A two-man crew from Precision Construction and Concrete returns after the new tennis courts’ concrete pad is poured for the post-tension process. Noel Lopez (right) uses a hydraulic jack to pull the cables while Oscar Martinez monitors the pressure.
Post tensioning lengthens tennis court construction time but promises years without cracks
What’s taking the new Webb City High School tennis court complex so long to get finished?
Basically, steps are being taken now to make them last longer.
The School Board took a more expensive option offered by the contractor, Precision Construction and Concrete, of Lee’s Summit, to have the concrete slab post tensioned. With the extra expense comes a 10-year warranty.
The post tension technique uses reinforced cables to tighten the concrete as it cures to prevent it from settling and heaving.
In the case of the Webb City tennis courts, cables were set in the concrete on the south and west ends. Attached to them and extending to the opposides were cables enclosed in plastic so they could be pulled through the concrete as it dried.
Those cables in plastic are tightened in stages as the concrete cures.
In mid-October, Oscar Martinez and Noel Lopez returned to the site to perform the post tension process.
All concrete is going to crack by its own weight, Martinez explained. But concrete that has been post tensioned won’t separate. “It might crack, but you’ll never see it,” said Martinez, because it won’t have the space to separate.
They used a hydraulic jack to apply 4,500 pounds of pressure as each exposed cable was pulled.
“It can be dangerous if not done right,” Martinez said.
After the final pull, the exposed cables will be fastened, cut and sealed to keep out moisture.
The surface of the slab was intentionally left somewhat rough with broom strokes to give the paint a better surface to stick to. An extended cure time for the concrete is necessary before the special paint can be applied.
The process is supposed to require less maintenance and less frequent painting.
There is a lot of information online about post tensioning. Here’s a video explaining a process similar to the one used on the high school tennis courts.
Oscar Martinez measures the cable length after tensoning. When the process is finished, the cables will be cut off and the openings will be sealed to keep out water.