Study On Simulation And Control Of Temperature Field In Hot In-place Recycling

Hot in-place recycling(HIR)of asphalt pavement can treat multiple distresses,achieve 100% reuse of old materials,and have faster construction speed and has become one of the most popular maintenance technologies.As a highly integrated construction technology,the heating of the original road surface is a key part of the HIR.The quality of heating directly affects the performance of recycled pavement.At present,there are still no indices and standards to evaluate the heating quality to regulate the heating process;the traditional intermittent multi-stage heating method still produces overheating,which easily leads to problems such as asphalt transition aging.Therefore,this paper mainly studies the quality field evaluation and optimization of geothermal regenerative heating.Firstly,the on-site heating temperature field of various heating units is collected by infrared thermal imager,and the distortion thermograms collected on the scene are corrected by digital image processing and artificial neural network,which provides the possibility of quantifying the temperature of the heating temperature field.Then,from the aspect of heating temperature uniformity,heating effect and overheating,three indexes:transverse uniformity coefficient T_u,representative value RT,proportion of temperature above 200?PTA200 were proposed to evaluate three kinds of heating systems respectively.The result indicates that the flame system and infrared radiation system have better heating effect,and the hot recycling wind system has better temperature uniformity.As the road surface temperature rises,in order to prevent overheating,the heating uniformity has higher requirement.When 200? is used as the high temperature critical temperature,RT+RT×Tu should be less than 190?.Secondly,a two-dimensional mesoscopic model of asphalt mixture was established by random aggregate algorithm.The effects of gradation,oil-stone ratio and void ratio on the thermal properties of asphalt mixture were analyzed by simulation test.Then,the one-dimensional heat transfer model of asphalt pavement is established.The on-site test of HIR is carried out and the temperature of the key point is measured through buried the temperature sensor.Then the heating temperature field of the asphalt pavement is reconstructed through fitting the heat transfer model and the heat flux density of preheater is calculated at the minimum and maximum power.The genetic optimization algorithm is used to find the optimal combination of heating units at different operating speeds,which not only can meet the milling temperature requirements but also minimize energy consumption.Finally,through the numerical simulation analysis,the traditional continuous constant power heating and intermittent constant power heating are prone to overheating.The improved continuous constant temperature variable power and intermittent sensitive temperature constant power heating method can avoid overheating,but it is difficult in practical engineering.Finally,the ideal constant temperature heat flux density curve is discretized into several constant values,and a discrete constant temperature heating method is proposed,which can still meet the constant temperature heating requirements,and can be applied in the actual heating unit.The layered heating construction process greatly increases the heating rate.