Strength and thermal stability of enhanced metakaolin-based geopolymer composites with sand and fibers

The growing demand for sustainable materials in construction and ceramics has driven interest in geopolymer technology as an eco-friendly alternative to traditional cement-based systems. Geopolymers, synthesized from aluminosilicate precursors like metakaolin, offer high mechanical performance, chemical resistance, and lower carbon footprints. This study presents the development of innovative metakaolin-based geopolymer composites reinforced with natural mineral particles and fibers to enhance mechanical and functional properties while maintaining environmental sustainability. A tailored formulation combining commercial metakaolin, optimized waterglass, and a hybrid reinforcement strategy was employed. Three compositions were evaluated: (1) 20 wt.% ball-milled fine sand and 40 wt.% Prairie fine sand (B20P40); (2) B20P40 with 5 wt.% basalt fibers (B20P40Bas5); and (3) B20P40 with 5 wt.% bamboo fibers (B20P40Bam5). The composites demonstrated flexural strengths of 12.1, 17.1, and 14.6 MPa, respectively, with corresponding apparent densities of 1.93, 1.88, and 1.81 g/cm³. Incorporation of natural fibers improved strength, ductility, and thermal stability, while reducing density, water absorption, and pore volume. The results indicate that these fiber-reinforced geopolymer composites are promising candidates for sustainable construction and ceramic applications, offering a viable path toward high-performance, low-impact building materials.