| Concrete structures that have been in service environments such as groundwater,salt lakes and oceans for a long time.It not only bears different forms of load,but also suffers from chemical corrosion of sulfate for a long time.The sulfate ions in the environment are immersed in the concrete through various forms,and react with the hydration products of cement,causing damage to the concrete and reducing its mechanical properties.The load leads to the expansion of micro-cracks in the concrete,resulting in damage and accelerating the process of sulfate attack.Therefore,the combined effect of sulfate erosion and loading is an important reason for the degradation of mechanical properties of concrete materials and premature structural failure in sulfate-based service environments.Therefore,in this thesis,experimental research,theoretical derivation and numerical simulation are used to study the mechanical properties and internal ion diffusion law of concrete under sulfate attack from the two levels of no stress and bending load.The main research work of this thesis is as follows:(1)The deterioration law of mechanical properties of concrete under the combined action of bending load and sulfate attack is revealed.Firstly,the sulfate attack concrete test without stress was carried out,and the mass loss rate and compressive strength degradation law of concrete under different water cement ratio,erosion concentration and erosion age were analyzed.On this basis,the deterioration process of mechanical properties of eroded concrete under bending load is further explored.It is found that the relationship between concrete strength and erosion age is quadratic function,which increases first and then decreases.Finally,the concentration of l sulfate ions inside the concrete was measured,which laid the foundation for the subsequent model research.(2)The diffusion-reaction model of sulfate ion in concrete without stress was established,and the influence of different factors on the diffusion of sulfate ion was revealed.Based on Fick ’s second law and reaction kinetics,considering the tortuosity of sulfate ion diffusion in concrete,combined with the influence of cement hydration reaction,corrosion product filling and damage function on pores,the diffusion-reaction model of sulfate ion in concrete is established.The spatial and temporal distribution of sulfate ion concentration in concrete is quantitatively characterized.Compared with the experimental results,the error is less than 20%.The effects of different parameters on the diffusion of sulfate ions were analyzed.It was found that the water-cement ratio mainly affected the concentration and diffusion process of sulfate ions immersed in concrete.The erosion concentration mainly affected the chemical reaction inside the concrete,and the increase of the chemical reaction rate k hindered the diffusion process of sulfate ions to a certain extent.(3)The influence mechanism of bending load on the diffusion of sulfate ions in concrete was clarified,and the prediction model of maximum erosion depth was established.Based on the diffusion-reaction model without load,the damage variable is introduced as the link between load and sulfate ion diffusion,and the diffusion coefficient of sulfate ion in concrete under different load levels is deduced.The calculated value of the model is compared with the measured value of sulfate ion concentration in concrete,and the error is less than 20%.The diffusion depth of sulfate ions in concrete under different load levels was analyzed.It was found that the increase of diffusion depth of sulfate ions gradually increased with the increase of the same level of load.Finally,by simulating the diffusion distribution of sulfate ions in 10 years,the maximum erosion depth model of sulfate ions was established.It was found that the maximum erosion depth had a cubic function relationship with time,which gradually slowed down in the early stage and accelerated again with the continuous erosion. |
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