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Federal Highway Administration Research and Technology
Coordinating, Developing, and Delivering Highway Transportation Innovations

 
REPORT
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Publication Number:  FHWA-HRT-15-074     Date:  September 2016
Publication Number: FHWA-HRT-15-074
Date: September 2016

 

Pavement Structural Evaluation at the Network Level: Final Report

 

CHAPTER 1. INTRODUCTION

State transportation departments invest billions of dollars each year on providing and managing the transportation infrastructure assets to meet legislative, agency, and public expectations. Pavements are a major component of those transportation assets, with pavement rehabilitation being one of the most critical, costly, and complex elements. This is especially true at present, since a large percentage of pavement networks are reaching the end of their serviceable life, and pavement rehabilitation has become even more daunting given the funding constraints faced by State transportation departments.

At the heart of rehabilitation decisions is the pavement management system (PMS), which provides network-level condition indices or scores for each pavement segment in the system. Earlier generations of PMSs were driven by ride quality and distress as a direct result of the American Association of State Highway Officials Road Test, which introduced the concept of the Present Serviceability Rating and Present Serviceability Index.(1) With advances in technology, pavement engineers started to use distress (i.e., cracking, rutting, etc.) and longitudinal roughness, typically in the form of the International Roughness Index (IRI), as key pavement performance indicators in the pavement management decisionmaking process.

Both distress and roughness are important indicators that merit emphasis within the PMS process. However, another important indicator necessary to make rational pavement investment decisions is structural adequacy. A few State transportation departments are beginning to consider structural adequacy as part of their routine PMS activities by incorporating deflection testing.

At present, there is a large array of equipment that can be used to measure the deflection basin resulting from an applied load. The most commonly used device in the United States since the 1980s is the falling weight deflectometer (FWD). FWDs rely on impact loads to produce a pavement response similar to that produced by actual traffic loadings, which is then measured by deflection sensors located at varying distances from the load.

While FWDs represent the state-of-the-practice, they are not without shortcomings. Since FWDs are a stop-and-go operation, lane closures are required, which cause traffic disruptions and, in turn, create a safety hazard to personnel involved in the operation as well as the traveling public. Their frequency of testing is also significantly less than a continuous operation, which affects operational costs. These shortcomings are especially important in terms of network-level pavement management applications, which by their nature require information on a large pavement network measuring in the thousands of miles.

To overcome these shortcomings, several organizations in the United States and Europe have developed devices over the past several decades that can continuously measure pavement deflections at posted traffic speeds (up to 50–60 mi/h (80.5–96.6 km/h)). The modern versions of these moving deflection testing devices that are actively used today include the following:

Much work has been done over the past decade toward advancing the state of the technology of moving pavement deflection testing. However, one main question is whether the TSD and/or RWD are ready for immediate implementation in the structural evaluation of pavements for network-level PMS applications. If so, how should the measurements from one or more of these devices be used within the context of network-level PMS? These questions are at the heart of the project presented in this report, whose stated objectives were to perform the following:

  1. Assess, evaluate, and validate the capability of traffic speed deflection devices (TSDDs) (including both RWDs and TSDs) that measure deflection or other pavement responses for pavement structural evaluation at the network level for use in pavement management application and decisionmaking.

  2. Develop analysis methodologies for enabling the use of the device(s) capable of meeting the first objective or alternatively develop recommendations to further advance promising device(s) and/or technologies if the devices do not meet the first objective.

The ultimate goal of the project was to establish a reliable measure of the structural condition of all bound pavement layers above the unbound base layer as it deteriorates over time under traffic and environmental loading based on moving pavement deflection technology and measured at posted traffic speeds (up to 50–60 mi/h (80.5–96.6 km/h)). Moreover, this measure needed to be robust enough in capturing the structural condition or deterioration of the pavement layer notwithstanding the seasonal and spatial variation in base and subgrade layers.

To accomplish the above stated goal and objectives, the following 2 phases and 10 tasks were carried out as part of the project:

This report presents the findings, conclusions, and recommendations from the referenced phases and tasks and is organized as follows:

 

 

 

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