The design post-tension is becoming more and more popular globally both in residential and commercial spaces. This is because the structure can span further and be more efficient today. High-strength steel tendons are employed in this construction technology for supporting concrete slabs, which has several advantages over traditional reinforced concrete.
What is the Post-tensioned slab?
When the concrete has reached its strongest point, then strength steel tendons are inserted into the concrete using hydraulic jacks to produce compression and increase strength in a variety of slab forms. This construction method is known as post-tensioning.
What are the types of Post-tensioned slabs?
There are two types of post-tension slabs.
- Bounded Post-tensioned slab
- Unbonded Post-tensioned slab
What is bonded and unbonded post-tensioning?
Bonded post-tensioning: The tendons are directly connected to the concrete through grout then a bond forms between the concrete and the tendons. Bonded tendons are seven-wire strands are placed inside steel or plastic ducts, and when the strands are stressed, grout is injected to fill the duct.
Unbonded post-tensioning: There is no bond between the pre-stressing tendon and concrete. Unbonded tendons are made up of greased seven-wires strands and coated with grease and encased in a plastic sheath to protect from corrosion.
What are the components of the PT slab?
|To save a strand from concrete use the bearing plate.
|Also known as a looping plat used to support the bearing plate.
|Used at the time stretching of HT strands
|Vent coupler used for grouting purposes used at ends
|7-inch-strength steel wire wound together and placed inside a plastic/metal duct.
|This is used to anchor the tendons into the concrete while terminating or joining the two tendons.
How to construct the Post-tensioned slab?
Here are several steps to follow to construct the post-tensioned slab.
Formwork: Install slab formwork to support the slab.
Pour Concrete: After the formwork is placed, initially the concrete is cast around the sheathing. The concrete includes ducts constructed for the installation of tendons.
Place tendons: The duct is filled with the tendons, is placed flush alongside the rebar and locked with anchors.
Tensioning Tendons: After the concrete is hardened the tendon is tensioned by hydraulic jacks and anchored.
- In the bounded-type tendons the duct is grouted with enough slurry.
- In the unbounded type of tendons, grouting is not required.
Cut the Wires: The axis ends of pendants are then cut away and the depth will be routed and covered with concrete.
What is the difference between the bounded and unbonded Post-tensioned slab?
|The pre-stressing tendon and the concrete have a strong connection.
|Bonding to Concrete
|the pre-stressing tendon and concrete are unable to establish a connection.
|Grout is used to directly connect the tendon to the concrete.
|The tendon is protected with a sheath instead of connecting to the concrete directly.
|Tendons are protected from corrosion by being enclosed in grout-filled conduits.
|To prevent coming into contact directly with concrete, tendon sheaths are covered with grease or wax.
|Transfer the load through Friction between the tendon and the grout
|The tendon itself transfers load; there’s no direct bond with the concrete.
|The repairs could be more challenging.
|The repairs could not be more challenging.
|Bounded surfaces and grout have a risk of corrosion.
|Protective sheathing decreases the risk of corrosion.
|Cost is cheaper
|Cost can be slightly higher
|Frequently used in projects where long-term upkeep and durability are essential
|Ideal for constructions that prioritize flexibility and low upkeep
|Easy and quick to install
|More time require for the installation
|Provide the less flexibility
|Provide the more flexibility
What are the advantages and disadvantages of the post-tensioned slab?
These are a few short reminders of the main pros and cons that post-tensioning provides:
|Long term planning
|Good crack behavior
|Needed of professional workers
|Permanent protection of the steel against corrosion
|Construction is complex
|High fatigue strength
|Improper tendon location can cause uplifting.
|Higher punching shear strength is possible with the right tendon arrangement.
|A must suitable Force be applied to the tendon
|Require high quality dense concrete of high strength
What are the applications of the Post-tensioning slab?
The post-tensioned slab has been used for many years in larger than regular spans. Here are some of the fields where pre-stressed concrete is widely used.
- Floor slabs
- Driven piles
- Water tanks
- Concrete pipes
Frequently Asked Questions:
Q. What is the minimum thickness for a PT slab?
For exposed slabs in hostile situations, it is advised to utilize a minimum slab thickness of 5 in. (125 mm). The relevant building codes restrict beam dimensions.
Q. Can post-tension slabs crack?
Yes, when the large or overloaded vehicles are placed upon the structure the slab undergoes tension and the chances of the crack increase.
Q. What is the life expectancy of a post tension slab?
15 to 20 years the lifespan of the post tension slab.
The world has improved a lot after the invention of the post-tensioning slab. In terms of durability, design flexibility, and load-carrying capacity, post-tensioned slabs are a modern solution for today’s construction.
Post-tensioning techniques are expected to be utilized more frequently as the construction sector develops, helping to build structures that are sustainable, visually beautiful, and efficient.