Influences of the Geopolymer Composition on the Strength and Durability of Fly Ash-based Geopolymer Stabilized Compacted Soil

Compacted earth materials are sustainable construction alternatives, but their durability is commonly enhanced using Portland cement, which has a high environmental impact. Geopolymers offer a potential low-carbon replacement and demonstrate promising mechanical properties, durability, and environmental performance. This study investigates the influence of geopolymer composition on the mechanical properties and durability of geopolymer-stabilized compacted earth (GSCE). Samples were prepared using Na2SiO3/NaOH ratios ranging from 1.0 to 2.0 with 10 M NaOH. In the first stage, compressive strength was optimized by varying curing temperature and curing time. The highest strength was obtained for specimens with a Na2SiO3/NaOH ratio of 1.5, cured at 90 °C for 24 h. In the second stage, durability was evaluated for GSCE prepared under these optimal conditions through wetting–drying cycles (C = 1–12) in tap water, salt water, and acidic solution (pH = 4). Under acidic conditions, compressive strength increased and reached a maximum after six wetting–drying cycles. XRD and FTIR analyses were used to identify phase development and chemical bonding within the geopolymer matrix. The results highlight the potential of geopolymer-stabilized compacted earth as a durable, environmentally sustainable construction material that incorporates industrial by-products.