CC-2 Test Item : NDT Plan & Data
HWD testing was conducted March 5 to December 17, 2004. The following summarizes this testing.
Heavy Weight Deflectometer Test Details
The FAA’s HWD, Kuab Model 240 shown in Figure 2, has been extensively described in . During the CC2 HWD testing, the FAA standard configuration was used: 12-inch (30.5-cm) diameter plate, pulse width of 27-30 msec, and four drop heights: 36-kips (160-kN) seating drop followed by impact loads of 12-kips (53-kN), 24-kips (106-kN), and 36-kips (160 kN).
HWD tests were performed on the slab centers and on both sides of the outboard longitudinal joints opposite the slab centers (Figure 1). The tests were performed prior to trafficking, periodically during trafficking, and at the end of trafficking. Tests were performed twice during trafficking of the MRC test item. During a longer traffic period, the MRG and MRS test items were subjected to HWD runs at intervals of 15 test vehicle wanders up to 5,000 passes, 30 wanders up to 7,000 passes, and 60 wanders for the remainder of the testing which exceeded 30,000 passes.
Figure 1. Heavy Weight Deflectometer
Heavy Weight Deflectometer Test Procedure
HWD tests had also been run on the exposed Econocrete, P-306, after demolition of the CC-1 slabs and prior to placement of the CC-2 slabs, MRS, February 9, 2004. The data were used for back-calculation of the layer properties without the influence of the upper concrete pavement layer.
CC2 Test Items deflections were measured at the center of the load plate (D0), at 12-inch (30-cm) offset (D2), 24-inch (60-cm) offset (D3), 36-inch (90-cm) offset (D4), 48-inch (120-cm) offset (D5), 60-inch (150-cm) offset (D6) and 72-inch (180-cm) offset (D7). An additional sensor was placed at 12-in (30-cm) offset (D1) on the front of the loading plate.
The CC2 NDT plan specified the HWD testing locations per test item (MRC, MRG and MRS):
• at the center of each slab, to verify the pavement uniformity, elastic modulus backcalculation for each layer, to track the deterioration of the different support conditions and the deterioration rate of the pavement itself; and
• at the longitudinal and transverse joints of the slabs, to verify the loss of joint load transfer efficiency (LTE).
Originally, CC2 was planned for trafficking using 6-wheel loading (north side) and 4-wheel loading (south side) with 55,000 lbs. (24,950 kg) per wheel at a speed of 2.5 mph (4 km/h) and standard wander pattern of 66 passes per cycle. However, due to the variable flexural strength of the built test items and the short life predicted by FAA design procedures, test item MRC was tested with 4-wheel loading using the standard wander pattern on the south side and an abbreviated wander pattern on the north side. Because of the different loading used in MRC, the HWD data collected from this test item are not comparable to the data collected from MRS and MRG and have not been included in the analysis.
HWD tests were performed every 15 wanders or approximately every 990 passes until 5,000 passes were completed, then every 30 full wanders to 7,000 passes completion, and finally intervals of 60 full wanders for the remainder of the testing. A total of 15 sets of HWD readings were collected, and were used to track the progress of the pavement deterioration. Test items MRS and MRG were trafficked from July 6 until December 10, 2004, when the pavements were declared failed.
Table 1 shows the total number of passes (coverage) applied to final failure on CC2 test items. The pavement deterioration was monitored using periodic distress surveys and HWD. Rolling’s structural condition index (SCI) concept  was used to declare the pavements failed.
Total Number of Passes (Coverage) to Final Failure.
CC2 Test Item MRG MRS
South (4-Wheels) 30,996 (6,117) 30,996 (5,784)
North (6-Wheels) 31,020 (6,480) 20,262 (4,855)
Although, the data collected from each of the 15 sets of HWD tests are available, this paper includes the analysis of only 2 sets of HWD data, before the pavement was trafficked and after the traffic was completed.
The level of deflection under a given load provides information about the flexibility of the pavement. Conversely the required load for a unit deflection reflects the local pavement stiffness. This stiffness, called the Impact Stiffness Modulus (ISM), has been used in this paper as an indicator of the strength of the rigid pavement and its rate of deterioration.
Stiffness of Rigid Pavement Test Item MRS
The ISM0, calculated using the maximum basin deflection (D0) under the load, is an indicator of the pavement condition itself.
ISM0 = HWD Load/D0
On the other hand ISM7, calculated using the deflection 72-in from the center load (D7), usually indicates the subgrade condition.
ISM7 = HWD Load/D7
Plan of FWD tests for MRG & MRS during the Traffic Tests
(1) Collect FWD data along with the slab deterioration under traffic;
(2) Measure the variation of the joint load transfer capabilities during the traffic test;
(3) Verify the cracks detected by strain sensors but before they are observed from slab surface
Slab Deterioration Test
Location: Center of each slab in the two in-lanes in MRG and MRS, ten drops for MRG and MRS, twenty drops in total.
Time: After every 15 wanders of traffic are completed for MRG and MRS. The tests will be done at end of 15, 30, 45, 60, wanders until special notice to change the testing frequency. (If the data received from two consequent tests are almost the same, next test could be done after additional 30 wanders. However, whenever the received data show significant change in D0 comparing to the previous ones, next FWD test should be done after 15 wanders)
Plate Size: 12 inch
Procedures: Three drops, 12,000, 24,000 and 36,000 lbs at each location plus a seating drop with load 36,000 lbs
Joint Load Transfer Variation Tests
Location: At four inside transverse joints, in-lane slabs only (the two end-joints. Do not need tests). Loads need to be dropped on two sides of each joint and tangential to the joint. The spacing between the FWD loading plate edge and the joint center line should be smaller than one inch. Eight drops are on each side of MRG and MRS, 32 drops are in total.
Time, Plate size and proceure: The same to Slab Deterioration Tests
Verification of Bottom Crack Tests
Location & Time To be determined and informed. It is expected that both MRG and MRS will have cracks initialized from slab bottom, and near the center of longitudinal joint but not observed from the slab surface. When a crack has been observed by strain gages, the FWD tests will be done and the loading location will be determined based on the data received from the strain gages. Number of locations will be limited no more than five in total.
Procedure The same to slab deterioration tests. Loads need to be dropped on two sides of the longitudinal joint.
Click the provided links for additional FWD test data & output : 0414MRC 0414MRG 0414MRS 0629MRC 0629MRG 0629MRS 0629MRC2 0629MRG2 0629MRS2
Click the provided links for additional PLATE LOAD test data & output MRG: Data Output MRS: NWT-Data SWT-Data Output