In cold regions, freeze-thaw (F-T) cycles pose a severe challenge to the long-term durability and structural reliability of foamed concrete (FC). In response, this study proposes a comprehensive multi-level evaluation system integrating macro and micro scales, aiming to thoroughly investigate the decline mechanisms of compressive strength of FC under F-T cycles. Through macroscopic experiments, the extent of mass loss and strength degradation has been quantified. The evolution of internal damage, progression of surface displacements, and changes in pore structures have been effectively tracked and captured by using non-contact techniques. The findings reveal that after F-T cycles, the mass loss rate and strength loss rate of FC can be up to 6.62 % and 37.61 %, respectively. There is a marked acceleration in the expansion rate of non-stable internal cracks; peak displacements show significant growth, and the failure mode changed from brittle to brittle-ductile. Furthermore, the porosity and the proportion of irregular pore shapes have increased by 25.84 % and 18.39 %, respectively. Additionally, a discrete element model incorporating irregular pore characteristics has been established, elucidating the profound impact of F-T cycles from a microscopic physical perspective. Specifically, the weakening and the increased number of fracture events of the contact forces between cement particles lead to the deterioration of FC's strength.
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