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Techbrief: Performance-Related Specifications for Portland Cement Concrete Pavements
This TechBrief discusses the development and application of performance-related specifications (PRS) for the construction of portland cement concrete pavements. It provides a background summary of the basis for and early experiences with PRS, including a brief description of the PaveSpec software. This is followed by a summary of PRS trial implementations and experiences in three States: Tennessee, Florida, and Wisconsin.
Performance-related specifications (PRS) are an outgrowth of current end-result, quality assurance (QA) specifications (Kopac 2002). In highway construction, PRS are defined as specifications for key materials and construction quality characteristics that have been demonstrated to correlate significantly with long-term pavement performance (Chamberlin 1995). PRS include sampling and testing procedures for acceptance quality characteristics along with acceptance or rejection criteria. A major feature of PRS is the development of rational pay adjustments based on the projected performance of the pavement.
The Federal Highway Administration (FHWA) has been promoting the development and implementation of PRS since the 1980s. A working PRS was developed in the mid-1990s and was later employed on projects in Iowa, Kansas, Missouri, and New Mexico as a shadow specification. In 2000, the Indiana Department of Transportation (DOT) constructed a project in which the PRS served as the governing specification. Since 2004, additional field trials have been conducted in Tennessee, Florida, and Wisconsin as well as in a second project in Indiana. As more agencies and contractors become familiar with the PRS methodology, the approach is expected to lead to higher quality work, more cost-effective and innovative construction methods, and, ultimately, longer lasting roads.
Basis and Concepts
The current PRS approach for portland cement concrete (PCC) pavements is based on an innovative approach that uses measured acceptance quality characteristics (AQCs)—such as strength, slab thicknesses, and initial smoothness—to predict future pavement performance through mathematical relationships (Darter et al. 1993; FHWA 1999). Pavement performance is quantified in terms of key distresses (e.g., cracking, faulting, spalling) and smoothness over time and is related to the future maintenance, rehabilitation, and user costs of the pavement (FHWA 1999). This link between measured AQCs and the future life-cycle costs (LCCs) of the pavement provides the ability to develop rational and fair contractor pay adjustments that depend on the as-constructed quality delivered for the project, when compared to the as-designed quality (FHWA 1999). Figure 1 illustrates this concept.
A detailed description of some of the key features of the PRS approach is provided below (Darter et al. 1993; Hoerner and Darter 1999; FHWA 1999):
PF = 100 * (BID + [LCCDES – LCCCON]) / BID (Eq. 1)
This approach produces positive pay adjustments to encourage the contractor to provide high-quality products, but also produces negative pay adjustments to protect the highway agency from overpaying for low-quality work.
PaveSpec 3.0 is the current software required to demonstrate the PRS approach outlined above. This software allows an agency to define a PRS and then conduct the following operations (Hoerner et al. 2000):
The PaveSpec software was developed for the Microsoft Windows environment. The software and a comprehensive User’s Guide are available for download at the FHWA site http://www.fhwa.dot.gov/pavement/pccp/pavespec.
Early PRS Experience
After the development and refinement of the PRS in the mid-1990s, shadow field trials were conducted in four states: Iowa in 1996, and Kansas, Missouri, and New Mexico in 1997 (Kopac 2002). The objectives of these collective field trials were to demonstrate the procedure, verify the effectiveness of the draft PRS specification, identify potential problem areas, and determine the specification’s reasonableness (Hoerner et al. 1999).
Although the PRS were not the governing specifications on these four initial field trials, the projects did provide valuable information on the practical application of the PRS, including guidance on the necessary lot and sublot sizes, on appropriate sampling and testing frequencies, and on the general start-to-finish development and application of a PRS specification (Hoerner et al. 1999). Furthermore, it was demonstrated that the sampling and testing required by the PRS specification did not take more time or effort than the testing required under the current specifications (Kopac 2002). Finally, it was realized that a practical cap was needed on all PRS pay factors as the computed PRS pay factors for the trial lots at the field trial locations (which were computed for demonstration purposes only) were often high. PRS-based pay factors at the Iowa site were computed as high as 168 percent due to an extra 1 in. (25.4 mm) of thickness provided by the contractor. Pay factors at the other three sites ranged from 105.8 to 118.4 percent of bid price before a cap was applied (Hoerner et al. 1999).
In 2000, the first field trial where the PRS was the governing specification was constructed on a 1.5-mi (2.4-km) segment of I-465 in Indianapolis (Kopac 2002; Graveen et al. 2004). An agency representative indicated that the specifications provided a basis for rational acceptance and/or price adjustment decisions, and that the specification was well received by the contractors involved in the project (Kopac 2002). The researchers on this project noted that valuable information was gained in many areas including selecting AQC target inputs, construction quality and consistency, and the application and limitations of nondestructive testing (Kopac 2002). Lessons learned from this first project were used by Indiana to fine-tune their PRS approach in preparation for future trial PRS projects.
Recent PRS Implementation Projects
Since 2004, several highway agencies, in cooperation with the FHWA, have continued work on the application and implementation of PRS on highway construction projects. The recent experiences of three such projects are summarized below.
I-65, Nashville, Tennessee (Evans, Darter, and Egan 2005)
In 2004, the Tennessee DOT (TDOT) conducted a trial evaluation of PRS on a 3.5-mi (5.6-km) section of I-65 in Nashville. The pavement design for the 10-lane facility called for a 13-in. (330-mm) jointed plain concrete pavement (JPCP) on a 4-in. (102-mm) permeable asphalt-treated base, with doweled joints placed at 15-ft (4.6-m) intervals. The project was actually constructed under existing TDOT specifications, but PRS data collection activities were performed on the two outer lanes in both the northbound and southbound directions.
For this project, TDOT selected slab thickness, 28-day PCC compressive strength, and initial smoothness (based on profile index with a 0.1-in. [2.5-mm] blanking band) as the AQCs for use in the PRS. Sampling and testing plans were developed for each of these factors, and historical construction data were reviewed to identify appropriate target means and standard deviations. The PaveSpec software was used to generate pay factor curves for the specific project conditions.
PRS data from 14 lots (in both directions) were collected and analyzed. Table 1 summarizes the target and actual values for each of the quality characteristics. In all cases, the actual mean and standard deviation values were superior to the target values. Figure 2 provides a summary of the pay factors for the project, including the individual pay factors for each quality characteristic and the total pay factor. The average pay factor was 106.5 percent for the northbound lots and 105.2 percent for the southbound lots, indicating that the contractor significantly exceeded the target quality.
The trial PRS appeared to work very well, and both TDOT and contractor officials were supportive of constructing future projects under a full, governing PRS. Several key recommendations came out of the trial project, including the need for more rapid feedback on test results and pay factors and the establishment of maximum values for quality characteristics.
SR 9A, Jacksonville, Florida (Evans et al. 2006)
The Florida DOT (FDOT) developed and implemented a PRS in 2004–2005 on a short (0.25-mi [0.40-km]), six-lane highway construction project on State Route (SR) 9A in southeast Jacksonville. The design pavement was a 12.5-in. (318-mm) JPCP on a 12-in. (305-mm) permeable rigid pavement subgrade material, with transverse doweled joints placed at 16-ft (4.9-m) intervals.
Three AQCs were selected by FDOT for use in the PRS project: slab thickness, 28-day PCC compressive strength, and initial smoothness (based on profile index and a 0.2-in. [5.1-mm] blanking band). Sampling and testing plans were developed for each of these factors based on current FDOT specifications, and recent FDOT project data were reviewed to select appropriate target means and standard deviations for each quality characteristic. The PaveSpec software was used to generate pay factor curves for the specific project conditions based on the LCCs of pavements with various strength, thickness, and smoothness properties.
Six lots were included in the construction project, with each travel lane in each direction defined as a lot. Table 2 summarizes the overall target and actual values for each of the quality characteristics. In all cases, the actual mean and standard deviation values were superior to the target values. Figure 3 provides a summary of the pay factors for the project, including the individual pay factors for each AQC and the total pay factor. The average overall unconstrained pay factor for the project was 114.8 percent, indicating that the contractor significantly exceeded the target quality. However, during the development of the pay factor curves for the project, FDOT limited the maximum pay factor to 110 percent.
The implementation of the PRS on this project was considered successful. Because the contractor was easily able to meet and exceed the strength requirements, it was recommended that future PRS implementations give more judicious consideration to the selection of both the target strength value and maximum quality level value (i.e., that level of quality at which the pavement is unnecessarily more conservative than the design and above which no further pay increases will be applied). Furthermore, a need was recognized for more timely results on AQC values and pay factors to enable contractors to adjust their operations accordingly.
I-39/I-90/I-94, Madison, Wisconsin (Rao, Smith, and Darter 2007)
In 2006, the Wisconsin DOT (WisDOT) implemented a trial PRS on a project located on a 5-mi (8.1-km) segment of I-39/I-90/I-94 north of Madison. The design for the six-lane facility called for a 12.5-in. (318-mm) JPCP on a 6-in. (152-mm) dense-graded aggregate base, with doweled transverse joints spaced at 18-ft (5.5-m) intervals. The PRS was applied to both the mainline PCC pavement and the PCC shoulders within a 4.2-mi (6.8-km) segment of the project.
WisDOT selected four AQCs for the mainline paving (slab thickness, 28-day compressive strength, air content, and initial pavement smoothness), whereas three AQCs were selected for the PCC shoulders (slab thickness, 28-day compressive strength, and air content). No significant changes in the test methods from the current WisDOT specifications were specified, and the target and standard deviation values for the AQCs were based on a review of historical paving records. The PaveSpec software was used to generate pay factor curves for the specific project conditions based on the LCCs of pavements with various strength, thickness, air content, and smoothness values. The PRS was included as an overriding special provision in the December 2005 letting of the project.
The project included 18 lots for which PRS AQC measurements were obtained. Table 3 summarizes the overall target and actual values for each of the AQCs, and shows that all actual mean and standard deviation values either met or were superior to the target values. Figure 4 provides a summary of the pay factors for the project, including the individual pay factors for each AQC and the total pay factor. The average overall pay factor for the project was 104.9 percent, indicating that the contractor significantly exceeded the target quality.
The trial PRS was judged to have worked very well on this project, with high smoothness and strength levels resulting in significant incentives for the contractor. Several components were noted to be critical to the success of the PRS, most notably the clear definition of sublots and sampling procedures and the selection of appropriate target means and standard deviations for the AQCs. It was further noted that the balance of pay factors between different AQCs should be carefully monitored and adjusted to ensure that contractors do not start favoring one AQC at the expense of another. For future PRS applications, it was recommended that more complex projects (e.g., ramps, staged construction) should be considered.
Summary of Recent PRS Projects
Table 4 summarizes some of the features and results of these three PRS implementation projects. Working under the PRS for each of these projects, the contractor was able to achieve higher-than-specified levels of quality (as measured by the resultant AQC values and the overall pay factors).
Contact—For information related to concrete pavement, please contact the following:
Federal Highway Administration
CPTP Implementation Team
Research—This TechBrief was developed by Kurt D. Smith, P.E., and Todd E. Hoerner, P.E., as part of the Federal Highway Administration’s (FHWA’s) Concrete Pavement Technology Program Task 65 product implementation activity.
Distribution—This TechBrief is being distributed according to a standard distribution. Direct distribution is being made to the Resource Centers and Divisions.
Availability—This report is available online at www.fhwa.dot.gov/pavement/pccp/. A limited number of copies are available from the Research and Technology Product Distribution Center, HRTS-03, FHWA, 9701 Philadelphia Court, Unit Q, Lanham, MD 20706 (phone: 301-577-0818; fax: 301-577-1421).
Key Words—Concrete pavement design, performance-related specifications, quality assurance, pavement performance
Notice—This TechBrief is disseminated under the sponsorship of the U.S. Department of Transportation in the interest of information exchange. The TechBrief does not establish policies or regulations, nor does it imply FHWA endorsement of the conclusions or recommendations. The U.S. Government assumes no liability for the contents or their use.
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The Concrete Pavement Technology Program (CPTP) is an integrated, national effort to improve the long-term performance and cost-effectiveness of concrete pavements. Managed by the Federal Highway Administration through partnerships with State highway agencies, industry, and academia, CPTP’s primary goals are to reduce congestion, improve safety, lower costs, improve performance, and foster innovation. The program was designed to produce user-friendly software, procedures, methods, guidelines, and other tools for use in materials selection, mixture proportioning, and the design, construction, and rehabilitation of concrete pavements.