Effect of elevated temperatures on behaviour of recycled steel and polypropylene fibre reinforced ultra-high performance concrete under dynamic splitting tension

Abstract

This paper investigates the dynamic splitting resistance of ultra-high performance concrete (UHPC) incorporating recycled steel (RS) and polyethene (PP) fibres at various temperatures (i.e., 20, 200, 400, 600, 800 °C) and strain rates (i.e., 2.3−7.2 s−1). A series of tests are performed to evaluate the compressive strength, elastic modulus, uniaxial tensile strength, dynamic splitting properties and microstructural characteristics of UHPC at elevated temperatures. Results reveal that the maximum compressive strength, elastic modulus and uniaxial tensile strength of UHPC appear at 400 °C due to the promoted hydration of unhydrated clinkers at elevated temperatures. When the temperature increases from 20 °C to 400 °C, the dynamic splitting strength and dissipated energy of UHPC under the strain rate range of 6.8–7.2 s−1 increases by 30.9 % and 124.2 %, respectively. However, an opposite trend occurs with the dynamic splitting properties of UHPC decreasing with elevated temperatures of 400–800 °C, and accordingly the dynamic increase factor at 800 °C is only 61.8−73.7 % of that at room temperature. The synergistic effect of RS and PP fibre on the impact resistance of UHPC at elevated temperatures can be explained by: (i) the enhanced pore connectivity by PP fibres prevents explosive spalling of UHPC at elevated temperatures; (ii) the bridging and pull-out effects of RS fibres improve residual dynamic properties of UHPC after high-temperature exposure.