Study On Road Performance And Mechanical Properties Of The Warm Recycled Asphalt Mixture With High Volume RAP

In recent years,with the early construction of asphalt pavement gradually reaching the design life and the increasing traffic load,the focus of the development of China’s highway industry has gradually shifted from large-scale new road construction to the stage of reconstruction,expansion or overhaul of old roads.In this way,a large amount of waste asphalt mixture is produced.According to incomplete statistics,most of the waste materials are not used effectively,but simply buried or exposed to the air,which not only takes up land resources,but also causes pollution to the local environment.However,the current four mainstream regenerative technologies have their own merits and shortcomings,especially the small amount of RAP doping,which seriously restricts the widespread use of regenerative technology.As a result,temperature regenerative technology has emerged,which not only effectively regenerates pavement milling material,but also reduces the mixing and paving temperature of the mixture and realizes the secondary use of waste asphalt mixture.In order to compensate for the lack of significant cooling effect of traditional warm regeneration agents and the low dosing of RAP,this study was carried out on the regeneration performance of recycled old asphalt in pavement milling materials using a new surfactant type of warm regeneration agent developed independently.Firstly,the recycled RAP was processed,the RAP gradation type and the properties of old asphalt were analyzed,and the effects of different warm regeneration agents on the three main indicators of old asphalt and Bush viscosity were investigated to characterize the regenerating effect of warm regeneration agents,in order to determine the optimal warm regenerating agent.The results show that with the increase of the dosage of warm regeneration agents,the needle penetration and ductility of recycled asphalt gradually increase and 135°C viscosity and softening point decreases.In terms of conventional performance indicators,the recommended dose of warm regeneration agents is8% of the mass of the old asphalt.In order to investigate the rheological properties and load recovery capacity of warm recycled asphalt with different warm regeneration agents,this study investigated the rheological properties of five different doses of warm recycled asphalt with the help of DSR and BBR on the basis of rheological principles.The results show that the increase in the dosage of warm regeneration agents gradually decreases the recovery rate R of recycled asphalt and increases the creep flexibility of non-recoverable asphalt,which in turn weakens the recovery ability of asphalt pavement and adversely affects the high temperature rutting resistance of asphalt.However,the temperature sensitivity and low temperature cracking resistance of recycled asphalt were significantly improved.In order to investigate the road performance of warm recycled asphalt mixtures with large RAP doses,this study investigated the high temperature stability,low temperature crack resistance,water stability and fatigue performance of nine warm recycled asphalt mixtures with different RAP doses,new asphalt types and grading types based on conventional road performance tests and compared them with conventional hot mix asphalt mixtures.The results show that with the increase of RAP,the high temperature performance of warm recycled asphalt mixtures improved significantly,but the crack resistance and water stability performance of low temperature mixtures decreased,and fatigue life gradually decayed.With the same amount of RAP,AC-25 warm recycled asphalt mixture has better high temperature stability than AC-20 warm recycled asphalt mixture,but the low temperature cracking resistance and water stability are reduced.In order to investigate the mechanical properties of warm recycled asphalt mixture with large RAP doses,dynamic modulus tests,repeated load creep tests,uniaxial penetration tests and unconfined compression tests were carried out on nine warm recycled asphalt mixtures and conventional AC-20 hot mixed asphalt mixtures in this study.The results show that increasing RAP doses and adding new modified bitumen can improve the high temperature permanent deformation,uniaxial shear and elastic deformation resistance of the asphalt mixture,and improve the mechanical properties of the mixture.In order to investigate the relationship between some of the road properties and mechanical properties of warm recycled asphalt mixture at different RAP dosing levels,correlation analysis was carried out with Pearson correlation coefficients.The results show that dynamic stability has a good correlation with flow number,penetration strength,unconfined compressive strength,internal friction angle and cohesion;The correlation between the rutting depth of Hamburg at50℃ and other parameters is the worst,and the rutting test at 60℃ can better reflect the hightemperature rutting resistance of the mixture under actual road conditions to some extent.