Student Auburn University Auburn, AL, United States
Abstract: The National Center for Asphalt Technology Pavement Test Track consists of 200 ft full scale asphalt pavement sections subjected to accelerated trafficking in three-year testing cycles. While the research focus is on performance of the various asphalt materials, recent studies at the Test Track have indicated that the foundation layers (i.e., subgrade, aggregate base) may have a large impact on the surface performance due to variations in their as-built properties. During the construction phase, normal practice utilized the moisture and compaction readings from nuclear density gauge (NDG) testing to control and ensure the quality of the unbound foundation layers. In past testing cycles, despite materials passing the necessary checks on moisture and density, wide ranging backcalculated moduli were later obtained from in situ falling weight deflectometer (FWD) testing that presumably led to variations in performance of the asphalt layers. Consequently, there has been interest in subjecting the foundation layers to actual structural testing during construction in a fast and efficient manner. A commercially-available light weight deflectometer (LWD) was selected to develop a new quality control structural evaluation test during the 2024 Test Track rebuild. The LWD measured surface deflections under impact loading from which the modulus and surface stiffness of the unbound structural layers were computed in real time. The unbound foundation layers of six sections of the 2024 rebuild at the Test Track were tested continuously during their construction. Four longitudinal stations were marked in each section, while each station had three offsets made up of an LWD test location on the inside wheelpath, between the wheelpaths, and the outside wheelpath. These locations coincided with the test locations of the NDG during construction and future FWD testing. Over the four-month reconstruction timeframe, data were repeatedly collected from each location. The local chert subgrade and aggregate base were tested in five out of the six sections. In the sixth section, an outsourced clay and aggregate base with novel in situ stabilization were tested. The data were analyzed over time and statistically compared to both previous data within each section and the data of other sections. Significant variations in collected data were found based on environmental effects (e.g., rainfall) and time (e.g., drying). The data were also analyzed in relation to the NDG time series data to draw meaningful correlations between the data sets. As the three-year cycle at the Test Track continues, future FWD testing will be performed in the same locations as LWD testing to allow for analysis and comparisons between the methods of structural testing and characterization. The results in this investigation show the use of the LWD in pavement construction was beneficial in understanding the changes of the underlying materials during construction as well as for enhanced structural testing during construction.
Learning Objectives:
Attendees can expect to learn the following from this session:
Upon completion, participant will be able to distinguish differences in types of testing for foundational pavement layers.
Upon completion, participant will be able to describe the significance and applications of a lightweight deflectometer in a pavement construction setting.
Upon completion, participant will be able to interpret, discuss, and compare field data from multiple sources of foundational layer testing, i.e. lightweight deflectometer, nuclear density gauge, and falling weight deflectometer.
