Development and Implementation of a Performance-Related Specification for SR 9a, Florida: Final Report
Chapter 1: Introduction
This report documents the results obtained from the use of a performance-related specification (PRS) for construction of a section of concrete pavement highway. The construction project is located on SR 9A (I-295 Leg) in southeast Jacksonville, Florida, and was built in 2004-05. The primary objective of this study was to develop, implement, and evaluate a PRS for the construction of jointed plain concrete pavement (JPCP) in the State of Florida. The Federal Highway Administration (FHWA) sponsored the development and implementation of the PRS for this project by Applied Research Associates, Inc., with full cooperation and assistance of the Florida Department of Transportation (FDOT).
The PRS methodology builds upon the traditional materials-and-methods specifications or quality assurance (QA) specifications used by State highway agencies, by linking key materials and construction quality characteristics (e.g., strength, thickness, smoothness) with pavement performance and, subsequently, future pavement costs.
The underlying premise of the methodology is that lower or more variable materials and construction quality levels result in reduced pavement performance, which, in turn, requires an agency to spend more money in the future through sooner, more frequent, or more comprehensive maintenance and rehabilitation work. By passing the expected economic consequences of high or low construction quality on to the paving contractor through incentives and disincentives, a more rational approach to construction is achieved, one that promotes the minimization of as-designed and as-constructed life-cycle costs (LCCs) and is more equitable to both the highway agency and the contractor.
Initial development of the PRS methodology can be traced back to the mid 1980s and the work of the New Jersey Department of Transportation (Weed, 1989), which developed comprehensive procedures for deriving acceptance plans and payment schedules based on as-constructed portland cement concrete (PCC) thickness and strength. Using the American Association of State Highway and Transportation Officials (AASHTO) rigid pavement performance equation, the expected difference in performance between a pavement with as-designed and as-constructed quality levels could be computed, with the resulting LCC difference passed on to the contractor.
The first of four FHWA-sponsored studies on PRS for concrete pavements was performed in the late 1980s and resulted in an expansion of the procedure to include surface profile (i.e., smoothness) as a key construction quality attribute (Irick et al., 1990). It also introduced the use of concrete pavement performance models developed in National Cooperative Highway Research Program (NCHRP) Project 1-19.
The second FHWA-sponsored study took place between 1990 and 1993 (Darter et al., 1993a; Darter et al., 1993b; Okamoto, 1993). Under that study, the first demonstration software (PaveSpec 1) of JPCP PRS was developed, and an extensive laboratory testing program was conducted to evaluate various PCC material properties (strength, modulus, air content), inter-strength relationships (e.g., flexural versus compressive strength, core versus cylinder strength), and the effects of entrained air content on spalling.
In the third FHWA PRS study (1994 through 1998) (Hoerner and Darter, 1999; Hoerner et al., 1999a; Hoerner et al., 1999b; Hoerner, 1999), the variability of key materials and construction quality characteristics was investigated. Two new characteristics (air content and consolidation around dowels) and new pavement performance models were evaluated, and several field trials of the prototype PRS were conducted. In addition, version 2.0 of the PaveSpec software program was developed, incorporating many of the results of these undertakings.
Performance model refinement was the primary focus of the final FHWA PRS study, which was conducted between 1998 and 2000 (Hoerner et al., 2000; Hoerner and Darter, 2000). Each of four PRS models (transverse joint faulting, transverse slab cracking, transverse joint spalling, and smoothness) were evaluated, improved, and incorporated into PaveSpec Version 3.0.
Performance-Related Specification Concept
Specifications that describe how the finished product shall perform over time are described as performance specifications. PRS are defined as QA specifications that describe the desired levels of key materials and construction acceptance quality characteristics (AQCs) (e.g., concrete strength, slab thickness, and initial smoothness) that have been found to correlate with fundamental engineering properties that predict performance (TRB, 2005). PRS are improved QA specifications. Like QA specifications, PRS specify the desired product quality rather than the desired product performance. However, in PRS, when agency engineers specify quality, they know what performance they are specifying.
Another major difference comes from the methods used to determine the overall pay adjustment for a given lot (i.e., the amount of material or construction produced by the same process). Conventional QA acceptance plans use engineering judgment to establish individual AQC pay adjustments (and weighting factors for each) for determining the overall price adjustment for the lot (FHWA, 1997). PRS, however, use mathematical models (taking AQC values into account) to estimate future pavement performance and corresponding LCCs to compute one overall lot price adjustment (Darter et al., 1993a; FHWA, 1997; Hoerner and Darter, 2000).
As illustrated in figure 1, PRS pay adjustments are based on the difference between the LCCs associated with the target (as-designed) pavement and those associated with the as-constructed pavement. AQC target values represent the AQC values or range of values for which a highway agency is willing to pay 100 percent of the contracted unit price for PCC. These AQC targets are used to predict the future performance (using mathematical distress prediction models) and the associated estimated future LCCs defining the as-designed pavement. (Note: The future LCCs consist of those maintenance and rehabilitation costs expected to be incurred by the agency and potential users [user costs may be included by the agency] over a selected analysis period, assuming a given rehabilitation policy.)
The estimated LCCs corresponding to the as-designed AQC quality are then summarized into one overall LCC (LCCdes) representing the AQC quality of the as-designed pavement. The as-constructed AQCs are measured at the time of construction and used to predict the future performance and LCCs associated with the as-constructed pavement. The estimated LCCs corresponding to the measured as-constructed AQC quality are then summarized into one overall LCC (LCCcon) representing the AQC quality of the as-constructed pavement.
Figure 1. Basic concepts of life-cycle-cost-based performance-related specification.
AQC = acceptance quality characteristic; LCC = life-cycle cost; des = as designed; con = as constructed.
An incentive pay adjustment is computed if the as-constructed AQC quality is measured to be better than the agency-specified target values (due to an increase in pavement life, resulting in a corresponding decrease in LCCs). Conversely, a disincentive pay adjustment is computed if the as-constructed AQC quality is measured to be less than the agency-specified target values (due to a decrease in pavement life, resulting in a corresponding increase in LCCs) (Darter et al., 1993a). The amount of the pay adjustment (incentive or disincentive) is determined as a percentage of the bid price using the following equation:
PF = 100 * (BID + [LCCdes - LCCcon]) / BID Eq. 1
BID = contractor's unit price bid for PCC pavements.
LCCdes = as-designed LCC per unit length.
LCCcon = as-constructed LCC per unit length.
Study Objectives and Scope
The primary objective of this study was to develop, implement, and evaluate a PRS for the construction of JPCP in the State of Florida. This specification would provide the Florida DOT with a methodology that (a) assures that pavement design assumptions are being fulfilled, (b) promotes high quality construction, and (c) protects the department from poor workmanship. At the same time, the specification would allow the contractor the maximum freedom in deciding how to perform the construction.
Specifically, the contract objectives were the following:
- Develop initial PRS-Review Florida DOT specifications, meet with department personnel to identify a suitable construction project and determine the specific goals for PRS development, develop an initial PRS (complete with pay factor curves) for the selected construction project based on existing department specifications and goals, and develop a final PRS based on revisions requested by department staff.
- Implement final PRS-Educate and inform department personnel on use of the final PRS and provide on-site assistance to department field engineers in the areas of sampling and testing plan layout, AQC test value reporting, and pay factor computations for the selected construction project.
- Evaluate the PRS-Evaluate the effectiveness and performance of the PRS, based on assessments of the level of department and contractor satisfaction with PRS, contractor bidding practices and targeted AQC values, the overall adequacy of the PaveSpec 3.0 software, and the PRS-related pay factors in comparison with those computed using the department's current construction specifications.
- Summarize the project results-Prepare a final report documenting the development, implementation, and evaluation of the PRS.