Characteristics And Design Methods Of Asphalt Pavement In Plateau-Cold Region

Asphalt pavements exposed to adverse conditions such as application of heavy repeated vehicle loading and direct influence of external environment factors for a long period of time may exhibit unique structural behavior leading to inadequate service levels and/or premature distress. After rapid expansion of pavement construction for the last 20 years, the theory and practice of pavement engineering witnessed great achievement, especially in asphalt pavements. However, there still exist several aspects of asphalt pavements which should be addressed to advance asphalt pavement technology in China. First of all, the asphalt pavement structure types are still comparatively fixed at present and semi-rigid structural dominated design in practice. Secondly, there exist some disjoint phenomenon between the distress patterns and design indexes. Thirdly, the volumetric design parameters of asphalt mixture and pavement performance indexes are still not clear. Therefore, it is very important to study the design methods of asphalt pavement and materials based on consideration of the climate environmental factors and traffic characteristic as well to produce sound design.This dissertation reports a comprehensive research on the structure and material characteristics and their design methods in plateau-cold region. This project was supported by the Ministry of Communications' Western Transportation Construction Research Project (NO. 200431800054).In this study the following procedures were observed: firstly, a large number of relevant domestic and international literatures and findings were reviewed and the asphalt pavement distresses were investigated on the spot. Secondly, the basic theory problems analysis was discussed. Finally, by means of combining the theory and practice and considering the external environment factors, the traffic loading, as well as the characteristics of pavement structure and highway materials, the asphalt pavement problems in plateau-cold region such as the structure type and structure characteristic, the combination of asphalt mixture and its performance, and the assumed design methods were systemically and deeply investigated. Major remarks and findings of this research are summarized as follows:(1) On the basis of the damage investigation data of asphalt pavements collected in Sichuan and Tibet Plateau-Cold Regions, the six major defects found in these regions were accurately defined, analyzed, and summarized; the law and formation mechanism for the low temperature cracking, the reflection cracking, the permanent deformation, and other defect types were studied and presented. Among these, the temperature-shrinking cracking and the reflecting cracking are the most important breaking forms owing to pavement structure and material itself.(2) The structural analysis and the basic theories of asphalt pavement structure were discussed deeply based on the software ABAQUS; the interlayer state, the mode of vehicle loading, the synthetical effects of many factors, etc, and the influencing law that one factor or many factors acted on the key mechanics were also analyzed. The results indicate that the mechanics of the contact model is more fitable for the pavement's practical work state largely influenced by horizontal loads action. From the simulation results, the interlayer influence law of asphalt pavement characteristic at high or at low temperature was created and presented; the critical coefficient value of interlayer friction resulted in the pavement performance under the coupled action was confirmed to become worse at high temperature; some reasonable suggestions about the mechanics model and loads combination in asphalt pavement structural analysis in plateau-cold region were given out too.(3) The combinations of the concepts and new structure type of asphalt pavement are summarized in this work. Considering the temperature susceptibility of asphalt concrete based on the contact model focused on the new-type asphalt pavement in plateau-cold region, a systemic theoretical analysis such as temperature behavior with large temperature changes, coupled with temperature-loading behavior and anti-cracking behavior, were done. Results indicate that a thick asphalt pavement structure (see type 3) and hyperbatic or combined structure (see type 5) have a better performance in the cold regions and can resist to environment changes and pavement crackings. Because of the coupled action of large temperature changes on structures and vertical and horizontal loads, the pavements mechanics can behave distinctly when compared with vertical loading action; the difference existing between them consist not only on the mechanics responses but also on the position of extremum value of responses.(4)Based on the research on optimum design of acidic granite asphalt concrete material AC-13 composition, a lot of laboratory experiments were made with the method of orthogonal design and with the plateau-cold environment and the heavy traffic loads taking into account. A systemic analysis on the influence of asphalt concrete by factors such as the type of gradation, the temperature of compression, the way of compression, the Optimum Asphalt Content (OAC) and improving measures were considered. Based on the results of experiments, the low critical compression temperature and the experiment method were ensured. Furthermore, the principle and design of asphalt concrete for plateau-cold region were worked out; the optimum design method of asphalt concrete material composition based on the stability of freeze-thaw resistance and the processes control method which is composed by the parameter of volume and performance was also worked out.(5) Based on field test data, this system research has considered the temperature behavior, anti-cracking effects and anti-deflection characteristics in the design of the new asphalt pavement structures. Using FBG temperature sensor, the testing results show that the temperatures along the depth in the pavement changes dependant upon different environments and different time. A temperature forecast GM model has been established for each pavement structure in different environment and different time with different temperature. Cracking findings in the scene investigation are able to describe the cracking characteristics and evaluate the ability of the new structure's anti-cracking effect. Deflection test results clearly point out that if the deflections are too small, it may easy lead to reflection cracking. In this dissertation, a comprehensive theoretical analysis and field test results made here may improve to better the understanding of the design principles and requests needed for plateau-cold region. Some new and suitable asphalt pavement structures have been recommended for the plateau-cold region; the mechanic model for pavment structure design also has been established. Some structure and new structural design method for the plateau-cold region based on pavement's performance at low or high temperature conditions and different responses index (stress or strain) have been proposed in this thesis.