Impact behaviour of nanomodified deflection-hardening fibre-reinforced concretes

The behaviour of concrete under sudden impact loads is complex. Moreover, very little is known about the impact behaviour of high-performance fibre-reinforced concretes (HPFRCs). To account for this, nanomodified deflection-hardening HPFRC mixtures incorporating coarse aggregates were produced with three ratios of fly ash to Portland cement (0.0, 0.2 and 0.4), three nanomaterials (nanosilica, nano-alumina and nanocalcite) and two hybridised fibre combinations (hooked-end steel with polyvinyl alcohol, or hooked-end steel with brass-coated microsteel) and tested for basic mechanical properties and flexural impact resistance. After experimental testing, beams used in impact testing were modelled using Abaqus. Cubic compressive strength did not change significantly with the differences in mixture parameters, although this was not the case for flexural parameters. For a given fly ash/Portland cement ratio and nanomaterial type, mixtures with hooked-end steel and polyvinyl alcohol fibres exhibited higher displacement and lower flexural strength capacity than those with hooked-end steel and brass-coated microsteel fibres. Nano-alumina contributed best to the development of mechanical properties and impact resistance of HPFRCs, followed by nanosilica and nanocalcite. Results validate the idea that costly polyvinyl alcohol fibres can be fully replaced with brass-coated microsteel fibres without risking mechanical properties and impact resistance, as long as matrix properties are properly controlled.