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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 (Andrén 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. ˇ 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 ˇ 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 ˇ 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.
