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 (LCC_{CON}): 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 (LCC_{DES}): 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.
Level 1 Pay Adjustment—The Level 1 pay adjustment is computed using the
determined Level 1 lot composite pay factor (CPF). The actual Level 1 lot pay adjustment
is computed using the relationship presented in equation 1.
PAY_{LOT} = BID * (PF_{COMPOSITE}
– 100) * LOT_{LENGTH}
(1)
where
PAY
_{LOT} =
Adjusted payment paid to the contractor
for the as-constructed lot, $.
BID = Contractor bid price, $/km.
PF
_{COMPOSITE} = Determined Level 1 lot CPF, percent
(e.g., 101 percent is expressed as 101.0).
LOT
_{LENGTH} =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.
PAY_{LOT} = BID * (PF_{LOT}
– 100) * LOT_{LENGTH}
(2)
where
PAY
_{LOT} = Adjusted payment paid to the contractor
for the as-constructed lot, $.
BID = Contractor bid price, $/km.
PF
_{LOT } = Determined Level 2 overall lot pay factor, percent
(e.g., 101 percent is expressed as 101.0).
LOT
_{LENGTH} = Measured actual as-constructed lot
length, km.
Pay Factor (PF): The percent of the bid price that the contractor is paid for
the construction of a concrete pavement lot. There are a number of different pay
factor-related definitions used within this report.
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.
PF_{LOT} = 100 * (BID + [LCC_{DES}
– LCC_{CON}])/BID
(3)
where
PF
_{LOT} = Overall pay factor for the as-constructed
lot, percent.
BID =Representative contractor's unit bid price for the lot, $/km.
LCC
_{DES } = As-designed life-cycle unit cost for the
lot (computed using target AQC's), PW$/km.
LCC
_{CON} =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 LCC
_{DES} based on
SHA-defined AQC target values, and estimate the LCC
_{CON} 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.
Present Worth (PW) Method: A discounted cash flow analysis that
involves the conversion of all of the present and future costs to a base
of today's costs.^{(10)} Expected future costs are translated
into equivalent present worth costs using equation 4.
PW_{COST} = C / (1 + i)^{T}
(4)
where
PW_{COST} = 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.
Quality Assurance (QA): All those planned and systematic actions necessary to
provide adequate confidence that a product or service will satisfy given requirements of
quality. Within an organization, QA serves as a management tool. In
contractual situations, QA serves to provide confidence in the supplier.^{(9)}
Quality Control (QC): The sum total of activities performed by the seller
(producer, manufacturer, or contractor) to make sure that a product meets contract
specification requirements. Within the context of highway construction, QC includes
materials handling and construction procedures; calibration and maintenance of equipment;
production process control; and any sampling, testing, and inspection done for these
purposes.^{(9)}
Rejectable Quality Limit (RQL): Agency-chosen minimum limit for acceptable AQC
specimen sample quality. If an AQC specimen sample value is measured to have poorer
quality than the defined RQL, AQC retesting procedures will apply. For concrete
strength, slab thickness, entrained air content, and percent consolidation around dowels,
poorer quality than the RQL is identified by specimen sample values less than the
RQL; however, for initial smoothness, poorer quality than the RQL is identified by
specimen sample values greater than the RQL.
Sample Mean: The average of n random AQC sample values. This sample mean
is computed using equation 5.
MEAN_{SAMPLES} = å(x_{i} )/n
(5)
where
MEAN
_{SAMPLES} = The computed mean of
n
random AQC samples.
x_{i} = 1 to n random sample values.
n = Total number of random samples.
(Note: If m replicate samples are taken from each sampling location, the mean of
each set of m test results is used to define a random sample value.)
Sample Standard Deviation: An estimate of the true population standard
deviation, s. If this estimate is to be unbiased, a correction
factor must be applied. This unbiased sample standard deviation is computed using
equation 6.
SD_{SAMPLES} = ({[å(x_{i}
–MEAN_{SAMPLES})^{2}]/(n – 1)}/m)^{0.5}
/ C_{SD} (6)
where
SD
_{SAMPLES} = The computed unbiased standard
deviation of all of the random sample values.
MEAN
_{SAMPLES} = The computed mean of all of the
random sample values.
n = Total number of random samples.
x_{i} = 1 to n sample values.
m = The number of replicate specimen test results used to compute one sample value.
C
_{SD} = Correction factor (based on the total sample size, n) used to obtain unbiased estimates of the actual lot sample standard
deviation,
s. Appropriate C
_{SD} values
are determined using table 2.
Number of Sample Values, n |
Correction Factor, C_{SD} |
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
(Note: Unbiased estimates of the standard deviation are automatically
calculated and used in the determination of lot pay factors within PaveSpec
2.0.)
Sample Value: An AQC value used to represent one sample location
within a sublot. A representative sample value may be the direct measured
value from one test taken at a sample location (no replicate test result
values, i.e., m=1), or equal to the mean of m replicate
test result values (from m replicate tests) taken at the same sample location.
Seller: Any entity providing materials and work required for the
completion of highway or transportation work. This includes the contractor
and all subcontractors. The term may be used interchangeably with producer
or supplier.^{(9)}
Sublot: A portion of a lot. Each lot is divided into sublots of
approximately equal surface area. Sublot lengths are selected so that
one or more samples may be taken from each sublot for each considered
AQC. The minimum sublot length cannot be less than 0.16 km (to accommodate
the measurement of initial smoothness). Any section of lesser length will
be added to the preceding sublot. Note that in PRS, measurements for all
AQC's must be obtained from each sublot so that performance can be predicted.
Target Sublot Length: The chosen default linear length for each
sublot. Each as-constructed sublot should initially be assumed to be equal
to this target sublot length.
Test Result Value: The computed AQC value from one AQC test. For
concrete strength, slab thickness, and entrained air content, this is
the testing result from one specimen. For initial smoothness, this is
the value obtained from one pass of the profilograph.; For percent consolidation
around dowels, this is the value obtained from one relative density comparison.
Transverse Joint Faulting: A difference in elevation between the
adjacent slabs across a transverse joint or crack. Faulting is primarily
caused by the erosion of the supporting material from underneath the leave
slab and a buildup of the loose material underneath the approach slab
at the joint.^{(12)} The development of transverse joint faulting
greatly adds to the roughness of the pavement.Transverse joint faulting
is expressed as an average faulting per joint in units of mm.
Transverse Joint Spalling: The breakdown or disintegration of the
concrete (near the surface) at a transverse joint. Spalled transverse
joints are rated as having low-, medium-, or high-severity spalling. Under
the PRS approach, transverse joint spalling is expressed in terms of the
number of medium- or high-severity spalled joints per unit length (number
of spalled joints per km).^{(12)}
Transverse Slab Cracking: Cracks occurring parallel to transverse
joints and at the midslab of JPCP slabs. The transverse cracking predicted
for the PRS is due solely to fatigue of the slabs from the application
of traffic loading. Typically, these midslab cracks begin as a single
crack at the edge of the slab and propagate through the entire slab.^{(12)}
Transverse cracks are rated as having low, medium, or high severity. Under
the PRS approach, transverse slab cracking is expressed in terms of the
number of all severity cracks per unit length (number of cracks per km).