Research On Mixing Condition And Performance Prediction Of High Content RAP Thermal Reclaimed Asphalt Mixture

Since 1978 reform and opening up,our country has gradually changed from vigorously building new highway stage to vigorously maintaining the stage.In the maintenance stage,a large amount of used pavement materials will be generated,which stimulates the development of recycling technology under the pressure of resource shortage and environmental protection.However,at present,the content of RAP(asphalt mixture recovery material)in practical application is basically within 30%,and when the content reaches more than 30%,the fusion degree of the old and new asphalt decreases sharply,and it is difficult to reach 100% fusion.In the specification,it is usually assumed that the old and new asphalt are completely integrated,coupled with the inconsistency between the indoor test and the actual project.As a result,the regenerated asphalt pavement needs to be overhauled again after several years of service,which is difficult to reach the designed service life.In this thesis,the aging degree of asphalt and the suitable mixing temperature range are predicted by asphalt aging kinetics and composite viscosity-temperature curve.Then,considering the incomplete integration of new and old asphalt,the ore mobility is introduced to optimize the mix design.The RAP content studied in this thesis are: 20%,30%,40% and 50%;For the content below 30%RAP,it is assumed that the old and new asphalt are completely fused.When the RAP content is greater than 30%,by changing the RAP content,combining the specification and the mixing interval calculated above,changing the mixing temperature(150℃,160℃,170℃)and mixing time(120s,150 s,180s)of the mixture,we can get several different AC-16 type hot reclaimed asphalt mixtures.Taking high temperature stability performance and water stability performance as the main performance testing indexes,the optimal mixing conditions for thermal regenerated asphalt mixture under different RAP dosage are obtained.When RAP dosage is 20%-30%,the mixing time is 150 s and the mixing temperature is 160℃,which meets the specification requirements and is economical.When RAP content is40%,the water stability performance decreases greatly.The mixing time is 180 s and the mixing temperature is 160,which can meet the specification requirements.When the mixing amount is 50%,the mixing time should be 180 s,and the mixing temperature is170℃,the recycled asphalt mixture has better water stability.On the other hand,in order to greatly improve the predictability of the road performance of the thermal reclaimed asphalt mixture in the actual project,the BP neural network of MATLAB is used to predict the performance.The mixture density,void fraction,asphalt saturation,mineral gap rate,stability and asphalt dosage are taken as the input layer,and the dynamic stability,residual stability and freeze-thaw splitting strength ratio are taken as the output layer.Network training and learning.The maximum relative error of the prediction results is 4.28%,and the minimum error is2.35%,which is proved to be feasible to use BP neural network for performance prediction within the requirement of numerical analysis specification(±5%).In order to further reduce the error,a new prediction model was established by introducing genetic algorithm combined with BP neural network,and the maximum relative error was only2.26%.The error is significantly reduced and the prediction results are more accurate.The neural network model can not only correctly predict the performance of recycled asphalt mixture,but also help to find a series of problems that may occur in the use of asphalt pavement in the future,saving human and material resources,which is of great significance.