Using Epifluorescence Optical Microscopy to Identify Causes of Concrete Distress: Case Study

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Using Epifluorescence Optical Microscopy to Identify Causes of Concrete Distress: Case Study

Sutter, Lawrence L. / Peterson, Karl R. / Van Dam, Thomas J. / Smith, Kurt

Materials-related distress (MRD) has affected many portland cement concrete pavements. Identifying the specific cause of MRD is not always possible, but with the use of appropriate techniques and a diagnostic approach, the cause can be determined in many cases. In a case studied as part of an FHWA project titled Detection, Analysis, and Treatment of Materials-Related Distress in Concrete Pavements, apparent MRDs were identified. In one case study, determination of the effective water-to-cement ratio (w/c) by epifluorescence microscopy was the key to understanding the cause of distress. The effective w/c, which may not be exact for a given concrete on an absolute basis, was used to compare two concrete microstructures on a relative basis. Stereo-optical microscopy, petrographic optical microscopy, and scanning electron microscopy were also used to identify the MRD diagnostic features present in the distressed concrete. As a result of this analysis, evidence of paste freeze–thaw and deicer attack was identified, but the principal cause of the distress probably was a high w/c in the distressed concrete.