U.S. Department of Transportation
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Federal Highway Administration Research and Technology
Coordinating, Developing, and Delivering Highway Transportation Innovations
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Publication Number: FHWA-HRT-08-056
Date: November 2008
Testing performed in the field has indicated that the spacing between the centerline of the footpads in various Dipsticks® that are used in the LTPP program is not exactly 304.8 mm. Therefore, each RSC is required to perform a field test annually to determine the footpad spacing of each Dipstick® in their possession. This appendix describes procedures for performing the field test and the procedure for computing the footpad spacing of the Dipstick® from that data.
This test should be performed on a smooth AC or PCC pavement that is free of distress. Use the following procedure to layout the section and perform the test.
Figure 99. Illustration. Test section layout.
Figure 100. Illustration. Location of back footpad of Dipstick® at start of the section.
Figure 101. Illustration. Back end of front footpad is past the end of the test section when last reading is obtained.
Figure 102. Illustration. Back end of the front footpad is before the end of the test section when last reading is obtained.
Footpad spacing (mm) = (30480 + X) /100 (3)
X is in mm.
If back edge of front footpad was before the end of the test section when the last reading was obtained (case shown in figure 102), use the following formula to compute footpad spacing:
Footpad spacing (mm) = (30480 - X) / 100 (4)
X is in mm.
If the back edge of the front footpad is exactly in line with the end of the section, the footpad spacing is 304.8 mm.
Compute the average footpad spacing for each Dipstick® by averaging the values obtained for the three runs (to two decimal places).
Table 3. Suggested format of RSC office log.
|Dipstick Model||Serial Number||Diameter of Footpad |
|Test Number||Offset at End of Section(1)|
|Average Footpad Spacing|
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Topics: research, infrastructure, pavements and materials, LTPP
Keywords: research, infrastructure, pavements ,Pavement Profile, Profile Measurements, Inertial Profiler, Road Profiler, Pavement Data Collection, long Term pavement Performance
TRT Terms: research, infrastructure, pavements and materials