Characteristics and Microstructure of Self-Compacting Lightweight Aggregate Concrete with Manufactured Sand Under Freeze–Thaw Environment

To promote the sustainable application of self-compacting lightweight aggregate concrete (SCLC) in cold regions and mitigate river sand shortages by substitution, this study investigates the impact of manufactured sand (MS) content on its freeze–thaw resistance. However, the micro-damage mechanism and a reliable damage model for MS-SCLC under freeze–thaw conditions remain lacking. Five groups of SCLC with varied manufactured sand content (0%, 30%, 60%, 80%, and 100%) were prepared. This study examined the behavior of SCLC under freeze–thaw conditions, with a focus on its frost durability and microstructural evolution. Furthermore, an SCLC freeze–thaw damage model for the manufactured sand content was established based on the Weibull distribution. Increasing the manufactured sand content conferred benefits on the compressive strength loss rate and relative dynamic elastic modulus; however, it had adverse consequences for the apparent morphology and mass loss rate. In conclusion, the SCLC mixture containing 60% manufactured sand displayed superior frost resistance, demonstrating a mass loss rate of 4.79%, a relative dynamic elastic modulus of 0.624, and a compressive strength loss rate of 38.46% after 200 freeze–thaw cycles. The identified optimal MS content (60%) and the established Weibull-based damage model provide crucial quantitative guidance for designing durable MS-SCLC structures in freeze–thaw environments.