased by 19.7% and 10.8%, respectively, while the CO2 emissions and CO2 index decreased by 14.4% and 21.9%, respectively. The mechanism of early activation of the CWC3 carbon aluminate reaction includes two aspects: the crystallite grain size and crystallinity of CaCO3 in carbonated waste are much smaller and lower than those of CaCO3 in natural limestone with a polycrystalline crystal cluster morphology. This structure introduces a higher density of crystal defects, thereby enhancing chemical reactivity. CaCO3 crystal clusters and silica gel are interlaced in a carbonated waste particle, and the volcanic ash reaction of silica gel disperses the CaCO3 crystal clusters, thereby inducing more carbon aluminate reaction interfaces. In addition, the nucleation of highly active CaCO3 accelerates the hydration kinetics of CWC3, generating more hydration products (such as Hc, Mc, and Ms), inducing denser pores, and ultimately contributing to the improved compressive strength. The carbonated waste exhibits the highest CO2 sequestration amount of 513.4 g/kg, underscoring the significant environmental sustainability of CWC3.