Time-dependent Gas Permeability And Microstructure Evolutionin Concrete Under The Tidal Environment

Under the coupling load and environmental actions,the durability degradation of reinforced concrete structures in the coastal areas occurs due to the performance deterioration of structures and corrosion of steel bars.The gas permeability of concrete is one of the important indicators to evaluate the durability of concrete,and its time-dependence is affected by the evolution of pore structure.Therefore,investigating the relationship between gas permeability and evolution of pore structure of concrete under the natural tidal environment is of great scientific significance for accurately evaluating the durability of concrete structures.A long-term exposure test of gas permeability of concrete under the natural tidal environment was conducted based on the previous studies.A indoor exposure test under the simulated tidal environment was designed.The micro-structural parameters of concrete at different exposure times under the natural tidal environment and simulated tidal environment were measured by the nuclear magnetic resonance(NMR)method.The time-dependent relationship between macroscopic permeability and micro-structure of concrete was further studied.The main contents in this paper are shown as follows:(1)The gas permeability coefficients of concrete at 680 d and 840 d exposure time under the natural tidal environment and at 80 d under the simulated tidal environment were measured.The time-dependence of gas permeability of test concrete at 0 d~840 d exposure time was investigated.Besides,the time-dependent models of gas permeability coefficient of concrete under the natural tidal environment were updated.Moreover,the differences in the effects of water-binder ratios and admixtures on gas permeability of concrete were studied.Finally,the similarity of gas permeability of concrete under the natural tidal environment and simulated tidal environment was analyzed.Results show that,the gas permeability coefficient of concrete has good time-dependence.There is a positive correlation between gas permeability coefficient and water-binder ratio of test concrete.The admixture can effectively reduce the gas permeability of concrete,and the effect depends on type of admixture.(2)The micro-structural parameters of concrete under the natural tidal environment for different exposure times and under the simulated tidal environment for 80 d were measured by NMR.And then,the time-dependent micro-structural parameters of concrete under the natural tidal environment was studied.Finally,based on the results of field exposure test and indoor artificial simulated test,the similarity of gas permeability coefficient and porosity of test concrete under the tidal environment was preliminarily analyzed.Results show that,the micro-structural parameters of concrete have good time-dependence,and different water-binder ratios and admixtures have different effects on improving the pore structure of concrete.(3)The correlation between gas permeability coefficient and porosity of test concrete under the natural tidal environment and simulated tidal environment was analyzed.The correlation between gas permeability coefficient and contribution porosity within different pore sizes of test concrete under natural tidal environment was studied.Besides,the time-dependent relationship of gas permeability coefficient and micro-structural parameters of test concrete under the natural tidal environment was studied.Results show that,there is a good correlation between the gas permeability coefficient and micro-structural parameters of test concrete in both tidal environments.