In this article, we examine the workings of post-tension slabs. These slabs consist of traditional reinforcement plus additional high-strength steel tendons that are tensioned after the concrete has been set. This combination results in a thinner slab with longer spans and no column-free spaces. We will also explore its components, construction process, and benefits.

Working Principle of Post Tensioning 

It is widely recognized that combining concrete and steel results in an increase in load-bearing efficiency, as concrete has high compressive strength and steel has high tensile strength.

When a structure is subjected to heavy live loads, its concrete slab can experience tension that leads to cracks and deformations. To counteract this, post-tensioned steel tendons are embedded in the concrete during the pouring process and later tensioned along with conventional rebar. This process compacts the concrete, increasing its compressive strength, while the tensioned steel tendons increase its tensile strength, resulting in a stronger overall structure.

Components of Post-Tensioning Slab

1. Sheathing Ducts

Standard thin metal Sheathing pipe, either with claw couplings or overlapped welded seams, comes in lengths of 5 and 6 meters. They are connected using external screw couplings and sealed with PE tape. In addition, water-tight, frictionless, and fatigue-resistant plastic ducts are also available in the market.

2. Tendons

A post-tensioning tendon, the fundamental component of a post-tensioning system, consists of one or more prestressing steel pieces coated with a protective layer and housed in a duct or sheathing.

Prestressing steel used in post-tensioning is manufactured according to ASTM A-416 standards with typical diameters of 0.50 or 0.60 inches. It has a yield strength of 243,000 psi, compared to the 60,000 psi yield strength of typical rebar.

3. Anchors

Anchor Cone & Anchor Head in prestressing secure tendons into concrete during termination or jointing and transfers the stressing force to the concrete after the stressing process is completed.

Construction of Post-Tensioned Slab

  1. The installation and tensioning of post-tensioning tendons in concrete require skilled labor and personnel certified in performing tensioning work.
  2. Tendons are placed with traditional rebars and positioned by engineers. They are enclosed in plastic or steel ducts to keep them separate from the concrete's water.
  3. One end of the tendons is anchored with an anchor while the other end is left open with a plastic pocket former for tensioning. Couplers are used at construction joints.
  4. The tendons are carefully positioned during concrete pouring to maintain their alignment. After the concrete reaches approximately 75% of its strength, around 20 to 23 days, the tendons are tensioned using stressing jacks.
  5. The tendons are tensioned to 80% of their tensile strength. For example, a typical ½-inch grade 270 strand is tensioned to 33,000 pounds. This tensioning elongate the steel and compacts the concrete.
  6. The prestressing steel is secured by anchoring it in place once the correct tensioning force is achieved. These anchors create a lasting mechanical connection, holding the steel in tension and compressing the concrete.

Advantages of Post-Tension Slab

1. Architectural Benefits

The Post-Tensioned Slab offers a unique advantage as a floor design foundation due to its ability to create thin slabs and column-free spaces in large spans. This allows architects to have greater design freedom.

2. Commercial Spaces

Post-tensioning allows for the creation of thinner concrete slabs, providing the opportunity to save on floor-to-floor height, leading to the addition of extra floors within the same overall building height, resulting in increased rentable space.

3. Reduces Deadload

By using post-tensioning technology, the thickness of concrete slabs can be decreased, leading to a reduction in the amount of concrete and reinforcement required, often by 20-30% compared to conventional concrete slabs.

4. Structural Durability

Post-tensioned slabs have several benefits, including reduced cracking, improved durability, and lower maintenance costs. The deflection of these slabs can be precisely managed by adjusting the amount of post-tensioning to balance any applied loads after stressing.

5. Popularity

The popularity of post-tensioned slabs is on the rise globally, due to the many advantages they offer to various stakeholders, including developers, architects, engineers, contractors, and end-users.


In conclusion, Post-Tensioned Slabs offer numerous benefits over traditional concrete slabs. These slabs are more efficient and provide greater design freedom for architects. The use of post-tensioning results in thinner concrete slabs with reduced concrete and reinforcement used, leading to cost savings. Post-Tensioned slabs show reduced cracking, improved durability, lower maintenance costs, and better deflection control. Additionally, the demand for these slabs continues to grow due to the benefits they offer to all stakeholders.