Research On Damage Behavior Of Concrete Under Sulfate Corrosion

Sulfate in the rock diffuses into concrete shaft, causing a series of chemicalreaction among concrete components. Ettringite produced by the chemical reaction isexpansive, it will cause concrete shaft lining corrosion.In the process of concrete corrosion, the component concentration changes, suchas sulfate, which will cause damage to concrete, that is the mechanical properties ofconcrete weaken. It will furfher make concrete displacement field and stress fieldchange. The alteration of displacement field and stress field in turn affect the sulphatediffusion coefficient and concentration field. Therefore, the coupling effect existsbetween the machine movement (deformation) and non-mechanical movement(chemical reaction) in concrete shaft lining. The coupling will cause local material ofthe shaft damage. When the damage accumulates to a certain degree, it will bringpartial or total destruction to concrete shaft. So the concrete corrosion damage willseriously affect the safety of concrete shaft lining.In this paper, a complicated dynamic behavior about concrete deformation,sulfate diffusion and chemical reaction coupling system was researched by integratedapplication of experimental, theoretical analysis and numerical calculation method,and concrete damage mechanism caused by sulfate corrosion was revealed. The maincontents and results are as follows:(1) A accelerated test with four factors and five levels was done in the laboratory,and the sulfate ion concentration in different time and at different different crosssections was tested from the high strength concrete equipped in the test. Thecorresponding diffusion coefficient was got by the error function. The functionrelationship between diffusion coefficient and water-binder ratio, sulfate solutionconcentration, curing time and stress ratio were established, and the diffusioncoefficient calculation formula with four factors integrated influence was set up.(2) Hydration reaction and the corrosion reaction in concrete were reasonablysimplified and each component quality change was analyzed. According to the massconservation of concrete components in the process of chemical reaction anddiffusion, reaction rate equations were built which contains eight reaction rateconstant and fifteen kinds of component concentration. Fifteen kinds of componentconcentration field and sulfate solution diffusion velocity field with differentwater-cement ratios, sulfate solution concentrations, curing time and stress ratios werecaculated by numerical method. The laws of the impacts of four factors on the component concentration field were obtained.(3) A accelerated test with four factors and five levels was done in the laboratory,and concrete compressive strength in different corrosion time was tested from thehigh strength concrete equipped in the test. Take the compressive strength as index,the damage degree was defined. The function relationship between damage degreeand water-binder ratio, sulfate solution concentration, curing time and stress ratiowere established, and the damage degree formula with four factors integratedinfluence was set up.(4) According to the conservation mass law, the equation about concretecorrosion strain rate-component concentration variation rate was built. Straincomponent expression of concrete under the common action of stress and corrosionand the change condition of concrete failure state considering corrosion strain weregiven. Based on the Drucker-Prager and Lagrange criteria, concrete flow rules aftershear yield and tensile failure in the process of concrete corrosion damage wereestablished.(5) A kind of coupled system dynamics model about concrete shaft lining andsurrounding rock deformation, hydration reaction and corrosion reaction and sulfatediffusion was built, system response computation method was designed, responsecalculation program was programmed. The system responses were caculated withdifferent different initial and boundary conditions, and the effects of water-binderratios, curing time and sulfate concentration in surrounding rock on the rupture status,stress, displacement, component concentration of concrete shaft lining were got.(6) The interacting among concrete shaft lining deformation, sulphate diffusionand concrete component concentration were analyed. According to the coupling effectdiagram of corrosion and damage, concrete shaft lining damage mechanism caused bysulfate corrosion was revealed.