Numerical Simulation Of Temperature Field Of Asphalt Pavement By Hot Air Circulation Heating Method

Control the heating temperature of asphalt pavement is the key to ensure the quality of hot in-place recycling.However,there is no practical and feasible control scheme for the pavement temperature at the construction site.Usually,real-time monitoring is used to adjust the operating parameters of the recycling unit,resulting in over-temperature or under-temperature frequently of the pavement.The heating level of the pavement in the same operation segment is uneven,and there are differences in the performance of the recycling pavement.In order to ensure the construction quality of recycled pavement,the heating temperature of the pavement should be strictly controlled.This requires construction workers and managers to master the methods of adjusting the mechanical parameters under specific environmental conditions.Based on the theory of heat transfer and the principle of hot air circulation heating,the paper establishes the heat conduction equation and boundary conditions,which is suitable for the asphalt pavement temperature field by hot air circulation heating,deduces the analytical solution of the temperature field.And,with the ABAQUS finite element calculation software,the temperature field simulation model under complex conditions was established,and the effect of different factors on the temperature field of pavement heating was systematically analyzed.By comparing the sensitivity relationship between each factor and the temperature of each layer of the pavement,the main factors that influencing the temperature field of pavement heating are determined.And take the main factors as the reference targets and control objects,give the recommended values and the reference values of operation units under different working conditions,as a construction guide in the usual semi-rigid asphalt pavement structure.Firstly,based on the basic theory of heat transfer theory,the heating process of asphalt pavement is simplified as an unsteady heat conduction model of a semi-infinite object.From the energy conservation law,the heat conduction differential equations of the heating temperature field of pavement are deduced.According to the working principle of the hot air circulation heating machine,it is proposed that the pavement heat is provided by two parts:one is the convection heat transfer effect of hot air on the asphalt pavement,and the other is the radiation heat transfer effect between the surface of the high temperature mechanical metal base plate and the road surface.Discuss and determine the calculation formula of convective heat transfer coefficient h and system blackness εs.The separation of variables method was used to solve the temperature field control equations under two kinds of boundary conditions,and the results were combined to obtain the analytical solution of the asphalt pavement temperature field by hot air circulation heating.The analytical solution can calculate the temperature value at any depth of the pavement at any time under simple conditions.However,the form of the analytical solution is complex and it is difficult to deal with the temperature field problem under complex conditions,so it can be used as a theoretical support for establishing a numerical model.Secondly,use ABAQUS to establish a numerical simulation model of pavement heating temperature field,and discuss the setting method of the model solution conditions.There is a small range of temperature fluctuation caused by heat loss in the heating boundary,which can be neglected under certain circumstances.With the existing research results references,it is emphasized that the thermal conductivity of the pavement material in the model must be set as a function of the road surface temperature change through calculation and comparison.Simulate the initial temperature distribution of the pavement structure heating by using the PARK pavement temperature calculation model,and use FORTRAN to edit external subroutines to implement two types of boundary conditions.By comparing the field measured data with the model simulation results,the model has a good effect on the surface temperature of the entire heating process and the milling surface.Thirdly,with the aid of the established simulation model,considering the mechanical parameters,construction parameters and environmental parameters,systematically analyze the effects of various factors on the temperature field of pavement heating.The results show that the hot air temperature has a significant effect on the temperature of each layer of the pavement.Increasing the flow velocity of the hot air only can increase the temperature of the shallow of the road surface.The heating time is the main factor determining the temperature transmission depth.The temperature of the road surface changes significantly when the operation speed of the unit is adjusted within a certain range.When the speed is increased to a certain value,the temperature change tends to be stable.Setting the mechanical heating interval can effectively increase the temperature of the deep road surface,which is conducive to the milling operation,but blindly increasing the interval time will reduce the work efficiency of the unit.Under the same conditions of the overall heating level,the process of gradual change of the road temperature will have a big difference when using different power combinations.The mechanical heating power does not increase monotonically.When the next mechanical power is not different,the road surface extremum temperature can be greatly reduced,and increase the temperature of the deep road surface.The pavement structure is always in a stable heating environment,and it is not easy to produce extremely high temperatures.During the construction process,changes in the ambient temperature have little effect on the road heating effect,but the initial temperature value of the road under different environmental conditions is an important factor that determines the value of mechanical parameters and construction parameters.The cooling time determines the effect on the road pavement.To do construction at a higher temperature environment,can reduce mechanical energy lost,and increase construction efficiency.Finally,the concept of sensitivity was introduced to analyze the effects of various factors on the road surface temperature.The sensitivity curves at various locations were compared to determine the hot air temperature,The main effective factor of the heating temperature field contains hot air flow rate,unit operating speed,and initial road surface temperature.Taking the common semi-rigid asphalt pavement structure as an example,eight commonly-used operation plans are drawn up,and the temperature cloud maps of key layers on the road under different working conditions are plotted.Based on the proposed temperature control conditions,the application of the operating plan is reversed.Combining with engineering fact,the recommended values and reference values of the unit working plan under different working conditions are given,which provides convenience for the adjustment and control of the pavement temperature during construction.