Engineering and microstructural assessment of fibre-reinforced self-compacting concrete containing recycled coarse aggregate

The use of recycled concrete aggregates from different sources on structural concrete is a sustainable solution to minimize the extraction of natural mineral resources and the detrimental impacts of the concrete industry to the environment. The present study aimed to assess the impact of partial replacement of recycled coarse aggregate (RCA), steel (ST) and polypropylene (PP) fibres on mechanical, durability and microstructural properties of self-compacting concrete (SCC). Compressive strength, splitting tensile strength, water absorption and chloride ion penetration of the hardened composites were investigated. The microstructure and interfacial transition zone (ITZ) at the interfaces of aggregate/cement paste and fibre/cement paste of SCCs were investigated using scanning electron microscope (SEM) technique. The experimental results indicated that the addition of fibres in SCC could slightly improve the compressive strength and the resistance to water absorption. Significant improvement in splitting tensile strength was observed in SCC with increasing fibre contents, particularly when both ST and PP fibres were used. The permeability of SCC containing RCA increased with the increase of fibres. Though the strength of SCC reduced with the presence of RCA, the strengths attained were still suitable for structural applications. The SEM results showed that the crack width occurred at fibre-paste interface was smaller when compared to that at aggregate-cement interface, and the microstructure of cement paste around the fibres appeared more compact. In general, SCC mixes made of 20% RCA containing either 1% ST or 1% PP fibres, or a combination of 0.75% ST and 0.25% PP fibres were recommended regarding to the economic efficiency and hardened properties. The potential replacement of such recycled construction and demolition waste due to the technical, economic and environmental improvements it provides, would assist to the sustainability of the construction industry.