Study On Deterioration Model Of Sulfate Attacked Concrete And Durability Failure

Sulfate attack is one of the most important durability problems for concrete structures.The damage caused by sulfate attack to concrete structures occurs occasionally.However,the deterioration model of sulfate attacked concrete is not yet completely clear.The durability design method of concrete structures under sulfate attack is still at a qualitative level.It is difficult to achieve the quantitative durability design of concrete structures.Taking this as a starting point,in this paper,the degradation mechanism of sulfate attack on concrete was deeply analyzed,a deterioration model of the mechanical properties of concrete under sulfate attack was established,the effects of solution concentration and temperature were emphatically studied,the damage evolution process of sulfate attacked concrete at a mesoscale was investigated,and the durability failure index and failure limit state of concrete material under sulfate attack were established,which provides methodological supports for the durability design and life prediction of concrete structures under sulfate attack.The main work is as follows:A meso-level finite element modeling method that can consider the characteristic information of aggregates was proposed.Based on X-ray computed tomography(CT)slices,the aggregate edge number,area,equivalent radius,and elongation ratio were statistically analyzed,and a two-dimensional polygonal random aggregate model with considering real aggregate information was established.The results show that compared to the circular random aggregate model,the proposed polygon random aggregate model can give a more accurate description of the mechanical behavior of concrete under uniaxial compression.In addition,mesoscopic models of different sizes and cross-sectional shapes with real aggregate information were generated,which is breaking the size limitation of the reconstruction model based on CT scanning.Moreover,it also provides methodological supports for studying the non-uniform deterioration of concrete under sulfate attack on a mesoscale.A chemo-transport-expansion sulfate attacked concrete model with multi-factors was established,and the influence of calcium leaching on sulfate attack was innovatively considered.A solid–liquid equilibrium curve was used to describe calcium leaching process.The influences of porosity changes caused by calcium leaching,and temperature on sulfate attack were considered.Then the parametric analysis of the material parameters in the established model was conducted.The results show that calcium leaching has a considerable effect on the deterioration of concrete under sulfate attack which cannot be ignored.Porosity,the diffusion coefficient of sulfate ions,and chemical reaction rate constant k₁are the key parameters in the established model.The accuracy of the established sulfate attacked concrete model was verified.Sulfate attack tests were designed,and the influences of sulfate concentration and temperature on the content of sulfate ion in concrete were measured.Numerical simulations on expansion deformation of concrete caused by sulfate attack were carried out,and the numerical results compared with the experimental results in published literature.Moreover,the effects of calcium leaching and temperature on expansion were comprehensively discussed.The comparative analysis of test and simulation results verifies the accuracy of the established sulfate attack model in this paper.The sulfate concentration and temperature affect the process of sulfate attack on concrete predominantly via the chemical reaction process.Both calcium leaching and temperature have a significant influence on the expansion.A deterioration model of the mechanical properties of concrete under sulfate attack was established.The development law of expansion deformation with immersion time under sulfate attack was studied,and the damage evolution process of sulfate attacked concrete was investigated at a mesoscale.The influence of tricalcium aluminate(C₃A)content on expansion,aggregate on the transport of sulfate ions were analyzed.In addition,the peak uniaxial compressive strength of the concrete after subjected to sulfate attack was simulated and analyzed,which provides a calculation method for the analysis of the bearing capacity degradation of concrete structures under sulfate attack.The study on durability failure of concrete under sulfate attack was studied.The failure thickness was defined as the durability failure index of sulfate attacked concrete,which was verified by the designed sulfate attack tests.The stochastic prediction model of failure thickness,related to the sulfate concentration,initial aluminate content of concrete,and diffusion coefficient of sulfate ions,was built.The failure limit stateof concrete material under sulfate attack was established,then the life expectancy of sulfate attacked concrete and the bearing capacity life of reinforced concrete beams were analytically predicted.This research is of guiding significance for the durability design and life prediction of concrete structures under sulfate attack.