Saturated hydraulic conductivity of compacted recycled asphalt pavement

Tests were conducted to determine the saturated hydraulic conductivity of three recycled asphalt pavement (RAP) materials being used as base course aggregate for pavement construction. Comparative tests were also conducted on a compacted crushed rock aggregate (Lodi gravel) that is used for base course in Wisconsin. All four are granular materials. The RAPs have saturated hydraulic conductivities ranging from 2.4 x 10(-5) to 9.0 x 10(-5) m/s when compacted with standard Proctor effort and from 4.5 x 10(-8) to 1.7 x 10(-6) m/s when compacted with modified Proctor effort. The Lodi gravel is less permeable, having saturated hydraulic conductivities of 5.8 x 10(-7) m/s (standard Proctor effort) and 2.4 x 10(-9) m/s (modified Proctor effort). Three conventional methods of predicting the saturated hydraulic conductivity of coarse-grained soils were evaluated in terms of their ability to predict the saturated hydraulic conductivity of RAP: Hazen's equation, Kenney's equation, and the Kozeny-Carmen equation. Each of these equations overpredict the hydraulic conductivity of RAP. Two empirical equations to predict the hydraulic conductivity of RAP were developed from the saturated hydraulic conductivity data. The empirical equations were found to work well for RAP as well as the Lodi gravel. However, the empirical equations are based on a small data set. Updating of the equations is encouraged as more data become available.