Deck Slab Repaired by Fibrous Concrete Overlay

The concrete deck on the visitors' overlook facility at Libby Dam became badly cracked and in need of repair. It was decided to overlay the existing surface with 0.75-in. to 2-in. (18 mm to 50 mm) of fibrous concrete. Cracks in the original surface and some expansion joints were overlain without special treatment. Union workers with no special training used standard tools and techniques to successfully place the overlay. By magnesium floating the surface they obtained excellent /0.125-in. per 10-ft (3 mm per 3 m)/ grade control and produced a skid resistant surface with virtually all fibers covered. A mix design procedure based on workability was developed for this placement. The simple procedure is available from the U.S. Army Corps of Engineers, Walla Walla District, and is good for mixes from mortar to 0.75-in. (18 mm) aggregates. After a couple years of service an evaluation of the overlay shows 90% reduction in cracking, 100% reduction in water leakage through the surface, and essentially no rusting or evidence of fibers at the surface.