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Development and Implementation of a Performance-Related Specification for I-65 Tennessee: Final Report
APPENDIX A: Final Performance-Related Specification
Project NO. 19012-3154-44 IM-65-3(104)91
TECHNICAL SPECIAL PROVISIONS FOR PERFORMANCE-RELATED SPECIFICATIONS for RIGID PAVEMENT
Prepared for Review By:
April 12, 2004
LIST OF ABBREVIATIONS
AQC: Acceptance Quality Characteristic
AREALot: Area of the As-Constructed Lot
BID: Contractor Bid Price of Concrete Slab
LCC: Life Cycle Cost
LCCcon: As-Constructed Life Cycle Cost
LCCdes: As-Designed Life Cycle Cost
MQL: Maximum Quality Limit
PAYLot: Adjusted Payment for the As-Constructed Lot
PAYADJLot: Lot Pay Increase (+) or Decrease (-)
PFcomposite: Composite Pay Factor for Lot
PFPI: Initial Smoothness (or Profile Index, PI) Pay Factor
PFstrength: 28-Day Strength Pay Factor
PFthickness: Slab Thickness Pay Factor
PI0.1: Profile Index with 0.1-in Blanking Band
PRS: Performance-Related Specifications
RQL: Rejectable Quality Limit
This Technical Special provision applies to 13-in mainline Portland cement concrete pavement on I-65 Project 19012-3154-44 IM-65-3(104)91 from Old Hickory Boulevard to CSX Railroad as shown in the plans.
Tennessee Department of Transportation (TDOT) will pilot performance-related specifications (PRS) for Portland cement concrete pavement as a part of this project. The PRS provides for incentive/disincentive pay to the contractor depending on the level of construction quality achieved in the field. The Composite Pay Adjustment Factor for a specific lot of pavement is based on the difference between the estimated long-term life-cycle cost (LCC) of the as-designed (target) pavement and the estimated long term LCC of the as-constructed pavement (lot) as computed by the PaveSpec 3.0 software on a lot basis. This methodology is defined in the report “FHWA-RD-98-155, Guide to Developing Performance-Related Specifications.” The Composite Pay Adjustment Factor will apply to TDOT pay item number 501-01.06 (13-in mainline pavement including the cost of joints). The Composite Pay Adjustment Factor is based on three individual lot pay factors: concrete slab thickness, concrete compressive strength, and initial smoothness (or Profile Index). The absolute minimum value of the Composite Pay Adjustment Factor for a given lot shall be limited to 80 percent and the absolute maximum value shall be limited to 110 percent.
The main objective of these performance-related specifications (PRS) is to provide the agency with a methodology to assure that the design assumptions are being fulfilled, promote high quality construction, and to protect the agency from poor workmanship. At the same time it allows the contractor the increased freedom and innovation in deciding how to perform the construction and provides significant incentives to produce a quality project. PRS provides a rational method for contract price adjustment based on the difference between the long-term as-designed and as-constructed life-cycle costs of the pavement.
The proposed PRS incentive pay schedules were developed using the FHWA methodology as defined in the report “FHWA-RD-98-155, Guide to Developing Performance-Related Specifications for PCC Pavements,” and implemented in the PaveSpec 3.0 software. PRS employ distress prediction models to relate the acceptance quality characteristics (AQCs) to future pavement performance and associated LCC. Figure 1 illustrates how the PRS methodology works. The FHWA Web site provides additional information about PRS and the PaveSpec 3.0 software (www.tfhrc.gov/pavement/pccp/pavespec/pavespec.htm).
The pay adjustment factor (PF) is defined as the percentage of the bid price that the contractor is paid for the construction of a concrete 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)
* The pay adjustment factor (PF) will be applied to pay item 506-01.06 only.
The LCC is computed using future maintenance and rehabilitation activities that are determined based on prediction models for slab cracking, joint spalling, joint faulting, and pavement PI. A key aspect of using LCC to define the PF’s is that the LCC of the as-constructed lot is the overall measure of quality, providing a rational way to develop an overall pay adjustment factor for the lot. The PF’s computed by this procedure have been adjusted slightly for practical application by TDOT.
ACCEPTANCE QUALITY CHARACTERISTICS
Pay adjustment in these specifications is based on the following key acceptance quality characteristics (AQC) only:
Several other quality characteristics (e.g., slump, dowel placement, tie bar placement, aggregate gradation, aggregate quality, surface friction) are very important but are not described in these PRS. These quality characteristics and construction requirements are considered according to TDOT’s existing Standard Specifications.
TARGET QUALITY LEVELS
If the TDOT mean and standard deviation targets for each of the AQCs used for pay adjustment are met, the agency will pay 100 percent of the bid price. Table 1 shows target quality levels (mean and standard deviations) at which TDOT will pay 100 percent of the bid price.
REJECTABLE QUALITY LEVELS
Rejectable quality level (RQL) is the level of quality below which for thickness and compressive strength or above which for PI of the pavement is deficient enough that a corrective action or remove-and-replace is warranted. Table 2 shows the RQLs (lot mean values) for each of the AQCs used for pay adjustment in these PRS.
If the quality of the as-constructed lot (as measured by the acceptance test results) of any of the AQCs is below the RQL, the Engineer will determine the appropriate corrective actions as follows.
When the thickness of the as-constructed lot is less than 12 in and the judgment of the Engineer is that the area of such deficiency does not warrant removal and the Contractor elects not to remove the pavement, there will be no payment for the area retained.
The Engineer may elect to use Impact Echo methods to identify the boundaries of the deficient thickness.
Concrete that fails to develop a compressive strength of 3,000 lbf/in2 within 28 days shall be removed and replaced at the Contractor’s expense or accepted at a reduced pay adjustment, as described in section 6 of this supplemental specification.
All surface profile areas represented by high points having deviations in excess of 0.4 in per 25 ft or less shall be corrected. If after these corrections are made, the average profile index of any sublot is greater than the RQL, corrective action shall be taken to reduce the profile index to the target value shown in table 1.
MAXIMUM QUALITY LEVELS
Maximum quality level (MQL) is the level of quality at which the pavement is unnecessarily more conservative than the design so that no further pay increase will be provided. Table 3 shows the MQLs (lot mean values) for each of the AQCs used for pay adjustment in these PRS.
If the quality of the as-constructed lot (as measured by the acceptance test results) of any of the AQCs is higher for thickness or compressive strength or lower for PI than the MQL, the pay factor at the MQL will be used for computing the composite PF and adjusting the payment. The actual values will be used to compute the standard deviation.
Table 4 lists the testing methods for slab thickness, concrete strength, and Profile Index. The testing methods for these AQCs are discussed further in the following sections.
The thickness of cores drilled in conformance with AASHTO T148, shall be used for determining slab thickness. Core shall be taken from one randomly selected location within each sublot and be a minimum of 4-in diameter. The slab thickness at a cored location shall be recorded to the nearest 0.1-in, as the average of nine caliper measurements of the core length. Individual caliper measurements shall be recorded to the nearest 0.1-in.
As designated by the Engineer, alternatively the ASTM C1383-98a Impact Echo method of measuring pavement thickness shall be used. Impact Echo thicknesses shall be measured at one random location within each sublot, as designated by the Engineer. Cores shall be extracted from the same location in the odd numbered sublots, and thicknesses shall be measured. If the Impact Echo measurement on even numbered sublots is less than the RQL, confirmation cores shall be extracted from the same location. Core thickness shall be measured and used in the pay factor computation.
Initial Smoothness (or Profile Index)
The contractor shall collect pavement surface profile index values as soon as practical and prior to sealing joints and opening to traffic. Profile Index shall be collected in the presence of the Engineer using a computerized Rainhart profilograph in conformance with ASTM E 1274-03. The blanking band shall be set to 0.1 in and the bump limit shall be set to 0.4 in per 25 ft. Vertical measurement accuracy of each profilograph shall be demonstrated to the Engineer upon request. Profile measurement accuracy of each profilograph shall be demonstrated immediately prior to initial profile collection and following final profile collection through comparison with the TDOT high-speed profiler. The contractor shall identify and lay out a 1,000-ft long PCC section with PI values between 5 and 7 in/mi. The average PI from of three profilograph runs shall be within +/-”1” in/mi of the average of five runs collected using the TDOT high-speed profiler. If the PI comparisons are acceptable, the profilograph PI values will be used for pay factor computation.
If the average of the three post-construction PI values measured by the profilograph does not meet this requirement, any equipment and operator problems shall be assessed and resolved. Five additional runs shall be completed using both the contractor’s profilograph and the TDOT high-speed profiler. If the supplemental PI comparisons are acceptable, the profilograph PI values will be used for pay factor computation. Otherwise, PI values measured using the TDOT high-speed profiler will be used in pay factor determination.
The required strength cylinders shall be cast from a randomly selected concrete truck within the sublot. The cylindrical specimens shall be molded and cured in accordance with AASHTO T23
and tested in accordance with AASHTO T22 standard test methods.
A strength test for each sublot is determined as the average of the 28-day compressive strength of two cylinders cast from a sample of concrete from the sublot. In the case of partial lots, the strength cylinders can be supplemented by cores. Thus, the strength sample size is one per sublot and the number of replicates per sample is two.
SAMPLING PLAN AND ADJUSTMENTS
The PRS Acceptance Quality Characteristics (AQC) of thickness, strength, and PI are measured within each sublot. All values measured within the lot are combined to compute a mean and standard deviation of the lot. The pay adjustment for a given lot is computed from these values. Pay is determined on a lot-by-lot basis, not by the sublot.
Sublot boundaries must be marked and maintained until finalizing the payment computation. The lot shall be divided into a minimum of three sublots for sampling and testing purposes. Markers shall be placed every 500-ft along the mainline traffic lanes to aid in determining the lot and sublot limits.
The definitions of lot, sublot, sampling frequency for thickness, concrete strength, and initial PI are presented.
Contract pay for concrete paving is determined on a lot-by-lot basis. A paving lot has the following characteristics:
Each lot is divided into discrete sublots and that sampling for each AQC be conducted randomly in each sublot. This means that thickness, concrete strength, and PI shall be measured within each sublot boundary.
Sampling Frequency Within Sublots
The sampling frequencies for slab thickness, concrete strength, and PI within a given 500-ft sublot are described below.
A thickness measurement for each sublot is determined by taking one core through the slab at one random location in the sublot. Alternatively, the Engineer may allow thickness measurements in the even numbered sublots to be measured using the ASTM C 1383 equipment and methods. Thus, the thickness sample size is one per sublot and the number of replicates per sample is one.
The concrete strength for each sublot is determined as the average of the 28-day compression tests of two replicates taken from one random batch of concrete from each sublot. Thus, the concrete strength sample size is one per sublot and the number of replicates per sample is two.
Initial Smoothness (Profile Index)
A longitudinal profile trace shall be taken in each 500-ft length along the wheelpaths (inside and outside wheelpaths located 3-ft from the edge of the slab for conventional width lanes, or 3-ft from the paint stripe for widened slabs) for each traffic lane included within the sublot. The mean PI for each discrete 500-ft section within the sublot shall be computed. The number of replicates per pass location for a paving width equals 2, the number of wheelpaths per traffic lane). Smoothness measurement shall terminate not less than 50-ft from the bridge approach joint.
PRS recognize that higher quality products have additional value and provide payment adjustment for this higher quality up to a maximum value. PRS also recognize that marginal quality products have reduced value and advocate payment reduction instead of requiring complete removal unless the pavement is so deficient that replacement or correction action is warranted (i.e., at the RQL).
INDIVIDUAL PAY ADJUSTMENT CURVES
Individual pay adjustment factors for slab thickness, comprehensive strength, and initial PI shall be determined using the pay factor curves shown in figures 2, 3, and 4 or tables 5, 6, and 7. These curves and tables were developed using the PaveSpec 3.0 PRS software and account for the mean and standard deviation of the AQCs for the subject pavement project. Linear interpolation or extrapolation shall be used between the values shown in these tables, if needed. Some adjustment was made to the curves to provide a more practical incentive and disincentive.
The determination of individual pay factors from figures 2, 3, and 4 or tables 5, 6, and 7 requires computing the mean and standard deviation of the slab thickness, compressive strength, and initial PI for the as-constructed lot based on the field testing results. These statistics shall be calculated as follows.
The lot thickness standard deviation (where number of replicates = 1) is computed as follows:
The compressive strength and PI unbiased lot standard deviation (where more than one replicate per sample are used) is computed as follows.
Computation of Pay Adjustment
The lot composite (overall) pay factor is computed as follows.
PFcomposite = (PFPI*PFstrength*PFthickness)/10000 (5)
The actual pay adjustment for an as-constructed lot is computed using the lot composite pay factor as follows. Pay adjustments will be made only on the individual lots.
PAYADJLot = BID * AREALot * (PFcomposite – 100)/100 (6)
PAYLot = BID * AREALot + PAYADJLot (7)
PAYLot = Adjusted payment for the as-constructed lot, $
The absolute minimum value of the Composite Pay Adjustment Factor for a given lot shall be limited to 80 percent and the absolute maximum value shall be limited to 110 percent.