Study On Optimal Design And Performance Of Mixture Ratio Of Hot Recycled Asphalt Mixture With High Volume RAP

With the rapid development of infrastructure construction in China’s highway industry,asphalt pavement has entered a crucialperiod of paying same attention to construction and maintenance.However,huge quantities of recle aimed asphalt pavement(RAP)milled from old asphalt pavement have not been well recycled.A large number of RAP adopt centralized accumulation treatment,which will not only seriously pollute the environment and waste renewable resources,but also occupy non-renewable land resources.Although the recycling technology of low-volume RAP has gradually matured,the amount of RAP is small and the utilization rate is not high.Therefore,how to carry out the research on the recycling of high-volume RAP to reduce the waste of resources and the cost of the project has become an urgent problem to be solved.The technology of plant-mix hot recycling can make the recycled mixture have abetter recycling effect.Therefore,this paper will study the gradation optimization design and the regeneration effect of the high-volume RAP plant-mix hot recycled asphalt mixture.Firstly,this paper analyzed the old asphalt content,aging degree,RAP gradation,and basic physical and mechanical properties in the RAP.S econdly,based on the response surface method,the gradation of the high-volume RAP plant-mix hot recycled asphalt mixture was carried out.Optimized the design,then studied the pros and cons of its road performance through experiments on the optimized mix ratio.Ultimately,based on the freeze-thaw cycle test,the freeze-thaw damage resistance of the plantmixed hot-recycled asphalt mixture with a large amount of RAP was studied.and the relationship between the Marshall stability,splitting strength and ultrasonic wave velocity of the recycled mixture was established.the establishment of the regeneration mix The relationship between Marshall stability,splitting strength and ultrasoni c wave speed.Exploring the application of ultrasonic non-destructive testing technology on asphalt pavement.The main research conclusions of this paper are as follows:(1)The gradation of RAP has been refined.the basic technical indexes such as moisture content and crushing value of RAP all meet the recycling technical specifications.The highest content of 0-5mm old asphalt in the 4th RAP was 7.62%,the lowest content of 15-20 mm old asphalt was 1.42%.With the increase of rejuvenator content,the penetration and ductility of recycled asphalt gradually increase,and the softening point and viscosity gradually decreas.(2)Based on the response surface method,the mix proportion optimization design of high-volume RAP plant-mix hot recycled asphalt mixture has a remarkable effect.Among the four influencing factors,the oil aggregate ratio has conspicuous influence on the voidage,aggregate voidage,asphalt saturation and Marshall stability of recycled Marshall specimen.The second-order model established in this paper has noteworthy accuracy,and the response surface method can be used in asphalt mixture design.(3)The optimized high-volume RAP plant-mixed hot regenerated asphalt mixture has good road performance.It shows that with the gradual increase of the RAP content,the high-temperature stability of the regenerated asphalt mixture gradually increases,while the water permeability and water permeability Stability and low-temperature crack resistance gradually decrease.(4)With the increase of freeze-thaw cycles,the damage degree of Marshall stability and splitting strength gradually increases,and the water permeability coefficient gradually increases.With the gradual increase of RAP content,the value of Marshall stability and splitting strength d ecreases faster,and the water permeability coefficient increases.After 18 freeze-thaw cycles,the Marshall stability and splitting strength of 70% RAP recycled asphalt mixture have the largest damage value.while the damage degree of Marshall stability a nd splitting strength of 30% RAP is the smallest.The temperature affect the ultrasonic wave velocity,while the emission voltage and the type of coupling agent has little influence on the ultrasonic wave velocity.There is a well correlation between the Marshall stability and splitting strength and the modified ultrasonic wave velocity,which indicates that the ultrasonic wave velocity can characterize the Marshall stability and splitting strength of asphalt mixture.It provides technical support for the a pplication and promotion of ultrasonic nondestructive testing technology on asphalt pavement.