| Under the guidance of the national renewable resources and remanufacturing strategy and low carbon environmental protection concept,asphalt pavement recycling technology has become a hot topic in road construction.The hot mix plant recycling is one of the key technologies because of the better performance of the output mixture.But the regeneration behavior of aged asphalt and the dispersion state of RAP are very complicated in the process of mixing.Therefore,exploring the influence of various factors in this process has important theoretical significance for the optimization of hot mix plant recycling,the design and performance evaluation of recycled asphalt mixture.The influencing fectors and mechanism of the compatibility of the fresh and aged asphalt and the performance of recycled mixture in the hot mix plant recycling were studied by the combination of laboratory test and discrete element simulation.It is expected to provide theoretical reference for the design and construction of heat-tracing recycled asphalt mixture.Based on fresh and aged superimposed miscible asphalt samples,temperature scanning rutting factor of DSR,creep stiffness S and creep rate m of BBR at-12℃ are used to inverse the degree of miscibility of new and old bitumen.The results show that G*/sinδ is the most regular,S is the second,m is the worst.The degree of miscibility increases with the increase of time or temperature.The influence of the two factors is interchangeability.The higher the initial temperature is,the longer the time required to raise the temperature is.In the construction of plant mixing hot recycling,if the time from discharging to rolling is extended for 40 mins,the miscibility effect is equivalent to the temperature increase of 40℃.Marshall uniaxial penetration test at 60℃ and bending test at-10℃ were tested.If the proportion of wet mixing time in the total mixing time increases by 22%,the penetration strength and maximum flexural tensile strain of the mixture will increase by 16.0%and 18.4%respectively.Therefore,the recommended value of time for mixing hot regenerated plants was proposed.At 100,120 and 140℃,the penetration strength increases at an average rate of 14.6%/20℃ with the increase of RAP preheating temperature,but the maximum flexural tensile strain reaches a peak at 120℃.The recommended preheating temperature of RAP is 120℃.Under the condition of aging degree corresponding to the service life of 3,6 and 9 years,with the deepening of aging,the overall improvement of penetration performance is small,but the low temperature performance is greatly reduced.The average decrease of RAP dosage by 8.9%is equivalent to the decrease of RAP service life by one year.The discrete element was used in Marshall uniaxial penetration test of recycled mixture with different RAP dispersion.With the increase of RAP dispersion,the simulation value of penetration strength of recycled mixture was improved,the distribution uniformity of meso contact force was improved,the contact number was increased,and the Displacement of material in the mixture is reduced.The uniformity of contact distribution and the’ amount of contact may be one of the factors for the difference in penetration strength of mixtures with different dispersibility. |
