Publication Number: FHWA-RD-98-156
Date: FEBRUARY 1999
Volume 2, Chapter 6
The prototype PRS
for jointed plain concrete pavement was demonstrated using three different
methods in order to assess its practicality. The methods used to
accomplish this task were the following:
- PRS shadow
field trialsFour shadow field trials (new construction projects)
were conducted and documented as part of this research project.
The PRS simulation software (PaveSpec) was used to develop preconstruction
output for each project (reflecting the project-specific design, climatic,
and traffic conditions). A PRS-based sampling and testing plan
was then applied, and the required samples were collected to demonstrate
the PRS procedures. Finally, the PaveSpec simulation software
was used to determine shadow pay factors and adjustments for
each project (i.e., the contractors pay was not affected by the
PRS-based pay factors and adjustments computed as part of the demonstration).
Chapter 2 contains a
discussion of the original shadow field trial (Ottumwa, Iowa).
Chapter 3 contains a discussion
of the three field trials conducted with OTA personnel.
of Level 1 specifications for three typical pavement designs (within
a given SHA)Level 1 PRS preconstruction output was developed
for three typical pavement designs used in Iowa. Chapter
4 contains a complete discussion of these specification development
procedures, as well as an analysis of trends observed within and between
the typical designs.
of actual pay adjustments (computed using the governing SHA specifications)
to PRS-based price adjustmentsHistorical (archived) AQC and
pay adjustment data were obtained for 33 pavement lots representing
7 projects from 3 SHAs. Level 1 preconstruction output (pay
factor charts and corresponding equations) were developed for each investigated
project. The retrieved AQC data were then used in conjunction
with the Level 1 preconstruction output to determine PRS-based Level
1 lot pay factors. Historical pay adjustment data representing
the same defined lots were then compared to the computed PRS-based pay
adjustments, and the results were discussed. Chapter
5 contains a complete discussion of this analysis (divided into
sections according to SHA).
This volume contains
detailed documentation of all three methods used to demonstrate the prototype
PRS. Conclusions of the three demonstration methods are summarized
in the following section.
Method #1Shadow Field Trials
valuable experience was obtained from the conduct of the four shadow PRS
field trials. Some practical recommendations resulting from the
field trial experiences are as follows:
- Fix the sublot
length to one constant valueAs a result of the original field
trial experience, it is recommended that one target sublot length be
chosen and used to lay out all sublots prior to the paving of each lot.
This should be done on a day-by-day (lot-by-lot) basis.
- Choose a practical
target sublot lengthThe target sublot length should be chosen
based on the anticipated amount of sampling and testing required, the
personnel available, and the location of the testing facilities relative
to the job site.
- Choose a minimum
length between longitudinal sampling locationsIt is recommended
that the SHA decide on a practical minimum length between sampling locations
when samples are required to be taken from the fresh concrete during
the construction process.
- Limit pay
factors to chosen practical maximum valuesPay factors must
be capped at an agency-chosen maximum practical value. The original
field trial demonstrated the need for practical maximum pay factors.
At this project, the contractor provided approximately 25 mm of extra
pavement thickness (in excess of the as-designed target value) on each
of the three investigated lots. This extra thickness resulted
in relatively large pay factors (approximately 160 percent) before the
application of caps. Since it would be impossible for almost
any SHA to make pay adjustments of this magnitude, pay factors must
be capped at some agency-chosen practical value. The pay factor
maximums could be applied to the individual AQC pay factors, the overall
lot pay factor, or both.
Method #2Level 1 Preconstruction Output for Three Typical Designs
1 pay factor charts and equations were developed for three typical JPCP
designs in Iowa. The three typical designs were based on medium,
heavy, and very heavy traffic levels. An analysis of the developed
preconstruction output showed a number of trends within and between the
constructed Level 1 pay factor charts. Many of these were found
to be valid for the four different AQCs used in this demonstration.
The observed general trends were the following:
- Pay factors increased
as the quality of the measured AQC mean improved (i.e., increases in
flexural strength, slab thickness, and air content mean; decreases in
initial smoothness mean).
- At a given AQC
mean, pay factors increased as the measured AQC standard deviation decreased.
- Pay factor curves
generally became flatter as traffic level increased. This trend
may be due to increased reliability factors built into the designs with
heavier traffic (increases in slab thickness).
Method #3Comparison of PRS-Based Pay Adjustments to Actual SHA Pay
pay adjustment comparison showed that PRS and actual pay adjustments can
differ greatly between projects. The study was conducted by limiting
the PRS-based pay factors to those maximum pay factors allowed by each
SHA. Overall, a majority of the lots (20 of 33) showed that the
Level 1 PRS pay adjustments were greater than those determined using the
governing SHA specification. Ratios of PRS-based pay adjustments
to actual pay adjustments were computed for each lot and project included
in the study. An analysis of the absolute values of these ratios
showed overall average lot and project ratios of 1.85 and 1.43, respectively
(i.e., on average, lot and project pay adjustments [positive or negative]
were 1.85 and 1.43 times larger under PRS).