Effect of iron tailing fines on dynamic properties and microstructure of recycled steel fibre reinforced ultra-high performance concrete

Iron tailings used as supplementary cementitious materials could solve the environmental problems caused by excess iron tailings. This paper investigates the effect of mechanical-thermal activated iron tailing fine (ITF) as a substitute for silica fume on the dynamic properties and microstructure of recycled steel fibre reinforced ultrahigh performance concrete (UHPC). Relevant tests are conducted to systematically study the elastic modulus, direct tensile strength, dynamic splitting properties, hydration heat and morphological evolution of UHPC containing ITF under substitution levels up to 100 %. Results show that the static and dynamic properties of UHPC are decreased with increasing substitution levels of ITF, and the promoted strain rate effect occurs at higher ITF contents. Compared with the referenced UHPC, the dissipated energy of UHPC containing 100 % ITF is decreased by 41.69 %-48.74 %, while the dynamic splitting strength is reduced by 23.66 %-29.17 % within the strain rate range of 1.9-6.2 s- 1. The mechanisms of ITF on the engineering properties of UHPC can be explained by the inhibited hydrate generation, the decreased stacking density and the weakened fibre-to-matrix bonding. Moreover, the suggested substitution level of ITF used in UHPC is 50 % considering the overall mechanical properties and environmental benefits.