Deterioration behavior and model of alkali-activated fly ash-slag concrete under freeze–thaw cycles

Concrete components in highways and bridges are susceptible to freeze–thaw deterioration in cold regions, compromising their service safety. Alkali-activated fly ash-slag concrete (AAFSC), which fully replaces Portland cement with industrial by-products, offers promising environmental and application benefits. However, research on its freeze–thaw damage remains limited, hindering its use in cold-region infrastructure. This study presents a systematic experimental and theoretical investigation into the freeze–thaw deterioration of AAFSC. For the first time, the damage process is described within the Kachanov–Rabotnov evolution framework, establishing an exponential damage model with well-defined physical boundary conditions—extending continuum damage mechanics to freeze–thaw action in concrete. The model quantitatively captures damage progression in AAFSC and demonstrates broad applicability across various concrete types reported in the literature. This work provides important guidance for predicting the freeze–thaw durability of AAFSC-based transportation infrastructure components in cold regions.