Engineers Trust Superior’s Foundations

We’ve been creating strong foundations from the start, and post-tension cables are no exception. 

Here’s How Post Tensioned Foundations Work:

 

First, high-grade steel cables in poly sleeves are placed in a grid pattern according to precisely engineered specifications inside the slab. Then, after the foundation is poured, the cables are hydraulically tightened to required pressures to secure the foundation into one mass – eliminating the problems commonly associated with expansive soils here in Mississippi.

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There are a wide variety of reasons for utilizing post tension slabs versus conventional slabs. Post tension slabs are a form of pre-stressed slabs which means they are compressed prior to use so that the slabs are able to bear weight or service loads beyond their own natural weight. This is accomplished by pre-stressing cables which run throughout the slab and by compressing the concrete. Thus, the cables and slab are able to handle over 33,000 pounds of tension, making the slab stronger and less likely to crack. The purpose behind this is to avoid the common problems which are associated with typical concrete slab structures. This technique has been around for over 30 years and is the industry standard for pouring slabs in areas with expansive soils. 

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Post Tension Slab Advantages

– Reduction of shrinkage and cracking in slabs which results in the use of fewer (or even no) joints.

– If cracks do form they are minimal and are held together.

– It enables the possibility of building on a wider variety of soil types which are typically difficult to build slabs on and prevents the associated problems with traditional slab-on-grade.

– The slab concrete can be thinner and the distance between cables wider.

– If a foundation shifts, post tension cables will help prevent the foundation from breaking, which makes repair work much easier.

For new builds, we also recommend installing helical piers to ensure you never have to call us for foundation repair.

Ever.

Post Tension Cables & Rebar

Understanding the method utilized in post tensioning, as well as how the cables are set up helps clarify why post tensioning is so effective and is beneficial over common rebar. The cables (steel bands wrapped together) are set up within the concrete in a grid pattern (usually about 48 inches apart) and are called tendons when they are covered by a plastic outer shell and held by an anchorage. The plastic duct, or outer plastic shell, prevents corrosion and allows the cables to be flexible and move as necessary. The anchorage enables the cable to be pulled during tensioning, while also securing the tendon in place within the concrete. Once the tendons are tensioned (pulled or stressed), they are grouted in the slab.

Benefits of Post-Tension Slabs and Difficult Soil Conditions

Don’t want to have post tension slab failure? Post tension slabs are particularly beneficial on expansive soils and organic soils which are found in the South and Southeastern United States. The expansive, or Yazoo clay soils such as those present here in Mississippi, shrink and swell based on the amount of water content in the soil which makes traditional slab-on-grade slabs crack and become weaker over time. Post-tensioning slabs solve this issue because they are stronger and able to bear the shrink and swell cycle without major cracking. This is particularly helpful when there is a wide variance in the amount of water in the soil.

Avoiding Post-Tension Errors Which Result in Cracking

There are several post tension slab problems which can be avoided. In order to ensure that the post-tension slab used will have the best chance of avoiding cracking, as well as ensuring the longevity of post tension slabs, there are several possible errors to consider. Avoiding post tension errors result in the best chance of a crack-free post tension foundation.

Installing the Slip Sheet Incorrectly

The slip sheet must be installed directly under the slab (between it and the bearing surface) which allows the slab to move smoothly across the ground. Incorrect placement can result in the inability of the slab to close cracks during curing, as well as forcing the slab to exert more force to move and increasing friction.

Inconsistent Slab Thickness

Level and compact the soil and gravel prior to any concrete layering. Slab thickness that varies leads to cracks because it causes the slab to resist movement. If the slab thickness is changing, such as around beams, the change should be gradual and smooth.

Curing Tendons Late

Ensure that the tendons are cured on time in order to avoid the slab from becoming too strong to close up small cracks during the curing process. This should be done within the first 4-10 days as then the concrete will be at the appropriate strength level, barring weather issues.

Call us today for a personalized plan to secure your concrete foundation!

What Our Customers Are Saying

“They just do an incredible job... when buyers look through and see the house has had foundation work, and they see that Superior Foundation did they work, they know they can trust that it was done right” - Keith Kinkade

What Our Customers Are Saying

“Being a contractor in the Jackson Metro area, I see foundation problems everywhere. My personal home was built in 1968, before they had the technology that Superior Foundation has, and I knew to call them when I knew it was time to repair my foundation.”-Chris Bond

What Our Customers Are Saying

“When I planned to move from an older home with foundation issues to a new build, I asked Superior to design a helical pier system for my new foundation. They stand behind their product and service, and now I’ll never have to call another foundation repair company.” -Chris Bond

What Our Customers Are Saying

“Out of everyone that I could recommend for foundation repair work, Superior is always going to do the right thing for my clients. My reputation matters to me, so that’s why I rely on them to get the job done right.” - Walt Bowie