Mechanical and fracture properties of ultra-high performance geopolymer concrete: Effects of steel fiber and silica fume

This study investigates the effects of steel fiber and silica fume on the mechanical and fracture properties of ultra-high performance geopolymer concrete (UHPGC). Four volume fractions of steel fiber (0%, 1%, 2% and 3%) and four contents of silica fume by the mass of total binders (5%, 10%, 20% and 30%) were used. The mechanical and fracture properties evaluated include the compressive, splitting tensile and ultimate flexural strengths, modulus of elasticity, flexural behavior, fracture energy and stress intensity factor. In addition, the correlations among the compressive and splitting tensile strengths, and compressive strength and elastic modulus were studied. The results indicated the increase of steel fiber dosage resulted in the decrease of the workability, but the continuous improvement of mechanical and fracture performance of UHPGC. The empirical equations for predicting elastic modulus of conventional ultra-high performance concrete overestimated the elastic modulus of UHPGC, however some prediction formulas for the splitting tensile strength of PC-based concretes could be applied for UHPGC. Silica fume had a complicated influence on workability and hardened properties of UHPGC, which is strongly dependent on its amount. The inclusion of 10% silica fume induced the increase of the flowability, but the sharp degradation of the mechanical performance, while the specimens with 20% and 30% silica fume possessed the superior mechanical characteristic to that with 5% silica fume. The steel fiber dosage could be decreased without sacrificing the mechanical and fracture performance of UHPGC, via the increase of silica fume content.