Performance Of Reclaimed Asphalt Pavement on Unpaved Roads: FHWA-WY-11/03F
The University of Wyoming's LTAP Center conducted a study examining the performance of reclaimed, recycled asphalt pavement (RAP) on unpaved roads in three Wyoming counties. Fifteen material and dust suppression treatment combinations were examined. Materials included three RAP sources rom Wyoming interstate millings and one milled cement-treated base (CTB) from Intersate 80. Dust suppressants included calcium chloride flakes, magnesium chloride brine, and brines made from blends of magnesium chloride with either lignin sulfonate or a proprietary polymer.
Three different construction methods were used: RAP was placed with haul trucks and shaped and blended with a motor grader; RAP was placed with haul trucks and blended with a reclaimer and shaped with a motor grader; and RAP was blended with virgin aggregate at the stockpile, then the blend was hauled to the roadway, shaped with a motor grader, and compacted with a single steel drum roller. The most critical element of placing, blending and shaping the RAP blends was the method's ability to provide complete blending, thereby avoiding segregation that led to several distresses including loose aggregate, dust and rutting.
Performance was assessed using Colorado State University's dustometer, the unsurfaced road condition index (URCI), and a variety of other materials tests and performance evaluations.
The following conclusions can be drawn based on the analysis performed:
CTB is not recommended as a surfacing material on unpaved roads.
RAP was shown to be an effective surfacing material for unpaved roads when blended with other aggregates. Dust was reduced. Further reductions were, in most cases, achieved by adding a dust suppressant to the RAP and aggregate blends. However, dust suppressants increased the RAP-blend surfaces' vulnerability to rutting and other surface distortions when compared to the RAP blends alone.
Economic analysis indicates that RAP should not be used when the alternative use is as an additive to hot plant mix asphalt. However, if the alternative use is as a road base material, it is likely that using the RAP as an additive to an unpaved road's surface is the most economically advantageous use of RAP.