Study On Three-Dimensional Heterogeneous Heat Transfer Model Of Asphalt Pavement

Hot in-place recycling of asphalt pavement is a kind of maintenance technology for asphalt pavement diseases.Through the construction technology of milling after heating,adding regenerant and re-paving after stirring,100%recycling of old asphalt pavement materials can be realized without destroying aggregate gradation,and the maintenance and maintenance of pavement diseases can be completed.It has the advantages of low energy consumption,low pollution,green environmental protection and early recovery of traffic.As a kind of heterogeneous material,the temperature field distribution inside the asphalt pavement is not uniform during the heating process of the asphalt pavement.Therefore,it is of great significance to accurately control the heating temperature of the asphalt pavement to improve the heating quality.Taking the AC-13 asphalt mixture of the upper layer of asphalt pavement as the research object,the CT scanning image with an accuracy of 0.136 mm was obtained by using the industrial CT scanning equipment,and the image segmentation was carried out by using the Trainable Weka Segmentation software.The three-dimensional heterogeneous model of asphalt mixture was established in MATLAB.Based on the theory of heat transfer,the heterogeneous heat transfer model of asphalt pavement is established.The finite difference method is used to solve the temperature of each node in the heat transfer model,and the calculation time step is determined.The accuracy of the model is adjusted to 0.272 mm.The node-by-node calculation form is rewritten into the matrix calculation form,and the GPU is used to solve the matrix.The operation speed is greatly improved.By comparing and calculating the parameters such as porosity,thermal conductivity and specific heat capacity,and designing the heating test,the temperature rise curves of the heterogeneous model and the homogeneous model simulation test are compared respectively.The results show that the R~2(coefficient of determination)between the heterogeneous model simulation data and the measured data is greater than 0.95,and the statistical indicators are better than the homogeneous model,indicating that the calculation results of the heterogeneous model are closer to the real asphalt pavement situation,which verifies the correctness of the heat transfer model.Based on the heterogeneous heat transfer model,the heat transfer law and temperature rise characteristics of asphalt pavement under hot air circulation heating mode are studied.The control basis of heating duration and interval time under intermittent hot air circulation heating mode is put forward.Under the condition that the temperature of at least 90%of the asphalt pavement is lower than 200°C,at least 90%of the area at 4cm depth of the pavement can be heated to more than 100°C.The input heat flux,total heat and temperature distribution characteristics of asphalt pavement under hot air temperature of 600°C and wind speed of 20m/s are analyzed.The results show that after 3524s(58.73min),90%of the area at 4cm depth is heated to100°C.During the whole heating process,the temperature of up to 10%of the asphalt pavement surface exceeds 200°C.After the heating is completed,99.62%of the area temperature is between 100°C and 200°C in the depth range of 0-4cm.The total heat energy input into the road surface is 3.6×10~7J/m~2,and the total heat energy transferred to the depth below 4cm is7.3×10~6J/m~2.The utilization efficiency of heat inside the asphalt pavement is 79.69%.