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Falling Weight Deflectometer Usage (2008)

Chapter: CHAPTER TEN Conclusions

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Suggested Citation:"CHAPTER TEN Conclusions." National Academies of Sciences, Engineering, and Medicine. 2008. Falling Weight Deflectometer Usage. Washington, DC: The National Academies Press. doi: 10.17226/13675.
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Page 45
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Suggested Citation:"CHAPTER TEN Conclusions." National Academies of Sciences, Engineering, and Medicine. 2008. Falling Weight Deflectometer Usage. Washington, DC: The National Academies Press. doi: 10.17226/13675.
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Page 46

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37 • From the survey results, the responding SHAs’ expen- ditures varied widely (ranging from no program to $850,000 annually) for their FWD programs. Based on work carried out in this synthesis, the following future activities are suggested: • Network-level FWD data collection could be more stan- dardized as SHAs implement FWD testing and data analysis into their pavement management systems. • FWD data, along with the international roughness index and visual inspections, could be developed into a comprehensive program for construction project acceptance. • The reference calibration method, as well as the various calibration, data analysis, and FWD operation software packages, should continue to be refined, especially as new technologies become available. • FWD data analytical software creators should provide their product to the open-source development com- munity to expedite software development, increase peer review, develop algorithm standardization, and increase user acceptance. They should incorporate the Pavement Deflection Data Exchange file format as a main input file format option for the FWD data analysis. • Traffic control guidelines for moving work zones, such as FWD field activities, should be developed. • The collection and use of time history data should be investigated. The following future synthesis topic was proposed by the panel members of this study. Synthesis of FWD Testing Pro- tocols: The purpose for collecting FWD data has a major influence on the SHA’s pavement testing protocol. This pro- posed synthesis of SHA practices for FWD testing could pro- vide information needed to support guidelines that advance SHA data collection practices. Information needed to quan- tify and document the various FWD data collection practices should include, but not be limited to, the following: • Purpose of the FWD Testing and the Data Analysis Requirements, which may also be applied in catego- ries by pavement type such as hot mix asphalt (HMA), portland cement concrete (PCC), and composite (HMA over PCC) pavements: Falling weight deflectometers FWDs have been in use since the 1980s and over time have become the predominant pave- ment deflection measurement device. Interpretation of FWD data helps state highway agencies SHAs evaluate the struc- tural capacity of pavements for research, design, rehabilita- tion, and pavement management purposes. The number of FWDs in use and the importance of their role in pavement engineering practice are expected to rise as agencies move toward mechanistically based pavement design. Based on work carried out in this synthesis, the following conclusions can be made: • SHAs are currently using 82 FWDs. Most were manu- factured by Dynatest, but Carl Bro, JILS, and KUAB were also represented. • Most SHAs are currently following FWD guidelines of their own creation rather than the Long Term Pavement Performance (LTPP) guidelines. • Although most SHAs do not have written FWD maintenance plans, maintenance activities are being performed. • The 1994 Strategic Highway Research Program/ LTPP FWD reference calibration procedure has been replaced by a newly developed 2007 FHWA calibration procedure, which has been adopted by FHWA/LTPP Regional Calibration Centers and several independent calibration facilities. • Of the SHAs surveyed, 55% review a written equip- ment inspection checklist before departing for testing and the same percentage follow a written warm-up procedure. • Despite accident prevention measures such as traffic controls, 29% of survey respondents reported acci- dents occurring within the past five years during FWD testing operations. • There is no standard for data storage time among SHAs. The survey indicated that 89% of survey respondents keep raw FWD field data for more than five years and 84% keep these data indefinitely. • Among SHAs with an FWD program, an average of 2,194 lane-km (1,363 lane-mi)—with a median of 644 lane-km (400 lane-miles)—are tested annually. Additionally, 187 full-time employees work for these programs. CHAPTER TEN concLusions

38 For each of the levels of testing (project, network, and research), the testing protocol for specific analysis may require separation by pavement categories. The testing pro- tocol’s purpose may not always apply to a different pavement type or to another level of testing. • Data Collection Methodologies for HMA Pavements − Equipment check guidelines (e.g., preparation, field, and return checks) − Testing protocol specifying load levels, load sequencing, data to record, and data collection pat- tern (e.g., HMA pavement rehabilitation/overlay design) − Auxiliary data collection [e.g., cores, ground pen- etrating radar (GPR), dynamic cone penetrometer (DCP), and temperature vs. depth] − Safety considerations (e.g., traffic control) • Data Collection Methodologies for PCC Pavements − Equipment check guidelines (e.g., preparation, field, and return checks) − Testing protocol specifying load levels, load sequencing, data to record, and data collection pattern (e.g., PCC pavement rehabilitation/overlay design) − Auxiliary data collection (e.g., cores, GPR, DCP, and temperature vs. depth) − Safety considerations (e.g., traffic control) • Data Collection Methodologies for Composite Pavements − Equipment check guidelines (e.g., preparation, field, and return checks) − Testing protocol specifying load levels, load sequencing, data to record, and data collection pat- tern (e.g., composite pavement rehabilitation/over- lay design) − Auxiliary data collection (e.g., cores, GPR, DCP, and temperature vs. depth) − Safety considerations (e.g., traffic control) • Data Collection Methodologies for Specific Analytical Techniques − Equipment check guidelines (e.g., preparation, field, and return checks) − Testing protocol specifying load levels, load sequenc- ing, data to record, and data collection pattern (e.g., back-calculation analysis and Mechanistic– Empirical Pavement Design Guide requirements) − Auxiliary data collection (e.g., cores, GPR, DCP, and temperature vs. depth) − Safety considerations (e.g., traffic control) − Project-level requirements − Network-level requirements − Research-level requirements − Why is the LTPP testing protocol not applicable (e.g., was it too rigorous of a research-level protocol and not needed for design purposes)? − Are the SHAs continuing to use existing testing protocols or developing new versions? − What are the SHA specified testing protocols for project level, network level, or research level (e.g., specific HMA, PCC, or composite pavement testing for evaluation of pavement performance, pavement management, forensic investigation, and overlay design)? − What are the SHA-specified testing protocols for specific data analysis techniques (e.g., back-calcu- lation, load transfer, and void detection)? • FWD and Auxiliary Equipment Requirements − Pavement load levels and load sequencing capabilities − Deflection sensor configuration (i.e., number of sen- sors and spacing) − Data file management, file formats, onboard error checking, data quality control methods, and file storage/transfer capabilities − Auxiliary data collection equipment needed for analysis (e.g., temperature data, global position- ing system data, distance measurement instrument data, etc.) • FWD Equipment Calibration and Maintenance Requirements − SHA requirement (e.g., frequency) − SHA procedure for FWD calibration certification and verification − SHA procedure for FWD maintenance record check (e.g., in-vehicle documentation) • Personnel Qualification and Training Records − SHA requirement for FWD operator qualifications − SHA procedure for FWD operator training record verification − Other record verification procedures

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TRB’s National Cooperative Highway Research Program (NCHRP) Synthesis 381: Falling Weight Deflectometer Usage examines usage by state departments of transport of the falling weight deflectometer (FWD) to measure pavement deflections in response to a stationary dynamic load, similar to a passing wheel load.

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