Explore methods to enhance the properties of RAC through the addition of supplementary cementitious materials (e.g., fly ash, silica fume) and advanced mixing techniques.

Abstract

The elevated porosity of recycled coarse aggregate renders recycled aggregate concrete (RAC) more susceptible to freeze-thaw (FT) damage and chemical degradation, significantly hindering the industrial use of RAC in civil engineering. This research reports an experimental investigation into the synergistic effects of freeze-thaw damage and sulphate assault on the
mechanical properties of high-performance recycled aggregate concrete. The impact of combined damage on the mass, solution-filled pore volume, dynamic elastic modulus, compressive strength, splitting tensile strength, and fracture energy of recycled aggregate concrete (RAC) was examined. The results indicated that water-exposed freeze-thaw cycles lead
to greater deterioration in mass loss, elastic modulus, and compressive strength, whereas sulphate-exposed freeze-thaw cycles exhibit more pronounced degradation in splitting tensile strength and fracture energy. Furthermore, the decline in splitting tensile strength is more pronounced than that in compressive strength. The peak losses in compressive and splitting
tensile strength were 28.7% and 35%, respectively. The fracture energy exhibited an upward trend until 60 FT cycles, subsequently declining to 180 FT cycles. The fracture energy demonstrates a maximum increase of around 45% and 39% for samples exposed to water and sulphate, respectively, after undergoing 60 freeze-thaw cycles. The examination of failure modes in coarse aggregate has demonstrated that FT damage leads to a substantial decline in the adhesive strength of mortar. Following 180 FT cycles, the area percentage of pulled-out failure rose from 7.3% to over 17.3%