Research On Key Technologies Of Hot Recycled Modified SMA Asphalt Pavement

In recent years,the structure of SMA asphalt pavement has been widely applied in China.The current SMA pavement in China has been more than twenty thousand km.In the process of large and medium repair,a large number of waste asphalt mixtures will be produced.The regeneration and utilization of the old materials will have high economic and environmental benefits.Therefore,it is necessary to regenerate large quantities of SMA waste asphalt mixture at present.At present,the recycling technology of SMA asphalt pavement in our country is still at the initial stage.Based on this,this paper systematically studies the regeneration technology of modified SMA asphalt mixture,in order to find out a suitable method for regeneration of modified asphalt pavement.First of all,this paper summarizes the methods and advantages and disadvantages of the Old Asphalt Extraction and recovery methods commonly used in the laboratory,and puts forward the improvement methods for the existing problems in the old asphalt recovery process.Based on the composition and aging mechanism of SBS modified asphalt,the composition changes and functional groups of SBS modified asphalt before and after aging are analyzed by four component asphalt and infrared spectrum test method.The results show that during the aging process of SBS modified asphalt,light components react with oxygen,SBS double bonds react,form a large number of carbonyl groups,and gradually change to a larger molecular weight substance,which increases the viscosity and hardness of asphalt.Then,starting from the regeneration mechanism and function of regenerative agents,the quality standards of domestic reclaiming agents were summarized and analyzed.The performance of reclaimed asphalt in two mixtures of SMA-13 and AC-13 was studied by three indexes test,rotating film heating test,dynamic shear rheology test,low temperature bending creep test and Brinell viscosity test.The test results showed that the regenerative agent can restore the technical performance of aging SBS,improve the ductility of asphalt obviously,and enhance the low temperature cracking resistance of asphalt.The G*/sin delta value of recycled asphalt is much lower than that of old raw asphalt.During the aging process of asphalt,the lightweight components of recycled asphalt and asphalt have undergone a certain degree of volatilization and physical and chemical effects,making the overall hardness and viscosity of recycled asphalt become larger.Finally,the best additive amount of recycled asphalt is 5%.Thirdly,the composition of SMA-13 old material was analyzed,and the three aggregate new aggregate was used to design the aggregate gradation.The amount of RAP old material was controlled by 90%,85% and 80% respectively.The mix proportion design of SMA-13 recycled asphalt mixture was designed.Finally,the best oil stone ratios of three RAP old materials were determined to be 6.15%,6.12% and 6.08%.When the ratio of oil to stone is higher,the optimum ratio of asphalt to aggregate is relatively reliable at the initial stage of construction,and in addition,under the same asphalt aggregate ratio,the void fraction of recycled asphalt mixture decreases with the addition of old materials,and the existence of old materials is not conducive to compaction of mixture.Thirdly,rutting test,low temperature bending test,immersion Marshall test,freeze-thaw splitting test and sherlburger leak test were carried out to study the road performance of three SMA modified asphalt mixtures with RAP content.The test results show that the increase of RAP content can effectively improve the high temperature stability of modified asphalt mixture,but the low temperature cracking resistance of recycled asphalt mixture is low.The water resistance of the three recycled SMA mixtures meets the standard requirements,but decreases with the increase of RAP content.The leakage loss of the three recycled SMA mixtures meets the specification requirements,and the compatibility between the regenerative agent,the new asphalt and the old modified asphalt is good.Finally,the key construction technologies of SMA geothermal recycling asphalt mixture are discussed.Taking the test section of SMA-13 type geothermal recycling asphalt mixture at an interchange road in Youyang,Chongqing as an example,the engineering application results show that the technical indexes such as flatness and skid resistance of the recycled asphalt pavement meet the technical specifications,and the overall performance of the road surface is good.