Hydration behavior and microstructure of low carbon cementitious materials containing calcined kaolin tailings in China

The Limestone Calcined Clay Cement (LC³) is a novel cementitious material based on clay materials, which can reduce carbon emission by up to 40 %. Considering the fact that clay is restricted to be directly used as construction materials in China, kaolin tailings, as one of industrial waste, might be a potential resource to make LC³. In this study calcined kaolin tailings (CKT) from Guangxi Province were blended with limestone as replacement of cement clinkers. The mechanical performance, hydration behavior, and microstructural evolution were investigated by various characterization methods. The results show that replacement of CKT and limestone enhances the long-term strength development, resulting in a comparable 28-day strength as pure Portland cement. The pozzolanic and synergistic reactions of CKT mainly occur after 3 days. The later formed AFm phases and C-A-S-H can further refine pore structure. When the replacement rate is over 30 %, the dissolved aluminum ions from CKT are more inclined to enter C-A-S-H rather than to form more AFm. At an equivalent gel–space ratio, CKT–limestone blended cements showed higher compressive strength than the reference cement and other blended cement reported in the literature, highlighting the potential of CKT–limestone systems as a low-carbon option for China.