Study Of Damage Evolution Of Concrete Under Different Temperature Gradients

With the rapid development of China’s infrastructure projects,there are more and more high-temperature diversion tunnel projects in China,such as Gonggeer hightemperature diversion tunnel,Bulunkou high-temperature diversion tunnel,Luogu hydropower station diversion tunnel,Qirehatar hydropower station diversion tunnel and other projects are high-temperature diversion tunnel projects.When the hightemperature diversion tunnel project is completed,the lining concrete in the tunnel encounters low-temperature cold water,and the temperature in the high-temperature state is reduced and a stable temperature gradient state is formed and the mechanical properties of the concrete are degraded.Therefore,it is necessary to study the damage evolution of concrete under different temperature gradients.In this thesis,the laboratory physical test and non-contact full-field strain measurement test of concrete under four temperature gradients and concrete under normal temperature are set up to study the macroscopic mechanical properties and strain variation of concrete under different temperature gradients.Finally,the discrete element model of concrete particles is established by discrete element method to simulate the mechanical loading test under temperature-stress coupling.According to the simulation results of particle discrete element model and laboratory physical test results,the mechanical properties and damage of concrete materials under temperature gradient are summarized from the microscopic point of view.The research results are as follows :(1)By exploring the heat conduction law of concrete materials in the process of temperature gradient formation and the mechanical test analysis after forming a stable temperature gradient,the mechanical properties and damage of concrete after temperature gradient are summarized.(2)The mechanical loading test of concrete materials under temperature gradient was carried out,and the mechanical properties and crack damage evolution law were summarized.The results show that with the increase of temperature gradient,the elastic modulus and peak stress decrease,while the peak strain increases,and the damage and deterioration of concrete are more serious.(3)The non-contact full-field strain measurement system is used to record the strain in real time during the mechanical loading test of concrete materials under temperature gradient,so as to reflect the reasons for the change of mechanical properties of concrete materials.The tensile strain component,compressive strain component and shear strain component of concrete specimens under temperature gradient increase with the increase of temperature gradient compared with the concrete specimens under normal temperature state,and change little at 40-4 °C,60-4 °C and 80-4 °C.Before reaching the peak strength,the strain component of concrete specimens increases continuously,and after reaching the peak strength,the strain component of concrete specimens increases rapidly.(4)Based on the particle flow discrete element method(PFC-2D),the numerical simulation of concrete specimens is carried out,and the thermal-mechanical coupling model is established to simulate the damage of concrete specimens under the action of temperature gradient.Compared with the laboratory physical test results,it is verified that due to the different expansion coefficients of aggregate and mortar in concrete,the temperature stress generated under the action of temperature gradient causes the number of cracks in the specimen to increase continuously,and its various mechanical parameters also deteriorate with the increase of the damage of the specimen.