Impact of Design Features on Pavement Response and Performance in Rehabilitated Flexible and Rigid Pavements

Chapter 1. Introduction

Background

Rehabilitation represents the majority of pavement design and construction activity in the United States, and the importance of improving the rehabilitation process cannot be overemphasized. It is well known that in addition to site conditions (e.g., traffic level, climatic conditions, subgrade support, drainage, etc.), the performance of rehabilitated pavement sections depends on the condition and design of the existing pavement, including any prerehabilitation measures to improve the existing structure.

Current pavement rehabilitation design procedures are based mainly on the American Association for State Highway and Transportation Officials (AASHTO) Guide for Design of Pavement Structures that uses limited performance models developed from the AASHTO road test in the late 1950s.⁽²⁾ The recently developed MEPDG reflects the state of the art in pavement design and is considered a significant improvement over the Guide for Design of Pavement Structures.^(1,2) However, gaps still exist in the knowledge base, particularly for rehabilitated pavements, and the mechanistic design methods still are supported by empirical relationships and judgments made by the designer (e.g., determining the representative response properties of a surface layer that exhibits a moderate level of distress).

One of the most critical aspects of MEPDG analysis for rehabilitated pavements is the characterization of existing pavement conditions prior to rehabilitation. Collection of reliable data is imperative because all major decisions regarding existing pavement problems and feasible rehabilitation alternatives depend on the accuracy and integrity of these data.

More importantly, relatively few of the rehabilitation sections from the LTPP program were included in the calibration of MEPDG compared to what is currently available. Many of the test sections were missing data considered mandatory for the calibration process, and many sections in the SPS experiments exhibited little distress because those projects were less than 5 years old. Most of this missing data are now available on the LTPP database, and most of the SPS projects are at least 10 years old and are starting to exhibit moderate levels of distress. As a result, more data are now available and can be used to evaluate the empirical and subjective relationships. LTPP performance data can also be used to recommend improvements to the MEPDG rehabilitated pavement analysis and design procedures.

Because of continued data collection and improvements over time, LTPP collected information on test sections that included a variety of rehabilitation and preservation strategies. Because of additional data available in the LTPP database, researchers have a better understanding of the effects of design and construction features on pavement response and performance of rehabilitated flexible and rigid pavements. These data were used in the analyses conducted in this study to examine the causes of distress. The information obtained in this study can be used to formulate improved models predicting performance of rehabilitated pavements for eventual use in MEPDG. In addition, the data collected and assembled during the study can be used to improve existing MEPDG calibration and validation. This project also offers a unique opportunity to evaluate MEPDG global calibration factors for rehabilitated pavements.

The results of this research enhance existing knowledge related to rehabilitation design in three primary areas: (1) the relationship between pavement design and construction features and pavement response and performance, (2) guidance for identifying appropriate rehabilitation treatments and features for different pavement types, and (3) recommendations for improving LTPP data collection activities and future MEPDG model improvements. In addition, preventive maintenance alternatives were evaluated in this study, and guidance on selecting effective preventive maintenance treatments was developed based on findings from the SPS-3 and SPS-4 experiments.

Project Objectives

The objectives of this project were to use SPS experiment data to determine the following for specific site conditions:

• The impact of the different design, construction, and rehabilitation features on pavement response.
• The contributions of these features to achieve different levels of pavement performance.
• The effectiveness of specific maintenance options for new flexible and rigid pavements.

More specifically, these objectives translate into practical conclusions to respond to the following questions:

• Which design/treatment alternative generally performs better for each type of existing pavement?
• Which design/treatment alternative performs better in the short term (5 years for SPS-5 and SPS-6)?
• Which design/treatment alternative performs better in the long term (10 years for SPS-5 and SPS-6)?
• Which design/treatment alternative performs better in each climatic region?
• Which design/treatment alternative performs better for low and high traffic volumes?
• Does preconstruction activity affect design/treatment alternative performance?
• Are MEPDG distress and roughness predictions biased for different traffic levels, climatic conditions, or pavement types?

Practical findings obtained from this study will help highway engineers and managers make improved pavement design, construction, and rehabilitation decisions.

Report Organization

This report documents findings from the investigation of the impact of design features on pavement response and performance in rehabilitated flexible and rigid pavements. The information presented in this report is organized into eight chapters and five appendices.