Field Evaluation of Interlayer-Reinforced Asphalt Overlay Performance

This proposed research plan supports the North Carolina Department of Transportation (NCDOT) Division 5 Maintenance field study of geosynthetic pavement interlayer performance. It includes designing and orchestrating field experiments with NCDOT engineers, performing laboratory tests using samples obtained from field test sections, analyzing the test results to assess the performance of different interlayer products, and verifying/calibrating/refining the recommendations that are based on laboratory tests of different interlayer systems conducted in previous and ongoing NCDOT projects. The research plan is designed to use the test procedures employed in the ongoing NCDOT project, RP 2019-19 Development of Geosynthetic Pavement Interlayer Improvements, which focuses on the laboratory evaluation of various geosynthetic interlayer products, including their resistance to reflective cracking and debonding failure. The candidate roadway for this proposed field study is NC 96 in Youngsville, Franklin County between Jack Jones Road in Wake Forest and Oak Grove Church Road in Youngsville. Geosynthetic interlayers that are included in the RP 2019-19 project will be installed prior to construction of the asphalt overlay. The location of the project will be selected to avoid a significant grade and major intersections. Cracks in the existing pavement will be mapped before placement of the interlayers. The tack coat application rates will follow the geosynthetic manufacturers' recommendations. The pavement conditions will be monitored by the North Carolina State University research team until the end of this proposed project and then by NCDOT personnel after this project is completed. Two 18-inch diameter cores will be taken from the center of the lane in each test section using the specially designed coring and sample extraction methods. Each core will produce two beam specimens and four 100-mm diameter cylindrical specimens. In addition, the asphalt mixtures, interlayer products, and tack coat materials used in the construction will be obtained from the field for the laboratory fabrication of performance test specimens. Shear strength tests and four-point bending notched beam fatigue tests will be conducted using both the field and laboratory-fabricated specimens to evaluate the debonding and reflective cracking mitigation potential of the different interlayer systems, respectively. The shear strength and reflective cracking performance of the specimens will be compared between the specimens obtained from the field cores and laboratory-fabricated specimens in the proposed study and the laboratory-fabricated specimens tested in the RP 2019-19 project. Pavement condition survey data and the performance test results will be used to verify/calibrate the results obtained from the NCDOT RP 2019-19 project. The experience gathered from the field construction of the geosynthetic interlayers will be used to develop construction guidelines for the different geosynthetic interlayer products. This research will also produce field-verified performance thresholds and project selection guidelines and long-term condition survey guidelines for interlayer-reinforced asphalt overlays. These products will be used to incorporate best practice techniques in the effort to make informed decisions when using interlayers as a maintenance application in the State of North Carolina.