Investigation of excessive settlement involving recycled asphalt pavement in highway embankment

Recycled asphalt pavement (RAP) refers to unprocessed (e.g., milled) or processed (e.g., screened) asphalt mixtures obtained from roadways or other resources. The use of in-situ RAP is a sustainable practice that potentially could contribute to reduced greenhouse emissions and costs as well as accelerating the construction process. However, it has been reported that some pavements that utilize RAP as embankment/fill material experienced excessive settlement soon after construction. In order to investigate this issue, a comparison between RAP samples from five sources in Illinois and two conventional soils was conducted. Laboratory experiments included basic soil/RAP characteristics, gradations, moisture-density relationships at different temperatures, permeability, and pilot drainage, one-dimensional consolidation tests, and settlement analysis. The results indicate that RAP, considered as a permeable material, should not be used directly underneath the pavement drainage layer, as it can act as a reservoir and saturate the underlying embankment soils, which leads to excessive settlement of the embankment. Results show that the increase in the temperature of the RAP increases the one-dimensional compression. Also, it is recommended that the settlement analysis during design stage should consider the potential settlement of embankment soil from as-compacted condition to saturated condition.