Experimental Study On Damage Characteristics Of Frozen Soil-concrete Interface Under Freeze-thaw Cycles

Alternating temperature cycles of small day and night cycles and large seasonal cycles in cold areas induce loss of shear strength at the frozen soil-concrete interface and deterioration of adhesion,which in turn causes building structural engineering disasters.In this paper,the following research is conducted to clarify the degradation mechanism of frozen soil-concrete interface under freeze-thaw cycles:(1)Carry out identification of microscopic test index information of interfacial adhesion degradation with different freeze-thaw parameters and soil characteristics(water content),and analyze the microstructure degradation characteristics at the interface between soil and concrete during the freeze-thaw process;(2)Carry out the shear test of the frozen soil-concrete interface to explore the law of shear strength loss at the interface of frozen soil and concrete under freeze-thaw cycles;(3)Based on the macro and micro test results,the internal correlation between the macro shear mechanical properties of the interface and the microstructure deterioration of the interface induced by freeze-thaw is revealed,and the mechanism of damage and degradation of the frozen soil-concrete interface under the freeze-thaw cycle is revealed,which is the stability of the construction in cold regions Provide scientific basis and theoretical basis.According to the degradation of the microstructure at the frozen soil-concrete interface under freeze-thaw cycles,a microscopic qualitative analysis of the interface was carried out and found that the integrity between the soil particle and the concrete is destroyed with the increase of the number of freeze-thaw cycles,the soil particle aggregates at the interface decrease,the pores between the soil particles increase significantly,the pore size increases,and the connection form between particles gradually deteriorated from face-to-face contact to point-to-face and point-to-point contact.Further microscopic quantitative analysis shows that the integrity degree of the interface decreases with the number of freeze-th aw cycles.In the initial state,the pore size distribution at the interface is characterized by more micro(small)pore distribution,less medium pore distribution,and almost no large pores.As the number of freeze-thaw cycles increases,the proportion of micropores at the interface gradually decreases,and the small pores and mesopores gradually increase.Among them,large pores appear at the interface under the condition of high water content.According to the strength loss of frozen soil-concrete interface under freeze-thaw cycles,a test of the degradation law of frozen soil-concrete interface under different freeze-thaw parameters and soil characteristics(water content)was carried out to the law of shear strength loss at the interface of frozen soil and concrete under freeze-thaw cycles.The study found that the interface strength gradually decreases with the increase of the number of freeze-thaw cycles,and the loss of interface strength mainly occurs in 0-3 freeze-thaw cycles;the cohesive strength of the interface strength index changes more obviously with the increase of the number of freeze-thaw cycles,and the decline law It is roughly the same as the law of interface shear strength.The internal friction angle of the interface is relatively stable during the entire freeze-thaw cycle and fluctuates within a certain range.According to the degradation mechanism of frozen soil-concrete interaction under freeze-thaw cycles,the gray correlation degree between the frozen soil-concrete interface shear strength index(cohesive force,internal friction angle)and its micro structure parameters(interface integrity,fractal dimension,average pore size)during the freeze-thaw cycle was evaluated based on the gray correlation method.It is found that the cohesion force is positively correlated with the integrity of the interface,that is,the higher the integrity of the interface after freezing and thawing,the greater the cohesive force,and this effect is significant.In addition,it is found that the factors such as the average pore size of the interface and the fractal dimension also have a certain correlation with the interface cohesion,but the degree of correlation is relatively small.The internal friction angle is less correlated with various microstructure parameters during repeated freeze-thaw cycles,and the internal friction angle fluctuates within a certain range.Through the gray correlation between the interface shear strength index and the micro structure parameters and the Mohr-Coulomb strength criterion,the degradation mechanism of the frozen soil-concrete interface under the freeze-thaw cycle is further explained.It can be seen that the decrease in the integrity of the soil and concrete under the freeze-thaw cycle leads to the decrease in the cohesion force of interface,which is the main reason for the degradation of the strength of the frozen soil-concrete interface.