Low-temperature performance of alkali-activated slag concrete with fine and coarse waste rubber aggregates

To improve the frost resistance of concrete in cold regions, rubber aggregate alkali-activated slag concrete (RA-AASC) was prepared by incorporating waste rubber aggregates into an alkali-activated slag matrix. Six mixtures with different fine and coarse rubber aggregate replacement ratios were tested for cubic compressive strength (CCS) and splitting tensile strength after exposure to low temperatures (0°C, −30°C and −60°C) and scanning electron microscopy (SEM) was used to examine their microstructure. The results showed that the mechanical properties of the RA-AASC responded non-linearly to decreasing temperature: strengths generally increased first and then decreased. The mixture with 50% fine rubber aggregate exhibited the best overall performance, whereas 100% fine aggregate replacement with rubber particles markedly reduced the CCS of the RA-AASC. The incorporation of coarse rubber aggregate produced only marginal strength improvement and the combined use of coarse and fine rubber aggregates led to significant deterioration in mechanical properties because of synergistic interfacial defects. SEM observations indicated that matrix densification induced by low-temperature exposure partially compensated for the weak rubber–matrix bonding, but excessive rubber incorporation increased interfacial discontinuities and microstructural damage. The findings of this work clarify the coupled effects of rubber particle size, replacement ratio and low temperature on RA-AASC performance.