The purpose of this activity is to assess in situ asphalt pavements to quantify the amount of aging embrittlement as it occurs, quantify the potential impact of that embrittlement on performance, and provide guidance for the selection of any appropriate maintenance or preservation solutions. The goal of the activity is to develop methods, which are practical yet more advanced than the status quo and provide user agencies with tools for evaluating and predicting service life in the field. Potential oxidation and aging of paving asphalts is considered during mixture design to select appropriate materials. Once a pavement is constructed, performance prediction models such as the National Cooperative Highway Research Program 1-37A Mechanistic Empirical Pavement Design Guide incorporate aging and its impact on predicted performance. However, agencies do not rely solely on mix design and pavement performance prediction, and thus use pavement management with periodic surveys to assess the condition of the pavement network. This aging characterization activity lies directly in condition assessment (pavement management) and intends to provide better, more useful information than mix design and performance prediction could provide. The current Accelerated Pavement Testing Facility sections afford the opportunity to pursue accelerated aging of the test pavements and associated full-scale fatigue cracking performance. Accelerated Pavement Testing Facility sections will be subjected to accelerated aging and then fatigue tested. This process adds value to the existing set of fatigue cracking data on those same sections because two data points will be provided representing two aging conditionsshort term and long term. In addition, two of the other sections were subjected to different elevated temperatures while conducting rutting experiments. This activity will be complemented with ground-penetrating radar to evaluate subsurface cracks and fundamental chemistry tools to characterize aging embrittlement with mechanical, chemical, and electrical characterization. Some recent proof of concept work by the Office of Infrastructure, Research, and Development (HRDI) has identified state-of-the-art step frequency ground penetrating radar as a method to identify and measure relative changes in asphalt chemistry by means of the dielectric constants as a function of aging. A suite of mixture tests will be performed on samples subjected to different aging conditions to link lab and field performance predictions. The entire process will be followed by incorporating and testing maintenance treatments in accelerated pavement aging and loading fashion. The intent will be to scientifically quantify the ability of the treatment to resist chemical aging as well as to assess the mechanical benefits, if any, in regard to the cracking performance.
The key project objective is to develop two methods to quantify the aged oxidized life of an in situ pavement; one with rapid, vehicle-based ground penetrating radar (GPR) measurements for network level evaluation, and the second where core samples are taken for laboratory tests included as part of project level evaluations.
Early ground penetrating radar (GPR) techniques were somewhat promising but required a second set of revised tests with redesigned GPR antennas for increased accuracy. Laboratory fatigue tests done on 38 mm diameter specimens and on 12.5 mm nominal maximum aggregate size (NMAS) mixtures proved feasible, allowing thinner lifts encountered in actual construction to be tested. Extracted asphalt binder from heavily aged pavements identified the lower range or lower limit of test values to be expected when taken from field cores as they related to the newly recommended Critical Tip Opening Displacement (CTOD) test.