Influence of micro basalt and recycled macro polypropylene hybrid fibre on physical and mechanical properties of recycled aggregate concrete

With the increasing need to promote "circular-economy" based design in the construction industry, this study developed a new hybrid fibre-reinforced recycled aggregate concrete (FRRAC) with recycled macro polypropylene fibre (PF) and micro basalt fibre (BF). A ternary binder system has been adopted using supplementary cementious materials (SCMs), which are ground granulated blast furnace slag (GGBFS) and silica fume (SF) to reduce the cement content in the proposed composites with recycled coarse aggregate (RCA) replacement ratio at 50% and 100%. The fibre dosage amounts adopted in this study were 4, 6 and 8 kg/m3 for PF, and 4 and 6 kg/m3 for BF in the proposed hybrid combinations. The laboratory tests were undertaken to investigate and quantify the physical and mechanical properties, supported by scanning electron microscopic (SEM) and energy dispersive x-ray (EDX) studies at the microstructure level. The results indicated that the mechanical properties of recycled aggregate concrete (RAC) can be improved by adopting the proposed hybrid fibre combinations concerning strength and ductility. Increasing RCA % replacement led to a reduction in the quasi-static mechanical properties. The proposed hybrid fibre addition into RAC could achieve up to an improvement of 17.5% and 23% for split tensile and flexural strength, respectively. Based on overall performance, a hybrid fibre combination of 6 kg/m3 PF and 6 kg/m3 BF is recommended for adoption in RAC, aimed towards structural applications.