Synergistic enhancement of thermal and mechanical properties in alkali-activated slag composites through silicon carbide-induced densification

Enhancing thermal conductivity in cementitious composites typically compromises mechanical integrity. Simultaneous enhancements in thermal conductivity and mechanical strength were achieved in alkali-activated slag composites through strategically substituting fine aggregates with silicon carbide (SiC) to induce microstructural densification. The synergistic effects of SiC particle morphology (coarse vs. fine) and substitution ratios (up to 100%) on macroscopic performance were experimentally evaluated under a fixed mixture design framework. Experimental results demonstrated that fully replacing silica sand with coarse SiC yielded a thermal conductivity of 4.10 W/(mK), representing a 78% increase compared to the control. Notably, this thermal enhancement was achieved alongside a 165% improvement in compressive strength, reaching 62 MPa. Microstructural observations obtained from mercury intrusion porosimetry and scanning electron microscopy suggest that the irregular and angular morphology of coarse SiC particles significantly reduced both cumulative pore volume and average pore diameter. These microstructural changes are likely associated with a denser and more compact microstructure within the composite matrix.