How to tell if you have a post tension slab. Most homes that have post tension slabs have a sign that is stamped into a concrete garage floor, often near the edge of the garage door in plain sight. Older home’s with post tension slabs may have a plastic or paper sign fastened to the wall.
How to post tension a concrete slab?
- You may only need preventive maintenance
- If very minor, then maybe you just need to monitor it
- If repair is needed, it is much cheaper to correct it in the early stages than after it has become a big problem
- If it is major, then you may need to consult a qualified professional
Do post tension slabs crack?
When errors are made on-site during the post-tensioning process, the ability of the reinforcement to prevent cracking is decreased. As a result, even though post-tensioning is meant to help prevent a slab from cracking, the slab can still crack if the tensioning process is done incorrectly.
Can post tension cables be cut?
Post-tension cables are steel wires inserted into plastic sheathing laid in place while pouring the concrete slab. Cutting a tensioned cable, or tendon, can endanger the contractor and compromise the structural integrity of the slab. Click to see full answer.
What is post tension in construction?
Post-tensioning provides active reinforcement and places the concrete structure under compression in those regions where load causes tensile stress. It is an efficient way of reinforcing concrete while you are building – often allowing the construction of something which might otherwise have been impossible.
What year did post tension slabs start?
When was post-tensioned concrete first seen in this country? The first use was on the Walnut Lane Bridge in Philadelphia in 1949.
Are garage slabs post-tensioned?
Concrete slabs that have post tension cables in them that have been pulled extremely tight, are referred to as “Post Tension Slabs.” Most concrete garage floors fall into one of three categories: A concrete slab with no reinforcement in it; neither rebar or post tension cables.
What happens if you drill into a post tension slab?
Post-tension slab drilling, cutting, and coring can be incredibly dangerous. Not only is there a risk of structural collapse, but you also risk severe injury and death.
How do you find post tension cables in concrete?
0:301:24Post Tension Cable Locating with Ground Penetrating Radar - YouTubeYouTubeStart of suggested clipEnd of suggested clipCall us to do a survey for them. They need to know where the tension cables are we can find those inMoreCall us to do a survey for them. They need to know where the tension cables are we can find those in beams columns walls floors. We can scan from the underside.
What does a post tension slab look like?
3:4111:45Concrete Slab - Post-Tension Foundation Review - YouTubeYouTubeStart of suggested clipEnd of suggested clipNow one way that you can tell if you're looking at an older slab of it's a rebar slab. Or if it's aMoreNow one way that you can tell if you're looking at an older slab of it's a rebar slab. Or if it's a tension slab is look for these telltale circles.
Can you jackhammer a post tension slab?
As post-tension slabs continue to be poured across the country, plumbers are learning more about how to work around the cables confidently and safely. The proverbial bottom line is tread lightly. Even if you get a clear reading on what's underneath, take your time with that jackhammer.
Do post tension slabs crack?
One of the biggest problems with a post tension slab is cracks. The cables laying in the concrete are generally not tightened until at least 7-10 days after the concrete is poured. Since the cables are not stretched or elongated, they cannot provide any crack control in those first few days.
Can you drill screws into post tension slab?
PT slabs on ground can be placed and stamped just like with any other concrete slab. Surfaces can be stained or overlaid. The only concern is to always remember not to cut or drill into post-tensioned concrete slabs, since once a tendon has been cut, it is very difficult to repair.
How long does post tension slab last?
about 15-20 yearsConventional concrete & rebar foundations last about 20-30 years before failure begins to occur. Post-tension slabs are lasting about 15-20 years and are failing at a much higher rate. Post-tension slabs are created with concrete trenches around the perimeter of the house where the external walls will be placed.
What is the difference between normal slab and post tension slab?
ØThe slab which is supported with Beams and columns is called conventional slab. In this kind of slab, the thickness of the slab is small whereas the depth of beam is large and the load is transferred to beams and from beams to columns. ØThe slab which is tensioned after constructing slab is called Post tension slab.
What happens if you cut through a post tension cable?
Cutting a tensioned cable, or tendon, can endanger the contractor and compromise the structural integrity of the slab. Building professionals frequently use ground-penetrating radar (GPR) to locate cables within concrete slabs and reinforce the slab during and after cutting operations.
Is post tension better than rebar?
Post tension foundations are what tract home and apartment builders use so therefore they are lower quality. Post tension foundations don't work for our soils. Rebar works better here. Those post tension cables can break one day and go flying out and might kill someone.
What is post tension slab?
A post tension slab generally refers to a section of cured concrete, which has tensile forces introduced into the slab after the concrete has set. These internal forces are provided by tensioning the high-strength steel that occurs before or after the concrete is positioned. When steel is stressed before applying the concrete, ...
When is a post tension slab required?
When Post tension slab is required: A concrete slab is pressured by a post-tensioning methodology when it signifies that the steel is being pressured and the concrete is being compressed. A concrete floor slab is subjected to forces, it flexes and bends. Including the post-tensioned reinforcements, instead of rebars reinforces ...
What is the purpose of anchoring to post tension slab?
The main function of anchoring is to transfer the stressing force into the concrete after the tensioning process is completed . Also read: Flat Slab & Waffle Slab.
Why is my concrete slab thin?
Subsequent stress results in a slab of thin concrete due to the valuable financial savings available from flooring top to extra flooring.
What is post stress concrete?
This means that the slab bends upwards, so all the concrete works in compression through the slab, it’s usually called post-stressed concrete, once the mix has hardened, you release the wires. The effect is the same as the slab is bent upwards by the tension and there are no sections of the slab where the concrete is “pulled”. by Admin.
How much is post tension concrete reduced?
Since the thickness in the post-tension slabs is reduced, the amount of concrete and reinforcement is also reduced by 20% –30% compared to the conventional concrete slab.
What is the fundamental element of a post-tensioning system known as?
Tendons : The fundamental element of a post-tensioning system known as the tendon. Many steel objects are constructed of post-tensioning tendons , which are coated with a protective coating located inside the duct or sheathing.
What happens when you post tension a slab?
The introduction of post tensioning within the slab can result in the full cross section of the slab remaining in compression when it is bending. Taking the simple example from the previous image, we can cut a cross section through a portion of slab to see the stress distribution across the section with and without post-tensioning.
What is post tensioning?
Post Tensioning: The assembly of the post tensioning cables ducts and embedment systems. This system provides the compressive force to the slab.
What is PT concrete?
A post tensioned (PT) concrete slab uses the compressive force of post tensioning cables to reduce the tension within the slabs cross-section allowing it to span further and have a thinner profile compared with a conventionally reinforced concrete slab.
How long after concrete is poured can you use a stressing jack?
24 Hours after the concrete has been poured around 25% stress load is applied to the cables using the stressing jack. This is to control shrinkage cracking.
How does self weight of concrete affect the building?
Therefore reducing the slab thickness can allow reduction in column sizes as well as depth and volume of foundations.
Why add a compressive force to a toilet roll?
Adding a compressive force at either end of the toilet roll system ensures that no net tension exists while it is bending. Tension capacity has not been added to the system but rather the need for tension capacity has been removed.
When a beam or slab bends downwards, what happens?
When a beam or slab bends downwards, the top portion of the slab goes into compression, and the bottom portion goes into tension. This is usually taught in Engineering 101 taken during the first year of University.
Why use post tension slab?
Sometimes due to natural calamities and overload slab got crack in some areas. It makes the steel rods inside the slab in contact with an atmosphere that corrode the steel and make the slab week.
How post tension slab works?
Because when tension is given in the slab then the slab has to shink somewhat to be strong in tension. If high-strength concrete is not constructed then there will be shrinkage cracks in the slab which may damage the entire slab.
Why does my slab crack?
Sometimes due to natural calamities and overload slab got crack in some areas. It makes the steel rods inside the slab in contact with an atmosphere that corrode the steel and make the slab week. To avoid crack as it is post-tensioned. To increase the strength of the slab with the help of tendons wire.
Why do you need high strength concrete for post tension?
First of all, we need high-strength concrete to prepare a post-tension slab. Because when tension is given in the slab then the slab has to shink somewhat to be strong in tension. If high-strength concrete is not constructed then there will be shrinkage cracks in the slab which may damage the entire slab.
What is the term for the slab that is subjected to tension with the help of tendons before casting?
The slab which is subjected to tension with the help of tendons before casting of concrete for slab or after casting of concrete for the slab is known as pre-tensioned and post-tensioned slab respectively.
Why are slabs provided with tension?
But nowadays slabs are provided tension with the help of tendons to reduce the amount of tension providing materials like steel rods.
How much of the strength of a concrete slab is provided by tension?
The tension force is provided about 80% of the strength of the slab when tension is provided into tendons it gets elongated and the concrete slab get compressed to bear extra load against tension.
What Is A Post Tension Slab?
A post tension slab is a type of foundation construction method. Becoming a popular method in the early 70s, many homebuilders switched to this method because of poor soil conditions found in the gulf coast region and the construction process being cheaper than general slab on grade construction.
Why Do Builders Use Post Tension Slabs?
There are two reasons why builders used post tensions slabs during the construction of a home or building.
Problems With Post Tensions Slabs
One of the biggest problems with a post tension slab is cracks. The cables laying in the concrete are generally not tightened until at least 7-10 days after the concrete is poured. Since the cables are not stretched or elongated, they cannot provide any crack control in those first few days.
WRITTEN BY David Brown
David Brown is the VP of Foundation Professionals of Florida and has over 40 years of experience in the construction and foundation repair industries.
Why do builders use post tension slabs?
Builders will often use post tension slabs because they can save money and still provide a structurally solid home for the buyer. A Win / Win for both. 3. Why have a sign saying Post Tension: there is a really good reason.
What are the advantages of post tension slabs?
Advantages. There are several basic advantages for a post tension slab. It reduces cracking of the concrete. It doesn’t eliminate it, but greatly reduces it. (As we all know, concrete tends to crack over time) It helps spread the load (weight) of the home over the entire slab area verses just on the footing area.
What is the most common form of reinforcement in concrete?
Rebar is probably still the most common form of reinforcement in concrete slabs. There is also a small but growing form of reinforcing slabs, and that is the use of fiber reinforcement. 6. The Bottom Line for buyers. Post tension cables are great for reinforcing a concrete slab, but so is rebar, welded wire mesh or fiber reinforced slabs.
What is post tension?
When did we start using Post Tension. What are other types of slab reinforcement. 1. What is a Post Tension Slab. It is a concrete slab that has steel cables running through it that have been put under lots of stress to reduce cracking of the concrete and increases the strength of the slab. The steel cables are usually wrapped in ...
How are steel cables pulled?
Once the concrete has been poured and has had a chance to harden some and build up strength, then the cables are pulled very tight with a hydraulic jack.
What happens if post tension cable is cut?
Occasionally, if the post tension cable is cut, it may suddenly rip out of the concrete and badly injure a person. Remember, these cables are under a tremendous amount of stress. Overall, this rarley every happens, but for safety reasons contractors put up the warning signs. 4.
Why is it important to spread load on a slab?
It helps spread the load (weight) of the home over the entire slab area verses just on the footing area. This is a real benefit in areas of the US that have expansive soils or soils that have have poor load bearing capacity.
