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37
CHAPTER TEN
Conclusions
Falling weight deflectometers FWDs have been in use since · From the survey results, the responding SHAs' expen-
the 1980s and over time have become the predominant pave- ditures varied widely (ranging from no program to
ment deflection measurement device. Interpretation of FWD $850,000 annually) for their FWD programs.
data helps state highway agencies SHAs evaluate the struc-
tural capacity of pavements for research, design, rehabilita- Based on work carried out in this synthesis, the following
tion, and pavement management purposes. The number of future activities are suggested:
FWDs in use and the importance of their role in pavement
engineering practice are expected to rise as agencies move · Network-level FWD data collection could be more stan-
toward mechanistically based pavement design. Based on dardized as SHAs implement FWD testing and data
work carried out in this synthesis, the following conclusions analysis into their pavement management systems.
can be made: · FWD data, along with the international roughness
index and visual inspections, could be developed into
· SHAs are currently using 82 FWDs. Most were manu- a comprehensive program for construction project
factured by Dynatest, but Carl Bro, JILS, and KUAB acceptance.
were also represented. · The reference calibration method, as well as the various
· Most SHAs are currently following FWD guidelines of calibration, data analysis, and FWD operation software
their own creation rather than the Long Term Pavement packages, should continue to be refined, especially as
Performance (LTPP) guidelines. new technologies become available.
· Although most SHAs do not have written FWD · FWD data analytical software creators should provide
maintenance plans, maintenance activities are being their product to the open-source development com-
performed. munity to expedite software development, increase
· The 1994 Strategic Highway Research Program/ peer review, develop algorithm standardization, and
LTPP FWD reference calibration procedure has been increase user acceptance. They should incorporate
replaced by a newly developed 2007 FHWA calibration the Pavement Deflection Data Exchange file format
procedure, which has been adopted by FHWA/LTPP as a main input file format option for the FWD data
Regional Calibration Centers and several independent analysis.
calibration facilities. · Traffic control guidelines for moving work zones, such
· Of the SHAs surveyed, 55% review a written equip- as FWD field activities, should be developed.
ment inspection checklist before departing for testing · The collection and use of time history data should be
and the same percentage follow a written warm-up investigated.
procedure.
· Despite accident prevention measures such as traffic The following future synthesis topic was proposed by the
controls, 29% of survey respondents reported acci- panel members of this study. Synthesis of FWD Testing Pro-
dents occurring within the past five years during FWD tocols: The purpose for collecting FWD data has a major
testing operations. influence on the SHA's pavement testing protocol. This pro-
· There is no standard for data storage time among SHAs. posed synthesis of SHA practices for FWD testing could pro-
The survey indicated that 89% of survey respondents vide information needed to support guidelines that advance
keep raw FWD field data for more than five years and SHA data collection practices. Information needed to quan-
84% keep these data indefinitely. tify and document the various FWD data collection practices
· Among SHAs with an FWD program, an average of should include, but not be limited to, the following:
2,194 lane-km (1,363 lane-mi)--with a median of
644 lane-km (400 lane-miles)--are tested annually. · Purpose of the FWD Testing and the Data Analysis
Additionally, 187 full-time employees work for these Requirements, which may also be applied in catego-
programs. ries by pavement type such as hot mix asphalt (HMA),
portland cement concrete (PCC), and composite (HMA
over PCC) pavements:
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- Project-level requirements For each of the levels of testing (project, network, and
- Network-level requirements research), the testing protocol for specific analysis may
- Research-level requirements require separation by pavement categories. The testing pro-
- Why is the LTPP testing protocol not applicable tocol's purpose may not always apply to a different pavement
(e.g., was it too rigorous of a research-level protocol type or to another level of testing.
and not needed for design purposes)?
- Are the SHAs continuing to use existing testing · Data Collection Methodologies for HMA Pavements
protocols or developing new versions? - Equipment check guidelines (e.g., preparation, field,
- What are the SHA specified testing protocols for and return checks)
project level, network level, or research level (e.g., - Testing protocol specifying load levels, load
specific HMA, PCC, or composite pavement testing sequencing, data to record, and data collection pat-
for evaluation of pavement performance, pavement tern (e.g., HMA pavement rehabilitation/overlay
management, forensic investigation, and overlay design)
design)? - Auxiliary data collection [e.g., cores, ground pen-
- What are the SHA-specified testing protocols for etrating radar (GPR), dynamic cone penetrometer
specific data analysis techniques (e.g., back-calcu- (DCP), and temperature vs. depth]
lation, load transfer, and void detection)? - Safety considerations (e.g., traffic control)
· FWD and Auxiliary Equipment Requirements · Data Collection Methodologies for PCC Pavements
- Pavement load levels and load sequencing - Equipment check guidelines (e.g., preparation, field,
capabilities and return checks)
- Deflection sensor configuration (i.e., number of sen- - Testing protocol specifying load levels, load
sors and spacing) sequencing, data to record, and data collection
- Data file management, file formats, onboard error pattern (e.g., PCC pavement rehabilitation/overlay
checking, data quality control methods, and file design)
storage/transfer capabilities - Auxiliary data collection (e.g., cores, GPR, DCP,
- Auxiliary data collection equipment needed for and temperature vs. depth)
analysis (e.g., temperature data, global position- - Safety considerations (e.g., traffic control)
ing system data, distance measurement instrument · Data Collection Methodologies for Composite
data, etc.) Pavements
· FWD Equipment Calibration and Maintenance - Equipment check guidelines (e.g., preparation, field,
Requirements and return checks)
- SHA requirement (e.g., frequency) - Testing protocol specifying load levels, load
- SHA procedure for FWD calibration certification sequencing, data to record, and data collection pat-
and verification tern (e.g., composite pavement rehabilitation/over-
- SHA procedure for FWD maintenance record check lay design)
(e.g., in-vehicle documentation) - Auxiliary data collection (e.g., cores, GPR, DCP,
· Personnel Qualification and Training Records and temperature vs. depth)
- SHA requirement for FWD operator qualifications - Safety considerations (e.g., traffic control)
- SHA procedure for FWD operator training record · Data Collection Methodologies for Specific Analytical
verification Techniques
- Other record verification procedures - 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)
