Test Analysis And Numerical Simulation Of Concrete Durability Under The Coupling Action Of Sulfate And Chloride

Reinforced concrete structures in service environments such as the coastal saline soil and the West Saline Lake are not only under various loads,but also corroded by sulfate and chlorine salt,leading to the reduction of the safety and durability.Therefore,study the degradation process of concrete caused by the coupling effect of sulfate and chloride has great significance on durability evaluation and service life prediction of concrete structures in complex salt environment.In this paper,the cylindrical mortar specimen under full immersion is used as the research object,and the related experiment and model study are carried out.The main research contents and conclusions are listed as follows:(1)The coupling transmission equation of sulfate ion and chloride ion under the full immersion is established.In the equation the coupling interaction between chloride ion and sulfate ion,which affect the pore filling and expansion cracking and the decomposition and release of chemically bound chloride ions in concrete is considered.Also,it can be used to calculate the content,porosity,micro crack density and diffusion coefficient of concrete in the process of coupling corrosion.(2)The coupling transmission equation of sulfate ion and chloride ion is transformed into matrix form and the three layer implicit difference method is used to solve the discretized equation.On this basic,the analysis program is developed using MATLAB language.(3)Test of ion concentration about sulfate and chloride in cylinder mortar immersed in the sulfate,chloride and compound solution are carried out.The results showed that the presence of chloride ions delay the transmission of sulfate ions,and the sulfate ion inhibited the diffusion of chloride ion in the early stage,but it will turn opposite after the appearance of cracks induced by the volume expansion.(4)The coupling transmission model is validated by the test value of the concentration of sulfate ion and chloride ion.Then the program is used to analyze the effect of parameters such as the time step,the space step,initial porosity,chemical reaction rate constant,effective capillary pore filling fraction and the AFm content to the change of sulfate ion concentration,free chloride ion concentration,chemical combination of chloride concentration,volumetric strain,ionic diffusion coefficient and calcium aluminate concentration in the process of coupling transmission.(5)A test device for stress-strain curve of corrosion damaged concrete is designed and made,and it was used to get the stress-strain curve of mortar which were soaked in sulfate,chloride and compound solutions under different days.The results show that the stress-strain curve of mortar specimens have no change before and after corrosion,but the key parameters such as peak stress,peak strain and descent slope are related to the type of corrosion solution and the number of immersion days.