Synergistic Enhancement of Performance and Microstructure in Eco-Friendly Mortar Using Recycled Cement and Silicon Carbide

To achieve sustainable development in building materials and alleviate environmental pressures, the preparation of eco-friendly mortar using solid waste represents an effective approach. This study investigated the effects of recycled cement (RC) and silicon carbide (SiC) on mortar workability, setting time, mechanical properties, microstructure, hydration products, pore structure, and nanomechanical properties. The results show that the incorporation of RC reduces the fluidity of mortar, whereas the incorporation of SiC increases the fluidity of mortar. When RC is mixed together with SiC, the synergistic effect of RC and SiC leads to significant microstructural refinement in the cement paste. This collaboration not only facilitates the conversion of low-density calcium silicate hydrate gel to high-density calcium silicate hydrate gel but also promotes the cement hydration, thus resulting in a denser matrix. Specifically, the 28-d compressive strength of the RC-SiC mortar is increased by 5.72% and the flexural strength is increased by 10.06%, and the porosity is decreased by 32.92%, compared to the control group. However, when SiC is incorporated alone, the strengths of the mortar decrease. This study not only demonstrates a viable resource utilization pathway for RC but also offers practical guidance for the application of SiC in cement-based materials.