Incremental Costs and Performance Benefits of Various Features of Concrete Pavements

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CHAPTER 1. INTRODUCTION

Introduction

The design of portland cement concrete (PCC) pavements is more than the determination of slab thickness. Other components of a PCC pavement "system"-such as transverse joint design, base type, drainage design, and shoulder type-have a significant impact on pavement performance and therefore must be considered during the structural design process. These components, often referred to as design features or design elements, must be carefully selected for the environment and traffic loading conditions to which a specific PCC pavement is exposed. As shown in figure 1, the careful selection of these features can result in an enhanced design that maintains a higher level of serviceability or extends the performance life of the pavement. Over the years, various studies have documented the importance of many of these design features to overall PCC pavement performance.^(1,2,3,4)

Figure 1. Design feature benefits.

While it is known that the combination of certain design feature choices can have a positive effect on pavement performance, the addition of such features to a PCC pavement also increases the overall cost of the pavement structure. This raises the question of whether the addition of the design features is worth the increase in cost; that is, are the design features cost effective? Although the pavement designer may implicitly believe that the design features are cost effective, this is not necessarily the case for several reasons. For one, the effects of individual design features on pavement performance are not independent from one another, and consequently some level of "performance redundancy" may occur. Furthermore, at some point the inclusion of additional design features may eventually reach a state of diminishing returns, in which fewer performance benefits are gained for ever-increasing costs of new design features. This suggests the need to consider both the performance benefits and the costs of design features when contemplating their use in a PCC pavement design.

Unfortunately, current design practices do not always consider this trade-off between performance benefits and costs when considering PCC pavement design features. In fact, these relationships are poorly understood. Thus PCC pavements are often designed as "premium" pavement structures, incorporating myriad design features without any realistic expectations of the performance benefits to be gained. This suggests that there is a strong need for a methodology and an evaluation tool that can be used to assess the costs and benefits of incorporating design features in PCC pavements.

Project Objectives

This project was initiated by the Innovative Pavement Research Foundation (IPRF) and continued under the auspices of the Federal Highway Administration (FHWA), with the objective of developing a simple methodology for comparing the impact of various PCC pavement design features on cost and performance of PCC pavements. Specifically, the overall objectives of this project are to:

• Document the relative performance benefits of different PCC pavement design features on PCC pavement performance.
• Establish relative construction costs associated with different PCC pavement design features.
• Develop a computer software tool for comparing and evaluating trade-offs in assessing the relative performance benefits and costs of various design features.

The primary product of this project is a computer software application that can be used to evaluate the benefits and costs associated with the addition of different design features to a PCC pavement design. The tool provides insight into general performance and cost trends associated with those modified pavement designs, and can help design engineers develop more cost-effective PCC pavement designs. However, it is emphasized that the tool is not intended for the design of PCC pavements, but rather for the assessment of the cost-effectiveness of new design features by considering the trade-offs between their cost and performance contributions.

Overview of Report

This report has three chapters (in addition to this one) and four appendices. Chapter 2 describes data collection activities conducted under the project, including a summary of the survey results collected from highway agencies and paving contractors. Chapter 3 describes the approach used in evaluating relative performance benefits and costs, and introduces the computer software tool developed under the project. Chapter 4 summarizes the entire project.

Appendix A summarizes the results of the comprehensive literature search conducted to identify information on PCC pavement design features, performance, and costs. Appendix B contains the performance and cost survey forms that were sent to highway agencies and paving contractors, respectively. Appendix C contains a summary of the raw survey data collected from the highway agencies and paving contractors. Appendix D is a user's manual for the computer software tool.