The Art of Slot Cutting

Imagine slicing a concrete dam like a piece of birthday cake. It seems an unlikely undertaking, but Bluegrass Companies technicians have been doing it for years. Their technique is simple but very difficult, rotate a loop of cable strung with diamond embedded beads through the structure — essentially, like using a loop of fishing line to cut a cake.

The industry term of this technique is “slot cutting” and is employed to create expansion joints in dams afflicted with compression stresses due to concrete swelling. Alkali Aggregate Reaction, or AAR, is a chemical reaction in concrete created where the aggregate has a high silicon dioxide content. The southeast USA is one such region, and dams in that area require periodic slot cuts to avoid cracking, leakage, and interference with mechanical components such as gates and turbines. The time intervals depend on the AAR specifics of each structure, but 10 years is an average.

While the concept is reasonably simple, the art of slot cutting is complicated by a laundry list of variables specific to each project, such as:

Structural Dimension

Dams are BIG. For example, Hiwassee Dam is 307 ft tall, and 1376 ft in length. That requires a lot of diamond wire and reliable equipment to keep it rotating and precisely on track.

Concrete Composition

Not all dam concrete is equal.

Mechanical Components

Hydroelectric dams are not solid pieces of concrete reinforced with rebar. Inside the dam are conduits, pipes, gates etc which require special handling.

Environmental Circumstances

Weather, road traffic, irrigation, and power sources all have to be factored in to the process.

Regulatory Requirements

Cutting concrete creates slurry, and slurry is a problem. Imagine if every crumb of the birthday cake was considered toxic and required special disposal techniques. Containing slurry and preventing that or any other potential contaminants from entering either the reservoir above the dam or the river below is a significant factor in slot cutting.