Evaluation of functional properties of porous asphalt pavements subjected to clogging and densification of air voids

This study was motivated by concerns that porous asphalt concrete (PAC) might not perform well under severe environmental and traffic conditions. It was feared that the drainability, friction, and noise benefits of PACs would be rapidly lost. PAC sections were constructed with three types of asphalt: nonmodified bitumen (NMB), polymermodified bitumen (PMB), and highly modified bitumen (HMB). These sections were completed in 2008 and evaluated twice a year for their functionality. Clogging and densification were shown to be the main reason for the reduction in PAC air voids. For the NMB and PMB sections, more than 70% of the reduction in air voids resulted from traffic compaction; this reduction was less than 30% for the HMB section. The decrease in drainability corresponded well with the decrease in air voids. Cleaning of PAC mixtures did not appear to be effective for the NMB and PMB sections because most of the reduction in air voids resulted from traffic compaction. Because of the significant amount of macrotexture produced within PAC pavement surfaces, PAC layers maintained adequate frictional characteristics even after becoming clogged and condensed. The noise characteristics of PACs depended on the air void content. No rutting, raveling, cracking, or other failures have been observed to any significant extent on the three monitored sections since they opened to traffic in 2008; these results suggest that PACs may be a viable type of pavement surface for use on highways to provide good performance, including good friction, reduced splash and spray, and reduced tire-pavement noise.