Is post tension concrete better than regular concrete?

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The early stages of the architectural process are a time to make large-scale decisions related to the building's form and structure. During this time, your design team may present different structural system options, discuss benefits and drawbacks, and make recommendations. 

One recommendation may be post-tensioned concrete. This method introduces tension to the concrete after curing to strengthen the structure, reduce the likelihood of cracks, and allow for thinner slabs. 

While this structural system offers many advantages, it can limit flexibility and complicate future modifications. We recommend considering your long-term goals and the potential for renovations and retrofits. 

To help you with your decision, this article will define post-tensioned concrete and outline its pros and cons. 

What is Post-Tensioned Concrete?

 

Post-tensioning is a method of reinforcing concrete by introducing tension after the concrete has achieved a specified strength. 

Tension is introduced through high-strength steel stands or bars, typically called tendons. During construction, these tendons are placed in forms before the concrete is poured. The tendons are then tensioned with hydraulic jacks after the concrete cures. 

While concrete works best under compression, steel works best under tension. Post-tensioning maximizes the use of each material for efficiency. It can be thought of as a 'sweet spot' that provides the strength of concrete and steel without overusing either one. 

Often, post-tensioned concrete works well for parking structures and high-rise commercial or residential developments. We have also seen this method used for tennis courts. 

In this situation, the tennis courts sat over an unstable site once occupied by a city dump. Post-tensioned concrete's strength prevented cracking or vibrating that would likely occur with a more traditional concrete system.  

Pros of Post-Tensioned Concrete

 

The most significant benefit of post-tensioned concrete is its strength. The combined performance of concrete and steel allows for thinner slabs and longer spans. 

Achieving the same strength with another structural system would require more columns and deeper beams. For this reason, post-tensioned concrete best aligns with structures where longer spans are desired, like parking structures.

Post-tensioning's ability to provide longer spans works well for parking garages. 

Post-tensioning also allows designers to decrease a building's floor-to-floor height'the vertical distance between the finished floors of two consecutive levels. Other systems require deeper beams and thicker slabs, increasing the distance between floors. 

As such, post-tensioning can reduce a building's overall height and lower costs for components like façade treatments. In short, post-tensioned concrete improves material efficiency, minimizes waste, and allows for more open interiors. It can help solve multiple challenges'from cost concerns to aesthetics and performance. 

Cons of Post-Tensioned Concrete

 

Although post-tensioned concrete offers many benefits, it can complicate future modifications to the building. Vertical penetrations must be planned during the design process due to the tendons, and after construction, you can only cut through these pre-planned areas. If you cut through the tendons, the structure loses its strength. 

With these limitations, post-tensioned concrete works best for buildings with stacked layouts, like residential construction and parking garages. Buildings requiring more flexibility, like healthcare facilities, may run into problems in the future. For this reason, some organizations'like the General Services Administration (GSA)'have rules against using post-tensioned concrete. 

Although post-tensioned concrete can be limiting, other structural systems present a degree of inflexibility. A more traditional concrete system requires more columns, which can also complicate modifications. You and your design team should discuss the potential for future changes to determine the right approach. 

At the same time, post-tensioned concrete can add complexity to construction. It requires precision and specialized knowledge, potentially limiting your options to a smaller set of contractors. 

Is Post-Tensioned Concrete Right for Your Project?

 

Post-tensioned concrete is a popular structural system for large-scale developments. Depending on your project type and goals, your architect may recommend it in the early stages of the design process. 

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Combining concrete and steel's strength, post-tensioning can reduce cracking and help achieve longer spans and lower floor-to-floor heights. It can also lower initial costs by improving efficiency and reducing building height. 

Despite the benefits, post-tensioned concrete is not ideal for every project. If you desire more flexibility, a more traditional concrete or steel structural system may be a better fit. 

For buildings with stacked layouts'like parking structures and residential developments'post-tensioned concrete may be the right solution. Learn more about these building types by reading about the rules of thumb for parking structure design and considerations for high-rise construction. 

Almost any construction project that involves large slabs of concrete is going to require some concrete reinforcement. That's a fact. But the way you go about reinforcing the concrete may not be as clear-cut. 

That's because there is more than one way to reinforce concrete. The two most common methods of concrete reinforcement are conventional slab reinforcement and post-tensioned slab on grade reinforcement. Which method is best for your project will depend on a number of factors, which we explore in depth below.

Tendon Systems is a leading provider of concrete reinforcement, construction and restoration services. To get help with your concrete construction project, reach out to us today. 

Post-Tensioned Slab on Grade

At Tendon Systems, we specialize in post-tensioned slab on grade reinforcement. That's because we believe post-tensioned slab on grade offers undeniable advantages over traditional concrete slab reinforcement.

How Post-Tensioning Works

Post-tensioning isn't something you can see in a slab on grade foundation with the naked eye. Instead, this term implies a process that was completed before the foundation had to bear its intended service loads.

Post-tensioning tendons are steel cables that are placed inside the foundation's mold form before the concrete is poured. The post-tensioning of the cables happens after the foundation's concrete is poured but before load stress is applied to the slab on grade foundation. Inside their plastic sleeves within the newly poured concrete, the cables are pulled tight and anchored to the slab on either side.

This is called 'post' tensioning because it happens after the concrete is poured, but it happens before the foundation has to bear any real weight.

Pros of Post-Tensioning

Post-tensioned slab on grade offers several key advantages. Chief among them is this type of slab's ability to withstand more pressure without cracking. This advantage comes from the fact that the interior cables are already placed under stress. That means the concrete is held tightly together, and the cables are contributing their reinforcing properties at all times.

The following are some other pros of post-tensioned slab on grade:

• Fewer joints. Post-tensioning prevents cracking from shrinkage, meaning it requires fewer joints. This reduces costs.
• Thinner slabs. By adding tensile reinforcement to the slab,

  post-tensioning

  allows the slab to be thinner. This is both a design benefit and a cost-reduction perk, as thinner slabs require less concrete.
• Foundation flexibility. More strength means a greater ability to lay foundations on soft ground.

• Footing sizes are typically shallower in a PT system

Cons of Post-Tensioning

Post-tensioning is considered the gold standard of concrete slab reinforcement, but there are some potential drawbacks in certain situations:

• Complex work. Post-tensioning work is complicated, so it requires highly skilled professionals to do it right. 
• Possible corrosion. This issue is most often prevented by using high-quality materials, but in some cases, the tendons inside the slab can corrode through exposure to certain materials, such as salt. Higher-quality materials will resist corrosion.

Conventional Slab Reinforcement

Like post-tensioning, conventional slab reinforcement isn't obvious when you look at a completed slab. It's all about what's done ' or not done ' to the slab in the construction process.

How Conventional Slab Reinforcement Works

The conventional slab reinforcement process is similar to the post-tensioning process. Steel cables called tendons are placed inside a concrete slab foundation to add tensile strength. But there is a key distinction between conventionally reinforced slabs and post-tensioned slab on grade: in conventional reinforcement, the cables are not stressed before the slab has to bear its load.

Ultimately, this means that the interior steel tendons will not resist a load until the concrete slab has been compressed or cracked to the point that the service load places stress on the tendons.

Pros of Conventional Slab Reinforcement

In truth, conventional slab reinforcement offers few advantages over post-tensioned slab on grade. However, there are a couple of pros of conventional slab reinforcement that could apply in some situations:

• The construction work is relatively simple. Compared to post-tensioning, conventional concrete reinforcement is relatively simple, so less experienced and knowledgeable crews can handle it.
• It's better than no reinforcement. If the choice is between conventional reinforcement or none at all, some reinforcement is better than none, especially when it comes to foundations.

Cons of Conventional Slab Reinforcement

Conventional slab reinforcement simply doesn't hold its own in the post-tensioned slab on grade vs. conventional slab reinforcement fight. Here are a few of the key disadvantages:

• More steel required. This concrete reinforcement method requires more steel tendons to even come close to the strength of a post-tensioned slab.
• It's less strong. Even with more steel, a conventionally reinforced concrete slab is going to be more likely to crack and break than a post-tensioned slab.
• It's more expensive. The fact that conventional reinforcement requires more concrete and more steel means that this method is much more expensive than post-tensioning.

• Footing sizes are typically deeper in a conventional system

Top-Notch Slab Reinforcement with Tendon Systems

There's more than one way to reinforce concrete, but there is only one concrete construction services partner that does it best. At Tendon Systems, we work hard every day to provide the highest quality post-tensioned slab on grade reinforced concrete available anywhere.

We believe we accomplish that mission ' just ask any one of our countless happy customers how their concrete is holding up. To discuss your concrete reinforcement needs with certified professionals, reach out to Tendon Systems today. Give us a call at (678) 835- or contact us online.

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