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steel rebar and post tension cable foundations

As a continuation of my blog Foundations of Quality, I wanted to expand a bit.  The foundation is perhaps the most important part of your new home. Given the unstable nature of Texas soils, you can be sure your foundation will shift and move as the soil underneath expands and contracts- this is normal.

The key is to make sure the foundation moves as a single unit, otherwise the walls anchored to it could crack and separate. To ensure a foundation can withstand uneven forces from the soil, it is built using reinforced concrete. The reinforcement is provided by either embedding steel rebar (reinforcement bar) or using tensioned steel cables. In theory, both methods should yield acceptable results. In practice, however, a post tension foundation is much more susceptible to human errors that can occur during the construction process.

To understand why, it helps to know a little bit about how foundations are built. First, form boards are set in place. This creates a giant “sandbox” into which concrete is poured. Before this happens, steel reinforcement must be added, because concrete alone lacks the tensile strength to withstand extreme forces from unstable Texas soils.

Reinforcement with Post Tension Cables

In the case of a post tension slab, steel cables are laid out in grid fashion inside the forms. The foundation gains tensile strength when the cables are tightened after the slab has been cast. The tricky part comes when concrete is poured into the forms. Great care must be taken to ensure the cables remain perfectly straight during the pour. Unfortunately, concrete is extremely heavy, and can easily displace the cables as it shoots into the forms. If the cables are shifted from their designed position, they won’t perform the way they were supposed to. In fact, the tensioning (tightening) process can actually weaken the concrete if a cable is misaligned.

Reinforcement with Steel Rebar

The more conservative/fail proof approach is to set engineered steel rebar inside the forms. With rebar, there’s nothing to tighten. Steel rebar doesn’t move the way cables can when concrete is poured into the forms. In other words, a rebar foundation is inherently more forgiving of the typical conditions experienced at a construction site.

Diamante Custom Homes believes concrete reinforced with steel rebar provides a superior foundation system. Yes, it costs more, but we would rather spend a little more on the most important part of your new home, rather than run the risk of future problems- we are sure you would agree!

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