Study On Reduction Behavior Of Void Structure Of Double-Layer Drained Asphalt Pavement

Drainage asphalt pavement usually uses a high void ratio asphalt mixture(generally 18% to 25%)for the upper layer of the pavement structure(or the upper layer and the middle layer),and has good functions of drainage and noise reduction.However,with the wide application of porous asphalt pavement,the durability problem is gradually serious,mainly manifested by the decay of the void structure.The porous asphalt pavement bears the load of the vehicle during use,and the asphalt mixture tends to be compacted,resulting in a slow decrease in the void ratio of the asphalt pavement.In addition,the dust on the road surface,the discards in the driving process of the car and the garbage generated in the surrounding environment of the road may enter the pavement void structure,causing the void structure of the porous asphalt pavement to decay after being used for a few years and thus losing the original function.In order to improve the application of the current porous asphalt pavement,a double-drainage asphalt pavement has been introduced in China.The double-drained asphalt pavement,known as the second-generation drainage asphalt pavement,consists of a thin layer of finely-divided drainage asphalt and a layer of thicker underlying coarse asphalt.Since the paving of double-drained asphalt pavement is still in the experimental stage in China,it is urgent to study the relevant design theories based on China's national conditions and regional characteristics.In view of the fact that void decay is the main disease in the application of single-layer drainage pavement,the paper studies the void decay law of double-drainage pavement,and provides a theoretical basis for the application and maintenance of double-drainage pavement.First of all,the double-drainage pavement slab is formed based on the gradation of the test section of Jiangxi Guangji Expressway.Then,the void structure is reconstructed by CT scanning technology and PFC3 D software,and the void structure is classified according to different drainage functions,and the void structure is divided into a communication gap,a semi-connected gap and a closed gap.The void structure was analyzed by using the indexes of void ratio,number of voids and surface area of voids.Secondly,this paper has established a three-dimensional database of aggregates,simulated asphalt mortar mixing process,and formed a double-layer drainage asphalt pavement virtual test model by simulating the static pressure method.Through rutting test comparison and layered void fraction extraction,it is shown that the new forming method can be used to simulate the performance test of asphalt mixture.The uniaxial creep test and the rutting test were carried out on the virtual test model.It was found that the communication gap was gradually reduced,the semi-connected space and the closed space were gradually increased,and the shape of the gap did not change greatly.There is a good correspondence between the void ratio and the strain at the double-drained asphalt pavement wheel track and the non-wheel track.Based on the road surface temperature and vehicle distribution in Jiangxi,the prediction model of the gap structure under the load of double-drained asphalt pavement was established.Thirdly,this paper collected the data of road surface blockage and conducted a virtual road blockage test,which respectively obtains the single-day average void ratio attenuation coefficient on sunny or rainy days.The influencing factors of the anti-blocking ability of the double-drained asphalt pavement were analyzed.It was found that the anti-blocking ability of the double-drained asphalt pavement was mainly related to the void structure of the upper layer,and had little relationship with the seepage velocity of the rainy road.At the same time,as the quality of pavement deposits increases,the rate of increase in the quality of road blockages increases gradually,showing a quadratic function.Finally,this paper considered the influence of load on the anti-blocking ability of doubledrainage drainage pavement to study the decay law of void structure under the coupling of vehicle load and dust blocking effect,and established the decay model of double-layer drainage asphalt pavement.As the rutting strain increases,the anti-blocking capacity of the double-drain asphalt pavement is slightly improved.After considering the dust blocking effect,the rate of attenuation of the connected void ratio of the asphalt pavement is accelerated.After 1.5 years of use,the void ratio at the wheel track has been reduced to 15%.After 2 years of use,the void rate at the center of the road has been reduced to 15%.It is recommended to clean the road as soon as possible to ensure its good drainage function.