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Federal Highway Administration Research and Technology
Coordinating, Developing, and Delivering Highway Transportation Innovations

This report is an archived publication and may contain dated technical, contact, and link information
Publication Number: FHWA-RD-01-165
Date: March 2002

Chapter 4. Conclusions

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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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