Effect of strain rate on splitting tensile strength of geopolymer concrete

The splitting tensile strengths of geopolymer concrete and geopolymer mortar under strain rates from 10⁻⁷ s⁻¹ to 25 s⁻¹ were investigated. Five mixes – one ordinary Portland cement (OPC) concrete, three geopolymer concrete and one geopolymer mortar – were considered. A Shimadzu AG-X 300 kN testing machine and a split Hopkinson pressure bar were used to conduct the tests. The dynamic increase factors of the splitting tensile strength (DIF_ft) of the geopolymer concretes were measured and compared with modified CEB recommendations. The results show that alkaline activators have a significant influence on the quasi-static splitting tensile strength of geopolymer concrete. For low strain rate loadings, the geopolymer concrete with low compressive strength had a larger DIF_ft and the viscous effect was found to be the main cause for an increase in DIF_ft. With high strain rate loadings, crack inertia was found to be responsible for the improvement in DIF_ft of geopolymer concretes. The existing formula for OPC concrete underestimates the DIF_ft of geopolymer concrete and therefore new empirical equations are proposed. In addition, the failure modes under various strain rate loadings were found to be similar due to the confinement of splitting tensile test on the crack path.