Research On Functional Asphalt Mixture Based On Meso-mechanical Performance

The key to solving the problem of early functional damage of asphalt pavement is todesign the functional asphalt mixture according to the functional requirements of pavementusing. So far, rutting is one of the main reasons of asphalt concrete pavement damages. Themost common technical preventive measure to solve this problem is using modified asphalt,but it would to great increases in construction cost. Due to its good performance in rutresistance by the wedging effect of the skeleton, framework dense structure has beengradually taken seriously in the process of graded mixture design. However, the currentunderstanding of the internal framework structure of the asphalt mixture is very vague. Hence,it is hard to say whether the mixture has truly formed the best framework structure. What’smore, the existing criterion of coarse aggregate skeleton state also appears to be too broad andsimple, and the design methods of coarse aggregate skeleton could not effectively guaranteethe designed asphalt mixture with excellent framework structure.Based on the above backgrounds, the dissertation took the constitution of the mainframework and its mesoscopic contact characteristics as the main research points, the digitalimage processing technique and discrete element analysis being the research methods. Thisdissertation analyzed the internal structure characteristics of the asphalt mixture from themicroscopic view, revealing the properties and the inherent laws of the meso constitution ofthe main framework and contact characteristics of coarse aggregates. By combiningMultilevel Mixing Method with microscopic quantitative evaluation indexes, it also putforward an asphalt mixture design method which has a framework dense structure and afunction of rut resistance. Considering the practical engineering work, this dissertationapplied the proposed design method to practice through UM rock asphalt modified pavementexperiment road tracking test, which verified the feasibility of the design theory and methodand achieved a good economic benefits. Meanwhile, it employed visualization gradationdesign method with a discrete element method for reducing errors and test quantities in designof asphalt mixture. The main processes and innovations of this dissertation are as follows:1. The constitutional and the micro structural characteristics of the inner framework andthe main framework are systematically researched by digital image processing technique and Discrete Element Method. On this basis, the calculation formula of VCAmixwas optimized inconsideration of aggregate contact characteristics. The dissertation put forward that theaverage coordination number and the content of "suspended" coarse aggregate C could beused as the microscopic quantitative evaluation indexes of the main framework quality.2. The framework dense structure rut resistance functional asphalt mixture designmethod is put forward based on the combination of Multilevel Mixing Method andmicroscopic quantitative evaluation indexes. This method ensured that coarse aggregatesinterlock with each other to form an optimal main skeleton, thus was good in reliability,economic in test times and fine in rut resistance performance. The functional asphalt mixturedesigned by proposed method had been proved practical in engineering practice afterlaboratory tests and verified the feasibility of the design theory and method through road tracktest.3. The dissertation investigated the influence factors of main framework structurecharacteristics and stability such as coarse aggregate contact characteristics of differentasphalt mixtures, contribution rate of each grade coarse aggregates, coordination number,horizontal angle of coarse aggregate, morphological structure stability of the contact chainand the characteristics of the primary and secondary contact chain using statistical andmeso-mechanical approaches. Then the optimization measures and microscopic evaluationcriteria are put forward to design excellent framework structure and enhance its overallstability, in order to ensure that the framework structure have strong ability to resist externalloads, and improve the overall rut resistance.4. By using the Discrete Element Method, a useful attempt of visualization gradationdesign was carried out to test the process whose errors and test quantities are large during thedesign process of framework dense structure anti-rutting functional asphalt mixture, obtaininga mixture gradation with optimal main skeleton. Having the advantages of convenientoperation and small discreteness of data, the design method overcomes the traditional testshortcomings of large errors and test quantities, and greatly improves the efficiency andeconomy of mixture design. Thus, it has good guiding in realistic practice.5. The effects which the UM rock asphalt mixing amount had on the pavementperformances of base asphalt, including high temperature properties, low temperature properties and aging resistance properties, were studied from the perspective of constrainmain skeleton. The dissertation established the high and low temperature PG grade of UMrock asphalt modified asphalt and further studied the pavement performances of the UM rockmodified asphalt mixture. A kind of framework dense structure rut resistance functionalasphalt mixture was designed by applying the design method presented in this dissertation.The mixture incorporated cheap UM rock asphalt to improve the performance of asphaltmortar and improved the rut resistance performance of asphalt mixture by strengthening themain skeleton constraint. The tracking observation results of the experimental road showednotable economic and social benefits.