Hydration Characteristics and Mechanical Properties of Cement-Based Materials Modified by Calcined Zeolite and Montmorillonite

Cement manufacture contributes 5-7% of global anthropogenic CO 2 emissions, having harmful impacts on air quality and climate change. Adding calcined clay minerals as supplementary cementitious materials to prepare new cement-based materials has become an effective way to reduce carbon emissions. In this study, montmorillonite and zeolite were used as representative materials to prepare calcined montmorillonite-cement and calcined zeolite-cement binary cementitious materials. The influence of different amounts of clay minerals on the fluidity and mechanical properties were analyzed. The microscopic morphology and phase changes of hydration products as well as hydration heat were revealed. The results show that the calcined clay mineral improves the fluidity of cementitious material as compared with the uncalcined group. The incorporation of proper amount of calcined montmorillonite (CMT) improves the development of mechanical strength. The optimal compressive strength reaches 85 MPa at 28 days of curing with 8% CMT, by mass. However, the activity of the calcined zeolite (CZL) is weak with few reaction sites, which slightly reduced the mechanical strength as compared to blank sample. The introduction of CMT changes the microscopic morphology of hydration products such as C-S-H and C-A-H, leading to the formation and transformation of AFt at early age. Meanwhile, it promotes the gradual polymerization of Si-O bonds into Si-O-Si bonds, and accelerates the early hydration process. In contrast, CZL acts mainly as physical filling function in the cementitious system. This work provides the guideline for the application of calcinated clay in cement considering the effects of clay type on the workability and mechanical strength.