Performance and microstructural assessment of clay stabilization using ceramic siding waste powder and metakaolin-based geopolymer

The increasing demand for sustainable and low-carbon construction materials has intensified research into alternative soil stabilization techniques that reduce reliance on conventional cementitious binders. Conventional additives, although effective in improving the mechanical behavior of weak soils, is associated with high energy consumption and significant CO 2 emissions during its production, making it environmentally unsustainable for large-scale geotechnical applications. In response, geopolymer-based stabilization has emerged as a promising alternative due to its ability to utilize industrial by-products and aluminosilicate-rich waste materials to form cementitious binders under alkaline activation. This study investigates the stabilization of low-plasticity clay using a geopolymer system incorporating ceramic siding waste powder (CSWP) and metakaolin (MC) activated with sodium silicate solution. Ten mix formulations containing single and combined precursors at total additive contents up to 15% were evaluated through compaction, unconfined compressive strength (UCS), soaked California bearing ratio (CBR), water absorption, ultrasonic pulse velocity (UPV), X-ray diffraction (XRD), and scanning electron microscopy (SEM). Results showed that combined CSWP-MC mixtures generally performed better than single-precursor systems at equivalent additive contents. The optimal mixture containing 7.5% CSWP and 7.5% MC achieved a 28-day UCS of 4.05 MPa, soaked CBR of 30.5%, water absorption of 7.1%, and UPV of 2080 m/s. These improvements were accompanied by increased matrix densification and reduced visible porosity, as indicated by UPV and SEM observations. XRD analysis showed development of a broad amorphous hump between 20° and 40° 2θ, suggesting formation of geopolymeric reaction products under alkaline activation. The improved performance of the combined precursor system may be associated with complementary particle packing and balanced silica–alumina availability, which may have promoted more effective geopolymerization. The findings indicate that CSWP and MC-based geopolymer stabilization offers a promising and eco-friendly alternative for improving the engineering performance of clay soils.