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Shotcrete done right: failed repair teaches lessons about shotcrete.

Article Excerpt
The concrete dam that created Dix Reservoir in Barre, Vt., was constructed in 1950. Over decades of service, erosion and deterioration became increasingly apparent on the dam's spillway and training walls. Water began seeping through fine cracks and other damaged areas. In 1978, when the U.S. Army Corps of Engineers first conducted a condition survey of the training walls and spillway, they discovered a loss of concrete section and exposed reinforcing steel.

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Years later, in conjunction with the building of a new water filtration plant in 1995, the city set out to repair and resurface the spillway and training walls. As city engineer and director of public works, I was tasked with hiring an engineering consultant to design and specify the repairs, and to oversee and inspect the construction. Unfortunately, we hired a consultant who had limited experience and expertise with the specific materials planned for this project. As a result, we paid for a generally ineffective repair project and endured a lengthy process to reach a financial settlement. Along the way, however, we learned valuable lessons about hiring a consultant, ensuring quality construction, and repairing concrete.

The original repair design called for removing the outer 4 inches of concrete from the spillway and training walls, then cleaning out and pressure-grouting visible cracks. The contract called for the application of a bonding agent to the sealed surface of existing concrete, and the installation of horizontal and vertical...

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