Research On Gas Permeability And Chloride Diffusivity Of Concrete Under The Tidal Environment

When the reinforced concrete structure exposed to the tidal environment,corrosion media such as chloride ion enter into concrete by cracks and pores,leading to the corrosion of reinforcement and reducing the durability of concrete structure.The gas permeability and chloride diffusivity are important indicators to characterize its durability,while the pore structure characteristics are important factors affecting the permeability.Therefore,it is necessary to explore the time-varying pattern of gas permeability,chloride diffusivity and pore structure of concrete under the tidal environment,which can provide a theory support for the time-varying permeability based durability assessment of concrete.The long time exposure tests of gas permeability and chloride diffusivity of concrete under the tidal environment were designed and conducted in this paper.The pore structure parameters of concrete after different exposure times were measured by mercury intrusion porosimetry(MIP).The time-varying pattern of macroscopic permeability and microstructure of concrete and their relationship were investigated.In this paper,the main contents and results are shown as follows:A modified and self-design gas permeability testing device was adopted to test the gas permeability of ten kinds of concrete with different water-binder ratios and admixtures after standard curing 28 d.The influences of water-binder ratio and admixture on the gas permeability of concrete were investigated.Moreover,the relationship between strength and initial gas permeability of concrete was analyzed.Results show that,there is a good correlation between water-binder ratio and initial gas permeability.The addition of admixtures except basalt fiber(BF)can decrease the gas permeability of concrete and silica fume(SF)has the most obvious reducing effect.There is a good linear relationship between strength and gas permeability,however,the strength cannot reflect the permeability of concrete after adding admixtures.A long time exposure test of concrete under the tidal environment was carried out and the gas permeability was measured.Besides,the influences of water-binder ratio,admixture and exposure time on gas permeability were analyzed.The time-dependent model of gas permeability of concrete under the tidal environment was established.Results show that,there is a positive correlation between water-binder ratio and gas permeability.The addition of admixture influences the gas permeability of concrete,but the effect depends on the types of admixture.The time-dependent model of gas permeability can reflect the decay process of gas permeability effectively.The chloride diffusion coefficient of concrete at 28 d and other different exposure time were tested.Besides,the influences of water-binder ratio,admixture and exposure time on chloride diffusivity were analyzed.The time-dependent model of chloride diffusivity of concrete under the tidal environment was established.Results show that,there is a good positive correlation between water-binder ratio and chloride diffusion coefficient.Admixtures have different influences on chloride diffusivity.The time-dependent model of chloride diffusivity can reflect the decay process of chloride diffusivity effectively.There is a good correlation between chloride diffusion coefficient and gas permeability coefficient.The pore structure parameters at different times were determined by MIP.Then the relationship between gas permeability and pore structure parameters was analyzed.Results show that,there is an obvious time dependent characteristic of pore structure parameters.In addition,there is a good correlation between pore structure parameters and gas permeability.The formation mechanism of time-varying characteristics of gas permeability is revealed preliminarily.