Shear behviour of metakaolin-fly ash based geopolymer concrete deep beams

Abstract

The production of geopolymer binders has a significantly smaller environmental footprint than conventional binders produced using ordinary Portland cement. This fact encouraged research in the area of geopolymer concrete produced utilizing various waste products and natural materials. Following promising results in producing geopolymer concrete with superior mechanical properties, more interest is now directed toward investigating the behavior of geopolymer concrete at the level of structural members. This study considered filling the gap in the literature on the shear behavior of geopolymer concrete deep beams. Six metakaolin-fly ash based geopolymer concrete beams were tested in four-point bending configuration until failure. Test parameters included the content of steel fiber (0, 0.35% and 0.70% by volume) and the shear reinforcement percentage (0 and 0.67%). The beams’ behavior in terms of the cracking patterns and failure modes was generally similar to the behavior of conventional cement concrete deep beams. For geopolymer deep beams without shear reinforcement, the addition of steel fibers at rates of 0.35% and 0.70% (by volume) significantly improved the shear strength by 16.7% and 31.6%. The mid-span displacement capacity at peak strength increased with the increased content of steel fibers for beams with and without shear stirrups. A predictive model relying on the strut-and-tie approach is proposed and shows an excellent match with the measured shear strength of the tested geopolymer deep beams. Also, five empirical models proposed in the literature of conventional cement concrete beams were evaluated for their adequacy in predicting the shear strength of geopolymer concrete deep beams.