Research On The Proportion Design And The Performance Of The Hot Recycled Asphalt Mixture

During long service period of the asphalt pavement, due to the influence of vehicle loadsand the natural factors, the asphalt binder may become aged, and the aggregate may be worndown and then become thinner, which may lead to relatively troublesome diseases ofpavements and even influence the performance of the asphalt pavement. In China, manynew-built high-grade roads and municipal roads are facing or wil face maintenance tasks ofthe asphalt pavement, and they are transited from the period of “Focusing on the construction”to the period of “Focusing on both of the construction and the maintenance”. In order to settleproblems of the environmental pollution and the ecological damage caused during themaintenance process of roads in our country and reduce the consumption of resources, therecycling technich of the asphalt pavement are gradually gaining attentention. Compared withother recycling techniches of the asphalt pavement, the hot recycling technich of the asphaltpavement has relatively wide scope of application, so the hot recycled asphalt mixture arestudied in detail by this paper.First of all, the reclaiming and preparing ways of the RAP material are analyzed, and thecentrifuge separation method is determined to be adopted to extract the aged asphalt in theRAP material in experiments in this paper, and the Abshen method is adopted to do therecycling. Then, the gradation of the aged aggregate, the property and the volume of the agedasphalt in the RAP material are analyzed, and the aged asphalt is found to be seriouslydeteriorated. Secondly, based on studies of predecessors, the mechanism and the method ofthe reclamation of the asphalt are analyzed, and through the analysis, the recycling way that isto simultaneously add the regenerant and the new asphalt is adopted. Then according to therelational graph of the viscosity, the best amount of the regenerant is determined, and thenthrough the diffusion test of the regenerant, the appropriate adding way of the regenerant istentatively probed, and it is found that the diffusion of the regenerant to the aged asphalt inthe RAP material is a complex process. Thirdly, three different proportions of the RAPmaterial which are30%,40%and50%are chosen to do the target proportion design of thehot recycled asphalt mixture. In the proportion design, in order to make the proportion of theRAP material to be a simple variable, the gradations of the aggregate of the hot recycledasphalt mixture with three different proportions of the RAP material are allocated to be closed,and for the maximum theoretical specific gravity of the hot recycled asphalt mixture, afterconsidering the regenerant and the aged asphalt and the aged aggregate in the RAP material,modified formulas that are different from the formulas to calculate the maximum theoretical specific gravity of normal asphalt mixture are adopted to do the calculation. Then, it isfound from the results of the proportion design that the best proportion of new asphalt that isestimated by formulas is larger than the practical situation.Last, the performances of the hot recycled asphalt mixture under different proportion ofthe RAP material are studied. Through experiments, it is found that the high-temperaturestability and the anti-cracking ability under low temperatures of the hot recycled asphaltmixture under three different proportion of the RAP material could reach the requirement ofthe standard; however, the water stability with50%RAP material could not reach therequirement. With the increase of the proportion of the RAP material, the high-temperaturestability of the hot recycled asphalt mixture increases, the water stability is on a decliningcurve, and the varying pattern of the anti-cracking ability under low temperatures isunremarkable. The reason of the unremarkability may be the experimental error, thevariability of the RAP marerial, the influence of large mineral aggregate particles and thelow-temperature performance of the recycled asphalt and so on. Then, based on theperformance, for the experiments in this paper, the reference value of the proportion of theRAP material of the hot recycled asphalt mixture with the RAP material on the Yuqianhighway is determined to be40%.