Experimental Study On The Impact Compression Performance Of Concrete Under Freeze-thaw Cycle

As a commonly used building material,concrete is often in the construction environment of freezing and thawing cycles in the construction of cold areas.In the development of deep underground engineering such as tunnels and mines,the geostress of different strength grades will be generated inside the rock mass with different depths,and the concrete as a lining material will be subjected to complex confining pressure.In addition,the impact load generated by blasting,the dynamic water pressure received by the dam,and traffic load are also the dynamic loads that concrete often faces.For a long time,scholars have mainly studied the static properties of concrete,but few have studied the dynamic properties of concrete at extreme temperatures,especially under complex confining pressures.Therefore,considering the effects of freeze-thaw cycles,confining pressure and high strain rate,the study of the mechanical properties of concrete can provide a theoretical basis for the construction of cold regions.In this paper,C35 concrete is taken as the research object,and the SHPB test system is used to systematically develop the dynamic compression test of concrete specimens subjected to different freeze-thaw cycles.By comparing and analyzing the stress-strain curve,the relationship between peak stress,peak strain and strain rate and the number of freeze-thaw cycles was analyzed.Finally,the crushing and screening test was carried out to analyze the fractal dimension of the fractured block,revealing the uniaxial impact load.The fracture law of concrete specimens,and from the energy point of view,the relationship between the macroscopic fracture state of concrete and energy absorption is analyzed.The main research contents and conclusions of the full text are as follows:(1)The concrete specimens were subjected to a freeze-thaw cycle test to observe and record the crack development and basic physical quantity changes of the concrete specimens after various freeze-thaw cycles.Studies have shown that during the freeze-thaw cycle,as the number of freeze-thaw cycles increases,the mass loss rate,volume growth rate,and porosity of the specimens have been increasing.After 50 cycles of freezing and thawing,the specimens were damaged more seriously.(2)The impact compression tests under uniaxial and active confining pressures and three strain rates were carried out on specimens after freeze-thaw cycles.The stress-strain curves were analyzed and compared.The effects of freeze-thaw cycles,loading rates and confining pressures on the impact compression properties were revealed.The results show that the peak stress has obvious strain rate strengthening effect,and the freeze-thaw cycle has a deteriorating effect on the mechanical properties of concrete.With the increase of freeze-thaw cycles,the peak stress decreases;confining pressure can improve the mechanical properties of specimens,and the damage degree of specimens decreases with the same loading rate and freeze-thaw cycles.(3)Screening tests were carried out on crushed blocks after uniaxial impact,The fractal dimension of fractured blocks is analyzed,and the rule between fractal dimension and freezethaw cycles is revealed,The results show that the larger the fractal dimension is,the greater the degree of fragmentation is.The energy dissipation law of concrete under uniaxial impact loading is studied from the point of view of energy.It shows that the absorption energy increases with the increase of loading rate and decreases with the increase of freeze-thaw cycles.