| In recent years,with the promotion and application of the concept of sponge city,more and more pavement asphalt paving has been applied to pavement and maintenance.The drainage type asphalt mixture is a graded mixture,which has a high void ratio,can quickly eliminate road surface rainwater,prevent road glare,water mist,side slip and other phenomena,and improve the safety of the vehicle.It can absorb tire noise and improve the comfort of driving.Studies have shown that voids are an important structural feature of drainage asphalt mixtures,and their drainage performance is characterized by the permeability coefficient.The meso-structural characteristics of the drainage asphalt mixture have an important influence on the water permeability,including not only the void ratio of the asphalt mixture,the number and size of the voids,but also the aggregate gradation and molding method.Has a big impact.Therefore,the research on the mesoscopic void characteristics of the drainage asphalt pavement and the influence on the water seepage characteristics are of great scientific value.In this paper,three standard grading standard Marshall test pieces and rutting plates are cut separately.After surface polishing,high-definition digital equipment is used to obtain cross-section image as data source,and digital image information processing technology is used to extract the void characteristic parameters,including plane.Void ratio,void area,equivalent diameter,perimeter,specific surface area,curvature and specific surface area,etc,systematically studied the internal void characteristics of the drainage asphalt pavement from a microscopic point of view.The standard Marshall specimens were cut horizontally and vertically,and the transverse plane characteristics and longitudinal spatial distribution characteristics of the voids were analyzed from a two-dimensional perspective.Comparing the void characteristics of standard Marshall test pieces and rutting plates,the effects of different forming methods on their internal void characteristics were studied.The effects of void internal void characteristics,void ratio and connected voids and fractal dimension on the permeability coefficient were analyzed.The theoretical study was used to estimate the permeability coefficient,and the permeability of the drainage asphalt pavement was reflected from the mesoscopic level.The results of this study show that in the distribution of planar voids,the number of large voids is the largest;as the void area increases,the number of voids increases,and the number of voids is larger;the number of planar voids is along the test.The reduction of the height of the section height is gradually increased,and the proportion of the area of the plane voids is significantly reduced;the cumulative proportion of the area of the micro-voids and the small gaps is much smaller than that of other types,but the proportion of the area from the middle gap to the super-large gap is increased,and the super-large gap is the largest;The smallest void elliptic rate is the highest,that is,the flatness is the highest,and the small void to the extra large void gradually increase;the larger the fractal dimension,the more complicated the void morphology;along the height of the cross-section of the specimen,the number of planar voids gradually increases,and the proportion of the planar void fraction decreases.The internal void fraction of the rut plate is too large,indicating that the internal void has a high complexity,and the plane void ratio of the upper part of the rutting board is slightly larger than that of the Marshall test piece;the KC formula containing the fractal theory is in good agreement with the measured permeability coefficient. |
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