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How Concrete Strength is Affected by Post-Tensioning
by TRP Ready Mix on July 15, 2021
How The Collapse Of Florida International University Bridge Could’ve Been Prevented
Concrete is the most popular construction material in the world. It’s strong, durable, and economical. However, concrete can only support so much weight on its own.
That’s where post-tensioning comes in. Post-tensioning is a process that adds tension to the concrete after it has been poured, which greatly increases concrete strength and stability.
In this article, we will discuss the advantages of post-tensioning and how to ensure your concrete retains its desired strength during and after the process.
What Is Post-Tensioning And Why Is It Important In Construction?
Post-tensioning is a process that adds tension to the concrete after it has been poured.
The same goal can be achieved in two ways:
- Prestressed concrete is concrete that has already been tensioned before it is placed in the formwork.
- Post-tensioned concrete is concrete that is tensioned after it has been poured.
The main advantage of post-tensioning over prestressing is that it allows for more accurate placement of the concrete, which leads to a higher quality finished product.
Pre-stressing concrete requires the use of heavy equipment and can only be done in a limited number of places. Post-tensioning, on the other hand, can be done anywhere after the concrete has been poured.
This makes post-tensioning a more versatile process and allows for greater flexibility when it comes to construction. We’ll elaborate on pre-stressing in another guide, but this article will focus on post-tensioning.
In addition to treating concrete to increase its load-bearing characteristics, post-tensioning can be used to repair concrete that has already been damaged.
Why Is It Important?
Concrete is the most commonly used construction material on earth and for good reason: it’s strong, long-lasting, and cost-effective. However, concrete can only bear so much weight on its own. That’s where post-tensioning comes in.
Benefits Of Post-Tensioning
- Increased concrete strength
- Increased concrete stability
- Allows for more accurate placement of concrete
- Can be used to repair concrete
- Drawbacks Of Post-Tensioning
Drawbacks Of Post-Tensioning
- Increased concrete cost
- Increased construction time
- Requires specialized knowledge and equipment
Maintenance (Repair, Rehab, Strengthening Tendons)
Like any other material, concrete needs to be periodically maintained to keep it functioning properly. Concrete that has been post-tensioned requires even more maintenance, due to the added tension.
This includes regular inspections and repairs of the concrete structure as well as the tendons themselves. If left untreated, concrete that has been post-tensioned can become weak and unstable. Then, added weight on concrete can cause it to collapse.
This happened in the Hyatt Regency walkway collapse, where concrete that had been post-tensioned failed under the weight of people walking on it.
It was a tragic event that left hundreds of people injured and 114 killed.
It also happened in the Florida International University bridge collapse, where concrete that had been post-tensioned failed under the weight of a heavy vehicle.
In both cases, if the concrete had been properly maintained, it would have been able to withstand the added weight.
Construction Process Of Post-Tensioning
In order to achieve the effect of post-tensioning concrete the concrete is placed in the formwork and allowed to cure (harden) for a while. Once it has hardened, the post-tensioning process begins. First, the concrete is tensioned by pulling on the tendons. This adds compressive strength to the concrete.
Next, the concrete is cured again to allow the tension to set in. This process takes a few days to complete.
The curing method used will depend on the concrete mix and the weather conditions. After the concrete has been cured, the post-tensioned concrete is ready for use.
How To Ensure Proper Concrete Strength During Post-Tensioning
One of the most important aspects of post-tensioning is ensuring that the concrete retains its desired strength. There are several ways to do this:
Choose A Qualified Contractor
Make sure you choose a contractor who has experience with post-tensioning and is familiar with the required procedures. Or if you’re a contractor, become one!
Monitor Concrete Strength
Have a qualified engineer regularly monitor the concrete’s strength during and after the post-tensioning process to ensure that it does not fall below desired levels. The strength of concrete can be affected by several factors, including weather and age.
Use Proper Materials
Make sure the materials you use are compatible with post-tensioning and meet all required specifications. The materials required for post-tensioning include concrete, tendons, anchors, and plates.
Why You Need To Measure Concrete Strength Before Post-Tensioning
Before post-tensioning, it is important to measure the concrete’s strength and make sure it is at the desired level. If the concrete is too weak, it could collapse under the added tension of the post-tensioning process.
On the other hand, if the concrete is too strong, it could crack or even shatter under the tension.
It is, therefore, monitoring concrete strength is crucial during and after post-tensioning to ensure a safe and lasting finished product.
Complications Of Cold Weather When It Comes To Post-Tensioning
In cold weather, concrete cures more slowly than in warm weather. This can cause problems when post-tensioning is involved, as the concrete needs to be cured again after it has been tensioned.
If the curing process is not completed properly, the concrete could crack or even shatter under the tension.
It is therefore important to take into account the effect of cold weather on concrete when post-tensioning is planned.
The Takeaway
Post-tensioning is a process that adds tension to the concrete after it has been poured. This tension greatly increases the concrete’s strength and stability, making it an important step in any construction project.
By choosing a qualified contractor (or becoming one) and monitoring the concrete’s strength, you can ensure a safe and lasting finished product. In cold weather, it is important to take into account the effect of temperature on concrete strength.
If you have questions about any of our concrete products get in touch!
