Self-compacting steel fibers reinforced geopolymer: Study on mechanical properties and durability against acid and chloride attacks

This study aimed to investigate the effects of steel fibers on the properties of self-compacting geopolymer (SCG), including flowability and fillability, compressive and flexural strength, and durability against harmful chemical substances such as acids and chloride. In the first stage, the study involved determining the optimum fiber content for geopolymer that meets the criteria for self-compacting concrete. The second stage involved investigating the mechanical properties and durability of self-compacting fiber-reinforced geopolymer (SCFRG). For SCG, the binder phase consisted of fly ash and slag at different proportions, while for SCFRG, the geopolymer was mixed with hooked-end steel fiber at 0.5–1.5% by volume fractions. The study found that adding 0.5% to 1.5% steel fibers by volume fraction to create self-compacting fiber-reinforced geopolymer (SCFRG) improved compressive strength by 8.7%, toughness by 88%, and residual strength by 83.7%. However, it slightly reduced slump and filling ratio while increasing T50. Both SCG and SCFRG's durability were assessed by immersing samples in 5% concentration chemical solutions, resulting in weight loss to varying degrees depending on the type of chemical. In terms of weight loss, immersion in 5% sodium chloride showed no effect, while immersion in 5% magnesium sulfate and 5% sulfuric acid resulted in a reduction in weight compared to samples cured in ambient conditions. Additionally, SCFRG samples submerged in MgSO4, H2SO4, and NaCl demonstrated relatively stable compressive strength when compared to ambient samples. The addition of steel fibers to SCG reduced the chloride penetration depth and diffusivity, indicating better resistance to chloride ion penetration. In summary, the study demonstrated that although the addition of steel fibers decreased flowability and fillability, it potentially improved the mechanical and durability properties of self-compacting geopolymer.