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1The research in this volume was developed by the research team as listed on the title page. It was lead by Dr. Nam Tran. Field testing of the 3d-Radar ground-penetrating radar (GPR) system was carried out at sites in Florida, Kansas, and Maine. The equipment configuration used for this testing is shown in Figure 1.1. The data were collected at 3 nominal speeds: 40 mph, 20 mph, and 5 mph, and the level of detail of the data increased as the speed was lowered. The data analysis was carried out on the lowest-speed data, because these data had the highest level of detail. This data collection was car- ried out on a smaller section of pavement that was selected to most likely include delaminations. The selection of the test area was based on a review of the higher-speed data, on observation of surface distress, and on core data available from previous testing conducted by the corresponding state department of transportation. The primary purpose of the initial review of the GPR data was to identify a 2,000-ft-long section for testing of the mechanical wave system. An additional objective was to iden- tify specific locations for coring, which was carried out in con- junction with the mechanical wave testing. Mechanical wave testing was carried out only in Florida and Kansas, so those sites were reviewed. The section selected for a more detailed analysis was based on a review of the three-dimensional (3-D) GPR data and on the observed surface conditions. The focus was on the south- bound section, particularly the segment between Milepost (MP) 413 and the southbound rest area entrance. Surface distress observed in this area suggests some moisture damage in the layers below. See Figure 1.2. Core data in this area show a total asphalt thickness of approximately 9 in. In 1997, the pavement was milled approximately 5 in. and replaced with a 1-in. friction course, a 1.5-in.-thick layer of 12.5 mm mix, a 1.5-in.-thick layer of 19 mm mix, and a 0.5-in. layer of asphalt rubber mem- brane interlayer (ARMI). It is believed, on the basis of core data, that moisture damage was occurring either between the 12-mm and the 19-mm mixes or between the 19-mm mix and the ARMI layer. Figure 1.3 shows an overview of the GPR layer structure data for this southbound region. The section is fairly homoge- neous, but it appears that the overall asphalt thickness is lower in the segment north of the rest area. Figure 1.4 shows local detail of the pavement cross section. Note that what appears to be the ARMI layer is evident periodically in the GPR data structure. It is possible that if this layer is impermeable, a layer boundary will appear in the GPR data where moisture has been retained. On the basis of a qualitative review of the depth slice data, it was recommended that the mechanical wave testing be carried out on a 2,000-ft-long section that began 2,000 ft south of MP 413. Table 1.1 is a summary of the field observations and selected core locations. The surface reference marks are used to tie the location of test data files to physical observations of distress or other features on the surface of the pavement. Figures 1.5, 1.6, 1.7 and 1.8 show the core locations super- imposed on the GPR horizontal slice and profile data. The top figure is the horizontal (depth) slice, the bottom left fig- ure is the longitudinal profile, and the bottom right figure is the transverse profile. The numbers in circles are the core numbers. Figure 1.9 shows the automated activity analysis for the Gainesville site. The likelihood of distress is color coded. The location of each core was added to the analysis. Table 1.2 is the summary log of GPR images correspond- ing to the surface reference marks and sites identified as potential core locations. The table includes the references to Figures 1.10 through 1.20 where the GPR images are located. C h a p t e r 1 3d-Radar Ground-Penetrating Radar Field Testing Results for Locating CoresâFlorida
2Figure 1.1. 3d-Radar equipment used for field tests. Figure 1.2. Pavement conditions between MP 413 and rest area. MP 413 MP 410 MP 409 Bottom of AC Bottom of Base Rest Area Entrance Figure 1.4 Distance Pavement Surface Figure 1.3. Overview of 20-mph GPR data for I-75 southbound (centerline). ARMI Layer Bottom of Asphalt Figure 1.4. Local detail of layer structure from 5-mph GPR data (MP 413 at 112 m).
3 Table 1.1. Pavement References and Core Locations at I-75 Southbound Test Section Description of Surface Reference Mark File Distance (m) Distance from MP 413 (ft) Offset MP 413 111.65 0 na Hole 139.25 91 Centerline Unknown 156.00 146 Full width Crack 381.25 885 RWP to LWP Crack 386.00 900 RWP to LWP Hole 712.77 1,972 Left of centerline Crack 717.50 1,988 Full width, at small angle Start of test 721.25 2,000 na Crack 901.50 2,591 Full width Crack 903.25 2,597 Full width Crack 905.20 2,604 Full width Hole 943.40 2,729 RWP Traffic loop and cores 1,317.40 3,956 Centerline Core locations 1 792.0 2,232 RWP 2 795.0 2,242 RWP 3 798.0 2,252 RWP 4 1,211.0 3,607 RWP 5 1,218.7 3,632 RWP 6 1,221.0 3,640 RWP 7 1,252.1 3,742 RWP 8 1,253.0 3,745 RWP 9 1,413.0 4,270 RWP 10 1,418.0 4,286 RWP Note: LWP = left wheelpath; RWP = right wheelpath; and na = not applicable. Data used in this table are taken from GPR File 12-5 (No. 12 at 5 mph).
41 2 3 Figure 1.5. Core locations 1, 2, and 3. Figure 1.6. Core locations 4, 5, and 6.
5 7 8 Figure 1.7. Core locations 7 and 8. 109 Figure 1.8. Core locations 9 and 10.
6Figure 1.9. Automated activity analysis of Gainesville, Florida, site with core locations shown.
7 Table 1.2. GPR Surface Image Log Description of Surface Reference Mark File Distance (m) Distance from MP 413 (ft) Offset Figure MP 413 111.65 0 na Hole 139.25 91 Centerline 1.10 Unknown 156.00 146 Full width 1.11 Crack 381.25 885 RWP to LWP 1.12 Crack 386.00 900 RWP to LWP 1.12 Hole 712.77 1,972 Left of centerline 1.13 Crack 717.50 1,988 Full width, at small angle 1.13 Start of test 721.25 2,000 na Crack 901.50 2,591 Full width 1.14 Crack 903.25 2,597 Full width 1.14 Crack 905.20 2,604 Full width 1.14 Hole 943.40 2,729 RWP 1.15 Traffic loop and cores 1,317.40 3,956 Centerline 1.16 Potential core locations Anomaly at 12-cm depth 795.0 2,242 RWP 1.17 Anomalies at 4-cm depth 1,218.7 3,632 RWP 1.18 Anomaly at 11-cm depth 1,252.1 3,742 RWP 1.19 Anomaly at 13-cm depth File 8, 20 mph 2,837 Centerline 1.20 Note: na = not applicable. Data used in this table are taken from GPR File 12-5 (No. 12 at 5 mph). Figure 1.10. Hole (red arrow) at file distance 139.25 m.
8Figure 1.11. Unknown mark (red arrow) at file distance 156.00 m. Figure 1.12. Crack (left red arrow) at file distance 381.25 m (885 ft from MP 413) and 386.00 m. Figure 1.13. Hole (left red arrow) at file distance 712.77 m and crack (right red arrow) at file distance 717.50 m. Figure 1.14. Crack (left red arrow) at file distance 901.50 m, 903.25 m, and 905.20 m.
9 Figure 1.15. Hole (red arrow) at file distance 943.40 m. Figure 1.16. Traffic loop (right arrow) and cores (left arrow) at file distance 1,317.40 m. Figure 1.17. Anomaly at 12-cm depth, file distance 795.0 m.
10 4 5 6 Figure 1.18. Anomalies at 4-cm depth, file distance 1,218.7 m. 7 8 Figure 1.19. Anomaly at 11-cm depth, file distance 1,252.1 m.
11 109 Figure 1.20. Anomaly at 13-cm depth, File 8, 20 mph.
