Post Tension Slab – Step-by-step Process

This construction video shows the detailed methods for developing post tension slab. Post-tensioning is just a process of developing pre-stressed concrete, masonry, and other structural elements.

Prior to pour a post-tension slab, steel strands or cables known as tendons with superior strength, are placed in a tight grid. These provide support as well as strength to the slab as soon as it has cured. The tendons are covered in plastic in order that they are not directly connected with the concrete. Once the grid is formed, the concrete is poured. Additional precaution must be taken to ensure that the tendons stay at the exact depth.

Construction of post-tensioned slabs on grade is identical to applying reinforcing steel, exclusive of the tensioning step. Cables are organized with the instructions provided by the engineer and run through the center of the slab. For residential construction, generally tendons at 48 inches are found. Commercial foundations contain much more steel. Tendons are routed around obstructions.

A residential post-tensioned concrete slab is usually 8 inches thick and applies 3000 psi concrete. As soon as the concrete has achieved strength to 2000 psi, usually within the 3 to 10 days suggested by PTI, the tendons are stressed.

Now-a-days Tendons belong to seven high-strength steel wires which are tied together and arranged within a plastic duct. At each end, there is a PT anchor in pockets implanted into the slab edge. If the strands are stressed, the wires are expanded around 4 inches for a 50 foot strand to use 33,000 pounds of load. Stressing should be performed by competent workers. Once the stressing is finished, the tendon is segregated and the pocket in which the anchors are situated is stuffed with grout to safeguard them from erosion.

If a post-tension slab is used in place of normal concrete, cost is saved significantly as there is a low depth of concrete applied to get the similar end result, construction costs are minimized. This is specifically useful for developing skyscrapers and office buildings.

Image Courtesy: hhc-gulf.com