Study On Tensile-compressive Dynamic Characteristics And Failure Criterion Of Freezing-thawing Deteriorated Concrete Under Biaxial Dynamic Compression

With the development of social economy and the needs of the people.Our country pays more and more attention to the construction of water conservancy projects.In recent years,a large number of water conservancy projects have been constructed in China.These projects will inevitably suffer from the erosion of the natural environment and natural disasters during their service.In high latitudes,many buildings and structures will be damaged by freezing and thawing because of the influence of temperature.According to the current research results,the research on the mechanical properties of concrete under special environment needs to be further deepened.Considering the effects of freeze-thaw cracking degree,strain rate and lateral pressure,Static(strain rate is 10^-5/s)splitting-pulling tests were carried out on mixtures with different freeze-thaw cycles（0 times,10 times,20 times,30 times and 40 times）under different lateral pressures（0 MPa,2 MPa,4 MPa,6 MPa,8 MPa）,and the splitting tests of normal concrete with different strain rates(10^-5/s,5?10^-5/s,10^-4/s,5?10^-4/s,10^-3/s)under different lateral pressures（0 MPa,2 MPa,4 MPa,6 MPa,8 MPa）were carried out.And acoustic emission technology was used synchronously to monitor the change of internal damage of concrete in the course of test.The conclusions are as follows.1)The relationship between concrete mass loss rate and freeze-thaw times is quadratic curve;During loading,the failure rate of coarse aggregate decreases with the increase of freeze-thaw times and increases with the increase of lateral pressure;The splitting peak stress decreases with the increase of number of freeze-thaw cycle times,and increases with the increase of lateral pressure;The peak strain increases with the increase of freeze-thaw times and lateral pressure.2)The ultimate splitting peak stress level of normal concrete increases linearly with the increase of strain rate and lateral pressure;Peak strain decreases with the increase of strain rate and increases with the increase of lateral pressure.3)Compared with other scholars’research results,the axial tension crack extends from the inside of the specimen to the surface of the specimen,and the splitting crack occurs at the contact point between the splitting pad and the specimen,and extends to the inside of the specimen.When the lateral pressure is small,it will increase the peak stress,while when the lateral pressure is large,it will weaken the peak stress.4)Damage development of concrete under uniaxial loading at different strain rates without freeze-thaw has experienced three stages:non-damage,damage accumulation and damage destruction.Damage development under normal biaxial loading and uniaxial and biaxial loading after freeze-thaw deterioration has experienced four stages:non-damage,damage accumulation before peak stress,damage accumulation after peak stress and damage destruction.5)Based on the test results and the static failure criterion,the tension-compression failure criterion of concrete considering the effects of freeze-thaw deterioration and strain rate was established in the principal stress space and octahedron stress space.