Very Thin Concrete Repairs in Spillway Tunnels
* What are the best materials to use to repair shallow damage (less than one-inch deep) to concrete in dam spillways that are susceptible to cavitation?
* What are the best materials to use to repair shallow concrete damage when the area to be repaired can not be completely dried out?
* What are the best repair materials to use to repair shallow concrete damage when the repair must be performed where the surface temperatures are cold (i.e., 40 to 50 degrees)?
Need and Benefit
Concrete flow surfaces exposed to high velocity water flows (e.g., in dam spillway tunnels) need to be very smooth and flat to ensure that damage as a result of cavitation does not occur. If very smooth concrete surfaces do not exist, the concrete surfaces can quickly deteriorate as a result of the highly destructive effects of cavitation that can occur in high head, high velocity flows.
Concrete surfaces often become rough as the concrete ages through a variety of deterioration mechanisms, or they may have surface defects as a result of poor construction practices. The standard repair methods in Reclamation's M-47 Standard Specification for Repair of Concrete typically calls for excavation of the damaged concrete to a depth of 1 ½-inches, or the use of polymer concrete for shallower repairs. Both options have potential drawbacks. By increasing the depth of the surface defect to accommodate cementitious repairs, the chances of making the situation worse increases if the repair fails. Conversely, many polymer repair materials are not suitable for placement on wet or damp surfaces and/or lose strength once they become submerged. Depending on the materials selected for repair, systems can have problems developing strength in low temperatures. In addition, many times it is desirable to place structures back in service as soon as possible, so having materials that cure quickly is an important benefit. This further limits the choice of materials that could traditionally be used.
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