Rapid Structural Evaluation of the Foundational Layers during Pavement Construction

The National Center for Asphalt Technology Pavement Test Track consists of 200 ft full-scale asphalt pavement sections subjected to accelerated trafficking in 3-year testing cycles. The testing is mainly focused on asphalt performance; however, recent studies at the Test Track have indicated that the foundation layers (i.e., subgrade and aggregate base) may have a large impact on the surface performance due to variations in their as-built properties. The current practice at the Test Track, to control construction quality, is to utilize the moisture and density values of the foundation layers by using a Nuclear Density Gauge (NDG), but it was previously found that materials passing these criteria still may have problems. To further address this issue during the 2024 Test Track reconstruction, a commercially available lightweight deflectometer (LWD) was chosen to test the unbound layers alongside the NDG. Notable findings from this research were the relationship between moisture and density readings of the NDG to the modulus readings of the LWD. Strong correlations were found between the in-place moisture content and modulus, while in-place density had a lesser influence on the modulus through LWD testing.