Evolution Of Water Permeability And Chloride Diffusivity Of Concrete And Their Time-varying Relationship Under The Tidal Environment

Under the tidal environment,the durability damage of concrete structures will be incurred,due to the ingress of chloride ion.Therefore,the chloride diffusivity of concrete is an important parameter for evaluating the durability of concrete.The durability test of chloride-induced corrosion on concrete usually lasts for a long time.On the contrary,the time of water permeability test of concrete is relatively shorter,since the water permeability test is much maturer and easy to operate.In addition,many studies have shown that the water permeability of concrete can indirectly reflect the chloride diffusivity of concrete.The chloride diffusivity is related to the characteristics of microstructure of concrete which is the same as the water permeability of concrete.And both of them are time-varying.Therefore,it is significant to explore the time variation of water permeability and chloride diffusivity of concrete for evaluating the durability of concrete under the natural tidal environment accurately.In this paper,the main contents and results are shown as follows:1.Concrete with different mixtures was designed.The properties of raw materials of concrete were tested and analyzed.And then,a test with a long exposure time under the tidal environment was designed and conpleted.Finally,the test device,principle and method of water permeability and chloride diffusivity were introduced.2.The initial water permeability coefficients of concrete and the water permeability coefficients of concrete exposured different time under the tidal environment were obtained.Influences of water-binder ratio and admixture on the water permeability coefficient were studied and the relationship between water-binder ratio and water permeability coefficient was obtained.Besides,the time variation of water permeability coefficient of test concrete was investigated,and the time varying models of water permeability coefficient were established.Results show that,the proposed time-varying model can well reflect the attenuation process of water permeability of concrete under the natural tidal environment.In addition,admixtures can effectively reduce the water permeability of concrete,but the effect depends on the types admixture.3.Influences of water-binder ratio,admixture and exposure time on the concentration distribution of free chloride ion and chloride diffusion coefficient of concrete in the field test were analyzed.The chloride diffusion coefficient was obtained by fitting with Fick's second law and meanwhile the time-varying model of chloride diffusion coefficient was established.Results show that the time-varying model of chloride diffusivity under the natural tidal environment can reflect the decay process of chloride diffusion effectively.Water-binder ratio has a significiant influence on chloride diffusion.4.Variations of water permeability and chloride diffusivity with water-binder ratio,admixture and exposure time were compared.In addition,reletionship between water permeability coefficients and chloride diffusion coefficients of concrete with different specifications was established.Results show that the time variation of water permeability can well reflect the time-varying progress of the apparent chloride diffusion coefficient.The water permeability coefficient and chloride diffusion coefficient of test concrete both decrease with exposure time and the addition of admixture,but increase with water-binder ratio.