Macro-micro mechanical property evolution of manufactured sand concrete incorporating mineral admixtures under salt-freeze-thaw cycles

Chloride-based snow-melting agents are commonly used on urban roads during winter to ensure traffic safety and maintain transportation efficiency. Nevertheless, these agents often negatively impact surrounding infrastructure, such as causing surface spalling of concrete, which compromises its functional performance. This study focused on the scientific utilization of snow-melting agents to minimize damage to manufactured sand concrete (MSC). The mechanical properties of MSC were evaluated under varying snow-melting salt solution concentrations and freeze-thaw (f-t) cycles. The differences in its macro- and micro- mechanical properties were clarified using microstructural analysis and the interaction mechanisms of mineral admixtures. The results indicated that MSC damage under salt-freeze-thaw (s-f-t) cycles did not intensify with increasing concentration of snow-melting salt solutions, with the most severe damage observed at a concentration of 5%. Microhardness measurements revealed that reducing the width of interfacial transition zone (ITZ) and lowering the contents of CH and AFt enhanced MSC strength. Macro mineral admixture ratios and micro–X-Ray Diffraction (XRD) tests demonstrated that appropriately increasing the silica fume (SF) dosage and reducing the steel slag (SS) dosage effectively improved the compressive strength of MSC after s-f-t cycles; however, the SS dosage should not exceed 42.5%. Both the fractal dimension and compressive strength decreased as the number of s-f-t cycles increased, exhibiting a positive correlation with an R² value of 0.8988. Semi-quantitative analyses using Energy Dispersive Spectroscopy (EDS) confirmed that s-f-t cycling increased chloride (Cl) element content within MSC, and on average, the Cl element content doubled for every additional five s-f-t cycles. This study offers valuable insights for enhancing the secondary utilization rate of solid waste resources, promoting MSC application in cold-region projects, and rationalizing the quantity of snow-melting salts to be dispersed. • The higher the concentration of snow-melting salt solution, the lower the effect on the compressive strength of MSC. • Reducing the content of calcium hydroxide and ettringite in the ITZ or decreasing the width of the ITZ could effectively enhance the microhardness of MSC. • As the number of s-f-t cycles decreased, fractal dimension was positively correlated with compressive strength, with R 2 = 0.8988. • Higher active SF promoted secondary hydration reactions and reduced Friedel's salt (Fs) generation from both physical and chemical aspects.