, Professor & Department Head, Civil, Environmental and Geo-Engineering
Currently, the Minnesota Department of Transportation (MnDOT) pavement design recommends a granular equivalency value (GE) of 1 for non-stabilized full-depth reclamation material (FDR), which is equivalent to class 5 material. For stabilized FDR, there is no guideline for GE. Some local engineers believe that the GE of FDR material should be greater than 1, especially for stabilized FDR. In addition, very little information is available on the seasonal effects on FDR base, especially on stabilized FDR base. Because it is known from laboratory studies that SFDR contains less moisture and has a higher stiffness (modulus) than aggregate base, it is assumed that SFDR should be less susceptible to springtime thawing. Falling Weight Deflectometer (FWD) tests were performed on seven selected test sections on county roads in Minnesota over a period of three years. During the spring thaw of each year, FWD testing was conducted daily during
the first week of thawing in an attempt to capture any spring thaw weakening of the aggregate base. After the spring thaw period, FWD testing was conducted monthly to study base recovery and stiffness changes through the seasons. GE of SFDR was estimated through a method established by MnDOT using FWD deflections, and the GE of SFDR was found to be about 1.5. The value varies from project to project as construction and material vary from project to project. All the materials tested showed seasonal effects on stiffness, with the stiffness generally weaker in spring than in the summer and fall.