Study On Numerical Test Model Of Hydraulic Concrete Under Sulfate Attack And Life Influencing Factors

The nature of sulfate erosion of concrete is that sulfate ions(SO₄^2-)undergo physical and chemical reactions with cement hydration products in the process of free diffusion,convection,and electromigration to produce swelling products,causing concrete to crack,erodes,and other damage.It is water One of the main reasons for the deterioration of the durability of industrial concrete.Therefore,by establishing a mesoscopic transmission model of SO₄^2-ions in concrete,exploring the influence of different factors on predicting the service life of concrete.It can offer the theory evidence for the layout,construction and operation management of hydraulic concrete.Through literature research,this paper summarizes the mechanism and influencing factors of sulfate corrosion of hydraulic concrete,and summarizes the research progress of meso-numerical simulation and the research status of concrete life prediction.This paper first establishes a mesoscopic model of concrete with three-phase structure,and then establishes a mesoscopic transport model of SO₄^2-ions in concrete according to Fick’s law,and conducts numerical experiments on sulfate erosion;finally,based on the results of numerical experiments on sulfate erosion,carrying out the research on the service life of concrete under sulfate erosion.（1）According to the aggregate grading theory and Monte Carlo method,the mesoscopic model of concrete containing three-phase structure is generated,and the concrete mesoscopic model is verified under uniaxial compression,and it is found that the damage and destruction results are consistent with the actual failure law:The internal aggregate distribution of the concrete specimen is uneven,and stress concentration is prone to occur.When it is under pressure,the interface transition zone（ITZ）first begins to break and produce micro-cracks;as time increases,the internal damage of the specimen continues to accumulate.The microcracks expanded from ITZ to the mortar,and continued to widen and increase in number,until the formation of penetrating cracks and the destruction of the specimen.（2）The transmission model of SO₄^2-ions in concrete was established according to Fick’s law,and the sulfate corrosion test was carried out.The experiment mainly executed the numerical modeling of the erosion of concrete specimens in the sulfate solution environment with different diffusion coefficients,different concentrations and different aggregate volume fractions to explore the influence of these factors on sulfate erosion.The simulation results reveal that the greater the diffusion coefficient,the more quickly the diffusion rate,the higher the concentration of SO₄^2-ions at the same depth,and the greater the maximum diffusion depth at the same time,indicating that the sulfate erosion degree is stronger.The more SO₄^2-ion concentration,the faster the diffusion rate,and the higher the ion concentration at the same depth,but the maximum diffusion depth under different environmental concentrations is the same.The larger the aggregate volume fraction,the tardier the diffusion rate,the lower the concentration at the same depth,and the smaller the maximum diffusion depth at the same time.This is because as the aggregate volume fraction increases,the diffusion path of SO₄^2-ions becomes more tortuous and longer,which reduces the transmission rate of SO₄^2-ions.（3）Based on the numerical test results of sulfate attack concrete,the effects of diffusion coefficient,external SO₄^2-ion concentration and aggregate volume fraction on service life are studied,so as to provide guidance for engineering practice.In this paper,meso-scale numerical experiments and life-span impact studies on the diffusion and chemical reactions of sulfate in concrete are carried out,which will provide a certain reference and reference for related research and practical engineering applications in the future.