Hydraulic Behavior of Maryland RAP Materials Used in Highway Shoulders

The objective of this study is to evaluate the hydraulic properties of RAP materials in highway shoulder applications collected from different locations in Maryland. In order to determine the hydraulic properties, a series of grain size distribution tests and bubble tube permeameter tests were performed on the samples. The results of grain size distributions indicated that the RAP samples collected from different locations within Maryland can be identified as well-graded sand sized with gravel sized material and poorly-graded sand sized with gravel sized material. The obtained hydraulic conductivity coefficients of as-received RAP samples ranged from 8.3x10-3cm/s to 5.5x10-2cm/s suggesting that the hydraulic conductivity of as-received RAP is similar to that of conventional granular material with similar gradation. However, the hydraulic conductivity of the RAP is significantly influenced by the particle size distribution. It decreased 10 times with an increase in fines content from 0% to 8% by weight. Similarly, an increase in sand-To-gravel ratio and a decrease in D₁₀ yielded lower hydraulic conductivity values.