Mechanism of concrete damage under the coupled action of freeze-thaw cycle and low-stress impact fatigue load：From pore structure to energy dissipation.

The interaction mechanism behind concrete damage induced by the combined effects of freeze-thaw cycles and fatigue load (FTF) remains insufficiently understood. This study aims to shed light on this mechanism by employing three sets of specimens, each subjected to different conditions: freeze-thaw cycles alone, low-stress impact fatigue (LIF) load alone, and FTF coupled action. Macro performance and microstructural changes of these specimens were measured after each testing round to analyze the evolution of concrete damage. Additionally, the influence of load duration on the damage under the coupled action was also explored. Results indicated that under FTF action, when LIF loading is applied for a short duration, freeze-thaw cycles play a dominant role in concrete damage, while the influence of LIF loading is minimal. However, when LIF loading is sustained for an extended period coupled with freeze-thaw cycles, it can accelerate concrete degradation. This can be attributed to the accumulation of micro-cracks during longer loading duration, eventually manifesting as visible cracks. These cracks link adjacent pores and increase the number of interconnected pores. This, coupled with freeze-thaw damage increasing the probability of crack forming, results in accelerated deterioration of concrete. The mechanism underlying this concrete deterioration was also analyzed from an energy dissipation prospect. • A setup was designed to simultaneously implement low-stress impact fatigue and freeze-thaw cycle. • The mechanisms of concrete damage under FTF action were discussed from the perspectives of pore structure and energy dissipation. • the influence of load duration on the concrete damage under the coupled action was explored. • The evolution of macro performance and microstructure properties were explored. [ABSTRACT FROM AUTHOR]