Mechanical Properties of High Strength Geopolymer Concrete Incorporating Silica fume and Hybrid fibers

Geopolymer is considered to be an eco-friendly binder and replacement for ordinary Portland cement as it leads to a reduction in CO2 emissions and energy saving.This study investigates the mechanical properties of geopolymer concrete, focusing on its early-age (7 and 28 days) and late-age (56 days) mechanical performance. Four experimental groups were designed, each incorporating different material compositions to assess their influence on compressive strength, splitting tensile strength, flexural strength and to develop optimal mix proportions for geopolymer concrete that balance mechanical performance, minimizing the carbon footprint while maximizing strength .A total of nine fly ash-based geopolymer mixtures designs were examined to obtain an optimal constituent mixes corresponding to high mechanical strength . Group 1 examined the effect of varying fly ash content, while Group 2 introduced silica fume at 10% and 20% replacement levels. Group 3 incorporated both silica fume and steel fibers (1%) to evaluate their combined impact, whereas Group 4 explored silica fume, introducing macro and micro polypropylene hybrid fibers .The results indicate that silica fume enhances strength moderately, but its effect is significantly amplified when combined with fibers. Steel fibers yielded the highest improvements in tensile and flexural strength, particularly in Mix M5 (1% Steel Fiber + 20% Silica fume), making it ideal for high-stress structural applications. Conversely, polypropylene fibers improve tensile and flexural strength, but not as significantly as steel Fibers . Compressive strength improvement was moderate, similar to steel fiber, making them suitable for lightweight or impact-resistant structures.so it contributed to durability and crack resistance, improving toughness rather than significantly increasing strength.