Experimental study on the compressive and flexural behaviour of recycled aggregate concrete modified with silica fume and fibres

The use of recycled concrete aggregates in structural concrete is a sustainable solution to reduce the extraction of natural resources and the detrimental impacts of waste concrete to the environment. The present study aimed to assess the compressive and flexural behaviour of recycled aggregate concrete (RAC) and normal concrete (NC) modified with silica fume and steel fibres or polypropylene fibres (PPFs). The coupling effects of the silica fume and fibres on the compressive strength, fracture toughness, modulus of elasticity, and failure mode of the RAC and NC were analysed following a series of axial compression and three-point bending tests. The results show that the thick steel fibre exhibited worse interfacial bonding with the cement paste than the PPF, but the addition of silica fume enhanced these interfacial bonds, resulting in an improvement in the compressive and flexural behaviour of the fibre-reinforced RAC. Additionally, the coupling effect of silica fume and steel fibre was better than that of the silica fume and PPF. Based on the synthetical consideration of the performance improvement and economic cost, 10% silica fume content by the equal quantity substitution of cement is optimal for the compressive and flexural strength of steel-fibre reinforced RAC.