Everything You Need To Know About PT Slabs

PT slabs are extremely strong and are used to support loads.

Post-tension slab (PT slab) is an abbreviation for flat slabs, banned beams, or ripped slabs. They are formed by combining conventional slab reinforcement with additional protruding high-strength steel tendons that are then subjected to simultaneous pressure after the concrete has set.

The primary technique that contributes to the immense strength of the slabs is the compression of the concrete at the start, which reduces the economic span range and material usage when compared to reinforced concrete. The PT slabs, which contain concrete that has been tested and compressed, are the thinnest slab types and are also known to have a longer span with column-free spaces.

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PT slabs: How do they work?

Because of their high compressive strength and steel content, PT slabs have tremendous strength and are used to carry loads. When a heavy load is lifted on a concrete slab that is under tension, it is susceptible to the formation of cracks or deformation. The PT slabs solve this problem by being inserted while concreting and then concreted with conventional rebars.

To put this method into simple terms, imagine concrete being squeezed, and then imagine post-tension steel tendons being stressed as a result of the same. As a result, when concrete is subjected to high pressure, its compressive strength increases. After being pulled, the tensile strength of the steel tendons increases, increasing the overall strength of the concrete.



PT slab: What is the PT slab made of?

1) Ducts

The ducts are the first component of a PT slab and are made of thin sheet metal pipes with welded overlapping or screw coupling. They are available in lengths of 5 and 6 metres, respectively. This is the industry standard measurement for PT slabs. These ducts are then joined together using an external screw coupling and sealed with PE tape. In today’s market, ducts made of plastic have also been made available due to their water-tight characteristics. Which make them frictionless and fatigue resistant.


2) The Tendons

The tendons are the next component used in the production of PT slabs. These are also known as the fundamental elements required for the operation and construction of a post-tension system. One or more prestressing steel pieces are coated with a protective coating and then placed within a sheathing or duct to prepare these post-tensioning tendons.

Notable characteristics of the tendons include the prestressing steel used during manufacture, which is made precisely according to the requirements of ASTM A-416, as well as the standard strand sizes of 0.50 and 0.60 inches in diameter.

The yield of a typical steel post-tensioning stand is estimated to be around 43000 psi. When compared to a standard piece of rebar, the difference can be calculated using the famous yield, which is approximately 60000 psi.


3) An anchor

  • To explain the role of the anchors, they function to secure the tendons to the concrete. The anchors’ job is to terminate or join two tendons while doing so. After the stressing process is completed, the anchors’ main function is to transfer the stressing force to the concrete.
  • It is clear from the description that PT slabs require precise handling and accurate measurements to function properly and ensure their job is completed without failure. The following are the steps to take and important points to remember when installing PT slabs:
  • Higher-skilled labour is required to install post-tensioning tendons within the concrete and stress it so that there is no room for failure. Only certified personnel are typically qualified to perform tensioning work.
  • The positions in which the tendons are to be laid must be determined by an engineer. He or she must also ensure that the strands are protected by ducts made of plastic or steel so that they do not come into contact with water while being placed in the concrete or afterwards. The tendons are laid in conjunction with conventional rebars.
  • Tendons used today are made up of seven high-strength steel wires that are wound together and then placed in a plastic duct. It is strongly advised that stressing be performed only by qualified workers to avoid anchors being mislocated or tendons having incorrect measurements. These workers also ensure that the anchors are installed in a grouted area to prevent corrosion.



PT slab

  • While one end of the anchor is left open in the area where the tendons are stressed with the help of a plastic pocket former, the other end of the tendons are anchored. Couplers are used when a construction joint is being formed.
  • The concrete is poured while taking care of the alignment of these tendons to ensure that the positions do not change. After approximately 20 to 23 days. The concrete is assumed to have reached approximately 75% of its strength. At which point these tendons are subjected to pressure via the machinery of stressing jacks.
  • This pressure or tensioning is equivalent to a force equal to 80% of the tensile strength of the strand. This is equivalent to tensioning a 12 inch grade 270 strand with a force of 33000 psi. When the tensioning mechanism is activated, the concrete is compressed, causing the steel to elongate.
  • A post-tension concrete slab used for residential purposes is typically 8 inches thick and made of 3000 psi concrete.
  • When the proper tensioning force is reached, the prestressing steel is anchored in place. These anchors, which are designed to provide a permanent mechanical connection. Keep the steel in tension as well as the concrete under pressure or compression.
  • If any extra tendons remain, they are trimmed on one end while non-shrink grouting is placed in the anchor pocket.
  • The only thing to keep in mind is not to cut or drill into post-tensioned concrete slabs. Because a tendon is extremely difficult to repair after it has been cut. For this reason, many PT slabs have stamps on them to alert owners or renovation contractors to the slab’s post-tensioning.


What are the benefits of a PT slab? 

PT Slabs : Architecture

When column-less places are in question for larger spans. Architecture PT slabs play a significant role in assisting an efficient base use for floor design with the help of thin slabs. Post tension slabs offer a significant advantage over others in terms of floor design. As well as a variety of options for the architect to work with all of his designs in mind, without hesitation.



PT Slabs: Commercial sectors

PT slabs provide thinner concrete slabs, resulting in savings on available floor-to-floor heights, implying the possibility of additional floors. As a result, the available rental space increases while the overall height of the building remains unchanged.


PT Slabs : The dead load has been reduced.

In comparison to conventional concrete slabs, PT slabs are thinner. Implying that the amount of concrete and reinforcements use in their construction is reduce by up to 20% to 30%.


PT Slabs : Structures’ long-term viability 

Because PT slabs are made from scratch, they have less cracking, are more durable, and have a lower maintenance cost. The deflection can be kept under control by using a variable amount of post-tensioning to balance any part of the apply load after stressing.



PT slab: Significant distinctions between normal and post-tension slabs


  • The amount of steel used in commercial foundations and post-tension foundations is one of the most significant differences. In the case of residential construction slabs, the tendons used for the centre are approximately 48 inches. Commercial foundations, on the other hand, contain far more steel.
  • A PT slab necessitates more formwork than a flat slab. Column caps are not required in the case of conventional slabs.
  • A purse-stressed concrete structure, also known as PSC. Is present in a PT slab or post-tension slab. Whereas a normal slab contains a reinforced concrete structural element, also known as RCC.
  • The reinforcement carried out to resist compression in a PT slab is carried out with a replacement of cables or steel tendons, and thus slabs that have been tensioned or pressure after construction are known as post-tension slabs.
  • Conventional slabs cannot overcome the natural concrete weakness. Whereas post-tensioning removes all of the natural concrete weakness through tension and has a better advantage of strength in compression.
  • Post-tension slabs are more advantageous when use in the construction of multi-story buildings because they provide more support as well as a higher floor-to-floor ratio due to the thinnest of the slabs and the strength accumulated through pressure.
  • Post-tension slabs, unlike conventional slabs, are compressed at the structure’s edge, which strengthens the concrete for resistance to tensile stresses. The use of high tensile steel tendons in the structure is also different from conventional slabs, giving it greater strength.



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