Sulfate resistance of hybrid fiber reinforced metakaolin geopolymer composites

This work aims to investigate the sulfate resistance of geopolymer composites prepared by alkali activation of metakaolin (MK) and reinforced with polypropylene fiber (PP), polyvinyl alcohol fiber (PVA) and wollastonite (WS). Compressive and flexural strength were measured to determine the optimum mix proportion of the composites. The sulfate resistance properties were evaluated by strength loss, mass loss, microstructure and pore structure changes after sulfate exposure. The experimental results show that the two groups containing 1% of PP + 1% of PVA and 2% of PVA +15% of WS, respectively, exhibit the highest compressive strength and flexural strength compared to non-reinforced mixtures. After sulfate exposure, the decreased compressive strength and mass loss are correlated to the concentration of sulfate and exposure period. In the simulated extreme marine environment, the deterioration of composites induced by high concentration of sulfate after 28 days of exposure reaches to the maximum level or a threshold. The average pore size and porosity increase after the sulfate exposure. The role of fibers in mechanical properties and microstructure after sulfate exposure were also investigated. The uses of hybrid organic fiber and inorganic mineral microfiber reinforcement are effective to enhance the resistance to sulfate attack.