Study On Durability Of Concrete Resistant To Sulfate Attack

Sulfates are widely distributed in the oceans,salt lakes,groundwater and saline land in China.The sulfate attack is one of the environmental factors that cause the durability of concrete to be damaged.In the sulfate environment,the depth and concentration distribution of sulfate ion and the expansion strain of concrete are important factors in predicting the degree of sulfate attack of concrete.It is of great theoretical significance and application value to develop the study of the anti-sulphate durability damage of concrete to improve the safety of concrete structure design in engineering and predict its service life.In this paper,the durability of sulfate attack concrete is studied.The mechanism of sulfate attack of concrete and the diffusion and diffusion model of sulfate ions is studied in depth.The major contents and conclusions are as follows:Through literature research,research progress on the durability of concrete structures at domestic and abroad and the sulfate diffusion damage diffusion model was introduced.The degradation mechanism of sulphate erosion concrete and the expansion stress and strain process caused by ettringite growth was analyzed.Based on Fick's second law,considering sulfate diffusion and kinetic reaction,a diffusion reaction model of sulfate ions was constructed.The diffusion coefficient after injury was corrected by introducing tortuosity and damage degree from a microscopic angle to obtain the diffusion coefficient of sulfate ion after damage expression.According to the finite difference method,the finite difference model of the one-dimensional diffusion reaction equation is established using the Crank-Niconlson difference scheme.The differential equation is solved by matlab programming,and the influence of different erosion concentrations and different tortuosities on the diffusion law is analyzed..And using the alternating direction implicit format(ADI)to establish the finite difference model of the two-dimensional diffusion reaction equation to influence the sulfate ion concentration distribution and damage.The consequence demonstrates that:(1)As the concentration of the erosion solution concentrate increases,the driving force of sulfate ions into the concrete increases,so that the content of sulfate ions in the concrete increases,the erosion thickness increases,the effective bearing surface decreases,and the macroscopic performance is that the strength is deteriorated and the deformation is large.(2)With the increase of erosion time and concentration,the increase of the diffusion depth of the damage model is increasing.Due to the initial stage of sulphate erosion,the expansive product fills the pores,so that the ion diffusion slows down and the interior of the concrete reacts with the reaction.Cracks are generated,and the effect of damage accelerates the diffusion of sulfate ions.In the case of sufficient calcium aluminate,the diffusion reaction and damage promote each other.(3)The tortuosity and porosity are the important factors affecting the diffusion of sulfate ion in the concrete structure.The greater the tortuosity,the more complicated the transmission path,the inhibition of sulfate ion diffusion,the slower diffusion rate,and the smaller diffusion depth.(4)As the concentration of corrosive concentration increases,the two-dimensional interaction increases;as the diffusion depth of the specimen increases,the two-dimensional interaction of sulfate ion diffusion decreases;the two-dimensional interaction of sulfate ions plays a role in the erosion damage of concrete enhancement.