Effect of The Polypropylene Fiber Size and Alkaline Solution to Binder Ratio in GGBS-FA based Fiber Reinforced Geopolymer Concrete; Mechanical Properties and Fire Resistance

The increasing demand for sustainable construction materials has driven the exploration of alternative binders to reduce the environmental impact of conventional Portland cement. Geopolymer concrete (GPC), synthesized through the alkali activation of aluminosilicate materials such as fly ash (FA) and ground granulated blast furnace slag (GGBS), has emerged as a promising candidate due to its superior mechanical properties, lower carbon footprint, and resistance to aggressive environments. However, the brittle nature and susceptibility to explosive spalling under elevated temperatures remain critical challenges for GPC. This study investigates the influence of polypropylene (PP) fiber size (6, 12, and 18 mm) and Alkaline solution-to-binder (S/B) ratio (0.40, 0.425, and 0.45) on the mechanical and thermal properties of two-component geopolymer concrete (FA + GGBS). The results indicate that 12 mm PP fibers significantly enhance compressive strength, elastic modulus, and tensile strength, while 18 mm fibers provide superior crack-bridging effects but may lead to fiber clustering and reduced thermal stability. The optimal S/B ratio of 0.425 balances workability, fiber dispersion, and matrix bonding, resulting in improved mechanical performance and thermal resistance. At elevated temperatures, PP fibers melt, creating microchannels that reduce internal pressure and mitigate spalling risks, with 6 mm fibers offering the best fire resistance due to smaller, more uniform voids. This study provides critical insights into optimizing fiber-reinforced GPC formulations for high-performance, fire-resistant structural applications, offering a sustainable alternative to conventional cement-based composites.