Experimental Study on Damage Evolution Model of Freeze–Thaw Mortar under Different Strain Rates

In order to study the damage evolution characteristics of freeze–thaw mortar materials under impact load, this paper uses cement silica powder mortar to prepare cylindrical samples, and performs freeze–thaw cycle tests on mortar samples under water saturation based on a programmable constant temperature and humidity test chamber. Combined with the analysis of scanning electron microscope and longitudinal wave velocity test results, this paper reveals the influence of freeze–thaw cycles on the deterioration of mortar mechanical parameters, performs uniaxial compression and impact tests under different strain rates on mortar samples that have undergone different freeze–thaw cycles, reveals the damage and deterioration mechanism of mortar materials under freeze–thaw cycles and impact loads, and establishes the dynamics of freeze–thaw mortars under the different strain rates compressive strength degradation prediction model. The results show that the effect of freeze–thaw cycles will aggravate the damage of mortar, continuously deteriorating its mechanical parameters, and with the constant decrease of static compressive strength and elastic modulus. The number of freeze–thaw cycles and strain rate jointly determine the dynamic compressive strength of mortar when one of the factors is constant; the dynamic compressive strength of mortar decreases exponentially with the number of freeze–thaw cycles, and linearly increases with the strain rate. The dynamic strength factor (DIF = dynamic compressive strength/static compressive strength) of mortar is affected by the number of freeze–thaw cycles and strain rate, and the latter is more significant. Finally, from the perspective of the reduction rate of the dynamic and static compressive strength of the mortar under the action of different freeze–thaw cycles, a solution for the Dongfeng Tunnel project to deal with the influence of the freeze–thaw cycle is proposed. The research results can provide theoretical reference for more engineering construction in cold regions.