Numerical Simulation Of The Process Of Sulfate Attack On Concrete

Sulfate is widely distributed in our country,and most of the seawater,salt lakes,groundwater and saline-alkali soils have sulfates.Sulfate erosion is one of the most extensive and common forms of deterioration of concrete.Sulfate ions are transmitted to the inside of the concrete structure through various ways,causing the concrete material to expand,crack,and the loss of strength.As a result,the concrete structure is destroyed.The long-term effect will lead to a lot of economic losses and huge waste in the energy field.Therefore,researches on the failure process and degradation mechanism of concrete under sulfate attack have important significance for prolonging the service life of reinforced concrete structure and improving the efficiency and economic benefit of the engineering structure.This paper focuses on the mechanism of coupling degradation caused by the influx of external sulfate ions into the concrete,and the erosion process is numerically simulated.The main contents and conclusions are as follows: 1.The basic theory of sulfate attack on concrete are summarizedThe research status of concrete durability and sulfate erosion at home and abroad are introduced.On this basis,the transport theory of sulfateion in concrete and the erosion and expansion mechanism of sulfate on concrete are summarized.The formation process of expansion product ettringite and the calculation model for the expansion deformation are given.2.The "equivalent temperature method" is proposed to model the volumetric expansion of concrete caused by sulfate erosionIn view of the numerical simulation of the process of volume expansion of concrete caused by sulfate erosion,the "equivalent temperature method" is proposed."Temperature" is used as a bridge for connecting chemical reactions and mechanical calculations.The complex chemical reactions are unified and the reactant concentrations is converted to equivalent temperatures,aiming at using transformational thinking to simulate the process of chemical reactions in finite element software.The basic principles and assumptions of the "equivalent temperature method" are introduced,and then the conversion method between the concentration and the equivalent temperature is expounded.According to a specific example,the quantitative correspondence between concentration and equivalent temperature is derived.3.The coupling analysis method of sulfate ion diffusion-concrete damage is establishedCombined with the damage theory of concrete,the coupling deterioration mechanism caused by the influx of external sulphate ions into the concrete is studied.After the sulfate ions penetrate into the concrete through diffusion,they react with the cement hydration product in concrete to generate swelling ettringite,which will cause the expansion and cracking of concrete structures.,which in turn increases the flow of sulfate ions in concrete.The increase of sulfate ion transport channels in turn further promotes the production of expanded products,therefore,sulfate ion intrusion and concrete cracking are a mutually reinforcing nonlinear coupling process.The coupling analysis method for this coupling process is established 4.The damage evolution process of concrete under the coupling mechanism of diffusionreaction and concrete damage is simulatedBased on the finite element analysis software ABAQUS platform,through secondary development,the simulation of this nonlinear coupling process is realized effectively.Using the related experimental data in the literature,the validity of the established method was verified.Through the numerical simulation of the coupling process,the following conclusions are drawn:(1)Whether to consider the coupling effect between sulfate ion diffusion and concrete damage cracking has significant influence on the assessment of the state of use of the concrete structure,and the prediction of coupling analysis is more reasonable.(2)The diffusion coefficient D of sulfate ion in concrete increases with the degree of damage of concrete,and in turn promotes the average crosssectional expansion of concrete,which in turn accelerates the reduction of the durability of the concrete.Therefore,during the actual research process,the influence of sulfate ion diffusion coefficient on the durability of concrete cannot be ignored.