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35 CHAPTER NINE Current Research This synthesis study identified the following FWD research tests to be about 28.5%, but this error was greatly reduced by project topics. Each topic represents several research projects, repeating the PFWD test. some of which were recently concluded as of this writing. Carl Bro's PRIMA 100 lightweight FWD (LFWD) is compared in another study with a standard FWD and to a In-Motion Deflection Testing plate load test (Nazzal et al. 2004). Tests were conducted at three stations on U.S. Highway 190 and at four stations Although the FWD is a useful tool to determine layer stiff- along Louisiana State Highway 182. The LFWD-measured ness and detect voids, it must be stationary during its opera- elastic modulus ELFWD showed a statistically significant cor- tion. This feature inconveniences agencies, as lanes must be relation to the standard FWD-measured resilient modulus closed to perform network-level testing. Ideally, a deflection (MFWD = 0.97ELFWD, R2 = 0.94). Plate load tests showed measuring device should travel at highway speeds. In 1997, similarly strong correlations to ELFWD in the PLT device's SweRoad under the tutelage of the Swedish government initial and reloaded cases (EPLT(i) = 22 + 0.7 ELFWD; R2 = developed the Swedish Road Deflection Tester. The device 0.92 and EPLT(R2) = 20.9 + 0.69 ELFWD, R2 = 0.94). Based on was tested on roads in Sweden and the United Kingdom and these strong correlations, the LFWD is a suitable device for found to correlate closely with the FWD. Additional sec- evaluating pavement layer moduli. tions of the report give brief histories of roads, profilers, and deflection devices (Andrn 2006). Because traditional trailer or vehicle-mounted FWDs can be expensive and cumbersome, an agency's testing ability In a TxDOT study (Jitin et al. 2006), a suitable replace- may be limited. In areas prone to freeze-thaw conditions, ment for the FWD was sought. Because the FWD must be these limits may lead to incomplete network-level tests. One stationary while in operation, the device is potentially unsafe solution, a PFWD, was tested in this study for its compliance to use on network-level pavements. A handful of in-motion with traditional FWDs. The PRIMA 100, formerly manu- deflection detection devices have been developed and this factured by Dynatest, was compared with a JILS 20C FWD project reviews those that are readily available to TxDOT. provided by the Maine DOT and two Dynatest 8000 FWDs, The researchers reviewed University of Texas at Austin's one provided by VTrans and the other provided by the U.S. Rolling Dynamic Deflectometer, Dynatest's Airfield Roll- Army Corps of Engineers' Cold Regions Research and ing Weight Deflectometer, Applied Research Associates' Engineering Laboratory. Although the VTrans FWD was Rolling Wheel Deflectometer, SweRoad's Road Deflection operated per the FHWA/LTPP manual, the Cold Regions Tester, and Greenwood Engineering's High Speed Deflecto- Research and Engineering Laboratory added one sensor 8 graph. The researchers found the High Speed Deflectograph in. from the load plate. The study reached three conclusions to be the device most in keeping with TxDOT guidelines, (Steinert et al. 2006): because it is the only candidate device that takes multiple deflection measurements in the same location. PFWD composite moduli follow similar trends to com- posite moduli and subbase moduli as determined from FWD measurements on asphalt surfaced roads. PORTABLE FALLING WEIGHT DEFLECTOMETER The correlation between composite modulus derived by the PFWD and traditional FWD increases with In a research study by INDOT (Kim et al. 2006), a porta- decreasing asphalt thickness. ble FWD (PFWD) was evaluated for its correlation with a The PFWD can be used as a tool to evaluate whether standard plate bearing load test. Tests were done at 22 high- specific roadways experience strength loss during the way construction sites. The coefficient of subgrade reaction spring thaw and thus warrant load restrictions. k 30 was measured using the plate bearing load test and the PFWD measured the dynamic deflection modulus. A linear For roads where load restrictions are placed, the PFWD correlation (R2 = 0.77) was found between the two devices. can be used as an aid to determine when restrictions should Furthermore, the research found the error between the two be placed and removed.