Effect of Granodiorite Sand Content and Particle Size on the Mechanical and Thermal Performance of Metakaolin-Based Geopolymer Mortar

High Resolution Image Download MS PowerPoint Slide In this study, the coupled effects of granodiorite sand particle size and content on the mechanical and thermal performance of metakaolin-based geopolymer systems are systematically investigated using a holistic, geometry-sensitive approach. For block-type specimens compressive and flexural strengths, together with postheating mass loss after exposure to 300 °C, are evaluated to elucidate strength retention and thermal stability. The results demonstrate that granodiorite particle size plays a decisive role in governing the balance between mechanical integrity and thermal insulation. Coarse particles (0.5–1.0 mm) at 30 wt % content provided the highest mechanical performance, achieving a compressive strength of approximately 50–68 MPa depending on the skeletal structure formation. Thermal stability tests at 300 °C showed that incorporating granodiorite effectively controlled degradation, with mass loss ranging from 3.4% to 9.1%, where the BG1–20 composition outperformed the control sample’s 5.7% loss. For plate-type specimens, thermal insulation was assessed under 700 °C flame loading. Fine granodiorite particles (<0.25 mm) markedly improved insulation by reducing back-surface temperatures to as low as 93 °C, significantly lower than the 207 °C observed with coarse particles. Overall, the findings reveal an inverse yet predictable relationship between mechanical strength and thermal insulation, providing a rational framework for designing geopolymer blocks and plates tailored to application-specific requirements.