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Publication Number: FHWA-RD-98-155
Date: FEBRUARY 1999

Volume 1: Practical Guide, Final Report and Appendix A

 Introduction

Before an agency begins using the revised PRS prototype, it must understand a number of PRS-related terms. This chapter is provided as a summary of, and quick reference to, the main PRS-related terms. These definitions are organized in alphabetical order for the user's convenience.

 Definitions

Acceptance Quality Characteristics (AQC's): Inherent measurable pavement characteristics that significantly affect pavement performance, are under the direct control of the contractor, and are measurable at or near the time of construction. AQC's considered under the current PRS include concrete strength, slab thickness, entrained air content, initial smoothness, and percent consolidation around dowel bars.

Analysis Period: Period of time over which future M & R costs are to be considered in an LCC analysis. The analysis period is typically defined as twice the chosen initial pavement design life.

AQC Target Values: Agency-chosen AQC means and standard deviations that define the agency's desired quality (the AQC quality for which the agency is willing to pay 100 percent of the bid price).

As-Constructed Lot Life-Cycle Cost (LCCCON): The estimated post-construction LCC used to represent the as-constructed pavement lot quality. This value is based (in part) on the measured as-constructed AQC values (means and standard deviations).

As-Constructed Pavement: The actual concrete pavement constructed by the contractor. The as-constructed quality level of each pavement lot is assessed based on AQC sampling and testing (using defined AQC acceptance procedures) of the as-constructed pavement.

As-Designed Lot Life-Cycle Cost (LCCDES): The estimated post-construction LCC used to represent the as-designed pavement quality. This value is based on the as-designed AQC target values (means and standard deviations) selected by the agency.

As-Designed Pavement: The desired concrete pavement, as defined by the agency. The desired quality level of the pavement is specified in terms of target as-designed AQC means and standard deviations.

Buyer: That organization or entity ultimately responsible for the purchase of the materials and work required for the completion of a highway or transportation contract. May be used interchangeably with the terms agency, purchaser, consumer, or owner.(9)

Constant Values: Project-specific variables required by the distress indicator and cost models that do not differ between the as-designed and as-constructed pavements. These variables define many of the pavement's characteristics and can be grouped into general categories such as traffic, project location and description, climatic conditions, slab design and support, load transfer, and M & R unit costs.

Construction Pass: The defining width of an ongoing paving operation. This definition is used since the width of paving may consist of more than one traffic lane.

Discount Rate: Used to translate actual LCC's into equivalent present worth costs. It is estimated as the difference between the interest and inflation rates over a long time period, representing the real value of money over time. The interest rate, often referred to as the market interest rate, is associated with the cost of borrowing money and represents the earning power of money.(10) The inflation rate is typically defined as the rate of increase in the prices of goods and services (construction of highways) and represents changes in the purchasing power of money.(10)

Distress Indicator: A measure of the condition of an existing pavement section at a particular point in time.(4) These key pavement distresses are used to define pavement performance. Distress indicators included in the current PRS approach include transverse slab cracking, transverse joint faulting, transverse joint spalling, and pavement smoothness over time. Within the PRS, the distress indicators are predicted (over a chosen analysis period) using the best available empirical or mechanistic models. Model inputs include project-specific constant values and representative mean values of the selected AQC's.

Equivalent Single-Axle Load (ESAL): An 80-kN single-axle traffic loading. The ESAL is the standard traffic measure used by most SHA's and design methods. Average daily traffic (ADT) numbers are translated into equivalent ESAL's. Many of the distress indicator models are functions of the cumulative ESAL's applied over the chosen analysis life.(11)

Expected Pay (EP) Curve: A graphic representation of an acceptance plan that shows the relation between the actual quality of a lot and its expected pay (i.e., mathematical pay expectation, or the average pay the contractor can expect to receive over the long run for submitted lots of a given quality).(4)

Global Rehabilitation Activities: Rehabilitation activities applied to the entire lot at one time in response to declining global pavement conditions. These activities are specifically applied to address pavement condition indicators such as decreasing pavement smoothness, increasing amounts of localized distress, or increasing amounts of applied localized rehabilitation. Trigger values for these pavement condition indicators must be selected to determine the timing of a global rehabilitation. Examples of global rehabilitation activities include AC overlays, PCC overlays, and diamond grinding.

In Situ Sampling: AQC sampling procedures in which samples are taken directly from or on the in-place concrete pavement (e.g., cores and surface profile measurements).

Initial Design Life: Amount of time for which the chosen pavement design is expected to carry traffic loads without the application of a global rehabilitation (AC overlay, PCC overlay, diamond grinding).

International Roughness Index (IRI): The IRI is based on simulation of the roughness response of a car traveling at 80 km/h. It is a ratio of the accumulated suspension motion of the car divided by the distance traveled. The scale ranges from 0 (perfectly smooth surface) to 20,000 mm/km, with larger values indicating greater roughness. A value of 3,000 mm/km is often considered to be the breaking point between "rough" and "smooth" pavements on high-speed highways.

Jointed Plain Concrete Pavement (JPCP): A PCC pavement type characterized by short joint spacing (less than 6 m) and no reinforcing steel mesh or bars. JPCP pavements may or may not be constructed with dowels at the transverse joints. These pavements typically include tie bars at longitudinal joints. Slab thickness for this pavement type have historically ranged from 152 to 254 mm; however, newer pavements are being constructed with thickness of 305 mm or more.

Life-Cycle Cost (LCC): The estimated cumulative present worth cost of a pavement lot over a specified analysis period. The LCC, as used in PRS, may include estimated future maintenance, rehabilitation, and user costs over a chosen analysis period. The initial construction cost is not included in the LCC since it is identical for both the as-designed and the as-constructed pavements. LCC values are expressed in units of present worth dollars (PW$) per kilometer.

Localized Rehabilitation Activities: Rehabilitation activities that may be used to correct localized pavement distresses. Localized distresses are defined as those that may affect an individual joint (transverse joint spalling and transverse joint faulting) or slab (transverse slab cracking).

Lot: A discrete quantity of constructed pavement to which an acceptance procedure (and corresponding pay adjustment) is applied. All pavement placed within a lot should consist of the same mix design and material sources, should be subjected to the same support conditions (base type, base thickness, subbase type, subbase thickness, subgrade treatment), and should consist of the same design characteristics (joint spacing, drainage, shoulder type, dowel-bar diameter, traffic, and AQC design values).

Lot Length: Equal to one day's production or less. The minimum lot length should not be less than 0.16 km. Any section of lesser length will be added to the preceding lot or succeeding lot.

Lot Width: The lot width is defined as the total width of pavement, one or more traffic lanes, being placed at one time in the mainline paving process. This paving width is also referred to as a construction pass,since it describes the total width of pavement being placed in one pass of the paving train. The entire width of a widened lane is included; however, shoulders are to be excluded.

Maintenance Activities: Routine activities performed as preventive measures. This maintenance is typically applied at certain fixed intervals of time over the life of a pavement lot (commonly on an annual basis). Examples of maintenance activities include transverse crack and joint sealing.

Maintenance and Rehabilitation (M & R) Plan: The defined set of rules used to predict the type and timing of future M & R activities. Expected localized and global rehabilitation activities are determined based on chosen trigger values applied to each distress indicator. Maintenance activities are applied by defining the amount and application frequency (e.g., seal 100 percent of the transverse joints every 2 years).

Maximum Quality Limit (MQL): Agency-chosen maximum limit for acceptable AQC specimen sample quality. If an AQC specimen sample value is measured to have greater quality than the defined MQL, the representative specimen sample value (used in the acceptance procedures) is set equal to the defined MQL (i.e., the contractor does not receive credit for quality provided in excess of the MQL). For concrete strength, slab thickness, entrained air content, and percent consolidation around dowels, better quality than the MQL is identified by specimen sample values greater than the MQL; however, for initial smoothness, better quality than the MQL is identified by specimen sample values less than the MQL.

Nondestructive Testing: AQC sampling and testing methods conducted on the in-place pavement, without disturbing the pavement's structural integrity or surface characteristics.

Operating Characteristic (OC) Curve: A graphic representation of an acceptance plan that shows the relationship between the actual quality of a lot and the probability of its acceptance at various payment levels.(4)

PaveSpec 2.0: The revised PRS specification simulation software developed under this research project. This software is used to demonstrate the PRS approach by simulating pavement performance, determining corresponding LCC's, generating preconstruction output, and computing pay adjustments. Its specific functions are described in the PaveSpec 2.0 User Guide (appendix G, volume IV).

Pay Adjustment: The actual pay adjustment (incentive or disincentive in PW$) for the as-constructed lot. The computation of the lot pay adjustment differs between the Level 1 and Level 2 PRS. PAYLOT  = BID * (PFCOMPOSITE – 100) * LOTLENGTH      (1)

  where

PAYLOT  = Adjusted payment paid to the contractor for the as-constructed lot, $.

BID  = Contractor bid price, $/km.

PFCOMPOSITE  = Determined Level 1 lot CPF, percent (e.g., 101 percent is expressed as 101.0).

LOTLENGTH =Measured actual as-constructed lot length, km. Level 2 Pay Adjustment—The Level 2 pay adjustment is computed using the determined Level 2 lot pay factor. The actual Level 2 lot pay adjustment is computed using the relationship presented in equation 2. PAYLOT  = BID * (PFLOT – 100) * LOTLENGTH                 (2)

  where

PAYLOT  = Adjusted payment paid to the contractor for the as-constructed lot, $.

BID = Contractor bid price, $/km.

PFLOT  = Determined Level 2 overall lot pay factor, percent (e.g., 101 percent is expressed as 101.0).

LOTLENGTH = Measured actual as-constructed lot length, km. Basic Pay Factor Definition—The underlying equation used to compute a pay factor for a given lot (based on the comparison of LCC's) is presented as equation 3. This equation is used to compute the pay factor for each simulated lot. PFLOT  = 100 * (BID + [LCCDES – LCCCON])/BID                 (3)

  where

PFLOT  = Overall pay factor for the as-constructed lot, percent.

BID  =Representative contractor's unit bid price for the lot, $/km.

LCCDES  = As-designed life-cycle unit cost for the lot (computed using target AQC's), PW$/km.

LCCCON =As-constructed life-cycle unit cost for the lot (computed using AQC test results from the as-constructed lot), PW$/km. Level 1 Individual AQC Pay Factors—The pay factors (associated with the measured AQC's) computed using the developed Level 1 individual AQC pay factor equations. Each Level 1 AQC pay factor (expressed as a percentage) is a function of the measured as-constructed AQC lot mean and standard deviation. (Note: Level 1 individual AQC pay factor equations are based on data simulated using the PaveSpec 2.0 computer software.) The final Level 1 individual AQC pay factors may be limited to agency-chosen pay factor practical limits.

Level 1 Composite Pay Factor—The overall pay factor (expressed as a percentage) for an as-constructed lot computed using a Level 1 specification. This pay factor is determined using the agency-defined CPF equation (a simple mathematical function of the individual Level 1 AQC pay factors). The final Level 1 lot CPF (which may be limited to agency-chosen pay factor practical limits) is used to determine the contractor's Level 1 lot pay adjustment.

Level 2 Pay Factor—The overall pay factor (expressed as a percentage) for an as-constructed lot computed using a Level 2 specification. This pay factor is computed using equation 3 and may be limited to agency-chosen pay factor practical limits. The PaveSpec 2.0 computer software is used to simulate the required LCCDES based on SHA-defined AQC target values, and estimate the LCCCON based on the measured as-constructed AQC samples. Performance-Related Specifications (PRS): Construction specifications placed on key materials and construction AQC's (e.g., concrete strength, slab thickness) that have been demonstrated to correlate strongly with long-term pavement performance. These specifications are based on quantified relationships (or mathematical models) that relate measured AQC's to subsequent pavement performance and the corresponding costs.

Present Serviceability Rating (PSR): An indicator of pavement smoothness based on the subjective ratings of users. The PSR is expressed as a number between 0 and 5 with the smaller values indicating greater pavement roughness. The scale is translated into general pavement condition description categories using the following translations.(11)

     0 - 1   Very poor.

     1 - 2   Poor.

     2 - 3   Fair.

     3 - 4   Good.

     4 - 5   Very good.

PWCOST  = C / (1 + i)T                                                     (4)

  where

PWCOST = Present worth of yearly cost (C).

C  = M & R, or user cost incurred during year T.

T  = Year during which the observed cost (C) was incurred.

i  =  Chosen discount rate.

MEANSAMPLES  = å(xi )/n                                                 (5)

  where

MEANSAMPLES = The computed mean of n random AQC samples.

xi = 1 to n random sample values.

n  = Total number of random samples. SDSAMPLES  = ({[å(xi –MEANSAMPLES)2]/(n – 1)}/m)0.5 / CSD  (6)

  where

SDSAMPLES  = The computed unbiased standard deviation of all of the random sample values.

MEANSAMPLES = The computed mean of all of the random sample values.

n  = Total number of random samples.

xi = 1 to n sample values.

m = The number of replicate specimen test results used to compute one sample value.

CSD  = Correction factor (based on the total sample size, n) used to obtain unbiased estimates of the actual lot sample standard deviation, s. Appropriate CSD values are determined using table 2.

Number of Sample Values, n

Correction Factor, CSD

2

0.7979

3

0.8862

4

0.9213

5

0.9399

6

0.9515

7

0.9594

8

0.9650

9

0.9693

10

0.9726

30

0.9915

50

0.9949

Table 2. Correction factors used to obtain unbiased estimates of the actual standard deviation

 


The Federal Highway Administration (FHWA) is a part of the U.S. Department of Transportation and is headquartered in Washington, D.C., with field offices across the United States. is a major agency of the U.S. Department of Transportation (DOT).
The Federal Highway Administration (FHWA) is a part of the U.S. Department of Transportation and is headquartered in Washington, D.C., with field offices across the United States. is a major agency of the U.S. Department of Transportation (DOT). Provide leadership and technology for the delivery of long life pavements that meet our customers needs and are safe, cost effective, and can be effectively maintained. Federal Highway Administration's (FHWA) R&T Web site portal, which provides access to or information about the Agency’s R&T program, projects, partnerships, publications, and results.
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