Research On Meso Structure Of Porous Asphalt Mixture And Characteristics Of Drainage

The driving ability in rainy days has been a concern all the time. The traditionaldense-graded asphalt concrete pavement is not easy to penetrate water because of compactstructure. Its main way to drain away rainfall by road surface runoff results in a layer of waterfilm between pavement and tyre caused by surface water when vehicles are moving. Thiswater film can easily make vehicles splash, spray, glare at night and even drift and sideslip.Thus this way will affect driving stability and safety seriously. Porous asphalt pavement isconsidered to be an effective measure to solve this problem. Research shows that drainagecharacteristics of porous asphalt pavement is represented by permeability, and permeability isrelevant to aggregate gradation, aggregate shape, specimen thickness, compaction procedures,percent air voids, size and number of air voids, shape of air voids and flow paths. The minorchange of the design of asphalt mixture will cause dramatically change for permeability. Toensure good drainage of porous asphalt pavement, we have to assess permeability of porousasphalt pavement and relationship between permeability and composition of asphalt mixtureaccurately first, and then master the influence to flow characteristics caused by air void size,connectivity and spatial distribution. However, current research about permeability of asphaltmixture is focused on relationship between asphalt mixture permeability and air void content.Practice has proved that the prediction accuracy of permeability of asphalt mixture throughthis relationship is not enough. Therefore, it is very important to carry on the research betweenair void distribution characteristics of porous asphalt mixture and permeability.Firstly, this paper analyzes the basic theory of seepage flow of porous asphalt mixture, itprovides the theoretical support for calculation and analysis of seepage flow. Secondly, it mixdesigns the porous asphalt mixture and provides the best aggregate contact structure. In themeantime, it analyzes the internal air void feature of porous asphalt mixture in-depth andsystematically from meso angle based on X-ray CT and image processing，and enlarge on therelationship between air void feature and permeability by making use of numerical model,analyzes internal flow characteristics of water within porous asphalt mixture. Finally, itanalyzes drainage capacity of porous asphalt pavement of different rainfall by making use ofcomputation result，and proposes a method for objective porosities of controlling overlandrunoff. The main work is as follows:1. In order to coordinate the contradiction between durability and drainage of porousasphalt mixture well, and improve the existing design methods and gradation, it introducescourse aggregate void filling method（CAVF）to mix design of porous asphalt mixture and designs three different kinds of air void content porous asphalt mixture by using this method.2. It analyzes spatial distribution characteristics of air voids， including porosity,effective porosity, specific surface area and tortuosity based on the extraction of air voids ofPorous asphalt mixture from X-ray CT and image processing. It confirms vertical andhorizontal connected air voids paths of Porous asphalt mixture and calculates this path’stortuosity and constriction area.3. It establishes analytical permeability equations based on air voids microscopicdistribution characteristics and mixture properties of porous asphalt mixture, and predictspermeated capacity by using these equations.4. It establishes seepage flow numerical model of porous asphalt mixture and analyzesinternal flow characteristics of water within porous asphalt mixture, including pressuredistribution, velocity distribution and so on by using of finite volume method. It studies howthe size of air voids, degree of tortuosity and constriction size influence water flowcharacteristics. It also analyzes anisotropy permeability of porous asphalt mixture.5. After the analysis of runoff producing mechanism and methods of porous asphaltpavement, it analyzes permeability of it. It also studies seepage calculation model of Porousasphalt pavement, through which it calculates the seepage quantity under the circumstances ofspecific rainfull intensity. Secondly, application of seepage calculation model, calculates theextreme rainfall intensity that the porous asphalt pavement can deal with, and it proposes amethod for objective porosities according to characteristics of the rainfall in GuangdongProvince and pavement parameters.6. According to consult the domestic and foreign literature, scientific achievements,project examples and results of this study, it proposes some suggestions about structure designand application of Porous asphalt pavement.