The impact of recycled concrete aggregates and steel fibres on the structural performance of concrete

Construction is the most significant contributor to infrastructure-related emissions. The cement and concrete sectors are improving their efforts to create low-carbon concrete by offering various blends of low-carbon ready mix concretes. Using recycled concrete aggregate from end-of-life concrete members or using construction and demolition waste as a replacement for natural aggregate offers a further reduction in carbon emissions. Researchers agree that the quality of recycled aggregate is inferior to natural aggregates, however, recycled aggregate concrete has comparable structural performance to natural aggregate concrete, although at a lower percentage. The reduced performance is thought to be the result of the increased porosity and reduced purity of the recycled aggregate, therefore, secondary materials are added to the concrete to enhance either the aggregate physical properties or the finished concrete mechanical properties. In accordance with this critical direction, this research focuses on the performance of composite reinforced concrete continuous beams made from concrete containing two distinct recycled concrete aggregates at 25%, 50% and 100% replacement ratios, and two different steel fibres at 0.5% and 1% dosage. Beforehand, a comprehensive study was carried out to examine the impact of the different recycled aggregates and 3D and 5D steel fibre reinforcements on the compressive and tensile behaviour of recycled aggregate concrete. A total of twenty-five different mixes were produced for this experiment. Further research was done on the morphology, density, and particle size distribution of the two recycled concrete aggregates. The tensile stress-crack opening (σ-w) relationship was examined for the two different grades recycled concrete aggregate composite concrete notched beams in terms of limit of proportionality, residual flexural tensile strength, ultimate load and energy absorption capacity. The results were compared to natural aggregate concrete test specimens. The structural experiment consisted of twelve, three-meterlong long simply supported two-span beams subjected to point loads at mid-span. The development of crack spacing and crack widths with increasing loads was measured and analysed. Further, energy absorption and moment redistribution were analysed with increasing load beyond ultimate load conditions. Page | iv Further investigations were conducted to examine the recyclability of concrete in the context of the Circular Economy. In this experiment, eleven distinct concrete products were recycled three times to investigate the effects of multiple recycling on morphology, density, particle size distribution, and compressive strength. Keywords: aggregate material properties, recycled concrete aggregate concrete mechanical properties, fibre-composite recycled concrete aggregate concrete flexural strength, continuous beam structural performance, aggregate multiple recycling.