Synergism of steel fibres and PVA fibres on the fracture and mechanical properties of ultra-high-performance concrete

The influence of the volume fraction (VF) of steel fibres, polyvinyl alcohol (PVA) fibres and their combination on the mechanical and fracture mechanical properties of ultra-high-performance concrete (UHPC) was studied. To analyse the synergistic effect of steel fibres and PVA fibres on the deformation properties of UHPC, the gain ratios (the ratios of the mechanical properties of UHPC reinforced with hybrid fibres (HUHPC) with those of UHPC reinforced with steel fibres (SUHPC)) were obtained for equal total fibre VFs and equal steel fibre VFs. The steel and PVA fibres reduced the compressive strength of the UHPC to some extent and, with increasing VF, the ratios of flexural strength/compressive strength and tensile strength/compressive strength increased gradually. The fracture mechanical properties of the UHPC were significantly improved with the addition of steel fibres and PVA fibres; the latter were superior in improving the deformation properties of the UHPC. Except for compressive strength, the gain ratios of mechanical parameters of HUHPC to SUHPC calculated with equal steel fibre VF were higher than for equal total fibre VF; 0.25% PVA fibres mixed with SUHPC further improved the bending tensile and fracture mechanical properties.