Research On Meso-Structure Of Porous Asphalt Rubber Mixture And Optimization Of Permeability

At present,most of the urban roads in China mainly drains through road surface runoff with dense gradation asphalt concrete.Surface runoff reduces the friction between road surface and tires,which seriously affects traffic safety.Porous asphalt mixture can effectively eliminate surface runoff,but its permeability is affected by various factors,including thickness,void fraction,curvature of connected voids,flow path and so on.Domestic research on porous asphalt mixture permeability mainly discusses the relationship between permeability and void ratio.However,practice shows that void ratio is difficult to accurately predict the permeable performance of the mixture,and there is a phenomenon that the material design and function are out of phase.Therefore,it is necessary to deeply analyze its percolation performance based on the characteristics of porous asphalt mixture voids.It has been pointed out by some scholars that the connected voids play a real drainage role in the internal voids of mixtures,but there are many factors affecting the connected voids and the influence is still unclear.Based on the above background,this paper discusses the correlation among the types of asphalt,nominal particle size,critical mesh clearance rate and the connected voids,and tries to establish the prediction model of the connected voids.The main work and research results of this paper are as follows:（1）Three kinds of gradation porous asphalt rubber mixtures with different void ratios were designed based on CAVF method,and indoor experimental research was carried out.The drainage asphalt rubber mixture has good water stability,high temperature stability and drainage performance with 5.8%asphalt-aggregate ratio.（2）The skeleton characteristics of porous asphalt mixture were analyzed through X-ray and digital image processing technology.The archiving methods of different aggregate particle sizes were compared.The homogeneity of mixture is evaluated based on the spatial distribution characteristics of aggregate and the improved particle area ratio.The results show that the correlation between homogeneity index and strength of mixture is weak,the correlation between homogeneity index and strength variability is strong,and the better the homogeneity is,the smaller variability is.（3）The correlation among asphalt type,maximum nominal particle size,2.36mm passing rate with void fraction and connected void fraction was studied.The connected voids prediction model was established based on P2.36,VMA,G and N model parameters.Linear regression method was used to fit model parameters.The fitting results show that the model has a high degree of interpretation and can accurately predict the connectivity porosity of porous asphalt mixture.Due to the limitations of fitting samples,the prediction range of the model is restricted.When the pass rate of gradation P_2.36.36 is too small,there is a big deviation between the estimated value and the actual value.