Study On The Physical And Mechanical Properties And Damage Mechanism Of Concrete Mixed With Mineral Admixture In Marine Corrosion And Freezing-thawing Environment

The marine erosion and freezing-thawing environment brings serious damage to concrete structures in Chinese northern harbors. Study on the physical and mechanical properties and damage fracture mechanism of concrete in the environment is the basis to solve these engineering problems. In this dissertation, taking the concrete mixed with admixtures as the research objects, based on test results of local marine environment, study on physical and mechanical properties, microstructure features, mechanism of chloride ion transport, damage fracture mechanism etc. of concrete mixed with admixtures in the marine corrosion and freezing-thawing environment were carried out by using a large artificial climate simulation laboratory etc. testing technology, simulating marine erosion and freezing-thawing environment by setting UV-light, temperature and humidity, salt mist, freezing-thawing etc. environment factors, along with the integrated application of theoretical analysis, experimental research and numerical simulation and other methods and means. The main conclusions are as follows:(1) Through physical properties experiments, the apparent morphology, quality change rule of concrete after freezing-thawing action, and chloride ion transport rule of concrete mixed with admixtures in marine corrosion and freezing-thawing environment are obtained. The connection between the amount and type of mineral admixture, times of freezing-thawing cycle and corrosion time and the physical properties of concrete was established. The influence of coupling environment effect on chloride ion transport property is obtained.(2) Through mechanical properties experiments, the compressive strength, elastic modulus, and dynamic elastic modulus changing with admixture, freezing-thawing cycles and corrosion time are obtained. The connection between the amount and type of mineral admixture, times of freezing-thawing cycle and corrosion time and the mechanical properties of concrete was established.(3) With numerical fitting method and test data, porosity, permeability and chloride ion diffusion coefficient mathematical models considering the effect of freezing-thawing factors are established. Taking advantage of the seepage-diffusion theory and continuum mechanics theory, the chloride ion transport model considering freezing-thawing, convection, and diffusion effect is established, and the transport mechanism of chloride ion in concrete under the environment of marine corrosion and freezing-thawing is revealed. With the material parameters of concrete mixed with composite admixtures as initial parameters, the chloride ion transport model is solved by numerical methods. And, the rule of chloride ion concentration distribution, diffusion rate etc. are obtained.(4) The microstructure and pore structure of concrete in marine corrosion and freezing thawing environment are determined with the help of electron scanning microscope and mercury injection apparatus. And the laws of the microstructure and pore structure of concrete changing with the amount and type of mineral admixture, times of freezing-thawing cycle and corrosion time are obtained. In addition, the relation between microstructure of concrete and its macro performance is established.(5) Based on the theory of damage mechanics, the constitutive model and equations of concrete in the marine corrosion and freezing-thawing environment are established. When comparing the theoretical stress-strain curve and experimental stress-strain curve, it is found that the constitutive model established can fulfill the task to describe the damage evolution characteristics of concrete in the marine corrosion and freezing-thawing environment. The damage mechanism of concrete in marine corrosion and freezing-thawing environment was analyzed.(6) Basis on the elastic modulus and strength degradation model of concrete in the marine corrosion and freezing-thawing environment, by numerical methods, the damage process of a concrete pile component of high pile cap structure is simulated. And the displacement, deformation and damage of concrete are obtained.The research achievement of this dissertation will enrich the test data and theoretical knowledge about the material properties and damage of concrete in marine and freezing-thawing environment, and provides provide an important basis for solving the durability problem of concrete in marine erosion and freezing-thawing environment.The dissertation has 115 figures, 84 tables, 211 references.