Influence of CO2 in treating the recycled fine aggregate in concrete with polypropylene fibres: multiscale investigation on its mechanical, durability and structural properties

The Generation of construction wastes pose serious threat to environment seeking the possibility of recycling and reutilization as recycled aggregates. Various research involves utilizing coarser segments of recycled aggregates (RCA), treating it and using as substitutes for natural coarse aggregates (NCA) in the concrete. Nevertheless, due to its substandard performance, the investigation on utilizing finer fractions of recycled aggregates (RFA) has abridged compared to coarser fractions. This study intends to enhance the quality of RFA through carbonation technique and investigate the impact of polypropylene (PP) fibre on concrete properties with carbonated recycled fine aggregate (CRFA). The influence of PP and CRFA at different replacement percentages on the mechanical, durability and structural properties of the concrete were examined. The results inferred that the physical characteristics of CRFA were improved compared to RFA and the micro-structure of CRFA was enhanced compared to RFA. The optimum dosage of RFA was 25% beyond which it lowers the strength of RAC. The strengths (compression, tension and flexure) of the carbonated recycled aggregate concrete (CRAC) were enhanced in the range of 10.94-25.16% and fibre-reinforced carbonated recycled aggregate concrete (FRCRAC) was enhanced in the range of 13.79-31% than RAC. The absorption of water by CRAC and FRCRAC was lowered by 21.25% and 33.11% and the carbonation of CRAC and FRCRAC was lowered by 25.01% and 31.90%. The concrete mixtures with CRFA and PP fibre show 38.45% lesser shrinkage compared to RAC. The porosity of RFA was lowered through carbonation treatment which intensifies the interfacial transition zone (ITZ) of RAC and enhances the concrete properties. The load-deflection characteristics of RAC beams show 44.96% higher load-carrying capacity and 14.72% lesser deflection characteristics in FRCRAC and CRAC than in RAC.