Research On High Modulus Asphalt Mixing Technology With Plant Mixing Hot Regeneration

In this paper,the design concept of French high modulus asphalt concrete is applied to the plant-mixed hot recycled asphalt mixture,and the concept of graded recycling is proposed.The research is carried out from the aspects of evaluation and optimization of aggregate characteristics,gradation selection and design.Moreover,the comparison between graded recycling method and traditional recycling method,performance optimization and influencing factors of high modulus recycled asphalt mixture were investigated in this paper as well.So that the high proportion recycling of used materials and the improvement of recycled mixtures performance could be achieved.Firstly,this paper evaluated the clustering characteristics of recycled aggregates by graded extraction and crushing experiments.It was found that the clustering phenomenon of recycled aggregates mainly occurs in the coarse part of > 4.75 mm and the clustering level was improved with the increase of particle size.The clustering of recycled aggregates can be divided into three types: weak clustering,strong clustering and old aggregate,among which the content of weak clustering structure has the greatest influence on the performance of recycled aggregates.Quantitative evaluation methods of RAP clustering characteristics include Needle flake content(Q),Extraction loss rate(L),Crushing loss rate(S)and Stability index(w),as well as a rapid evaluation method of RAP quality by AIMS test.In addition,the optimized classification method of RAP was proposed,which includes two indexes: clustering level and asphalt content per unit of each sieve size.Secondly,by comparing the similarities and differences between EME20 gradation and AC20 gradation.It is concluded that the gradation that meets the requirements of AC20 can also be optimized to fit the gradation requirements of high modulus asphalt mixture(EME20).In order to solve the fusion problem in new asphalt and old asphalt,which is caused by the high viscosity of 30# hard asphalt,the graded recycling method is proposed.Compared with the traditional regeneration method,the recycled material obtained by the proposed graded recycling method is obviously superior to the traditional recycling method in terms of interfacial micro-structure characteristics,mechanical properties,and road performance.The differences between the two recycling methods were analyzed and summarized.Thirdly,by analyzing the influencing factors of recycled mixtures performance,this paper improved the performance of recycled mixtures from four aspects: gradation,asphalt-aggregate ratio,recycling agent and new asphalt label.The result could be concluded as follows: the improvement of gradation cannot improve the low-temperature performance;the mixture regenerated with 30 # hard asphalt has stable high-temperature performance and was less affected by the fluctuation of asphalt-aggregate ratio;the addition of regenerant can better improve the comprehensive performance of regenerated aggregate;the comprehensive performance of high modulus regenerated mixture can be improved by adding high modulus additive with higher label asphalt.Finally,according to the research results of this paper,several suggestions on the application of high modulus hot recycled asphalt mixture were proposed in the following aspects: RAP evaluation and treatment,gradation selection,performance demand,and regeneration scheme selection.It can provide a reference for further research and application of high modulus hot recycled asphalt mixture.