Experimental Study on Fiber-Reinforced Geopolymer Concrete Utilizing Fine Aggregate from Demolition Waste

This work aims to enhance the performance of 100% demolition waste fine aggregate (DWF)–added geopolymer concrete (GPC) by using steel, bamboo, and a hybrid fiber mix. Steel fibers (0.5%–2%), bamboo fibers (0.5%–2%), and a hybrid fibers mix (steel+bamboo) with a total fiber content of 2% were used to evaluate the mechanical and microstructural properties of fly ash–ground granulated blast furnace slag (GGBS)–based GPC under ambient curing conditions. The addition of steel fibers significantly improved the mechanical characteristics, yielding a 33% increase in compressive strength, 23.7% in split tensile strength, and 42% in flexural strength at a 2% fiber content. However, bamboo fibers adversely affected strength qualities, resulting in decreases of up to 37% in compressive strength, 25.4% in split tensile strength, and 25% in flexural strength. The hybrid fiber mixes enhanced performance, with 1.5% steel fiber and 0.5% bamboo fiber attaining 17% greater compressive strength, 18.6% increased split tensile strength, and 34% superior flexural strength relative to the control concrete mix. The findings indicated that steel fibers are the most effective in enhancing mechanical properties, while bamboo fibers reduce strength. The hybrid fiber mixes offer moderate improvements but do not match the strength gains provided by steel fibers alone.