Evaluation of Air Voids and Permeability Properties for Porous Asphalt-Treated Course (PATC)

Since the late 1980s, government agencies have used porous asphalt-treated courses (PATC) as drainage layers under Portland cement concrete and asphalt concrete to prevent premature pavement failure by allowing water to drain from the pavement structure. Although PATC has been used in other applications, its use in airports is relatively limited. Three different types of PATC mixes were evaluated for use as a permeable base layers for runways and taxiways: #57, #67, and porous asphalt concrete. A constant-head permeability test was developed in this study to measure the permeability coefficient of PATC mixes because traditional methods are inadequate to highly permeable materials. A linear relationship was found between total air voids and connected air voids for PATC specimens. The regression line approached the equality line as air content increased, with a slope greater than 1. Test results illustrate that as specimens become more porous, the air voids tend to become interconnected, and more voids are likely to be filled with water. To meet the permeability specification, the total air void content for PATC mixes should be controlled between 17% and 24%. Additionally, the addition of fine aggregate to the #57 and #67 mixes needs to be controlled between 17% and 34% to provide stability and proper permeability.