Investigation into the mechanical behavior of alkali-slag rubber aggregate concrete

This study designed 34 groups comprising 102 specimens to investigate the mechanical properties of alkali-activated slag rubber aggregate concrete (ASRAC). The effects of the replacement ratios of fine and coarse rubber aggregates, the water-to-binder ratio, and steel fiber content on the cube compressive strength and splitting tensile strength of the concrete were systematically investigated, and the underlying mechanisms were further elucidated through microstructural analysis. The results indicated that replacing natural aggregates with 100% rubber fine aggregate or 100% rubber coarse aggregate reduced ASRAC compressive strength by 71.9% and 83.3%, respectively, and reduced the splitting tensile strength by 52.5% and 70.9%. For specimens with 100% coarse rubber aggregate replacement, the water-to-binder ratio had no significant effect on the ASRAC compressive or splitting tensile strength. However, for specimens with 100% fine rubber aggregate replacement, increasing the water-to-binder ratio from 0.40 to 0.50 decreased the ASRAC compressive and splitting tensile strengths by 50.6% and 52.5%, respectively. Both the compressive strength and splitting tensile strength first increased and then decreased with increasing fiber content, reaching a peak at a fiber content of 2%. Microscopic analysis indicated that a low water-cement ratio combined with an appropriate steel fiber content significantly enhanced the micro-density of hydration products, whereas a high rubber content exacerbated pore and microcrack defects in the rubber-cement interfacial transition zone. XRD characterization confirmed that the core hydration mechanism in this system was C-(A)-S-H. These findings support the potential of ASRAC as a sustainable infrastructure material for pavements and protective, vibration-mitigating components.