| Porous Asphalt Concrete is an important way to achieve a high-quality pavement based on the high porosity abovet 15%because of its safety,comfort and low noise.However,the drainage performance reduced with the clogged of voids which is the main problem of the PAC and is also the main problem that restricts the development of PAC.The current research on PAC voids clogging is mostly focused on macro-testing,and some empirical law is obtained.During the using of PAC,there are many kinds of void clogging materials which are accumulated as time goes by,which lead to a complex void distribution.Moreover,it is difficult to scientifically and reasonably describe the quantitative relationship between the clogging particle and the void characteristics during the clogging process of PAC,and then clearly reveal the mechanism of clogging.In this paper,three kinds of PAC mixtures were prepared and three kinds of clogging materials were used in repeated clogging test and clogging-cleaning circle test.Mesostructure information based on X-ray CT of PAC was analysed and CFD-DEM coupling were carried out to simulate the clogging process of PAC.The principle of the permeable asphalt pavement blockage was obtained.Finally the void attenuation law was researched through the paving test section and the void life was predicted.Based on the above work,the research has achieved the following results:（1）According to the investigation results about clogging materials in different pavement in Gansu province,three kinds of clogging materials composition were proposed.Then the variation of permeability coefficient of PAC with different types were obtained based on repeated clogging tests.The results showes that the initial permeability coefficient has a significant linear correlation to the porosity（effective porosity）,also a law was obtained that different decay rate of the permeability coefficient of PAC varied with the different clogging materials.Furthermore,the times of repeated clogging is closely related to the particle size distribution of the clogging materials.A clogging sensitive particle was observed with a particle size distribution of 0.15-0.60mm while gradually increases with the increase of the porpsity.At last,a clogging factorβis defined,and a full-parameter model and a four-parameter simplified model ofβare proposed according to the principal component analysis method.（2）Based on the clogging-cleaning circle test,the permeability coefficient of PAC under different void clean methods was studied.The results showes that clogging materials and the cleaning methods are important external factors which affect the times and the law of clogging-cleaning circle test.It is found that the voids cleaning effect is ranked as high-pressure water>vacuum pump>manual brush.In addition,a regression model for clogging factorsβcleaning andβclogging of different void maintenance methods was established which could provide a theoretical basis for the selection of void maintenance methods of PAC.（3）The mesostructure information such as shape,number,equivalent diameter and fractal dimension of the voids of PAC before and after clogging-cleaning was obtained based on the X-ray CT test.It shows that the voids are refined and the fractal dimension changes slightly after clogging.Lastly,a unified model of clogging which was improved by the K-C formula was established with good correlation.（4）The voids clogging process of PAC was simulated based on void three-dimensional reconstruction model.The permeability pressure and velocity distribution as well as clogging particals migration was simulated by CFD and DEM.The results show that the clogging progress is stage development.At first,the particles quickly entered the interior of the model,and then the clogging developed steadily.Finally the clogging mechanism of PAC was revealed which three types of clogging was summed up including surface filling,void refinement and void bending/semi-connected.（5）A 200m PAC test pavement was applied on the Liangdang-Huixian Highway in Gansu Province in order to verify clogging.The attenuation of permeability coefficient and the changes of void mesostructure after 7 months of operation were analyzed.The model predicts the anti-clogging life of the traffic lane is 2.5years,the anti-clogging life of the overtaking lane is 3.5 years,and the anti-clogging life of the wheel track is 1.7 years,and the anti-clogging life of the wheel track after vacuum pump cleaning is 2.1 years.These results provide data and theoretical support for the maintenance of permeable pavement voids,and provide technical support for the long-life operation of permeable pavements.The research results of this thesis provide a theoretical and technical basis for objectively evaluating void clogging of PAC.It provides important theoretical significance and reference value for effectively preventing void clogging of PAC in order to maintaining and recovering permeable functions. |
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