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10 and KUAB 240 are available as single-axle trailer-mounted Giving operators an ownership stake in the FWD FWDs or as vehicle-mounted FWDs. equipment they operate Overhauling the equipment when needed Maintenance Practices A few SHAs reported that their FWDs have not yet needed "significant maintenance." Most SHAs perform regular maintenance on their FWD equipment and their tow vehicles. These maintenance activi- Manufacturers' Recommendations ties are separate from calibration and can include mechani- cal lubrication, replacement of consumable parts, leak FWD equipment manufacturers generally follow LTPP repair, cleaning, and other activities that keep the mechani- guidelines for equipment maintenance and offer mainte- cal devices in working order. nance services on the equipment they sell. For example, Carl Bro supplies a comprehensive maintenance list to its clients, State Highway Agency Falling Weight which breaks down maintenance activities by individual Deflectometer Maintenance FWD component. In their preventative maintenance check- list, Dynatest recommends that brake operation, hand brake Although most SHAs do not have a written FWD mainte- pump, load plate lubrication, tires, and belts be inspected on nance plan (Appendix B, Question 7), maintenance activi- a daily basis; their FWD equipment checklist is summarized ties are performed by SHA personnel. FWD equipment and in Table 4. tow vehicle maintenance is performed by SHA employees among 87% of survey respondents (Appendix B, Questions In addition to providing JILS-FWD maintenance ser- 910). Seventeen percent of SHAs reported that they fol- vices, Foundation Mechanics, Inc.'s maintenance personnel low the manufacturer's guidelines for regular maintenance. are able to log into their clients' JILS-FWD computers over Those who did not follow the manufacturer's guidelines usu- the Internet to review files and perform diagnostic tests. ally stated that maintenance activities are done when needed. Twenty-five agencies (listed in Appendix B, Question 11) KUAB offers a preventative maintenance program as an provided other suggestions on keeping their FWD equip- option with their FWDs, which includes cleaning, inspec- ment in working order, including the following (Appendix tion, and calibration. The procedures typically take between B, Questions 8 and 11): three and four weeks to complete and are done by KUAB personnel at their Savoy, Illinois, facility. Cleaning the sensors and holders with an emery cloth Storing FWD equipment and vehicles in a heated Merits of Falling Weight Deflectometer Versus garage when not in use Other Nondestructive Testing Devices Bleeding hydraulic lines annually Following a brief maintenance checklist before depart- The Missouri DOT (MoDOT) detailed the merits of FWD ing for a job usage in an undersealing study. Before employing FWDs to Including maintenance activities when FWDs are detect voids, MoDOT used to test load transfer efficiency calibrated (LTE) by the "proof-rolling method." A dump truck was filled to give a rear-axle load of 80 kN (18,000 lbf), and its TABLE 4 DYNATEST RECOMMENDED MAINTENANCE ACTIVITIES AND FREQUENCIES Frequency Activities Check brake operation, check hand brake pump for free movement, check load plate for lubrication, clean Daily, or as required clamping magnets/disks/springs. Tire pressure (approx. 32 psi), lug nuts tight (7590 ft-lb), check breakaway feature (actuator), check brake Weekly lock operation, inner catch parts lubricated with Teflon, external weight guides lubricated with Teflon, lubricate SD foam guides with silicone spray, check/refill battery level, clean infrared/air sensors. Check brake fluid level (DOT type 3 only), check rubber stabilizers for tightness, nuts and bolts tight, R/L cable checked for bends/breaks, check deflector holderstips tight, clean sensor cables with soapy water Monthly only, check charging system connections, coat terminals with corrosion inhibitor, check hydraulic fluid level, clean/inspect electronic connections, perform relative calibration, wash equipment. Annually Change hydraulic fluid, change hydraulic fluid filter, perform reference calibration. Source: DYNATEST.

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11 rear tire was placed 1 ft past a transverse joint between two Less manpower is required. slabs. Gauges then gave the deflections generated by the Lanes are closed for less time. load on each slab. When measured, LTE is less than 65% "No influence of shoulder movement to apparatus." and loaded side deflections were greater than 0.44 mm Dynamic FWD impulse loads provide a more realistic (17.5 mils), the slab was undersealed. FWDs are preferred simulation of truck movements. over the proof-rolling method, for the following reasons Multiple load levels are possible. (Donahue 2004):