The Synthesis and Characterization of Geopolymers Using Metakaolin and Mirror Glass Waste

This study investigates a metakaolin-based geopolymer matrix in which two types of non-recyclable mirror glass waste (MGW) were used as alternative aggregates. The composition, properties and contents of MGW materials as well as their impact on the structure and performance of the geopolymer composites (MGW-Gs) have been characterized using X-ray fluorescence (XRF), X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetric analysis (TG), and Fourier transform infrared spectroscopy (FTIR). Mechanical properties, porosity and thermal conductivity have been evaluated, and compared with silica sand reference composites. The results show that MGW-based composites achieved flexural strengths of 3.9–5.7 MPa and compressive strengths of 60–70 MPa, which are lower than those of sand-based materials (8–11 MPa and up to 93.5 MPa, respectively) but remain adequate performance for applications with moderate load. FTIR analysis has indicated that the incorporation of MGW does not adversely affect the geopolymer network. All composites display similar porosity (approximately 18–22%) and water absorption (12–14%), while MGW incorporation has improved their thermal stability and significantly reduced their thermal conductivity to values below 0.53 W·m−1·K−1, compared with up to 1.09 W·m−1·K−1 for sand-based composites, emphasizing their insulation potential and sustainability benefits. The findings indicate that MGW aggregates can influence the microstructure, mechanical performance, and thermal properties of geopolymer composites, suggesting their potential use in specific construction applications.