Post-Tensioned Concrete?

Question

A family member's brand-new house has the phrase, "Made with Post-Tensioned Concrete, Do NOT Drill!," stamped into the Garage floor in several places.

I saw a Discovery Channel show about Bridges built with the cables "Post-Tensioned," but how would this be done in a Garage Slab?

That is, can someone give me a summary of how, and why, a Garage slab would be build this way?

The property is located in Arizona, just north of Phoenix.

Answer 1

Post-Tensioned reinforcing has been used for many decades in bridges, elevated slabs (parking garages and residential or commercial buildings), residential foundations, walls, and columns. The use of post-tensioned reinforcing can result in thinner concrete sections, longer spans between supports, stiffer walls to resist lateral loads, and stiffer foundations to resist the effects of shrinking and swelling soils. The additional advantage of putting the concrete into compression can be used to construct slabs and walls that have fewer visible cracks that can allow the passage of moisture and termites.

The contractor and builder should make sure the property owner is aware of the necessity of ongoing attention to the foundation and soil. This is particularly important during the first 10 years after foundation construction because this is when the most severe adjustments between the environment and new construction occur, although the interaction continues throughout the life of the structure.

For more information on this technology, or to obtain a copy of the Construction and Maintenance Procedures Manual for Post-Tensioned Slab-on-Ground Construction, visit the PTI Web site, www.post-tensioning.org, or call 602-870-7540.

Answer 2

Never seen it done for residential slabs. But probably has to do witht he soil conditions making it necessary for the slab to be able to carry a bending load, span over either voids or soft soil.

I've also heard of this where soils contain expansive clays. In those cases the floor slab is designed to carry the building between piers and is poured on top of carboard. After the cardboard decays away. The floor is kept away from the clay by the void.

Better not drill in it.

Answer 3

As you already had seen on TV how post tension method of pre-stressing of concrete is used in making of structure. Concrete is very weak in tension comparing to its compressive strength. Due to compressive stress developed by tension in cable (tendon), pre-stressed concrete structure (means the concrete structure which has been stressed before the actual load applied on it) is able to bear more tensile force than a similar (size and quality) normal concrete structure.
Because these kind of structures can be pre casted in factory and fabricated at site, they allow faster construction speed. This can be of smaller size section with thin high-tension cables for short span and lightly loaded structure. Because of its better flextural characteristics they are better earthquake resistant. The can be used in various kinds of structure including residential structures.