Study On The Law Of Chloride Ion Transport In Concrete Under High Temperature And Humid Environment

In recent years,concrete structures in the marine environment have suffered from long-term erosion by chloride ions,leading to a reduction in structural performance due to steel corrosion,and most concrete structures require significant maintenance and repair costs after several years of operation,resulting in significant economic losses and wasted resources.Durability degradation due to chloride ion attack on concrete structures has become a hot topic of scientific research.Concrete structures in marine environments are located in a variety of locations and are subject to varying effects of erosion by seawater.Concrete structures located in upwelling and pinnacle areas are subject to long-term cyclic erosion by seawater,which is the most important resistance problem in marine environments.However,there are few studies on tidal fluctuations in areas affected by hot and humid air environments.The effects of hot and humid atmospheric environments on the internal laws of concrete and the transport mechanisms of chloride ions have not been elucidated,and the durability of concrete under the corresponding hot and humid environments requires further investigation.Therefore,based on the existing studies,analysis and numerical simulations on the chloride ion transport mechanisms of concrete in tidal zones under the influence of hot and humid atmospheres,The main work carried out on this paper are following:（1）Based on the existing research results,the attack mechanism of chloride ions in concrete and the factors influencing chloride ion transport are presented.A chloride ion transfer model is developed that integrates the material properties of concrete,the characteristics of the environment,the time-varying effects,and the bonding effects,and the reliability of the established multi-factor chloride ion transfer model is verified by numerical analysis of long-term exposure tests.（2）For the moisture movement characteristics during dry and wet cycles,the process of moisture movement change in concrete during dry and wet cycles of action was determined by numerical simulation analysis.Moisture transport is mainly considered for a Wet and dry cycle of 24 hours and a Wet and dry ratio of1:1.The process of moisture change during wet and drying phases and the process of moisture change with time at different depths were obtained.The results show that the wet and dry cycle of concrete within the moisture penetration depthΔx is more obvious,and when the moisture penetration depthΔx is exceeded,the internal moisture of concrete gradually decreases with increasing depth in accordance with the law of moisture change in the wet phase.The effect of temperature and ambient humidity on the variation of the internal moisture field of concrete is analysed,mainly by examining the role of temperature on the moisture diffusion coefficient and the process of change of the internal moisture of concrete under the action of hydrothermal coupling.The results of the study show that in low humidity environments,the change in humidity inside the concrete has little to do with the change in temperature,and the effect of temperature change in low humidity environments can be virtually ignored.In a high humidity environment,whether wet or dry,the humidity inside the concrete increases with temperature,and this trend of change is more apparent at the furthest distance from the surface of the specimen.（3）Concrete is considered as a composite material consisting of three phases,starting from fine grains,coarse aggregates,mortar and interface region,and based on the theory of Fuller aggregate classification and Monte Carlo methods,a shape model of random fine aggregate shape of concrete is constructed using MATLAB programming language and at the same time COMSOL to simulate the diffusion process of chloride ions in the random fine-grained aggregate model.The effects of fine-view parameters,mainly aggregate distribution morphology,volume fraction,particle size and diffusion characteristics at the interface zone,on the transport of chloride ions were analysed.The results show that the morphology of aggregate distribution in concrete has little effect on the transport of chloride ions.The higher the aggregate volume fraction,the lower the diffusion depth of chloride ions in concrete,and the lower the aggregate volume fraction,the higher the diffusion depth of chloride ions in concrete,and the diffusion depth of chloride ions showed an obvious downward trend with the increase of aggregate volume fraction of concrete.The larger the aggregate size of the concrete,the higher the probability of inhibiting the transport of chloride ions,but for the same aggregate volume fraction,the number of aggregate particles decreases with increasing aggregate size and,at the same time,the inhibitory effect of the aggregates on chloride ions decreases and,instead,the concentration of chloride ions inside the concrete increases.The chloride diffusion coefficient of the concrete interface phase has a great effect on the transport of chloride ions in concrete and the concentration of chloride ions in concrete increases as the D_itz/D_cpvalue increases.（4）For the environmental climatic characteristics of Beibu Gulf,the effects of ambient temperature,humidity,precipitation,tidal changes and wind speed on the surface of concrete structures are considered.Numerical simulations are used to analyze the chloride ion transport process under the coupling effect of temperature field,humidity field and chloride ion concentration field.The results show that the concentration of chloride ions in concrete with low water-cement ratio is significantly lower than that in concrete with high water-cement ratio,indicating that the diffusion depth of chloride ions increases with increasing water-cement ratio.The initial saturation inside the concrete has little effect on the transport of chloride ions under the action of wetting and drying cycles.The distribution of chloride ion concentrations in concrete is highly variable over time.According to the climate environment of Beibu Gulf sea,without considering the protective measures,the time of corrosion of steel bars in the 50mm position inside the concrete structure is 9.8 years.