Effects of Waste Glass and Expanded Clay Dust on Physical, Mechanical, and Thermal Properties of Autoclaved Silicate Composites

Incorporating mineral by-products into autoclaved silicate products can reduce virgin-material consumption and alter their thermal and mechanical performance. This study evaluated factory-derived sand-lime silicate composites modified with ground waste glass and expanded clay dust. An unmodified factory silicate mass served as the reference. It wascompared descriptively with three modified formulations containing silicate mass, waste glass, and expanded clay dust at mass ratios of 87/3/10, 75/5/20, and 60/10/30. Cylindrical specimens (50 mm in diameter and 50 mm in height) were produced by semi-dry pressing at 12 MPa and autoclaved under factory conditions. Bulk density, compressive strength, water absorption, and thermal conductivity were determined according to the standards cited by the authors. Optical microscopy, scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS) were employed for descriptive microstructural characterization. Across the investigated series, bulk density decreased from 1.80 g/cm³ for the unmodified silicate mass to 1.69 g/cm³ for the 60/10/30 formulation, corresponding to a 6.1% reduction. Thermal conductivity decreased from 0.87 to 0.56 W/(m·K), representing a 35.6% reduction, while compressive strength decreased from 47.8 to 30.3 MPa and water absorption increased from 15.2% to 20.2%. SEM observations revealed glass-rich particles embedded within the autoclaved matrix, while EDS indicated a Ca-Si-Al-rich elemental composition; however, these techniques did not establish the presence of specific crystalline hydration phases. Because replicate numbers,dispersion measures, and inferential statistical analyses were not reported, the results should be interpreted as descriptive trends rather than statistically validated differences. The combined additives reduced density and thermal conductivity but adversely affected compressive strength and water absorption. Among the modified formulations, the 87/3/10 mixture exhibited the most conservative balance of properties. Further investigation of durability, frost resistance, phase assemblage, statistical reproducibility, and life-cycle impacts is required before conclusions regarding standards compliance, environmental benefits, or industrial-scale applicability can be drawn.