Many low-volume roadways in the county road system in Minnesota consist of unpaved aggregate surfaces. It is the responsibility of the county engineer to make determinations regarding the design and maintenance of such roads, as well as determinations regarding specific criteria such as weight restrictions. One method used by several counties in Minnesota is to construct a bituminous-stabilized layer by adding several inches of new aggregate and stabilizing it with an engineered, water-based asphalt emulsion through mix-in-place methods. There is a need, however, for a design method to provide highway engineers and their staffs with technical backing for the designs selected. This paper describes the results of an ongoing research project to develop a design method for determining the required thickness of stabilized and unstabilized layers in this type of aggregate-surfaced road. The basic design method is based on the material properties and a correlation between layered elastic analysis, dynamic cone penetrometer testing, and falling weight deflectometer testing. Results of the materials testing and layered elastic analysis are presented, as well as the correlation between the analysis and measured falling weight deflection data. The load rating analysis uses the Minnesota Department of Transportation methodology of estimating load rating on low-volume roads on the basis of falling weight deflectometer data. This method of design will allow county and other agency engineers to determine the appropriate thickness of the stabilized layer in order to obtain the desired load rating.
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