Evolution Rule And Prediction Model Of Thermal Parameters Of Hydraulic Concrete Under Freezing And Thawing Condition

Freezing and thawing and temperature fatigue are important factors that affect the long-term service of hydraulic concrete structure durability and life prediction.In the process of freeze-thaw degradation,the thermal and mechanical properties of concrete are in a coupled evolution state,which together affect the safe operation of hydraulic concrete structures.At present,due to the high price and professionalism of indoor concrete thermal performance testing instruments.The evolution rule of the number of times,and then establish the evolution model of thermal parameters under the deterioration of hydraulic concrete freeze-thaw.The main research contents are as follows:(1)Test method for thermal parameters of hydraulic concrete under freeze-thaw degradation.During the freeze-thaw process,the temperature disturbance in the curing box(T = 40 ?,RH = 95%,Vw=0m/s,)was used to obtain the freeze-thaw cycle and each experience.The internal temperature-strain-time variation curve of hydraulic concrete specimens deteriorated by 50 freeze-thaw cycles;finally,the thermal parameters are reversed through the combination of orthogonal design + temperature field simulation calculation + neural network.(2)Evolution Law of Thermal Parameters of Hydraulic Concrete under Freezing-thawing Deterioration.Through the rapid freeze-thaw test and temperature disturbance test data of hydraulic concrete indoors,the thermal expansion coefficient,thermal conductivity,specific heat,and surface heat release coefficient evolution of hydraulic concrete after freeze-thaw cycle degradation are as follows: Before freezing and thawing,the thermal expansion coefficient of concrete decreases with the increase of water-to-binder ratio;As the number of freeze-thaw cycles increases,the thermal expansion coefficient of each group of test pieces fluctuates within 7% of the initial value;When the ambient wind speed Vw=0m/s and the temperature is 40 ° C,the concrete specimen is saturated,the thermal conductivity of the hydraulic concrete before freezing and thawing decreases with the increase of the water-binder ratio;The thermal conductivity of the hydraulic concrete before freezing and thawing decreases with increasing age;The thermal conductivity of hydraulic concrete with different amounts of fly ash before freezing and thawing is not much different,indicating that the appropriate amount of fly ash has no great effect on the thermal conductivity of hydraulic concrete;The specific heat overall change is not large;The heat release coefficient on the surface of hydraulic concrete increases with the increase of freezing and thawing times.(3)The evolution model of thermal concrete thermal parameters under freeze-thaw degradation is established.Because the thermal expansion coefficient and specific heat of hydraulic concrete freeze-thaw damage change with the increase of the number of freeze-thaw deterioration is not obvious.To construct the combined exponential model and fractional order model of thermal parameters evolution after freeze-thaw deterioration of hydraulic concrete considering the maintenance age.Through calculation,it is found that the thermal parameter evolution model of the 4 groups of hydraulic concrete after freezing and thawing deterioration fits the test results well.In the evolution model of the growth rate of the surface heat release coefficient,the average relative error and complex correlation coefficient of the two types of models are similar.The average relative error is around 0.25 and the complex correlation coefficient is around 0.90;The average relative error is around 0.2,and the complex correlation coefficient is above 0.96.