Study On Humidity Field Characteristics Of Early Age Conerete Struetures In Cold Area

When the concrete is exposed to a negative temperature environment in the early age,the internal relative humidity will continue to change under the action of ambient temperature and humidity,affecting its physical properties,and then causing changes in the performance of the concrete structure.Existing research is mainly concentrated on the temperature conditions above 0 °C to study the internal relative humidity of concrete,for the temperature conditions below 0 °C of the concrete internal humidity transport and concrete internal humidity field related research is relatively small,based on this,the article through the combination of theory,test and numerical simulation method,carried out under negative temperature conditions,heat and humidity coupling under the action of the early age of the concrete internal relative humidity transmission and distribution change law study.In the theoretical section,the causes of relative humidity changes in concrete in cold areas are summarized and analyzed.At room temperature,the moisture in the concrete is in the form of liquid and gaseous throughout the internal pores,and migrates under the drive of temperature gradient and internal and external humidity difference,and the transmission process conforms to Fick’s law;at negative temperature,the moisture in the concrete includes frozen solid ice crystals,unfrozen moisture in the pores of the frozen area and unfrozen moisture in the unfrozen area,and the content of the latter two kinds of moisture maintains a dynamic balance relationship with the environment,and satisfies the migration law of moisture at room temperature.The effect of the single action of ambient temperature and ambient temperature and ambient humidity in cold areas on the relative humidity change of concrete at different depths from the upper surface at different depths of different initial humidity was studied experimentally.In the process of testing,the temperature-relative humidity change of each specimen can be divided into five stages: temperature plummeting,relative humidity increase,slow decrease in temperature and decrease in relative humidity,temperature fluctuation,small fluctuation in relative humidity,sudden increase in temperature,decrease in relative humidity,slow increase in temperature,and increase in relative humidity.And for the same initial humidity of the specimen,the closer to the upper surface,the greater the relative humidity change,the greater the environmental impact;at the same depth from the upper surface,the larger the initial humidity of the specimen is affected by the environment.Simulation of humidity fields within concrete using COMSOL.According to Fourier’s law and Fick’s law of diffusion,the theoretical model of heat and humid coupling and transmission is established,the damp heat coefficient is modified based on the test results,the correctness of the model is verified by the test results,and the factors affecting humidity diffusion are comprehensively considered from the two aspects of the concrete’s own conditions and environmental conditions.The simulation results show that the internal humidity distribution of the concrete in the early age under negative temperature conditions is uneven,there is a significant humidity gradient,the humidity near the diffusion surface area will be lower,and the simulation results and the measured results are in good agreement.