This report summarizes the findings of one-year research study sponsored by the North Carolina Department of Transportation on the use of the DCP to develop a pavement distress evaluation model. Work included laboratory and field testing programs as well as modeling effort. In this report, a method was proposed by which the DCP PR data were utilized to evaluate pavement distress state. Such evaluation is needed on regular basis in order to categorize the implementation of rehabilitation measures. The principle idea was to use the DCP data to discern the integrity of the subase and ABC layers. Accordingly, if the structural integrity of subgrade and ABC layers is found to be adequate, maintenance measures can include simply resurfacing or treating the surface layer. However, in situations where the structural integrity of the ABC, the subgrade, or both, is found inadequate, extensive stabilization and soil improvement measures maybe needed and resurfacing alone will not be sufficient.
The laboratory work on the subgrade materials was performed on three residual soil types taken from test sites in Davidson County, North Carolina. Testing included compaction of soil specimens in a 150 mm (6 in) mold, performing the CBR test on the prepared specimens, and then penetrating the specimens with the DCP probe. In parallel, the laboratory testing on the ABC materials included the preparation of thirty-two CBR specimens using material from two different sources. The field testing included work at seven sites with three CBR tests, seven DCP penetrations, three nuclear gauge measurements, three FWD tests and one bulk sample extraction conducted at each site. A second phase of field testing at three sites was also performed. Modeling work included development of correlation between the PR and CBR of subgrade soils, PR and CBR of the ABC material, and PR and compaction unit weight and moisture content of the subgrade soils. In addition, the coupled PR-subgrade and PR- ABC data were used to develop a pavement distress level that provided an indication of the test sites pavement's serviceability level.
