<p>To address the challenge of enhancing the freeze-thaw resistance and mechanical properties of lightweight concrete blocks (LCB) in frigid environments, the effects of fly ash (FA) (25%–40%) and hydrogen peroxide (H₂O₂) (2%–8%) on the compressive strength and freeze-thaw resistance of LCB after freeze-thaw cycles were investigated. A quantitative relationship model was established through regression analysis, linking H₂O₂/FA content, cycle numbers of freeze-thaw, thermal conductivity, and freeze-thaw damage parameters (mass loss rate, strength loss rate). Additionally, macroscopic and microscopic analyses were conducted to determine the degree of damage after freeze-thaw cycles. Finally, a mechanistic analysis was performed to understand the synergistic enhancement of LCB’s freeze-thaw resistance and freeze-thaw damage mechanisms by FA and H₂O₂. The experimental results show that under the conditions of 35% FA and 4% H₂O₂, the volcanic ash activity of FA produced dense C-S-H gel, achieving a compressive strength of 8.62&#xa0;MPa, which is 11.08% higher than the control group (25% FA, 4% H₂O₂). Freeze-thaw tests indicate that LCB maintains structural integrity after 50 cycles, the structural integrity of LCB remained good, the mass loss rate was less than 5%, and the strength loss rate was less than 25%. The fitting equation shows that high levels of H₂O₂ and FA can inhibit the increase in thermal conductivity caused by freeze-thaw cycles and reduce the degradation rate of strength and mass due to freeze-thaw cycles. Finally, the analysis of the freeze-thaw damage mechanism reveals that the synergistic effect of H₂O₂ and FA makes the pores more complex, causing water within the pores to expand upon freezing. Through the stress dissipation effect of multi-level pore structures, significantly reduces expansion stress. This provides a theoretical foundation and technical approach for developing high-performance building insulation materials for cold regions.</p> Graphical Abstract <p></p>