Chloride Ion Diffusion Inside Concrete Considering Freeze-thaw Damage And Air Content

Due to freeze-thaw damage and chloride diffusion of concrete in marine tidal environment in cold regions,the research which investigates the development of freeze-thaw damage and chloride ion concentration in concrete was carried out considering the influence of air content by means of theoretical research,physical experiment and numerical simulation method.The specific works are as follows:(1)The freeze-thaw cycle test was carried out on ordinary concrete and air-entrained concrete.The effects of freeze-thaw cycles on the mass,resistivity and dynamic elastic modulus loss rate were investigated.The loss rate of concrete dynamic elastic modulus was used as a measure of concrete freeze-thaw damage.In order to describe the development of the dynamic elastic modulus loss rate of concrete during freeze-thaw cycles,based on hydrostatic pressure mechanism,the development model of concrete defects during freeze-thaw cycles is assumed,and a new concrete freeze-thaw damage model is advised.An equation describing the development of the loss rate of concrete dynamic elastic modulus during freeze-thaw cycle was proposed..The data of the dynamic elastic modulus loss rate of concrete was fitted and analyzed by the equation describing the development of the loss rate of concrete dynamic elastic modulus.The development equation of concrete dynamic elastic modulus loss rate considering the influence of air content was established.(2)Based on the ocean tidal simulation device independently developed by laboratory,the tests of chloride diffusion in different air-content concretes were carried out,and the influence of air content on distribution law of chloride ion concentration in concrete was explored.After different air-content concretes experienced the test of freeze-thaw cycle,the natural chloride diffusion tests were carried out for air-content concretes to investigate the distribution of chloride ion concentration in concrete considering the effects of freeze-thaw damage and air content.Combined with the above two parts,a model for chloride ion diffusion in concrete considering the effects of freeze-thaw damage and air content is established based on Fick’s second law.(3)Based on the ocean tidal simulation device independently developed by laboratory,the tests of chloride diffusion in mortar were carried out to investigate the chloride ion transport of concrete interface transition zone.Based on finite element calculation software “Comsol”,a three-dimensional mesoscopic numerical simulation method for concrete chloride ion diffusion was established.And a numerical model which can consider the interaction of "freeze-thaw cycle and chloride diffusion" for describing distribution of chloride ion concentration in concrete was established.The long-term field test of concrete chloride diffusion with the interaction environment of“freeze-thaw cycle and chloride ion diffusion” verified the applicability and rationality of the numerical simulation method.