Effects of Tuff Powder on the Macro-Performance and Microstructure of Self-Compacting Concrete under Freeze–Thaw Cycles

This study investigates the effects of tuff powder (TP) on the macroscopic performance and microstructural characteristics of self-compacting concrete (SCC) subjected to freeze–thaw cycles (FTCs). SCCs with 0%, 15%, and 30% TP replacement were assessed for compressive strength, splitting tensile strength, and freeze–thaw durability. Additionally, the micropore structure of SCC paste was analyzed using mercury intrusion porosimetry (MIP). The results indicate that increasing the TP replacement ratio leads to a reduction in compressive and splitting tensile strengths. However, the mass loss rate decreases, and the relative dynamic elastic modulus (RDEM) increases under the same FTCs with higher TP content. Furthermore, the proportion of harmful and multi-harmful pores in SCCs diminishes as TP content increases, suggesting that TP enhances the frost resistance and durability of SCCs. A damage model was employed to predict the evolution of mass loss rate and RDEM, demonstrating a high degree of accuracy in fitting experimental data. The predictive results confirm that TP incorporation significantly extends the service life of SCC, enhancing its durability in severe freeze–thaw regions.