Abstract: To investigate the impact of silica fume on the microstructure and salt frost resistance of recycled concrete in the Hetao saline-alkali area of Inner Mongolia, we prepared recycled concrete (RAC) with varying silica fume content for cyclic salt freeze-thaw tests, chloride ion permeation resistance tests, and scanning electron microscopy (SEM) analysis. Our findings reveal that the microstructure of RAC becomes denser due to the influence of spherical silica fume particles. This leads to an initial decrease followed by an increase in the mass loss rate, cubic compressive strength loss rate, and chloride ion mobility coefficient of RAC with rising silica fume content. However, the relative dynamic elastic modulus of RAC with 10% and 15% silica fume content shows minimal disparity after salt-frost cycles. Overall, the optimal salt-frost resistance is achieved when silica fume content is at 10%. In the RC10 group, the mass loss rate, cube compressive strength loss rate, and chloride ion mobility coefficient are only 54.3%, 50.3%, and 49.81% of those of RC0 group respectively after 90 salt-frost cycles. Additionally, we developed a freeze-thaw damage model accounting for silica fume content and freeze-thaw cycle number to predict the service lifespan of RAC in saline-alkali regions of Inner Mongolia.

Key words: recycled concrete, silica fume, salt freezing cycle, microstructure, service life prediction