U.S. Department of Transportation
Federal Highway Administration
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Washington, DC 20590
Federal Highway Administration Research and Technology
Coordinating, Developing, and Delivering Highway Transportation Innovations
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Publication Number: FHWA-HRT-05-068
Date: October 2005
In 1996, the Federal Highway Administration (FHWA) commissioned a national survey of frequent highway users that asked them what they wanted in their highway "product." The highway users clearly stated that their top priority was quality of road conditions, followed by safety and the need to reduce congestion.(1) In an effort to provide highway users with a smooth ride, highway agencies have implemented smoothness specifications for new pavements. A smoothness specification indicates the acceptable range of smoothness that contractors must achieve to obtain full payment. Several highway agencies are giving bonuses to contractors who obtain better smoothness than the minimal requirement, and they are assessing penalties for those who deliver unacceptable smoothness.
A survey conducted in 2000 indicated that 86 percent of the highway agencies in the United States currently use a smoothness specification for new portland cement concrete (PCC) pavements.(2) Those agencies that do not use a PCC smoothness specification are believed to be the ones that construct few or no PCC pavements. The number of highway agencies using a smoothness specification for the construction of PCC pavements has shown a sharp increase during the last decade. In addition, the smoothness level specifications standards in highway agencies have increased over the years as the contractors became familiar with the smoothness specification.
For a PCC pavement, it is important to achieve both a high level of smoothness during construction, as well as a satisfactory long-term performance. It is not acceptable to construct a pavement with high initial smoothness that will give poor long-term performance. The design features and material properties of the PCC pavement should be conducive to yielding satisfactory long-term performance.
Smoothness measurements for construction acceptance usually are performed shortly after paving is completed, using either a profilograph or a lightweight inertial profiler. The results from the smoothness measurements are used to judge whether the pavement has achieved the specified smoothness level. These results are also used to determine whether contractors receive bonuses or whether they will be assessed penalties.
However, it is unclear whether the smoothness of a pavement measured immediately after it is paved truly reflects the initial smoothness of the pavement, because the smoothness can undergo changes over the short term (e.g., within 3 months) due to curling or warping effects. In other words, a pavement can have a very high smoothness immediately after construction, followed by a decrease in smoothness over a short time period because of changes in slab shape that occur with curling and warping. Another concern with achieving high levels of initial smoothness relates to whether paving contractors are using construction procedures or making changes to the PCC mix design that result in a high initial smoothness but are detrimental to long-term pavement performance.
The objectives of this research project were to:
The roughness data collected at Long-Term Pavement Performance (LTPP) program test sections were used to study the roughness progression of jointed plain PCC sections. The initial and long-term smoothness of the test sections were evaluated and compared to determine what effect the mix design properties, material properties, construction procedures, and design features have on pavement performance.
The changes in smoothness that occur over the short term on PCC pavements were investigated by collecting profile data on test sections established on new PCC pavements. The test sections were typically profiled 1 day, 3 days, 7 days, and 3 months after paving. This investigation evaluated the short-term smoothness changes of a PCC pavement.
A literature review was performed to compile information related to these topics:
As part of the literature review, SHA and American Concrete Pavement Association (ACPA) personnel were asked to provide their views on how the concrete mix design may affect the smoothness of the as-built pavement.
Chapter 2 presents the results of the literature survey on procedures used to determine pavement smoothness for construction acceptance and smoothness indices used to judge pavement smoothness. Chapter 3 presents the literature survey results describing design, construction, and mix design properties that can affect the initial smoothness of a PCC pavement.
Chapter 4 presents an overview of the analysis procedures. Chapter 5 presents findings from the analysis of LTPP data, which were used to study roughness progression at LTPP test sections. The LTPP data were also used to determine factors causing pavements to show poor long-term performance and to identify factors allowing pavements to retain their smoothness over the service life. Chapter 6 presents the findings from investigations of short-term changes in the smoothness of PCC pavements. This chapter also presents findings from the analysis of data collected from five paving projects at 1 day, 3 day, 7 day, and 3-month intervals after paving.
Chapter 7 presents conclusions from this research. Chapter 8 presents recommendations and guidelines for design features, PCC material properties, and construction procedures to achieve pavements with both high initial smoothness and good long-term performance. Guidelines and recommendations on how to conduct smoothness testing are also presented in this chapter.