Research On Characterization Of Air Void Distribution And Its Fine Description In Porous Drainage Asphalt Mixture

The paper is supported by the National Natural Science Foundation (Project Number: 50608006)and Transportation Applied Basic Research Project of Ministry of Communications (Project Number: 2006 319 812 120).Asphalt mixture combine aggregates, asphalt, air voids and the micro-cracks of different sizes and shapes. The road performance of the mixture is not only susceptible to the volume factors such as VV, VMA, VCA but also related to the percentage and distribution of its components. However, the traditional volumetric design only can indicate the value of VV, VMA, VCA. but not give all the information of air voids. As a result, the dissertation chooses porous drainage asphalt mixture with a bigger air void ratio as an object and explores space information of air void deeply using computer tomography scanning technology, digital image processing and fractal theory to reveal its effect on mixture performance. Using air void ratio , air void equivalent diameter, air void outline fractal dimension and air void area fractal dimension, the dissertation analyzed the distribution of air void in horizontal or vertical direction and its special distribution. To the end ,it discovers that air void outline fractal dimension is always larger than air void area fractal dimension, and air void equivalent diameter are of 3mm to 9mm with the meanvalue between 3mm and 5mm. At the same time, the air void graduation diagram of porous drainage asphalt mixture is given in the dissertation. Also the dissertation obtained that the horizontal air void ratio are greater than that of vertical aggregate graduation in the sample and proposed that the drainability is stronger in horizontal direction than vertical direction in asphalt mixture. In addition, in respect of aggregate gradation, compaction effort and compaction process the paper analyzed their influences on air voids distribution in porous drainage asphalt mixture and proposed the air void ratio longitudinal distribution standard deviation as the norm for evaluating the separation of asphalt mixture .It analyzed the influence of compaction effort on air void distribution using compactions in different numbers of times in asphalt mixture and obtained that the increasing of compaction quantities based on 50 times had little effect on air void ratio besides making the air void sizes more homogeneous. Moreover, comparing with the specimens which are made by compaction process, the ones obtained by roller compaction have more uniform distribution of air voids by control experiments .The equation relation between air void ratio and air void outline fractal dimension is given according to fractal theory and the splitting tensile strength test and it is discovered that the air void outline fractal dimension reduces with a bigger air void ratio. Besides, the relation expression of air void outline fractal dimension and the splitting tensile equation is received and it is evident that the splitting tensile strength augments with the augmentation of air void outline fractal dimension. Furthermore, their validity can be inspected by the equations above. At the time, it can be used to explain the different strength when specimens have the same materials and air void ratio.In addition, the dissertation explores the decay of air void through the rutting test in porous drainage asphalt mixture. It is found that air void ratio and air void equivalent diameter become smaller but air void outline fractal dimension and area become bigger after roller compaction.