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Development and Implementation of a Performance-Related Specification for I-65 Tennessee: Final Report
Chapter 1. Introduction
This report documents the development and testing of a performance-related specification (PRS) for a section of I-65 near Nashville, Tennessee, in 2004. The study was conducted under the Federal Highway Administration (FHWA) Concrete Pavement Technology Program Task 7: Field Trial of Performance-Related Specifications for Portland Cement Concrete (PCC) Pavement in Tennessee, contract DTFH61-03-C-00109. The work was conducted in partnership with the Tennessee Department of Transportation (TDOT) which, under the leadership of Brian Egan, contributed significantly to the effort.
The purpose of this work was to continue the implementation of PRS for concrete pavement construction to more fully determine the benefits and any problems associated with PRS so that they can be improved for future implementations. Previous trials of PRS for concrete pavement were conducted in Florida and Indiana (two major projects), and shadow trials were conducted in Missouri, Iowa, Wisconsin, and New Mexico (see references 1–4 and 6–9).
PRS for highway pavement construction are similar to quality assurance specifications; however, a key difference is that the measured acceptance quality characteristics (AQCs) are related directly to pavement performance through quantifiable relationships. Performance is defined by key distress types and smoothness and is related to the future maintenance, rehabilitation, and user costs of the highway. This link between measured AQCs and future life-cycle cost (LCC) provides the ability to develop rational and fair contractor pay adjustments that depend on the difference between the as-designed “target LCC” and the as-constructed LCC (figure 1 illustrates these concepts).
The FHWA methodology (FHWA-RD-98-155, Guide to Developing Performance-Related Specifications) and software (PaveSpec 3.0) were used in developing the PRS for the Interstate 65 project.(4) As illustrated in figure 1, PaveSpec 3.0 computes pay adjustment (termed pay factor) for a given lot based on the effect of construction quality on the pavement performance and subsequent LCC. The pay adjustment is computed as the difference in LCC between the as-designed “target” pavement and the as-constructed pavement (lot).
A pay adjustment factor (PF) is defined as the percentage of the bid price that the contractor is paid for the construction of a pavement lot and is computed based on the difference between the as-constructed and as-designed LCC (in present worth dollars) as follows:
PF = 100(BID+ [LCCdes - LCCcon]) / BID (1)
For jointed plain concrete pavement (JPCP), the LCC is computed using prediction models for slab cracking, joint spalling, joint faulting, and pavement smoothness. A key aspect of using LCC to define the PFs is that the LCC of the as-constructed lot essentially represents the overall measure of quality, providing a rational way to develop an overall pay adjustment factor for the lot.
During the selection of this project for PRS implementation, it was intended to be a full test of PRS, where the contractor would be subject to the PRS in all of the concrete paving work. However, the best available project had just been bid and awarded. TDOT and the contractor agreed to a plan to place the northbound lanes under the existing TDOT method specifications (data were also to be collected on the northbound lanes using PRS procedures). Plans were for the contractor to be subjected to the PRS specifications for the southbound lanes and remaining inside lanes. After the PRS was developed and construction was underway on the northbound lanes (which included complete PRS data collection), other issues, unrelated to the PRS, arose between TDOT and the contractor that resulted in the contractor continuing work under the TDOT method specification. However, southbound PRS data were collected and analyzed. The PRS data from both the northbound and southbound paving are reported herein. These results are not a true independent test of the PRS implementation from beginning to end but provide results that would likely have been achieved under a full PRS implementation.
This report describes the PRS concept and provides an overview of the Tennessee I-65 project. The development of the PRS for the I-65 project is then described in detail, followed by a description of the implementation of the PRS on the I-65 project. The results from the construction monitoring are then presented. An evaluation of the PRS for this project is presented as judged by the resulting quality, the TDOT staff, the quality control (QC) representative, and the contractor staff comments. Finally, a summary and conclusions are provided. The specification is provided in appendix A, the data measured on the project in appendix B, and the expected pay charts for the PRS in appendix C.