North Carolina current allows two basic types of pavement design on NCDOT roadways;
1) those whose structural capacity comes primarily from asphalt concrete (flexible pavements) and 2) those whose structural capacity comes primarily from portland cement concrete (rigid pavements). These designs have been used successfully in many applications throughout the State; however, they utilize a large amount of relatively expensive and difficult to produce materials (asphalt concrete and portland cement concrete). A third technique, inverted pavement design that requires less of these materials and is purported to provide equivalent or superior performance is not currently allowed with the NCDOT specifications. Inverted pavements consist of a 2 - 3.5-inch asphalt concrete surface, supported by a 6 – 10-inch layer of unbound aggregate base and then by 8 - 12 inches of a cement treated subbase. Literature and experience have shown that these pavements can be designed and used in many applications at a substantial cost savings. However, there are many unknowns when directly adopting design specifications from elsewhere as local materials, practices, and experience may not be fully accounted for. Thus, there exists a need to gain state specific experience in the engineering and performance of these structure before their adoption can be considered.
With respect to this need, the proposed research plan will achieve four objectives; 1) design, construct, and monitor the constructability and initial performance of an inverted pavement in comparison with a similar traditional pavement design on a NCDOT project, 2) estimate the long-term performance of the inverted pavement section in comparison with the traditional pavement design, 3) estimate the costs and benefits for using inverted pavements on a wider scale, and 4) if found to be a viable technique, develop a design guide for inverted pavements in North Carolina.
The primary outcome of the proposed research will be a set of recommended guidelines for the use of inverted pavement in North Carolina. These outcomes can be used by the Materials and Test Unit of the NCDOT to improve pavement design procedures, which may result in cost savings through improved specifications and greater design flexibility.