Freeze-thaw cycle and strain rate effect on energy dissipation mechanism and synergistic deterioration characterization of LFMOC

Concrete in high-altitude cold regions is prone to shortened service life due to external freeze-thaw cycling, particularly for the novel green building material limestone powder-magnesium oxychloride concrete (LFMOC), whose durability in freeze-thaw environments urgently requires resolution. For LFMOC specimens, freeze-thaw cycle tests at −20°C to 20°C for 40 cycles were conducted, combined with macro-mechanical performance testing (dynamic elastic modulus, dynamic compressive strength, etc.) and microstructural characterization (XRD phase analysis, SEM morphological observation, NMR pore analysis), to establish a freeze-thaw damage structural strength model. A three-dimensional mesoscale model considering the evolution of interfacial transition zone (ITZ) thickness was constructed using LS-DYNA to simulate the dynamic mechanical response of LFMOC under different freeze-thaw cycle numbers. Results show that freeze-thaw cycles cause LFMOC to undergo appearance deterioration, significant reduction in relative dynamic elastic modulus, increased total porosity, and an increased proportion of micropores/mesopores. The stiffness difference between aggregates and paste is the key factor for ITZ freeze-thaw deterioration. The strain rate effect is unaffected by the number of freeze-thaw cycles; the energy dissipation density of the specimen is positively correlated with the strain rate and negatively correlated with the number of freeze-thaw cycles. Mortar and ITZ are the main energy absorbers, with peak internal energy decreasing as the number of freeze-thaw cycles increases. ITZ thickening promotes specimen damage accumulation and connectivity, accelerating the decay of dynamic compressive strength. The established freeze-thaw damage structural strength model accurately describes the nonlinear relationship between the overall strength of LFMOC and the number of freeze-thaw cycles. The research conclusions provide a reference for the durability design of LFMOC in high-altitude cold regions.