The Comparative Research Of Hot Air Single-step And Multi-step Heating Processes For Asphalt Pavements

With the gradual development of hot in-place recycling(HIR)for asphalt pavements,pavement heating as one of the key processes has received widespread attention in the pavement maintenance industry,in which hot air heating is one of the main heating methods,the heating process has problems such as uneven heating and long heating time.To address the above shortcomings,this paper aims to improve the effect of hot air heating on asphalt pavements by changing the heating process.According to the number of times the pavement is heated and milled during the regeneration process,the heating process is divided into a single-step method and a multi-step method.This paper compares and analyses the heating effect of the two processes of hot air heating of asphalt pavement through simulation to ensure that the pavement heating meets the temperature requirements and improves the pavement heating effect.This paper bases on the asphalt pavement structure and the internal thermal conductivity model of the pavement,combined with the convective heat transfer parameters of the hot air and the road surface.The mathematical model of the temperature field of the hot air heated asphalt pavement was established by the finite difference method.The simulation model was established based on the existing hot air heating device structure,and the accuracy of the simulation results was briefly verified by comparing the numerical calculation results with the Fluent simulation results using MATLAB.Based on the simulation results of the input heat flow density under different parameters of hot air,the mathematical relationship between hot air velocity,temperature,and heat flow density is established through regression analysis,which provides a theoretical basis for the power input of the hot air heating device.For the single-step process of HIR,the parameters affecting the heating effect of the pavement in the hot air single-step process are analyzed,and the temperature rise characteristics and temperature distribution of the asphalt pavement under different levels of each parameter are simulated and analyzed,and the effects of each parameter on heating uniformity,pavement energy absorption efficiency and aging ratio of road surface materials are studied.In response to the shortcomings of the hot air single-step process with a long heating time,the hot air multi-step process is proposed for heating the road surface.According to the relationship between hot air operation parameters and pavement temperature rise characteristics during hot air multi-step heating,the hot air operation parameters of the multi-step process to meet the pavement temperature requirements were determined,and the pavement heating uniformity,energy absorption efficiency and aging ratio of road surface materials under the parameters were analyzed.The simulations show that the heating speed of hot air multi-step method is higher than that of single-step heating,the aging amount of road surface material in multi-step heating process is lower than that of single-step heating,and the energy absorption efficiency of multi-step heating road surface is slightly lower than that of single-step heating.Through the comparative analysis of the two heating processes hot air heating effect,it provides a reference for engineering applications.