Failure Mechanism Analysis Of Ultra-high Performance Concrete Under Chloride Environment

As a new type of ultra-high performance material,ultra-high performance concrete suffers from the coupling effect of load and chemical corrosion due to its long-term high concentration of chloride ion corrosion environment,which eventually leads to the degradation of mechanical properties of ultra-high performance concrete,as well as the reduction of structural bearing capacity and durability.In the process of concrete corrosion,chloride ions react with the internal components of concrete to form compounds,which causes damage to concrete materials and changes the stress field in concrete.Therefore,there is a coupling effect between the mechanical and chemical reactions of concrete.This coupling effect will cause damage to concrete materials.When the damage reaches a certain extent,part or whole of concrete will be destroyed.Because the UHPC with deteriorated mechanical properties may not meet the expected service life requirements,which causes serious danger,it is of great theoretical and practical significance to study the failure mechanism of UHPC under chloride ion erosion environment.Based on theoretical analysis,numerical calculation and finite element simulation,the mechanical and chemical coupling behavior of UHPC is studied,and the damage mechanism of UHPC under chloride ion erosion environment is revealed.The main work of this paper is as follows:1.Based on Fick’s second law,the one-dimensional diffusion of chloride ion in ultra-high performance concrete is studied.The chloride ion concentration at different time and location is calculated by the finite difference method.The one-dimensional diffusion process of chloride ion in ultra-high performance concrete is simulated by using MATLAB programming.The functional relationship between chloride ion concentration and different diffusion depth is obtained by a function fitting.The chloride diffusion characteristics in ultra-high performance concrete under different chemical environments are studied.The results are compared with chloride ion corrosion test.2.Based on the damage mechanics theory and energy equivalence principle,the uniaxial elastic-plastic damage constitutive relationship under loading is introduced by deducing isotropic damage variable,and solved by numerical integration.Combined with experimental data,uniaxial elastic-plastic damage constitutive model of ultra-high performance concrete under chloride ion erosion is constructed.3.Based on the finite element software ABAQUS and its secondary development,the constitutive relationship established above is embedded in ABAQUS through the subroutine UMAT.The damage process of ultra-high performance concrete under chloride ion erosion is studied.The coupling characteristics of mechanical and chemical fields under different working conditions are numerically simulated,and the stress-strain curves of ultra-high performance concrete under different corrosion periods are obtained.The damage mechanism of ultra-high performance concrete under chloride ion erosion is analyzed.