U.S. Department of Transportation
Federal Highway Administration
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Federal Highway Administration Research and Technology
Coordinating, Developing, and Delivering Highway Transportation Innovations
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Publication Number: FHWA-RD-98-155
Date: FEBRUARY 1999
After the agency has defined the specification and developed the corresponding project-specific preconstruction output, the agency may then use the developed specification for acceptance. PRS-related contractor pay adjustments are then determined based on the actual samples taken from the as-constructed pavement lot (in accordance with the agency-defined AQC acceptance sampling and testing plan). This chapter describes the procedures to be used by an agency to determine Level 1 or Level 2 pay adjustments for a given as-constructed pavement lot.
Step 1: Dividing the As-Constructed Pavement Lot into Sublots
To judge the quality of the as-constructed in-place pavement lot, the agency must conduct sampling and testing in accordance with the previously chosen acceptance sampling and testing plan. (Note: The defined acceptance sampling and testing plan is determined in accordance with the guidelines presented in the section titled Selecting an AQC Acceptance Sampling and Testing Plan, in chapter 5 of this volume.) As a first step in the sampling of the pavement, the pavement lot is divided into sublots. Prior to the placement of any paving for the given lot, the agency must estimate the starting and ending stations of all of the sublots expected to be paved within that lot. These specific stations are determined by assuming sublot lengths equal to the chosen target sublot length (the target sublot length is determined in accordance with the guidelines presented in the section titled Selecting an Appropriate Target Sublot Length, in chapter 5 of this volume). An appropriate number of expected sublots are defined so that sublots are defined well past the expected lot length (see the section titled Definition of Lots and Sublots in chapter 5 of this volume).
Step 2: Determining the As-Constructed Acceptance Sampling Locations
The estimated sublot starting and ending stations allow the agency to determine random sampling locations prior to the placement of any pavement within the lot. For each AQC, the appropriate number of random sampling locations per sublot is identified by the agency in accordance with the guidelines presented in the section titled Recommended Number of AQC Samples Per Sublot, in chapter 5 of this volume. (Note: The chosen AQC sample types determine what sampling locations are required.) Specific sample locations are, therefore, determined based on the agency-chosen sample specimen types and in accordance with the guidelines presented in the section titled Selection of Random Sampling Locations, in chapter 5 of this volume.
Step 3: Conducting Lot Acceptance Sampling and Testing
Once the paving begins for a given lot, the actual sublot lengths are determined in accordance with the guidelines presented in the section titled Determining Actual Sublot Lengths in the Field, in chapter 5 of this volume. The appropriate sample specimens are taken at the random sample locations identified in the previous step. If replicate samples are taken at a given sampling location (e.g., three cylinders molded from a batch of concrete taken from one randomly selected longitudinal sample location), the replicate sample specimen testing values are averaged to give one AQC testing value representing the sample location. These sample location representative testing values are used to define the quality of the pavement lot.
Step 4: Determining the Overall Lot Pay Factor
The procedures used to determine an overall lot pay factor differ for Level 1 and Level 2 specifications. The Level 1 overall lot pay factor is computed using a chosen composite pay factor equation, while the Level 2 pay factor is based on a direct comparison of the simulated as-designed LCC mean and the estimated as-constructed LCC. The details of both of these procedures are described separately below.
If the Level 1 procedure is used to calculate the pay
adjustment, the following steps apply:
Summarizing the As-Constructed AQC Acceptance Data for the Lot
The first step in calculating a Level 1 lot pay adjustment requires that the measured as-constructed AQC acceptance data be summarized for the entire lot. Therefore, all of the representative testing values (representing every sample location within the lotall sublots are included) are summarized into one lot mean and unbiased standard deviation for each AQC. These AQC lot means and unbiased standard deviations are then used in the developed individual AQC pay factor curves and equations.
Computing the Individual Pay Factors for Each AQC
Individual pay factors are determined independently for each AQC based on the respective lot means and unbiased standard deviations computed in the previous section. For each AQC, the representative lot mean and unbiased standard deviation is used in the following step-by-step procedure to determine individual AQC Level 1 pay factors:
whereAQC-PFLOT = Representative individual AQC pay factor, percent.
Finally, this procedure is repeated so that representative individual AQC pay factors
are determined for each AQC included in the specification.
Computing the Level 1 Lot CPF
For Level 1, the overall lot CPF is calculated using the specific CPF equation determined by the agency in accordance with the guidelines presented in the section titled Defining a Level 1 Composite Pay Factor Equation, in chapter 6. Just as with the individual AQC pay factors, the agency has the option to apply pay factor limits to the computed lot CPF. The limited CPF, therefore, is the representative CPF used to compute the overall lot pay adjustment. Any such lot CPF pay factor limits shall be selected in accordance with the guidelines presented in the section titled Selecting Pay Factor Limits, in chapter 6.
If the Level 2 procedure is used to calculate the pay
adjustment, the following steps apply:
Summarizing the As-Constructed AQC Acceptance Data for Each Sublot
The first step in calculating the Level 2 lot pay adjustment requires that the measured as-constructed AQC representative testing values be summarized for each sublot independently. The means of these AQC testing values are computed for each sublot and are then used to define the as-constructed quality of the pavement lot in the PaveSpec 2.0 software. The future performance and corresponding lot LCC's (over the agency-chosen analysis period) related to the computed AQC sublot means are determined using the PaveSpec 2.0 software. The total PW value of the predicted lot LCC's (LCCCON) is used as the overall measure of quality for the as-constructed lot. The overall Level 2 lot pay factor is then computed as a function of this LCCCON, the simulated as-designed LCC (LCCDES), and the actual contractor bid price (BIDCONTRACTOR) using equation 3 in chapter 3.
As with the Level 1 CPF, the agency has the option to apply pay factor limits to the computed overall Level 2 lot pay factor. The limited lot pay factor, therefore, is the representative pay factor used to compute the overall lot pay adjustment. Any such lot pay factor limits shall be selected in accordance with the guidelines presented in the section titled Selecting Pay Factor Limits, in chapter 6.
Step 5: Computing the Lot Pay Adjustment
The total payment to the contractor for the as-constructed lot may be determined using equation 23.Contractor Lot Payment = BIDCONTRACTOR * (PFLOT / 100) * LOTLENGTH (23)
whereContractor Lot Payment = Adjusted payment paid to the contractor for the as-constructed lot, $.
LOTLENGTH = Measured actual as-constructed lot length, km.