L. L. Sutter, K. R. Peterson, and T. J. Van Dam, Transportation Materials Research Center, 1400 Townsend Drive, Houghton, MI 49931-1295. K. Smith, Applied Pavement Technology, Inc., 3001 Research Road, Suite C, Champaign, IL 61822. ceives approximately 660 mm of annual precipitation, and has a freez- ing index of 1,030 °C-days (where °C-days is equivalent to the num- ber of hours with an air temperature below °C times the temperature at each hour, expressed in days). The location extended from Mileposts 64.2 to 65.0 in both the north- bound and southbound lanes. It is a four-lane divided roadway sepa- rated by a concrete median; some sections also include an additional lane for left-turning traffic. The pavement, which was constructed in 1989, consists of a 200-mm jointed plain concrete pavement with a 75-mm granular base and a 305-mm granular subbase. The trans- verse joints are skewed and have a variable joint spacing pattern of 4.0 m-4.6 m-5.2 m-4.6 m. Load transfer is provided by aggregate inter- lock only; no additional load-transfer devices have been used. The longitudinal joints are not sealed. A 2.4-m-wide asphalt cement shoulder is placed at the outer edge; no inside shoulder exists because of the concrete median. Although the design and construction details are basically the same over the entire project length, the initial investigation revealed that the southbound lanes were in better condition than the north- bound lanes. The only construction variation observed between the two directions was the transverse joint sealant: a silicone sealant was used on the northbound lanes, and a hot-pour sealant was used on the southbound lanes. Thus two sections were selected for survey, one in each direction. Section 001 was located in the northbound outer lane, and Section 002 was located in the southbound outer lane. Both sections were constructed at grade. Section 001 exhibited worse performance, and most of the dete- rioration was limited to the transverse joints. Joint spalling and bitu- minous patching were predominantly along the transverse joints. The spalling appeared to be related to materials and had progressed to medium severity in most cases. In some cases, the surface had scaled off to expose aggregate particles. Every transverse joint was patched over a portion of its length to help address the spalling prob- lem. In addition, maintenance forces on hand during the surveys indicated that removal of the material during the patching operation often extended through the entire depth of the slab. The only other distress noted was a longitudinal crack that extended along the length of one slab. Some typical distress manifestations are shown in Figure 1. Section 002 was in better overall condition than Section 001 but still exhibited some deterioration at the transverse joints. Medium- severity spalling was observed at 6 of the 33 joints (18%) and bitu- minous patches were observed at 12 of the 33 joints (36%), but the deterioration at the affected joints was less severe than that observed on Section 001. Faulting could be measured on this section and aver- aged 2.0 and 1.7 mm at 0.30 and 0.75 m, respectively, from the outer 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 under- standing 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 con- crete 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. To make concrete pavements that are durable, attention must be paid to all aspects of the concrete production, from materials selection and design of the concrete mix to batching, placing, and curing. Perform- ing any of these aspects incorrectly can cause performance problems, including premature failure that necessitates repair or replacement. Often when examining concrete durability problems, it is difficult to attribute the distresses observed to any one cause. A recent FHWA project titled Detection, Analysis, and Treatment of Materials- Related Distress in Concrete Pavements involved the development of a set of guidelines to assist field engineers in the identification and treatment of materials-related distress (MRD) in concrete pave- ments (1–3 ). As a result of applying these guidelines, not only MRD but also distress stemming from other causes can be identified. As part of the research for developing these guidelines, several dis- tressed pavements were cored and examined to determine the cause of distress. The results of applying these guidelines (1, 2) to a con- crete pavement exhibiting durability problems are presented. This case study has been published in more detail in the final report for the FHWA project (4 ). BACKGROUND The research location, on Trunk Highway 65 in downtown Mora, Min- nesota, was experiencing severe durability problems concentrated at the transverse joints. This area is in a wet-freeze climatic region, re- Using Epifluorescence Optical Microscopy to Identify Causes of Concrete Distress Case Study Lawrence L. Sutter, Karl R. Peterson, Thomas J. Van Dam, and Kurt Smith 22 ■ Transportation Research Record 1798 Paper No. 02- 3201