Study On The Fatigue Damage Of Cement Concrete Subjected To Sulfate Corrosion And Alternating Stresses

Sulfate attack is an important concern in concrete durability and performance and occursall over the world. There are so many studies on the sulfate corrosion of cement concretewhich is affected by single factor such as sulfate concentration, temperature, and so on. Partof the experiment study is focus on the damage of concrete subjected to Sustained load andsulfate corrosion. However, as a widely used construction material, concrete is also subject toalternating load in many cases and requires high fatigue resistance when used in highwaypavements, bridge slabs, railway sleepers, airport runways, etc. Therefore, the damagemechanism of cement concrete subjected to sulfate corrosion and alternating stresses isstudied in this paper.With designing and developing mechanical corrosion fatigue system, the real engineeringenvironment is simulated. With the test of wet and dry quality, relative dynamic elasticmodulus and flexural strength, effects of sulfate concentration, stress level and cement waterratio on the damage of concrete are researched and damage evaluating indicators of concretesubjected to sulfate corrosion and alternating stresses are proposed. Based experiments, theinteraction of alternating load and sulfate corrosion is studied by the introduction of effectcoefficient K. Sulfate ion migration and crystallization in concrete is researched by chemicalanalysis. Combined with the SEM micro structural analysis technology, the variation of theporosity and interface which is caused by the action of alternating load and sulfate corrosionis researched, and the invasive power of sulfate attack is analyzed.The crack factor was derived based on the model of the concrete’s response to externalsulfate solutions through revised methods, such as diffusion path division and crackhomogenization. A formula for effective diffusion (coefficient Dt), which is used tocharacterize the effect of alternating stresses on the sulfate ion diffusion, was proposed. Theresearch uses Fick’s second law for the diffusion of sulfate ions. A solution to the diffusionequation was proposed to determine the sulfate concentration under corrosion fatigue as afunction of time and space. The sulfate concentration responses were obtained and comparedwith a variety of available data. A mathematical model is presented to simulate sulfate ionmigration in cement concrete that was subjected to the coupled action from sulfate solution and alternating stresses. On the basis of chemical reaction equations of calcium aluminatescrystallization expansion destruction, the calculation process of volume expansion ratio,swelling strain and internal mechanical response were deduced. The chemical-stress damageconstitutive model for the concrete under corrosion and fatigue environment was built. Finally,numerical solution of uniform design experiment and the fitting regression of life predictionequation were conducted.