Incorporation of rubber particles to mitigate freeze–thaw–induced flexural degradation in steam-cured concrete

The structural safety of steam-cured concrete track slabs in Northeast China is severely compromised by the combined long-term effects of bending loads and freeze–thaw (F–T) cycles. This study investigates the use of crumb rubber to mitigate F–T–induced flexural degradation in steam-cured concrete. Digital image correlation (DIC) and acoustic emission (AE) techniques are employed to characterize the post–F–T flexural behavior. This integrated approach is aimed at simultaneously revealing the evolution of surface and internal cracks during the failure process of the concrete specimens. Results demonstrate that rubber particles improve flexural performance, modify the stress–strain relationship, and control crack propagation, thereby extending the service life. Finite-element simulations reveal the mechanisms by which rubber mitigates F–T damage. A significant enhancement in F–T resistance is observed with crumb-rubber incorporation. During flexural failure, rubber-modified specimens exhibit delayed micro-crack initiation, extended macro-crack propagation, and retained 60%–80% strength after 300 F–T cycles, with acoustic emission hits increasing by 50%–120%. Simulations indicate that after 150 cycles, the stiffness degradation of rubber-modified concrete is 30%–40% lower than that of plain concrete, showing a strong linear correlation (R² > 0.9) between stiffness degradation and porosity at rubber contents of 25–50 kg/m³.