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Publication Number: FHWA-RD-01-165
Date: March 2002
This volume of the final report, Volume 3: Case Studies, has presented six case studies in which the developed guidelines were applied. In the primary case studies, the guidelines were found to be very useful in directing and organizing the laboratory analysis and in interpreting the data with the purpose of making a diagnosis. One of the two secondary case studies was used to illustrate how the guidelines functioned when analyzing a pavement section that turned out not to have an MRD at work. The other secondary case study presented an example when the guidelines were unable to be used to draw meaningful conclusions.
A major conclusion of this effort is that, when diagnosing a MRD using laboratory methods, data acquisition and interpretation must be performed simultaneously. As the data from a first set of tests are analyzed, new questions are posed requiring interpretation of that first set of data before a second set of analyses can be applied. Then, additional analyses are performed, often using different techniques, and the process is repeated. After the new results are interpreted, a new battery of tests may be required. As the laboratory/interpretation procedure continues, a diagnosis begins to form and the analyst must use caution not to stop at the first MRD identified. Final diagnosis comes after all necessary laboratory tests are completed and the results are summarized. The developed guidelines provide a systematic way of approaching this problem.
The diagnostic flowcharts frame the questions that should be asked about the
concrete, and the laboratory methods recommended in the guidelines provide the
means of answering those questions. How the analyst performs the work required
for each analysis is up to the individual. In general, the work tends to be
done following the process shown in figure II-1 in the second guideline where
specific techniques are applied in sequence and each technique allows the analyst
to progress incrementally through the flowcharts, answering a few more questions
each time. How far the analyst proceeds through figure II-1 before completing
all five diagnostic flowcharts varies. In general, all cases of MRD analyzed
require visual inspection and stereo optical microscopy and most progress to
the level of needing petrographic optical microscopy and/or SEM analysis. As
a result of applying the diagnostic flowcharts, a number of possible MRDs can
be identified. Then, referring to the diagnostic tables, the list of diagnostic
features identified in the laboratory can be compared to common diagnostic features
for the various MRD types. All diagnostic features listed are rarely all present
at one time for a given MRD. The analyst has to weight the significance of each
diagnostic feature relative to the magnitude, extent, and nature of the observed
MRD. It is this last step that results in final diagnosis and requires objectivity
and sound data to perform.
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Topics: research, infrastructure, pavements and materials
Keywords: research, infrastructure, pavements and materials, concrete materials; concrete pavements; concrete durability; concrete distress; concrete evaluation; petrographic examination; concrete mixture design.
TRT Terms: research, facilities, transportation, highway facilities, roads, parts of roads, pavements, Pavements, Concrete--United States--Testing, Pavements, Concrete--United States--Maintenance and repair, Concrete pavements, Portland cement concrete, Pavement distress