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Development and Implementation of a Performance-Related Specification for SR 9a, Florida: Final Report
Chapter 6: Summary and Recommendations
Implementation of a concrete pavement PRS on SR 9A (I-295 leg) in Jacksonville, Florida, was sponsored by the FHWA with full cooperation and significant assistance from the Florida DOT. This implementation provided FDOT and the pavement contracting industry with a better understanding of the methods, benefits, requirements, and results of PRS implementation.
Significant effort made by the FDOT staff, FDOT project managers, FHWA, and the researchers helped to define a reasonable specification that all parties understood and agreed upon. Three AQCs (PCC strength, PCC thickness, and surface smoothness) were selected for use in the PRS. Based on current FDOT specifications, evaluation of recent FDOT project data, and comments from the PRS implementation team, acceptance levels were selected, as shown in table 5. The team also collected and agreed upon the inputs for the PaveSpec 3.0 software that are shown in appendix A. This software was used to develop pay factor curves based on the life cycle costs of pavements with various strength, thickness, and smoothness properties. Following preparation of a practical field sampling plan, this information was compiled into the PRS shown in appendix A and provided to the contractors during bid letting.
Paving of the SR 9A PRS project was completed between January and April 2004. However, portions of the associated coring and smoothness measurements were not available until June 2005 due to delays in the surface grinding operations. Results of this field sampling and testing were compiled into pay factor computation spreadsheets for determining the final lot average and standard deviation values. Results of this testing and the associated pay factors are provided in chapter 4.
The average unlimited overall pay factor for the entire PRS project (all lots) was 114.8 percent. The contractor achieved incentive level properties in thickness, smoothness, and strength. Primarily, however, the very high strength levels controlled the overall pay factor for all lots. These levels in most lots exceeded the maximum quality limit of 5,500 lbf/in2 (37.92 MPa), where the pay factor was capped. If the maximum quality level were not included, the overall pay factor would be nearly 115 percent. This means that, according to calibrated PRS performance models and expected costs, FDOT paid 10 percent in additional initial cost to receive an estimated 15 percent improvement (reduction) in future pavement life cycle cost.
This conclusion was verified independently using the new Mechanistic-Empirical Design Guide program that was developed under NCHRP 1-37A (ARA, 2004). This procedure predicts IRI, joint faulting, and slab cracking for jointed plain concrete pavements. The same inputs associated with the PRS target pavement were used in the software to predict the life of the pavement. Next, the as-built AQCs (strength, thickness, smoothness) of the pavement were input to determine their effect on predicted pavement life. The increased as-built pavement properties resulted in an expected increase of 16 percent in pavement life.
Surveys were distributed to the primary FDOT, contractor, and FHWA participants in the PRS implementation. Many useful comments and suggestions were received. Comments from all participants were very supportive of the PRS approach, as described in chapter 5.
Implementation of a PRS on SR 9A in Jacksonville, Florida went well, with many supportive comments from FDOT and the contractors. A few recommendations for future PRS activities can be gleaned from this implementation, as follows:
- Select the AQC target mean and standard deviations carefully. These levels must be representative of those expected by the agency for achieving 100 percent pay.
- Select the MQL carefully. The standard mix on the project regularly developed strengths greater than the MQL. As a result, it was not difficult for the contractor to meet or exceed the MQL on the PRS project.
- Consider the effect of pay factor limits on the contractor and the agency.
- Provide contractors with timely results and pay factors so that they can adjust their methods accordingly.
- Consider alternative methods for increasing sampling rate and reducing destructive testing. Particularly, thickness measurements could be increased and improved using a nondestructive method such as that used by the Wisconsin DOT.
BENEFITS OF PERFORMANCE-RELATED SPECIFICATION
The clear and rational approach of PRS, with well-defined target quality levels that are understandable to the contractor, are expected to lead to significantly improved highway construction quality, improved pavement performance, and a reduction in LCC. The full possibility of PRS may also offer the opportunity to optimize the design and construction process to provide acceptable performance for lower LCCs. Key benefits of PRS are listed below, some of which were demonstrated on this SR 9A project:
- Better linkage between design and construction.
- Higher quality pavements (through incentives). The overall unlimited pay factor was nearly 115 percent, which indicates a significantly higher quality level of construction. The true effect of lower variability (all AQCs had standard deviations at or below the target) may also have benefits that are not known at this time.
- Testing that focuses on key quality characteristics that relate to the pavement long-term performance. Any factor that is measured and paid by incentive will receive a lot of attention and focus on the project. Other AQCs such as dowel alignment, tie bar alignment, and consolidation around dowels would add to the comprehensiveness of a PRS project and avoid a disastrous situation where something (such as tie bar location) is not measured until well into the project only to discover it is out of specifications.
- Incentives and disincentives that are justified through reduction or increase in future LCC. They are not merely an opinion of the benefit of varying quality levels. The PaveSpec program calculated reasonable pay factors for SR 9A. An independent estimate of increased life of approximately 16 percent represents a very significant benefit to highway users.
- Specifications that give the contractors more responsibility and flexibility yet increased accountability may benefit both the contractor and owner. Additional full PRS projects are needed to prove this possibility.
- Allow contractors to be more innovative and more competitive.
- Both the contractor and State staff thought that PRS may lead to the elimination of contractors who are less oriented toward quality.
- PRS may provide a lower "fear factor" for contractors and less administrative complexity and work over the long term for the agency compared to warranty specifications.
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