Falling Weight Deflectometer Usage (2008)

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35 tests to be about 28.5%, but this error was greatly reduced by repeating the PFWD test. Carl Bro’s PRIMA 100 lightweight FWD (LFWD) is compared in another study with a standard FWD and to a plate load test (Nazzal et al. 2004). Tests were conducted at three stations on U.S. Highway 190 and at four stations along Louisiana State Highway 182. The LFWD-measured elastic modulus ELFWD showed a statistically significant cor- relation to the standard FWD-measured resilient modulus (MFWD = 0.97ELFWD, R2 = 0.94). Plate load tests showed similarly strong correlations to ELFWD in the PLT device’s initial and reloaded cases (EPLT(i) = 22 + 0.7 ELFWD; R2 = 0.92 and EPLT(R2) = 20.9 + 0.69 ELFWD, R2 = 0.94). Based on these strong correlations, the LFWD is a suitable device for evaluating pavement layer moduli. Because traditional trailer or vehicle-mounted FWDs can be expensive and cumbersome, an agency’s testing ability may be limited. In areas prone to freeze-thaw conditions, these limits may lead to incomplete network-level tests. One solution, a PFWD, was tested in this study for its compliance with traditional FWDs. The PRIMA 100, formerly manu- factured by Dynatest, was compared with a JILS 20C FWD provided by the Maine DOT and two Dynatest 8000 FWDs, one provided by VTrans and the other provided by the U.S. Army Corps of Engineers’ Cold Regions Research and Engineering Laboratory. Although the VTrans FWD was operated per the FHWA/LTPP manual, the Cold Regions Research and Engineering Laboratory added one sensor 8 in. from the load plate. The study reached three conclusions (Steinert et al. 2006): • PFWD composite moduli follow similar trends to com- posite moduli and subbase moduli as determined from FWD measurements on asphalt surfaced roads. • The correlation between composite modulus derived by the PFWD and traditional FWD increases with decreasing asphalt thickness. • The PFWD can be used as a tool to evaluate whether specific roadways experience strength loss during the spring thaw and thus warrant load restrictions. For roads where load restrictions are placed, the PFWD can be used as an aid to determine when restrictions should be placed and removed. This synthesis study identified the following FWD research project topics. Each topic represents several research projects, some of which were recently concluded as of this writing. in-MoTion deFLecTion TesTinG Although the FWD is a useful tool to determine layer stiff- ness and detect voids, it must be stationary during its opera- tion. This feature inconveniences agencies, as lanes must be closed to perform network-level testing. Ideally, a deflection measuring device should travel at highway speeds. In 1997, SweRoad under the tutelage of the Swedish government developed the Swedish Road Deflection Tester. The device was tested on roads in Sweden and the United Kingdom and found to correlate closely with the FWD. Additional sec- tions of the report give brief histories of roads, profilers, and deflection devices (Andrén 2006). In a TxDOT study (Jitin et al. 2006), a suitable replace- ment for the FWD was sought. Because the FWD must be stationary while in operation, the device is potentially unsafe to use on network-level pavements. A handful of in-motion deflection detection devices have been developed and this project reviews those that are readily available to TxDOT. The researchers reviewed University of Texas at Austin’s Rolling Dynamic Deflectometer, Dynatest’s Airfield Roll- ing Weight Deflectometer, Applied Research Associates’ Rolling Wheel Deflectometer, SweRoad’s Road Deflection Tester, and Greenwood Engineering’s High Speed Deflecto- graph. The researchers found the High Speed Deflectograph to be the device most in keeping with TxDOT guidelines, because it is the only candidate device that takes multiple deflection measurements in the same location. porTaBLe FaLLinG WeiGhT deFLecToMeTer In a research study by INDOT (Kim et al. 2006), a porta- ble FWD (PFWD) was evaluated for its correlation with a standard plate bearing load test. Tests were done at 22 high- way construction sites. The coefficient of subgrade reaction k30 was measured using the plate bearing load test and the PFWD measured the dynamic deflection modulus. A linear correlation (R2 = 0.77) was found between the two devices. Furthermore, the research found the error between the two CHAPTER NINE currenT research

36 COST learned the need for network-level FWD testing was subject to six criteria (Use of Falling Weight Deflectometers at Network Level . . . 1998): • Road network size • Quality of bearing capacity data within the agency’s pavement database • Importance given to particular parameters within a PMS • Testing budget including time required • Customer requirements • Historic reasons, such as frequency of maintenance MechanisTic-eMpiricaL paVeMenT desiGn FWD data are essential to mechanistic–empirical pavement design, and two research projects are in progress, the first of which, Use of Deflection Testing with the MPEDG, is investigating [T]he current state of the practice and art in routine back-calculation of FWD data and develop[ing] recommendations for advancing FWD data analy- sis and interpretation, particularly in relevance to the rehabilitation procedures in the Mechanistic– Empirical Pavement Design Guide (MEPDG) developed under the NCHRP 1-37A project. This project will also develop best practices guideline for analyzing and interpreting FWD data for project level analyses with particular emphasis on the effec- tive and efficient use of FWD data with the MEPDG (Sivaneswaran 2007). The second research project is entitled Evaluation of State Highway Agency Adoption of Practices for Implementing Mechanistic Empirical Pavement Design (FHWA contract number DTFH61-06-P-00198). Ground-peneTraTinG radar inTeGraTion INDOT evaluated network-level FWD and GPR testing fea- sibility. The report recommended that Indiana perform com- plete network-level tests on 3,541 lane-km (2,200 lane-mi) of its Interstate highways annually, which would complete the state’s entire network in five years. Back-calculation of pavement layer moduli followed the ASTM D5858 standard, and FWD operation followed ASTM D4694. FWD and GPR should be included with the state’s PMS, along with “inter- national roughness index, pavement condition rating, rut depth, pavement quality index, texture and skid resistance”. FWD and GPR data can provide information to operators, which may prevent unnecessary coring. Furthermore, the following research is recommended by this INDOT study (Noureldin et al. 2005): • Develop prediction models using FWD center deflec- tion as a pavement performance indicator. • Develop an automated structural adequacy index employing both the FWD data and automated distress identification data (especially the structural-related distress component of the pavement condition rating) for pavement management purposes. • Use the GPR to characterize the dielectric characteris- tics of pavement surfaces, especially those with poten- tial to trap moisture. neTWorK-LeVeL TesTinG Members of the European Union commissioned a study of FWD usage. Confined to network-level testing, the study conducted a literature review, found other pertinent data from COST studies, Lisbon’s FWD workshop presentations, and FWD owners in Europe. Network-level activity was divided into four subcategories: budgeting, planning, pro- gramming, and prioritization. From the Lisbon workshop,