Test Description

The 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 method.

After 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.

Test Setup

Construction 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 to 325

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