Effect of Clogging and Cleaning on the Air Void Microstructure of Porous Asphalt Concrete

Porous asphalt concrete (PAC) is a low-impact medium with strong stormwater management capabilities. However, the air voids inside the PAC mixture will gradually be clogged due to sediment entering the interior of the PAC pavement in the service period. Meanwhile, the permeability of PAC pavements can be partially restored using cleaning equipment. This study investigates the changes in microscopic void characteristics of PAC under the effect of clogging and cleaning. Three kinds of PAC specimens with different void content were clogged by aeolian sand and cleaned by high-pressure water washing after complete clogging, in which the air void content, the shape parameters (roundness and aspect ratio), number, equivalent diameter, fractal dimension of air voids for the PAC mixes were quantified by X-ray computed tomography (CT) and image processing techniques before and after clogging and cleaning. Moreover, a relationship between air void microparameters and measured air void content (volume method) was established. It was found that air void shape, air void content, air void number, and equivalent diameter had a significant impact on the clogging and cleaning effect of PAC pavement, but the fractal dimension did not have a considerable impact. The migration depth of the clogging material increased gradually with the increase of air void content, and the most severe clogging was at about 10 mm from the top surface. The air void number within 1 mm increased significantly due to particle clogging. Before the construction of the road, some microscopic void parameters of PAC will be predicted from air void content measured by volume method, and combined with the results of local clogging particle size distribution, a reasonable PAC gradation will be selected to generate much larger voids than the clogging particles to improve the anticlogging performance of PAC pavement.