Project Objective:

The primary objective of this proposal is to develop a system to identify the source of rutting within the pavement system and/or the presence of mixture instability in the surface layer. Currently, the only accurate method of identifying the source of rutting is to cut trenches and observe deformation in the various layers of the pavement structure, a process that is inconvenient, destructive, and expensive. The proposed system encompasses analysis of the rut profile, measurement of air voids (AV) content from field cores, and backcalculation of in-situ moduli of each of the layers. The proposed procedure is unique in the sense that:

• It utilizes data routinely collected by State Highway Agencies (SHA) as part of their pavement management systems, particularly, transverse profile data from profilograph or profilers mounted on Rut Bars or Automated Road Analyzer Network (ARAN), falling weight deflectometer (FWD) data, and field core data.
• It is independent of the rut depth magnitude, a feature that allows the early identification of rutting due to instability of the surface layer and performing the necessary corrective action for remediation.

Project Abstract:

Rut depth is traditionally measured by determining a depression in the wheel path with respect to the median and the shoulder. Various studies have shown that rut depth (as measured traditionally) may not necessarily be an accurate reflection of pavement and mixture performance. There are times that rut depth may appear to be stabilized, implying that the mixture is performing well. A literature review has shown that continued instability may not result in an increase in rut depth because the rutted basin may broaden as traffic wander compacts or moves the dilated portion of the mixture. The primary objective of this proposal is to develop a framework to identify the most likely source of rutting within the pavement system and the presence of mixture instability in the surface layer, even in the very first few years of the pavement life. Currently, the only accurate method of identifying the source of rutting is to cut trenches and observe deformation in the various layers of the pavement structure, a process that is inconvenient, destructive, and expensive. The proposed system encompasses analysis of routinely collected data, including rut profile, measurement of air voids (AV) content from field cores, and backcalculation of in-situ moduli of each of the layers. The researchers are aware that sufficient data may not be available. A component is also added to quantify the risk to demonstrate the implications for the state agency due to differences in predicted performance using the proposed analysis and the traditional rut depth measurement tools. The proposed procedure is unique in the sense that it is independent of the rut depth magnitude, a feature that allows the early identification of rutting and instability of the surface layer so that the appropriate corrective action for remediation can be taken.

Preliminary results from this conceptual ideal have been validated on a limited number of pavement sections. Experts from the pavement industry, such as FHWA, DOT agencies and transportation consultants, have concluded that this proposed framework will have a broad and significant impact on the pavement infrastructure. The research team has already contacted officials from the New Jersey Department of Transportation (DOT), New York State DOT, and the National Center for Asphalt Technology to obtain the required data to continue with the development, improvement, and validation of this framework. As mentioned before, for decades, state agencies have been struggling with the problem of accurately identifying the source of rutting. On several occasions, state agencies have accepted pavements on distinctly engineering judgment and rut depth that may be too risky, especially for long term prediction of pavement performance. In addition, with the lack of a conclusive solution, pavement rehabilitation decisions have been made on the more conservative basis of conducting partial or full removal and repair. These costly decisions have ultimately come at the expense of taxpayers and consumers. The proposed methodology/system can be viewed as a state-of-the-art system that provides a microscopic approach to evaluate transverse profile measurements. This is very beneficial because state agencies are familiar with all the data that will be necessary to determine the source of rutting with no investment in additional equipment necessary. The methodology proposed will help structure cost-effective and timely rehabilitation strategies based on accurate evaluation of in-situ pavement conditions. In addition, the proposed methodology can be used in critical situations in the decision strategies of long term prediction of pavement performance and interpretation of the asphalt mixture performance. This issue is of the essence at a time when many state agencies are including warranties and performance related specifications in their highway construction and rehabilitation contracts.