Freeze–Thaw Performance Degradation and Damage Model of Composite Concrete with Multi-Byproduct Synergy and Optimized Machine-Made/Tailings Sand

An investigation was conducted to explore the freeze–thaw resistance of 60–90 MPa high-strength concrete blended with multiple industrial byproducts (limestone powder, fly ash, etc.) and mixed sand (machine-made/tailings sand), aiming to clarify freeze–thaw degradation mechanisms and build reliable damage prediction models. Three water-binder (w/b) ratios (0.30, 0.25, 0.20) and 15 mix proportions were designed, with 30–45% cement replaced by mineral admixtures and 90–100% natural sand by mixed sand. Results show lower w/b ratios improve resistance: the 0.20 ratio yields merely 0.06% mass loss and 96% relative dynamic elastic modulus retention after 400 cycles. Optimized silica fume and limestone powder refine pore structures; fly ash-slag synergy boosts durability via secondary hydration under specific dosage ratios. A 7:3 machine-made/tailings sand mix shows better frost resistance due to improved particle packing and interfacial transition zones. Three damage models were established, with Model III demonstrating high accuracy. This work’s novelty lies in multi-byproduct synergy and multi-factor models, supporting green concrete use in cold regions.