STATEMENT (Posted June 20, 2001):
Current trends in
pavement design philosophy rely on increasingly sophisticated
analytical modeling coupled with correlations with laboratory,
accelerated trafficking, and in-service tests. Overlay design
philosophy has tended to lag behind this trend, and much of today's
airfield overlay design still relies on empirical relations developed
in the 1950s. The FAA has developed an improved rigid pavement
overlay design methodology based on layered elastic theory, but
its performance correlations are based upon accelerated traffic
tests largely conducted in the 1940s and 1950s before analytical
models such as layered elastic theory were easily solvable in
practice. Consequently, material characterization and data collection
from these old tests do not necessarily provide the desired information
for use with more modern analytical models. The FAA is now in
the process of developing an advanced pavement design procedure
based on finite element modeling which requires modeling data
far more detailed than ever envisioned in these older tests.
This research shall
develop an experimental design for a large-scale, accelerated
testing program at the FAA National Airfield Pavement Test Facility
(NAPTF) or other locations in order to get performance data on
concrete overlays to support modern analysis based on layered
elastic theory and finite element analysis methods. The overlays
to be considered will be rigid overlays with various potential
degrees of nominal bonding over rigid and flexible pavements that
carry aircraft with single wheel loads greater than 30,000 lbs.
The analytical models to be considered will be layered elastic
theory and finite element analysis techniques that include finite
element models throughout the pavement structure and hybrid finite
element models that model the critical layers (e.g., the overlay
and base pavement) with finite elements that are then coupled
with simplified representations of underlying materials (e.g.,
Winkler foundation of springs). This overall program will concentrate
on structural behavior of overlays under aircraft loading, but
it should attempt to include environmental contributions such
as temperature and moisture extremes that clearly effect overlay
Task 1. Identification
of Critical Design Parameters.
This task will result
in the identification of the parameters that affect overlay pavement
performance and rank them in order of importance.
It is expected that
the person that is preparing the proposal will be intimately familiar
with airfield overlay design philosophy and methodology. Hence,
an exhaustive general state-of-the-art literature review and summary
should not be necessary to accomplish this phase. Any literature
review will be focused on specific issues needed to fully develop
critical design parameters. The FAA empirical overlay design equations,
layered elastic design method, and the evolving finite element
design methodology will be included as candidate design procedures;
but additional design methodologies besides these can and should
be considered. Critical information needed to assess, validate,
refine, or develop these design concepts shall be the critical
design parameters. Critical overlay design parameters that will
be considered for evaluation shall, as a minimum, be:
- Effect of varying stiffness
and material properties of the overlay, support conditions
of base or fill material, and subgrade materials.
- Impact of existing pavement
- Impact of joints and cracks
in existing pavement and performance of the overlay.
- Interface conditions and
effects on performance (how they should be modeled).
- Effect of progressive fatigue
cracking in different levels on stress conditions and performance.
Task 2. Develop
Experimental Design and Test Program.
In this task, the
proposer will develop a detailed testing plan to test and find
critical values for the parameters identified and approved by
the Project Technical Panel in Task 1.
Using the critical
test parameters defined in Task 1, carry out a critical assessment
of the identified critical parameters and compare those parameters
to the testing capability of the FAA National Accelerated Pavement
Test Facility (NAPTF). Develop a recommended experimental plan
for accelerated traffic testing at NAPTF, or other facilities,
that will result in the data collection needed to develop and
validate improved airport concrete overlay design procedures.
This includes understanding and including in the experimental
plan only requirements and material specifications that can be
readily used at the NAPTF, or other facilities. There are always
more variables and requirements than funding so the proposal must
fully develop the recommended experimental design and subsequently
assign a priority to each test item.
Each test item will
thoroughly identify the parameters which are being investigated,
provide complete details on all materials, dimensions, construction
requirements, traffic, quality control/quality assurance, evaluation
tests, and instrumentation, as well as design details for why
the test item was selected and what it is expected to accomplish.
Each test item will include an analysis plan that details how
the data will be analyzed and how it will contribute to improving
overlay design methods. Finally, each test item will have an estimated
cost and budget. Ideally, there will be a testing program and
budget for both a "minimum testing program" and an "optimized
Task 3. Technical
The proposer will
provide a final report summarizing the work performed, providing
a summary of the critical design parameters, and providing the
test item details. The main emphasis of this report will be the
final detailed testing plan.
The test plan will
be a "roadmap" to gather performance data on concrete overlays
to be used with modern analytical models and overlay designs.
Note that the design solution envisioned using this information
is one that will predict pavement performance as well as develop
a pavement thickness.
It is anticipated
that "roadmap" will include, as a minimum, the following items:
- Draft contract documents
for the construction of the large-scale test sections.
- Instrumentation plan.
- Schedule for construction
and testing phases.
- Post-testing and evaluation
- Estimated costs for the entire
1. The technical panel
believes that "pumping" is not a major concern for most overlays.
However, it is recognized as a significant cause of rigid pavement
distress. The views of the people preparing the proposal are requested
and should be included in the proposal.
2. After the technical
panel completes the evaluation of proposals, each of the proposals
will be rank ordered. The organization, group, or individual that
is ranked as the first and second choice for the recommendation
to award will be asked to make a presentation to the project technical
panel. The Principal Investigator and one other person from each
entity ranked first and second choice will participate in an interview
to discuss the project details, goals, and objectives. The IPRF
will reimburse the expenses (up to 2 people) to make this presentation
at a location yet to be determined in Skokie, IL. The interview
will occur within a 30-day window subsequent to the proposal submittal
3. The investigator
will be responsible for preparing and submitting quarterly reports
that describe the progress of the research effort. Reports will
be due in the offices of the IPRF on the last day of the fiscal
year quarter (i.e., last day of March, last day of June, last
day of September, and the last day of December). The reports will
be two pages maximum in a format that will be specified. Due to
the short time frame of the project, two quarterly reports will
be used as review and approval points by the technical panel.
4. The research team
must spend sufficient time at the NAPTF to thoroughly understand
the capabilities of the facility and the conditions under which
construction and data collection must be undertaken. At that same
time, it is expected that the contractor will become intimately
familiar and cognizant with the current FAA design procedures
in order that the detailed test procedure is compatible with the
test facility and addresses the gaps in the current procedures.
DIRECTOR: James W. Mack, P.E., (717)
Jim Lafrenz, Cooperative
Agreement Programs Manager