Moisture with harmful ions penetrates into the interior of concrete, which causes deterioration of the concrete structure. In this study, a moisture saturation equilibrium relationship of concrete was tested under different temperatures and relative humidity conditions to develop moisture absorption and desorption curves. Based on experimental data and numerical simulation, a model of moisture transport in concrete was established. The results from the model indicate that the moisture absorption rate was lower at higher temperatures and largely dependent on the saturation gradient, while the desorption was increased at higher temperatures and mostly affected by the saturation gradient. The proposed model was highly in agreement with the experimental data.
The revised abstract is as follows:As a new waterproof system with plastic in underground silos, three kinds of polypropylene plastic welds were designed and subjected to a water-pressure resistance test in pump-pressure mode. The failure modes, stress processes, failure mechanisms, and influencing factors of different weld forms with different thicknesses were studied. The water-pressure resistance on the groove-weld specimens with welded cover plates was increased by approximately 40%-85% compared with that of the groove-weld specimens. The water-pressure resistance for groove-weld specimens with pasted and welded cover plates was increased by approximately 10% compared with that of the groove-weld specimens with welded cover plates. The depth of the designed underground silos is generally lower than 35 m, and the 8-mm plate thickness and groove-weld specimens with welded cover plate combination can resist 58.16 m of water pressure with a recommended safety factor of 1.66.
Concrete structures in marine environments often face durability problems owing to the coupled action of external loads and chloride-ion erosion. Therefore, in this study, we conducted chloride ion tests on damaged concrete at four tensile stress levels and three varying number of load cycles. The test results indicate that an increase in the tensile stress and number of load cycles results in a gradual increase in the concrete damage coefficient. At fewer cycles, 50% tensile stress was the critical threshold point of damage; the damage was evident beyond this range. As the number of cycles increased, the damage increased gradually up to the critical threshold and thereafter increased rapidly. With an increase in the tensile stress level, the diffusion coefficient of chloride ions increased gradually; the loading degree improved the permeability of chloride ions. In addition, based on the theory of linear fatigue cumulative damage to concrete, a mathematical model of the relationship between the load factor and concrete damage coefficient was established. Using this model, a prediction model for the chloride ion diffusion coefficient was proposed considering the tensile stress level, load cycle number, and other load factors.
Marine atmosphere environment accelerates the process of chloride penetration into concrete under the coupling effect of ambient temperature and relative humidity, thereby reducing the durability and service life of concrete. This paper aims to investigate the change of water equilibrium saturation and the chloride transport properties of concrete materials in different environments. The water equilibrium saturation tests at three temperatures and five relative humidity (RH) and salt spray erosion tests at three temperatures were performed. The influence of RH and temperature on the equilibrium saturation of concrete and the influence of temperature and time on the chloride diffusion coefficient are investigated. The results show that, in the process of moisture absorption and desorption, the equilibrium saturation of concrete gradually decreases as temperature rises. At the same depth of concrete, the chloride content gradually increases with temperature increasing, as well as the chloride diffusion coefficient. However, as the corrosion time of salt spray increases, the altering of chloride diffusion coefficient becomes less. Based on the Kelvin equation, a relationship between capillary pressure and water saturation in concrete was established, and a moisture transfer model for concrete in the process of moisture absorption and desorption was derived. Further, based on the established chloride diffusion equation and heat balance equation, a model of temperature-wet-chloride coupling chloride transfer was derived. Theory model simulation results show the transfer speed of chloride under the coupling of diffusion and capillary is higher than pure diffusion in moisture in the absorption process. However, the opposite is true in the desorption process. Moreover, with the increment of saturation rate, the capillary effect on chloride transport is enhanced.
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