Effects of crumb rubber particles on the evolution of pore structure in steam-cured concrete under freeze-thaw cycles

Freeze-thaw damage to precast steam-cured concrete components in low-temperature environments has always been an influencing factor in their service life. In this paper, crumb rubber particles were mixed into steam-cured concrete to strengthen its freeze-thaw resistance, and the effect of incorporating crumb rubber particles on the mechanical loss and dynamic modulus of steam-cured concrete is assessed using rapid freeze-thaw testing. Additionally, the time-varying effects of crumb rubber particles on the pore structure evolution of steam-cured concrete during the freeze-thaw cycles were investigated using two non-destructive testing techniques: lowfield nuclear magnetic resonance (LF-NMR) and X-ray micro-computed tomography (MicroCT). The results suggest that incorporating crumb rubber particles can enhance and refine the capillary pores in concrete while efficiently mitigating the expansion of capillaries due to freezethaw cycles. Incorporating an appropriate amount of crumb rubber particles reduces the initial porosity growth rate in steam-cured concrete during the preliminary stages of freeze-thaw cycles and maintains stability in subsequent stages. Furthermore, the internal micron-sized pores of steam-cured rubber concrete show a uniform distribution after freeze-thaw cycles, with significantly reduced pore connectivity. This study demonstrates that crumb rubber particles can significantly enhance the pore structure of steam-cured concrete undergoing freeze-thaw cycles. A strength prediction formula for steam-cured crumb rubber concrete experiencing freeze-thaw cycles is proposed, considering the mixing amount of crumb rubber particles and the amount of freeze-thaw cycles. When the rubber content is 30.6 kg/m3, the rubber admixture is highly effective in mitigating the decline of concrete strength caused by freeze-thaw conditions.