Synergistic Optimization of Thermal and Mechanical Properties in SiO2-Aerogel- and Vitrified-Microsphere-Modified Cementitious Materials

To address the integrated demands of structural reinforcement and energy-efficient retrofitting for existing buildings, a cementitious material modified with vitrified microspheres and SiO2 aerogel was developed to realize the synergistic enhancement of thermal insulation and mechanical strength. By substituting fine sand with equal mass fractions of SiO2 aerogel and vitrified microspheres in the cement matrix, this study systematically investigated the synergistic regulatory effects of this binary modification on two core performance metrics—thermal conductivity and compressive strength. All performance tests were conducted in triplicate, and the results are presented as the mean values. The results indicated that the thermal conductivity of the composite exhibited a trend of decreasing first and then increasing with the rise in aerogel content. At an aerogel dosage of 6%, the thermal conductivity dropped to 0.2237 W/(m·K), achieving optimal thermal insulation performance while retaining a compressive strength of 17.96 MPa. The subsequent incorporation of 15% vitrified microspheres further reduced the thermal conductivity to 0.1642 W/(m·K) while maintaining a compressive strength of 15.34 MPa, thereby achieving an optimal balance between thermal insulation and mechanical performance. Microstructural characterization revealed that the incorporation of aerogel significantly increased the internal porosity of the composite, effectively reducing thermal conductivity by obstructing heat transfer pathways. Vitrified microspheres enhance thermal resistance via their closed-cell structure and promote the formation and densification of C-S-H gel. Synergistically with SiO2 aerogel, they construct a multi-scale porous composite system. By optimizing the interfacial bonding state and pore structure, this system achieves the synergistic optimization of mechanical strength and thermal insulation of cement-based composites, providing new materials and a theoretical basis for the functional integrated retrofitting of existing building structures.