Need: Current State highway administration's (SHA's) Pavement Management Systems are primarily based on surface condition data. Surface cracking is mainly used as an indicator of the pavement structural condition. However, with effective pavement preservation activities that intervene early to preserve and extend the life of pavements and increasingly thicker long-life pavements, the surface cracks no longer tell the true structural condition, or health, of the pavement structure. The true pavement structural condition and rate of deterioration are needed not only to plan optimal structural rehabilitation activities and future budget needs, but also for implementing a performance-based Federal-aid program. With an aging pavement network on our most trafficked highways, the fear is not when the next preservation treatment is needed, but (when that will no longer be effective) the need for major rehabilitation/reconstruction. The SHA's state-of-the-practice pavement condition data collection is inadequate to meet this increasingly critical need and network level deflection measurements; those collected using high-speed deflection devices can fill in this critical need. However, the use of deflection measurements from high-speed deflection devices, such as the Federal Highway Administration's (FHWA's) Rolling Wheel Deflectometer (RWD), has seen limited use in pavement management. One of the key hurdles is the lack of, or the difficulty in developing, performance curves for structural deterioration based on deflection measurements. Performance curves for deflection measurements are challenging in that they are sensitive to climatic conditions at the time of measurement, lack the history associated with other data, and there is a general lack of understanding for what deflections are considered good or poor. Without performance curves, network level deflection measurements by themselves are limited in their use; one can make the determination of weak and strong areas within a section of pavement but cannot use it for optimum treatment timing or predicting future performance. Purely empirical performance curves for pavement structural deterioration from deflection measurements are difficult if not impossible for the reasons above. Opportunity: With the development of more mechanistic pavement analysis with integrated climatic models, it appears suitable to develop pavement structural deterioration performance curves based on deflection parameters. Approach: This activity will investigate the potential for using Mechanistic-Empirical (M-E) analysis to develop pavement structural deterioration performance curves based on deflection measurements, and use data from the FHWA's RWD or other devices to adaptively calibrate them. Preliminary analysis shows that center deflection, such as that currently measured with the RWD, may not be a robust indicator of structural deterioration, and that slope or other deflection-based parameters may be needed. European devices that directly measure slope from velocity measurements or the model based on structured light pattern being developed by LCPC (Laboratoire Central des Ponts et Chaussees), France, appear to be promising in this regard. The performance models will be based on mechanistic analysis and material properties used in Mechanistic-Empirical Pavement Design Guide (MEPDG) models. However, it has to be simplified initially to pavement properties that are currently available in a typical SHAs Pavement Management System (PMS) (layer thickness, type, and age) along with empirical coefficients determined through adaptive calibration so that they can be used in current pavement management systems. With the implementation of the Mechanistic-Empirical Pavement Design Guide and more and more of the pavement network-based Mechanistic-Empirical Pavement Design Guide, these models can revert to fully mechanistic. The recently concluded second Strategic Highway Research Program (SHRP2) Project R06 identified a high-speed continuous deflection device as one of the technologies for a followup study and resulting SHRP2 R06-F that is currently underway. The initial efforts will focus on identifying one or more deflection-based parameters that can be measured at the network level and are robust and reliable for evaluating structural condition and developing structural performance curves. Subsequent efforts will build upon SHRP2 R06-F findings, critically evaluate available devices, further develop promising deflection device/technology, and associated analytical methods. This effort also has the potential to support a performance-based Federal-aid program by providing information needed to evaluate pavement structural health. Application: Reliable pavement structural deterioration performance curves can be of significant value to both project management (PM) and National Performance Management initiatives. They provide a means to evaluate and predict remaining structural capacity (i.e. structural health index) and when the deterioration is expected to accelerate for determining optimal timing for structural rehabilitation; similar to the current use of performance curves based on surface condition for determining optimum timing for preservation and surface rehabilitation.
The initial activity on this effort is focused on the identification of one or more deflection-based parameters that can be measured at network level or at close to traffic speed, and are robust and reliable for evaluating structural condition and developing structural performance curves.