Study On Damage And Fracture Mechanism Of Concrete Under The Sulphate Erosion And High Strain Rate Load

Coastal ports,sea-crossing bridges and other large-scale concrete structures in China have been seriously reduced in service life due to the long-term harsh marine erosion environment.Among the many erosion hazards,the erosion effect of sulfate on concrete has become one of the main environmental erosion affecting structural durability.Engineering examples of damage caused by sulfate erosion are not uncommon.Some civil or military protective concrete members in important service are not only affected by sulfate erosion,but also subjected to various dynamic loads.Under the action of vehicle and ship impact,explosion shock wave,seismic wave,etc.,the marine concrete structure will show different and more complex dynamic behaviors comparing with static loading.In this paper,using the split Hopkinson pressure bar?SHPB?test system,X-ray diffractometer and SEM scanning electron microscope and other test methods and means,according to the fracture mechanics,damage mechanics and other theoretical methods,the basic physics and mechanical properties,micro-fracture mechanism and damage evolution law of sulfate-eroded concrete under high strain rate are systematically studied.The main work and research results are as follows:?1?The distribution characteristics of SO₄^2-content in concrete specimens subjected to sulfate erosion were measured,and the variation of SO₄^2-content at different depths from the surface of the specimen with the erosion time and concentration of erosion solution was obtained.?2?Based on the porous medium seepage theory and diffusion theory,the SO₄^2-coupled transmission model and control equation of concrete considering the effect of chemical reaction is established,and the equation is solved by numerical method.The solution result of theoretical model is compared with the experimental results,showing a good confirmation.At the same time,the variation of SO₄^2-content distribution in the eroded concrete with the erosion time under the condition of sulfate concentration in seawater of a certain sea area is predicted,and the transmission mechanism of SO₄^2-in concrete is revealed.?3?The mechanical properties of sulfate-eroded concrete under impact compression were measured by the split Hopkinson pressure bar?SHPB?test system.The variation of mechanical properties?stress-strain curve,compressive strength,elastic modulus and peak strain?,macroscopic damage characteristics,etc.of sulfate-eroded concrete under high strain rate with erosion solution concentration,erosion time and loading strain rate were obtained.The results show that:with the increase of concentration of erosion solution and erosion time,the compressive strength and elastic modulus of concrete decrease obviously,while the peak strain increases and the degree of macroscopic damage increases.With the increase of loading strain rate,the compressive strength and elastic modulus of concrete increase,but the degree of macroscopic damage increases significantly.?4?The effect of concentration of erosion solution and erosion time on the content of hydration products and erosion products in concrete was determined by X-ray diffractometer.The micro-morphological characteristics of sulfate-eroded concrete at high strain rate was determined by using scanning electron microscopy?SEM?.The variation of development and expansion of the fracture,the micro-fracture mode,the failure morphology of the cement-aggregate interface and the distribution characteristics of the erosion products with the strain rate,the concentration of the erosion solution and the erosion time was obtained.Compared with the macroscopic failure characteristics of the specimen,the microscopic cracking mechanism of sulfate-eroded concrete under high strain rate is effectively revealed.?5?Based on the theory of damage mechanics,the evolution law of concrete damage degree with sulfate erosion time under high strain rate is studied.Based on the statistical damage model of Weibull distribution,the damage evolution equation and constitutive model of concrete considering the coupling of sulfate erosion and high strain rate load are established.The constitutive model and the experimental results show a great confirmation.The research results in this paper can provide an important reference for the durability study of marine concrete structures.