Test Background and Objectives
Construction Cycle 5 (CC-5) is the name given to a set of full-scale flexible pavement tests conducted at the NAPTF. The main purpose of CC-5 was to produce data on the relative performance of flexible pavements supporting simple 6-wheel and 4-wheel gears, versus large gear assemblies consisting of multiple 6- and 4-wheel landing gears in close proximity. These tests were largely motivated by the need to gain data for the design of flexible pavements accommodating new large multi-gear aircraft such as the A380.
The CC-5 tests consisted of two distinct phases: the CC-5 Test Strip and the CC-5 Test Items. Construction of the CC-5 Test Strip was completed in February of 2007. Full scale testing of the CC5 Test Strip was conducted between February 2007 and March 2007. Construction of the CC5 Test Items was completed in July 2008. Full scale testing of the CC-5 Test Items was conducted between August 2008 and October 2012.
CC-5 Test Strip
The purpose of the CC-5 Test Strip was to evaluate the adequacy of DuPont Clay (DPC) for use as stable, low-strength subgrade material. DPC had been used previously as a medium-strength subgrade material in CC-1, CC-2 and CC-4. It showed stability of moisture and strength with time. A different material, designated County Sand and Stone Clay (CS&S, a silty clay), had been used as a low-strength subgrade in CC-1 and CC-3. However, the CS&S clay showed a loss of moisture and a gain in strength with time, making it difficult to use in relatively long-term tests.
The CC-5 Test Strip effort involved the replacement of CC-3 Test Items LFC-1 and LFC-2 with new, similarly designated test areas. Removals of the old CC-3 test items penetrated some depth into the existing CS&S clay low-strength subgrade.
TTo provide for a side-by-side comparison of DPC and CS&S, an additional 36 inches of CS&S clay was placed on top of the excavated depth of subgrade on the south side. It was placed in five lifts, with four lifts at a thickness of 8 inches and a single lift of 12 inch thickness at the bottom. It was conditioned to an average CBR of 3.0 at an average moisture content of 25.4%. On the north side, DPC was placed above the existing CS&S subgrade to a depth of 36 inches. The DPC was placed in six lifts of 6 to 8 inch thickness and conditioned to an average CBR of 3.5 at an average moisture content of 36.0% (See Test Area Diagram).
A granular subbase material consisting of crushed quarry screenings and meeting the FAA P-154 specification was placed above the subgrade. It was placed in four lifts of 5 to 8 inch thickness, with the lifts of greater thickness below. The subgrade surface levels had been adjusted (stepped) so that of the 2 test strip test areas, designated LFC-1 and LFC-2, LFC-1 received 16 inches of the P-154 subbase, and LFC-2 received 24 inches. The LFC-1 subbase was placed in three lifts and LFC-2 subbase was placed in four lifts. A compaction level of 97% was achieved at an average moisture content of 4.2% in the subbase of LFC-1, and a compaction level of 96% was achieved at an average moisture content of 4.6% in the subbase of LFC-2.
An 8 inch depth of Dense Graded Aggregate (DGA) base was placed on the P-154 subbase. The base was placed and compacted in two 4-inch lifts. A compaction level of 102% was achieved at an average moisture content of 2.3%. The Test Strip pavement was completed with the placement and compaction of a 2.5 inch thick New Jersey Department of Transportation (NJDOT) Hot Mix Asphalt (HMA) Superpave surface. Five paving lanes were used. Construction was completed on February 13, 2007.
LFC-1 and LFC-2 were further designated as North and South (N and S) to cover the variablity of subgrade type. The Test Strip covered a total length of 170 ft. and a width of 64 ft. Within the test boundary, the limits of the designated test areas and transitions were as follows:
|Test Strip Area/Transition
||-20 to 0
|LFC-1 N LFC-1 S
||0 to 30
||30 to 50
|LFC-2 N LFC-2 S
||50 to 100
||100 to 150
*Station numbers are measured in feet from the origin located near the west end of the NAPTF.
One experimental Multi-Depth Deflectometer (MDD) was placed in the DPC subgrade, and that area of the Test Strip was tested with a single wheel. The effort served as the precursor to the development of the 4 Horizontal Position Devices (HPD’s) ultimately placed in the subgrade of the CC-5 Test Items.
Three longitudinal recessed strips were provided in the surface of the DGA base within Transition 2. One strip was 8.5 ft. wide, 1 inch deep, extending from station 110 to 150 at the north edge; the second was 9.5 ft. wide, 2 inches deep, extending from station 110 to 150 at the south edge; and the third 12 ft. wide, 2 inches deep, extending from station 100 to 150 at the pavement centerline. The top surface of the HMA was placed level with no recesses. The purpose of the recessed strips in the DGA base was to study the response of the asphalt paving machines to the resulting bumps, as determined by the FAA profiler and the accompanying FAA pavement roughness software.
CC-5 Test Items
The main purpose of the CC-5 Test Items was to test the interaction effects of closely spaced multiple-wheel landing gears. A secondary objective was to quantify the difference in performance provided by two different subbase materials. The two subbase materials were crushed quarry screenings conforming to FAA P-154 and a dense graded aggregate (DGA) meeting New Jersey highway specifications.
Construction of the CC-5 Test Items involved replacing both test areas of the CC-5 Test Strip, as well as test items LFC-3 and LFC-4 from CC-3. Removal of existing material extended to, and in some areas penetrated, the CS&S clay subgrade of the old CC-3 test items, and penetrated the CS&S clay subgrade of the CC-5 Test Strip.
The surface of the CS&S clay at the excavated depth was conditioned to an average CBR of 3.3 at an average moisture content of 26.7%. A new layer of DPC was placed above the existing CS&S clay to a depth of 30 inches. The DPC was placed in five lifts of 4 to 8 inch thickness, with the lifts of greater thickness below. The DPC was conditioned to an average CBR of 3.3 at an average moisture content of 37.6%. DPC was used for both its availability and its greater stability of moisture and strength over time.
A granular subbase material meeting FAA P-154 and consisting of crushed quarry screenings was placed above the subgrade in five lifts of 4 to 10 inch thickness, with the lifts of greater thickness below. Compaction levels of 91% to 98% were achieved at moisture contents of 2.5% to 5.0%. Lower compaction levels and moisture contents were relegated to the lifts below. Final DPC subgrade surface elevations were adjusted (stepped) so that Test Items LFC-1 and LFC-4 received 34 inches of subbase, and LFC-2 and LFC-3 received 38 inches. An alternate, and distinctly different, subbase material was used on the north side of LFC-3 and LFC-4. This material, which also met the FAA P-154 specification, consisted of a dense graded aggregate (DGA). The coarse aggregates in the DGA mix were much larger than those of the crushed quarry screenings mix. The DGA subbase was placed in four lifts, 8 to 12 inches thick, with the lifts of greater thickness below. Compaction levels of 91% to 93% were achieved at moisture contents of 1.5% to 2.0%.
An 8 inch thick layer of P-209 crushed stone base was placed on the P-154 subbase. The base was placed and compacted in two 4 inch lifts. A compaction level of 97% was achieved at an average moisture content of 1.9%.
The base and subbase materials were placed at below-optimum moisture contents and compaction levels. This was done to minimize the amount of free moisture reaching the subgrade surface. It has been found that moisture draining from certain P-209 and P-154 materials placed at optimum moisture content may contaminate the surface of the compacted subgrade, and ultimately weaken the subgrade over the life of the pavement.
The pavement was completed with the placement of a 5 inch thick asphalt concrete surface layer. The surface layer was placed and compacted in two approximately equal thickness lifts with a water based tack coat placed between the lifts. Each lift had five paving lanes. The joints of each lift were formed as wedge joints and were staggered by at least 1-½ ft. between the upper and lower lifts. A final surface survey revealed that the actual asphalt pavement layer thickness averaged 4.66 inches. Construction was completed June 30, 2008. Test Items LFC-3 and LFC-4 were designated as North and South to differentiate between pavement structures and wheel configuration loading conditions. Test Items LFC-1 and LFC-2 were also designated as North and South but required additional East and West designations to differentiate between pavement structures and wheel configuration loading conditions. The table below provides a breakdown of the pavement sections and transitions along with wheel configuration loading conditions.
The CC-5 Test Items and transitions covered a total length of 320 ft. and a width of 64.5 ft. Within the test boundary, the limits of the designated test items and transitions were as follows:
|| Wheel Configuration
||-20 to 0
|LFC-1 NW LFC-1 SW
||0 to 37.5
|| 6 wheel
||37.5 to 47.5
|LFC-1 NE LFC-1 SE
||47.5 to 85
|| 10 wheel
||85 to 95
|LFC-2 NW LFC-2 SW
||95 to 132.5
|| 10 wheel
||132.5 to 142.5
|LFC-2 NE LFC-2 SE
||142.5 to 180
|| 6 wheel
||180 to 190
|LFC-3 N LFC-3 S
||190 to 230
|| 6 wheel north/10 wheel south
||230 to 240
|LFC-4 N LFC-4 S
||240 to 280
|| 6 wheel north/10 wheel south
||280 to 300
A total of 135 sensors were embedded in the test pavement for data
collection. The sensors were of two types, static and dynamic. Only
6 static sensors were used. These consisted of 2 Thermistor Trees (T’s)
each with 3 sensors placed in the asphalt. Dynamic sensors consisted of
Asphalt Strain Gages (ASG’s), Multi- Depth Deflectometers (MDD’s), Horizontal
Position Devices (HPD’s), and Pressure Cells (PC’s). The asphalt layer
contained 20 ASG’s, 16 in mat locations, 4 in joint locations, and 2 T’s each
with 3 sensors at different depths within the thickness. The subgrade
contained 12 MDD’s each with 6 sensors at different depths, 4 HPD’s each with 7
sensors at different transverse positions, and 9 pressure cells with 8 at the
same depth. Test vehicle operations triggered data retrieval from the
dynamic sensors at an high sampling rate. Sensor data collected during
both traffic and non-traffic time periods were processed and stored in a
computer database. The CC-5 database can be searched using the search tools
available on this web page.
The traffic data for the flexible pavement test strip and test items are available in the Traffic Summary Tables. Daily and monthly traffic repetitions, as well as current traffic totals, are given for each test item.