Abstract
In this study, one type of porous asphalt (PA) mixture was designed at two different air void (AV) contents. Direct information regarding both the dimensional properties and AV distribution within two PA specimens in their natural states were observed, compared, and analyzed based on the X-ray CT (computed tomography) and digital image analysis techniques and fractal geometry theory. The characteristics of AV distribution, including AV content, AV number, and AV volume were quantified by comparing pore structure at different specimen heights. The dimensional properties of voids at different specimen heights were characterized by parameters in terms of equivalent diameter, specific surface area, and fractal dimension. The Pb(II) removal performance of the two PA mixtures was examined by an artificial rainfall event. The relationship between the PA microstructure and Pb(II) removal rate was then determined. It is observed from this study that the overall distribution pattern of AV inside PA specimen is independent of AV content. The distributional parameters including AV content, AV number, and AV volume show good correlations with three dimensional parameters, respectively. The Pb(II) removal in general appears to be independent of AV content because both PA mixtures have the same level of performance in removing Pb(II) during the rainfall period. The removal rate of Pb(II) shows good correlation with AV content, AV number, AV volume, and equivalent diameter of AV, indicating that a perfect distribution of AV within PA mixture is more important than the complex geometries of voids for getting a higher Pb(II) removal during rainfall event and without providing a temporary storage of stormwater in PA mixture. These findings provide an effective evidence to reveal that the AV distribution and properties characteristics have significant implications for pollutant removal in field PA pavement system.
Highlights
Porous asphalt (PA) pavement systems, a group of typical permeable pavement systems (PPS), are recommended as an effective infrastructure for current low-impact development (LID) and sustainable urban stormwater management [1, 2]
No significant difference was found in Pb(II) removal rates between PA specimens with different air void (AV) content of 16% and 20% in the T-test (p > 0.05). is result indicates that the Pb(II) removal capability of PA mixtures appears not to depend on the AV content. is is probably due to the very small difference in AV contents (20% and 16%) for PAC-16(A) and PAC-16(B) used in this study
A type of PA mixture, PAC-16, was designed at two different AV contents (16% and 20%). e AV properties and distribution inside PA mixtures were identified using the X-ray CT and related digital image analysis technologies, with both dimensional and distributional parameters. e removal performance of Pb(II) from stormwater with PA mixtures was investigated by creating an artificial rainfall event. e relation between the AV characteristics and Pb(II) removal capability of PA mixture in particular were determined. e main findings are as follows: (1) e mixture design parameter, AV content, does not appear to affect the overall vertical distribution of AV in the PA mixture but the distributional and dimensional parameters are affected
Summary
Porous asphalt (PA) pavement systems, a group of typical permeable pavement systems (PPS), are recommended as an effective infrastructure for current low-impact development (LID) and sustainable urban stormwater management [1, 2]. A standard PA pavement system consists of three main layers including PA surface, choker course and reservoir structure with various porous materials from top to bottom [3,4,5]. E AVs contained in PA mixtures make it an ideal surface layer material for the innovative full-depth PA pavement system. E proper functionality in terms of Advances in Materials Science and Engineering peak flow reduction, surface infiltration capacity, and stormwater treatment can be ensured. Erefore, PA mixtures are currently attracting more and more attention in both pavement engineering and stormwater management [12] PA mixture, known as new generation open-graded friction course (OGFC) mixture or permeable friction course (PFC) mixture, is a type of hot mixture asphalt (HMA) with high coarse aggregate content and low fine aggregate content when compared to conventional densegraded HMA that leads to a higher total AV content of 18∼25% [9,10,11]. e AVs contained in PA mixtures make it an ideal surface layer material for the innovative full-depth PA pavement system. e proper functionality in terms of Advances in Materials Science and Engineering peak flow reduction, surface infiltration capacity, and stormwater treatment can be ensured. erefore, PA mixtures are currently attracting more and more attention in both pavement engineering and stormwater management [12]
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