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Publication Number: FHWA-HRT-06-132
Date: December 2006

Long-Term Pavement Performance Program Manual for Falling Weight Deflectometer Measurements

Chapter 3. Test Procedure

The following list summarizes the general procedures FWD operators are to perform at each test site. The step summaries refer to sections in this manual that give the details of each step.

3.1 Before arriving at the site, an FWD operator must have a filled out copy of form F05 "FWD Operations Planning." A separate copy of this form must be filled out for each test section.

3.2 When an FWD operator arrives at the site, he or she should inspect the test section for evidence of maintenance activities. Any missing or defaced site markings should be replaced before continuing. If there is evidence of recent maintenance activities, contact the Regional Support Contractor (RSC) office. If quantitative evidence exists of the effect of the maintenance activities on the layer structure, reevaluate the temperature gradient hole section of form F05.

3.3 Prepare the temperature gradient holes as directed in manual section 6.1. List the depth of the holes on form F05 in the information blanks that are not crossed out. Previously drilled holes may be used if the operator first blows them out and remeasures the depths, which should correspond to those listed on form F05. If the operator drills new holes, the depths should be measured and filled out on form F01. The operator then fills the holes with mineral oil and waits at least 20 minutes (min) before taking the first temperature measurement.

3.4 Perform the before-operations activities listed in manual section 9.2.

3.5 Perform the standard buffer warm-up sequence or the cold weather buffer-warm-up sequence, as appropriate, outside of the test section limits. The buffer warm-up sequences and their appropriate temperature ranges are given in section 4.3.5.

After completing the buffer warm-up sequence, examine the data from the final four drops to ensure that the load levels are not all trending in the same direction (i.e., consistently increasing or consistently decreasing). If they are trending in the same direction, repeat the standard buffer warm-up sequence until the load levels stabilize.

After the last buffer warm-up sequence, examine the data from the four drops before the final four drops to ensure that the load levels for each drop height are within the limits given in section 4.2. If they are not, adjust the drop height targets accordingly and make an additional drop at each drop height to ensure that the targets are correctly set. If at any time during testing the load levels stray from the limits for their respective drop heights, stop testing, readjust the targets, and repeat the pass.

If the FWD is idle for more than 15 min, again perform a standard buffer-warm-up sequence.

3.6 Position the FWD so that the center of the load plate is on the section start limit (i.e., Station 0+000). Set the DMI to 0 centimeters (cm) (0 feet (ft)), ascending. The DMI must be set in units of "feet" for continuity with previous LTPP FWD testing.

3.7 Position the FWD at the first test location. Test locations for the appropriate test plan number (as given on form F05) are listed in manual section 5.

3.8 In the FWD data collection software, set the "Test Setup" as listed on form F05. Then open a new data file. Use the file name as listed on form F05.

3.9 Check the local time on the computer and evaluate whether the test pass can be completed before local midnight. If it is not probable that testing can be completed before midnight, do not start testing until after midnight. Any test pass that starts before midnight and ends after midnight cannot be uploaded to the LTPP database.

3.10 Perform the first temperature gradient measurement as described in manual section 6.1. Perform subsequent temperature gradient measurements every 30 min, plus or minus 10 min. For GPS sections, take temperature gradient measurements at alternate ends, with a 60-min interval between measurements at a given end.

3.11 Enter the lane specification appropriate to the test location in the field provided in the data collection software.

3.12 Start the testing sequence.

3.13 Exit the vehicle during testing and examine the pavement surface in the vicinity of the FWD for distresses and defects. Note any distresses in the area around the FWD as described in manual section 6.3.

3.14 During load transfer testing (i.e., lane specifications J4, J5, C4, C5, F4 or F5) measure the joint/crack width as described in manual section 6.2. Joint/crack widths must be measured for at least 25 percent of load transfer tests. If time permits, measure joint/crack widths for all load transfer tests.

3.15 If the data collection software generates errors during testing, follow the instructions in manual section 7. After testing, at the "Accept/Reject" prompt choose "Accept" only if no errors were generated, or after following the error resolution procedures in manual section 7.

3.16 After testing is complete and the load plate is up, proceed to the next test point.

3.17 If the next test point is at an even station (i.e., 1+00, 2+00) check that the DMI corresponds to the pavement markings. If it does not correspond, correct the DMI.

3.18 Repeat steps 3.11 through 3.17 for each test point in the test pass.

3.19 After completing each test point in the pass, close the data file. The data file must be closed and a new data file opened before beginning in a new test pass.

3.20 Return the FWD to the section start limit (i.e., station 0+000), and return the DMI to zero.

3.21 Perform steps 3.7–3.9 and 3.113.19 for the new pass. The temperature gradient measurement process does not need to be restarted, but it must be continued as long as FWD testing is being performed at the section.

3.22 Repeat steps 3.20–3.21 for each remaining pass at the test section.

3.23 After completing FWD testing at the section, perform one more temperature gradient measurement, regardless of the time since the previous measurement.

3.24 If traffic control conditions permit, perform data backup and preliminary data processing before leaving the site as described in manual section 12.1. Check that forms F01 and F02 are correctly filled out, and that form F05 is initialed and dated.

3.25 Perform after-operations activities described in manual section 9.3.

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