Relationships among gradation curve, clogging resistance, and pore-based indices of porous asphalt mixes

When properly designed, porous asphalt functions both to make safer the driving in wet condition, and to provide hydrologic restoration while functioning as a filtration interface. This study examined the role of aggregate ranulometry both on the pore-based indices of porous asphalt and on the clogging resistance. Three groups of porous asphalt gradations comprised of 12 series of samples and separated based on gradation size indices have been examined. For all samples the vertical (kv) and horizontal (kh) permeability were measured with the commensurate total void contents (e) and total porosity (n). Also clogging resistance was evaluated by measuring hydraulic conductivity before and after 1 year of exposure of the samples to dust intrusion. Marshall tests were also performed in order to control the stability of the mixes. There was a strong relationship between the permeability and the void content. For a given aggregate gradation, each increment of asphalt content increase caused a decrement in permeability and porosity. As for the clogging resistance potential, it seems to be more related to the initial permeability than to the other pore-based parameters. Results indicated that in addition to the coefficient of uniformity (U) and the total void content, a size-based granulometric index (P5·P2·Dmax) provided a relationship with vertical permeability and the total void content that were very consistent for the entire range of porous asphalt mixes. Results of this study allow the role of mix design on the permeability to be examined. These mix design results are a necessary precursor to examination of in-situ permeability after placement, and degradation of such permeability as a function of time and rainfall-runoff hydraulic and particulate loadings