The project designated "Concrete Durability Studies" comprises case studies of unusual durability, either in kind or extent. These case studies are directed toward situations in which appearances suggest materials or construction rather than structural causes. Included in this project as Case Study #3 is an occurrence of severe scaling and pattern cracking in bridge decks of an interstate project: one deck showed severe scaling after only one winter's exposure. Because the aggregate used in these decks was from a source known to contain potentially reactive carbonate rocks, the combination of scaling and chemical reaction was investigated as a likely dual cause. Concurrently with this case study, an extensive study of potentially reactive carbonate aggregates was in progress. One aspect of that study was an evaluation of field manifestations of the alkali-carbonate reaction based upon field surveys of bridge decks in the region of the severely scaled deck. Thus this report, while primarily a case study of the Concrete Durability Study, is also considered to be a report of field performance for the project "Potentially Reactive Carbonate Rocks." The field survey for evidences of carbonate reactivity covers more decks than are treated in this report so that this report serves as a partial Progress Report #6 for that project.