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RESEARCH PROBLEM STATEMENT
Project 9-22, Fiscal Year 2000
In the 1990s, the Federal Highway Administration (FHWA) and
the American Association of State Highway and Transportation Officials (AASHTO) sponsored a series of research projects to develop a Performance
Related Specification (PRS) for Hot Mix Asphalt (HMA). In February 2000, the
WesTrack project (conducted since October 1994 through FHWA contract
DTFH61-94-C-00004 and NCHRP Project 9-20) delivered an HMA PRS in the form of
an alpha-tested version of a computer program incorporating advanced
performance-prediction models for HMA and a guide specification.
The alpha version of the HMA PRS includes two application
levels. Level I is based on material and construction properties (e.g.,
asphalt content; gradation; field-mixed, laboratory-compacted volumetrics;
in-place air voids; and ride quality) currently obtained by public agencies
for use in materials-and-method, end-result, and QC/QA types of
specifications. Direct regression equations relating these properties to
pavement performance (specifically, permanent deformation and fatigue
cracking) exhibited in the WesTrack experiment are the primary basis for
calculation of pay factors in the Level I HMA PRS. The Level II HMA PRS uses
a more sophisticated, mechanistic-empirical analysis of the results of
laboratory performance tests as well as the WesTrack property-performance
relationships to determine pay factors. Regardless of whether the Level I or
Level II performance model is used, the HMA PRS calculates pay factors by
comparing the life-cycle cost of the as-designed and as-built projects. This
is a significant improvement over current specifications as the HMA PRS
provides tools for objective calculation of equitable, consistent pay
factors.
The initial step in the implementation of this HMA PRS
into routine practice by state highway agencies will be to evaluate and
refine it by application on a series of trial projects, first in parallel
with the customary agency specification and then in place of that
specification. These trial projects will introduce the HMA PRS to the
industry and provide benchmarks for judging the impact of its adoption on the
state highway agencies and the highway contracting industry.
Of necessity, the performance models in the HMA PRS are
grounded in the results of the WesTrack experiment. This experiment measured
the effect on pavement performance of deviations in material and construction
properties from design values for a single climate and a limited number of
aggregates and asphalt binders. A second step in the implementation of the
HMA PRS is to broaden the calibration of the performance models using new and
existing data from accelerated pavement tests and full-scale field projects
representing the range of material types, climate, and project
characteristics found in the United States.
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OBJECTIVES
The objectives of this project are to (1) evaluate and
refine the HMA PRS and supporting software developed through the WesTrack
project in a series of field trials, (2) calibrate and validate the Level I
and II performance models, and (3) develop a training course curriculum and
materials to assist the implementation of the HMA PRS and software by state
highway agencies.
Accomplishing these objectives will require the following
tasks:
Phase I
 Task 1. The project team will plan and conduct a
comprehensive beta test program for the HMA PRS software prior to its use on
trial projects in Tasks 2 and 7. The team will recruit participants for the
beta test program from state highway agencies, paving contractors, and
interested consulting firms. In addition, the team will analyze the results of
the beta test and submit, within 6 months of the effective date of the
contract, a revised release 1.1 of the HMA PRS software that incorporates
changes to its technical content, programming, or both, required to correct
problems or enhance the applicability and practicality of the PRS in routine
pavement construction projects.
Task 2. Plan and conduct an evaluation of the Level I and
Level II HMA PRS on a minimum of five, 25,000-ton or larger field projects in
at least three geographically diverse states. Arrange with the participating
state highway agencies to apply the HMA PRS side by side with the agency
specification used to formally bid and construct the project. Assist the
agencies to integrate relevant data from their pavement management systems, materials
databases, and maintenance and rehabilitation strategies (e.g., decision
trees) into the trial specification and HMA PRS used for the evaluation.
Conduct sampling and testing necessary to evaluate the Level I and Level II
PRS. Insofar as possible, collect sufficient additional materials from all
projects for use in Task 8 to calibrate and validate the performance models
in the PRS.
Note: The FHWA is going to make its mobile asphalt
laboratory available to the research agency to assist in obtaining and
testing material samples from some of the field projects.
Note: The HMA PRS will be used in Task 2 only as a
"shadow specification" and will not affect pay adjustments on the
projects.
Task 3. Prepare a detailed, statistically based experiment
design for the calibration and validation in Task 8 of the Level I and Level
II performance models incorporated in the HMA PRS software. In the experiment
design, identify materials and performance data collected from specific
accelerated laboratory testing, accelerated pavement testing (APT), and
full-scale field pavement sections that represent the range of climate,
material types, and project characteristics found throughout the United
States.
Note: Insofar as possible, the research agency will make
use of existing calibration and validation data; it will also coordinate
selection of APT, field projects, and data collection with other relevant
studies, in particular the calibration and validation of material
characterization and performance models in NCHRP Projects 1-37A and 9-19.
Task 4. Submit, within 18 months after the effective date
of the contract, an interim report that presents (1) any changes to the HMA
PRS and software identified in Task 2 to correct problems or enhance the
applicability and practicality of the HMA PRS in routine pavement
construction projects and (2) the detailed experiment design for Phase III
prepared in Task 3. The research agency will meet with the NCHRP
approximately 1 month later to obtain approval to proceed with Phase II.
Phase II
Task 5. Prepare a revised HMA PRS and software release 1.2
incorporating the specific changes to the technical content and programming
approved by NCHRP in Phase I.
Task 6. Develop a 2- to 3-day National Highway
Institute-type training course on the HMA PRS and present it to the state
highway agencies and paving contractors participating in Task 7. In addition
to the classroom course work, establish and deploy a "help team" to
provide assistance to agencies, material suppliers, and contractors
implementing the HMA PRS on construction projects included in Task 7.
Task 7. Plan and conduct a trial evaluation of the HMA PRS
and software on a minimum of five field projects in at least three
geographically diverse states. Assist the participating state highway
agencies and paving contractors to formally bid and construct each project
with the HMA PRS and software in lieu of the current specification of the
state highway agency.
Note: Application of pay adjustments based on the HMA PRS
will be made on the trial projects at the discretion of the participating
state highway agencies.
Task 8. Conduct concurrently with Task 7 the experimental
plan for calibration and validation of the PRS performance models approved in
Phase I.
Task 9. Based on the results of Tasks 7 and 8, submit,
within 35 months of the effective date of the contract, an interim report
that identifies specific changes recommended to the performance models, HMA
PRS, and software to correct problems or enhance the applicability and practicality
of the PRS in routine pavement construction projects. The research agency
will be required to meet with the NCHRP approximately 2 weeks later to obtain
approval to incorporate the recommended changes in the Task 10 deliverables.
Task 10. Prepare a final report that summarizes findings,
draws conclusions, and documents the results of Phase II including (1) the
calibrated and validated Level I and II performance models, (2) a revised HMA
PRS and software release 1.3 incorporating the calibrated and validated
models, and (3) an updated NHI-type training course curriculum with
supporting audiovisual media and student's and teacher's training manuals.
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PROJECT
TEAM
(CLICK IMAGE FOR LARGER VERSION)
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PROJECT
TIMELINE
| TASK |
START
DATE |
COMPLETION
DATE |
DURATION
(months) |
|
0 – Amplified Research Plan |
October
3, 2000 |
October
18, 2000 |
˝ |
|
1–Beta Test and V1.1 Release |
October
18, 2000
|
March
31, 2001
|
5˝
|
|
2–Shadow Specification
|
April
1, 2001
|
December
31, 2001
|
9
|
|
3–Develop Calibration/Validation Plan
|
November
1, 2001
|
January
31, 2002
|
3
|
|
4–Interim Report
|
January
1, 2002
|
March
31, 2002
|
3
|
|
5–Version 1.2 Release
|
May
1, 2002
|
July
31, 2002
|
3
|
|
6–Develop NHI Training Course
|
May
1, 2002
|
October
31, 2002
|
6
|
|
7–Implement PRS with Pay Adjustment
|
July
1, 2002
|
March
31, 2003
|
9
|
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8–Conduct Calibration and Validation
|
May
1, 2002
|
August
31, 2003
|
16
|
|
9–Summary Report for Tasks 7 and 8
|
October1,
2002
|
December
31, 2002
|
3
|
|
10-Final Report
|
September
15, 2003
|
January
2, 2004
|
3˝
|
(CLICK IMAGE FOR LARGER VERSION)
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