Experimental Study And Numerical Simulation Of Temperature And Humidity Field Of Early-age Concrete

After the completion of pouring,the concrete has experienced a changing process of behavior from flow state to plasticity to final solidification.At the same time,it has experienced drastic changes in temperature and humidity,and there is a coupling effect between temperature and humidity.Due to the low strength of concrete in this period,the cracking phenomenon of concrete caused by temperature and humidity deformation in the early stage is very common.Most of the existing research methods ignore the changing process of behavior of early-age concrete and the coupling effect between temperature and humidity,which is not enough to reveal the change law of temperature and humidity of early-age concrete.Therefore,from the perspective of coupling,it is of great significance to study the temperature and humidity field of early-age concrete and establish the relationship between the temperature and humidity field of concrete to evaluate the cracking performance of early-age concrete.The main research contents and conclusions of this paper are as follows:Firstly,based on the theory of concrete temperature and humidity field,the early-age concrete thermal-hydraulic coupled model is established.The adiabatic temperature rise test and internal humidity monitoring test were carried out for three groups of concrete with different water-binder ratio(0.33,0.43 and 0.57),the values of thermal-hydraulic coupled model parameters were determined,and the hydration heat release law of concrete and the distribution characteristics of internal humidity were studied.It is found that the hydration exothermic rate of concrete decreases first,then increases and then decreases with time,and finally tends to be stable.The maximum hydration exothermic rate decreases with the increase of water-binder ratio.The distribution and development of internal relative humidity of early-age concrete are affected by time,space and initial moisture distribution at the same time.The self-drying effect decreases with the increase of water-binder ratio of concrete.The external drying effect mainly acts within 8cm from the drying surface.At the later stage of hydration reaction,when the relative humidity of C30,C50 and C60 concrete is lower than 96%,93%and 88%respectively,the hydration reaction rate is close to 0.Secondly,based on the measured data of the internal humidity monitoring test,the BP neural network is used to invert the humidity field.The error of humidity field after inversion is small.At the same time,the humidity field under different calculation schemes is simulated,and it is found that the change of parameters has a great influence on the concrete humidity field.Based on ANSYS parametric language,The temperature field of concrete supporting platform under three different working conditions is simulated.The results show that:The peak temperature and maximum temperature difference of the hydration degree model based on the equivalent age are higher than those of the traditional model,and the peak time is also advanced.The thermal conductivity and specific heat of all parts of the structure decreases with the passage of time and remains basically unchanged.However,for the structure similar to the adiabatic state,the specific heat increased slightly and then decreased gradually in the early stage.Finally,using the thermal-hydraulic coupled model established in this paper and the model parameters determined by experiments,the concrete thermal-hydraulic coupled simulation of concrete embankment is carried out.The results show that after considering the thermal-hydraulic coupled,in the humidity saturation period,the temperature and humidity are the same as those without considering the coupling effect.After entering the humidity decline period,comparing with the condition of without considering the coupling effect,the temperature will be low,the relative humidity will be high.The moisture diffusion coefficient decreases from the inside to the outside of the structure,and the moisture diffusion coefficient near the surface of the structure is close to 0,which hinders the development of external drying to the inside of the structure.