Toward unpaved highway shoulder specifications allowing virgin and recycled aggregates

This paper evaluates unpaved highway shoulders with emphasis on narrow shoulders of lower volume asphalt pavements where shoulders were re-established during overlay projects. The primary objective of this work is to document results of a full-scale shoulder aggregates test section on State Route 388 in Mississippi (United States of America) and to use this section alongside literature review and Mississippi Department of Transportation practices to make recommendations for how to update their standard specifications to make effective use of several virgin and recycled aggregates. Gravel, limestone, reclaimed asphalt pavement, recycled concrete aggregate, and steel slag were evaluated in service for roughly 3 years. The best performing shoulder aggregate was recycled concrete aggregate, although the study concluded that all five materials should be allowed in shoulder aggregate specifications. A table of gradations was provided for these five materials, as were findings from a fairly extensive edge drop-off evaluation and from visual evaluations from a panel of raters.