Freeze–thaw performance of self-compacting concrete with GGBFS, fly ash and limestone powder: linking strength loss to air-void parameters

), and spacing factor (L). Selected mixtures were examined by SEM/EDS and complemented by a limited quantitative SEM texture assessment at fixed magnification to support microstructural interpretation. Statistical analysis (two-way ANOVA and Tukey HSD) and regression-based relationships were used to strengthen the comparison. The results show that FA primarily improved flowability, reaching a slump flow of 740 mm at 30% replacement, whereas GGBFS provided the most favorable balance between late-age mechanical performance and freeze-thaw resistance, achieving 69 MPa compressive strength at 90 days and only 0.2% mass loss and 1.0% strength loss after F150 at 30% replacement. LM contributed to stabilizing the protective air-void network, while the lowest spacing factor (L = 0.11 mm) was observed for GGBFS30 and LM30. Importantly, freeze-thaw strength loss was more strongly associated with spacing factor L than with total air content, highlighting void spacing as a practical durability-oriented predictor for SCC incorporating SCMs. Overall, the findings support clinker reduction strategies while maintaining durable SCC performance.