Unlocking Thermal Insulation Performance and Mechanisms in Decoration Waste Aerogel Mortar: A Multi-Factor Study on Paste-to-Aggregate Ratio, Silica Aerogel Content, and Air-Entraining Agent Dosage

To improve the resource utilization of decoration waste and enhance the thermal insulation performance of building mortar, this study designed and prepared decoration waste aerogel mortar (DWAM) using decoration waste recycled fine aggregate (DWRA) combined with silica aerogel. The effects of paste-to-aggregate ratio (30/70, 35/65, and 40/60), aerogel content (60–100 vol.%), and air-entraining agent (AEA) dosage (0.1–0.5 wt%) on workability, dry density, mechanical strength, and thermal conductivity were systematically investigated. Microstructural evolution and pore characteristics were analyzed using scanning electron microscopy (SEM) and X-ray computed tomography (X-CT). Results showed that increasing the paste-to-aggregate ratio improved workability and mechanical strength, while aerogel and AEA incorporation significantly reduced thermal conductivity at the expense of strength. An optimum mix with a paste-to-aggregate ratio of 40/60, aerogel content of 80 vol.%, and AEA dosage of 0.4 wt% achieved a dry density of 623.8 kg/m3, compressive strength of 1.27 MPa, flexural strength of 0.61 MPa, and thermal conductivity of 0.0784 W/(m·K). X-CT revealed that closed micropores enhanced thermal insulation by disrupting heat transfer. The developed DWAM offers balanced workability, mechanical properties, and thermal insulation, demonstrating strong potential as a sustainable material for building applications.