main objective of Construction Cycle 3 (CC-3) was to provide full-scale test
data to improve FAA thickness design procedures for flexible pavements
supporting 4-wheel and 6-wheel aircraft gears. A second major objective was to use
the comparative performance data for 4- and 6-wheel gear traffic from these
tests to validate new alpha factors for 4- and 6-wheel gear airplanes in the ACN-PCN
completion of the initial traffic testing phase (Phase 1), additional tests
were performed on the used test items to satisfy various supplemental
objectives: To measure wheel load interaction for 4- and 6-wheel gears; to
obtain a video recording of the pattern of failure of a flexible pavement
structure being rapidly failed; and to compare the number of load repetitions
to failure for the same structure with and without wander. The latter test was
performed by trafficking the center of the test area (between the failed north
and south test items) with no wander of the load carriage.
Cycle 3 (CC-3) involved the replacement of existing CC-1 test items and an
existing portland cement concrete (PCC) test strip with a series of four new
flexible pavement sections with varying subbase thicknesses. All new test items
were designated in the format LFC[-number],
with the letters LFC referring to low-strength, flexible, conventional (i.e.,
using unbound aggregate base) construction.
The existing CC-1 test items and PCC test strip were
removed to a depth of 3 feet into the existing clay subgrade. The new pavement surface
consisted of 5 inches of P-401 hot-mix asphalt (HMA) placed in two 2-½-inch
lifts. A tack coat was placed between the lifts. The base material consisted of
8 inches of P-209 crushed stone base placed in two lifts and compacted as
one. The subbase was composed of uniformly graded, manufactured argillite
screenings conforming to the FAA P-154 specification. The subbase was placed
and compacted in lifts of about 6 inches. Four subbase thicknesses were used,
producing four pavement test items having a progressively greater number of
passes to failure when subjected to traffic loading. Subbase thicknesses in
LFC-1, LFC-2, LFC-3, and LFC-4 were 16, 24, 34, and 43 inches respectively. The
upper two feet of the subgrade, for all the sections, were reprocessed and
compacted in 6 inch lifts using clean material from the excavation.
Construction was completed in August 2002.
The CC-3 test area diagram shows the locations of all
CC-3 test items. The test items covered
a length of 345 feet and a width of 66 feet. Limits of the test items were as
follows (the station number is the distance from the origin in feet):
Transition 0: Station -20 to 0
Test Items LFC-1, LFC-2, LFC-3, LFC-4 (including Transitions 1,
2, and 3): Station 0 to 300
Transition 4: Station 300
About 200 sensors were embedded in the pavement structure. The
sensors were of two types, static and dynamic. Static sensors were used to
monitor temperature in the asphalt and moisture in the subgrade on an hourly
basis. Dynamic sensors measured strains in the asphalt, pressure and
compression in the subgrade, and deflections throughout the depth of the
pavement structure. Deflections were measured using Multi-Depth Deflectometers,
or MDDs. Two pressure sensors were also placed at the horizontal interface between
the base and subbase layers. Test vehicle operations triggered the dynamic
sensors. Traffic testing was performed with 6-wheel loads on the north side of
each test item and 4-wheel loads on the south side of each test item. Rut depth
and profile measurements were made on the top surface of the asphalt as the
traffic testing progressed. Static and dynamic sensor data were processed and
stored in a computer database. Search the CC3 database.
Traffic Test Information
- September 3, 2002: started trafficking of CC-3 with 55,000 lbs. wheel loads.
- September 4, 2002: stopped testing on LFC1.
- September 6, 2002: 990 passes.
- September 12, 2002: stopped testing on LFC2 at 3,168 passes.
- September 13 and 16, 2002: 2 test pits in LFC2.
- September 17, 2002: tried MWHGL wander on LFC3 and 4.
- September 18, 2002: increased wheel loads to 65,000 lbs. and continued testing on LFC3 and 4 with old wander.
- October 18, 2002: stopped at 23,826 passes.
Test Vehicle Configuration and Wander Pattern
Tests were planned and executed with six-wheel and four-wheel landing gear loads. The gear configurations are illustrated on the Gear Configuration page. The wander patterns are illustrated on the Wander Pattern page.
Summary of Daily Traffic Repetitions
Daily traffic data for the flexible pavement test items are available by searching the Traffic Table. Daily and monthly traffic summaries, as well as traffic totals for each test item, are given in the Traffic Summary.