Concrete cover is defined as the distance between the outermost surface of embedded reinforcement and the closest outer surface of the concrete. For flat or single plane formwork, providing the proper cover is fairly straightforward considering the appropriate tolerances. The issue becomes more complex when considering architectural rustication, reveals, or drip grooves on the concrete surface. Architectural formliners further complicate the issue because of the multiple amplitudes likely present on the form surface. In all cases, the concrete cover to the embedded reinforcing steel must be properly considered on the concrete surface. This article examines these concrete cover issues as they affect some basic structural elements.

When completed in 1977, the Koror-Babeldaob Bridge in Palau held the world-record span of 241 m (790 ft) for segmentally erected prestressed concrete box girders. Within 18 years, its total deflection, compared with the design camber, reached 1.61 m (5.3 ft.) and the prestress loss was measured as 50%. In 1996, the bridge was retrofitted, but three months later the bridge suddenly collapsed. It wasn’t until 2008 that the technical data necessary for complete analysis were released. This article shows that the existing models for creep and shrinkage prediction grossly underestimate the deflections and prestress loss, although one model, model B3, does so much less than the others and, if calibrated by the 10-year tests of Brooks, matches the observations.