# Study of Damage Mechanism and Evolution Model of Concrete under Freeze-Thaw Cycles
###### Abstract  
Researching the mechanical characteristics of concrete subjected to the freeze-thaw cycle is crucial for building engineering in cold climates. As a result, uniaxial compression tests were performed on concrete samples exposed to various freeze-thaw (F-T) cycles, and the measurements of the pore size distribution, porosity, and P-wave velocity of the saturated concrete samples were obtained, both before and after being exposed to the F-T cycles. Concrete's F-T damage mechanism and damage evolution model were thoroughly examined. Using rock structure and moisture analysis test equipment to observe the T\({}_{2}\) spectrum, the results showed that the F-T cycles can cause the internal structure of the samples to deteriorate. Porosity and F-T cycles have a positive correlation, although P-wave velocity has a negative correlation with the F-T cycles. As the F-T cycles increased, the specimens' peak strength and elastic modulus steadily declined, while the peak strain clearly exhibited an increasing trend. A microscopic F-T damage model that takes into account the pore size distribution was developed, based on the relative changes in the pore structure distribution (PSD), before and after the F-T cycles. The concrete sample damage evolution law under various F-T cycles was examined using the following metrics: total energy, pore size distribution, static and dynamic elastic moduli, porosity, and P-wave velocity. Uniaxial compressive strength (UCS) and peak strain tests were used to evaluate the accuracy of the pore size distribution damage model, as well as that of five other widely used damage models. f 202420202416 August 2024202416 August 2024202416 August 2024202416 August 2024202416 June 2024202416 August 2024202416 June 2024202416 August 2024202416 June 2024202416 June 2024202416 June 202420  
deteriorate with time, causing the building's bearing capability to be lost. Building stability and safety are seriously threatened by the F-T cycle [12; 13; 14; 15; 16; 17; 18; 19; 20]. Thus, one of the key elements influencing the stability and longevity of engineering structures is the F-T resistance of the concrete material. Studying and precisely identifying the F-T damage process of concrete is crucial for cold climate resource utilization and structural engineering [21; 22; 23; 24; 25]. Figure 1 illustrates the typical instances of F-T damage to structural elements and concrete materials in engineering. In frigid climates, a large number of dams and other hydraulic structures have experienced significant F-T degradation prior to the completion of their planned service life [26; 27; 28; 29]. The interior pore structure of the concrete must be saturated with water infiltration for F-T degradation to occur, and the concrete must exist in a temperature environment that is subjected to both positive and negative change [30; 31]. Surface denudation and the internal loose cracking of concrete are caused by the free water of the solidified and hardened concrete being subjected to the alternating action of freezing (when the temperature is below the freezing point) and thawing (when the temperature is above the freezing point) when the temperature changes [32; 33; 34; 35]. Concrete's internal pore structure deteriorates due to the cold weather, causing the water within to remain in an alternating state of F-T cycles for extended periods of time. This ultimately results in irreversible F-T damage to the concrete's mechanical and physical properties [36; 37; 38]. The majority of researchers have conducted a significant number of theoretical investigations, as well as experimental work, to determine the impact of F-T cycles on the mechanical and physical characteristics of concrete materials [39; 40; 41; 42]. The five-damage models listed below serve as a basic summary of the findings of this theoretical analysis.