What is pre-stressed concrete? Which reinforcement is used in prestressed concrete?

Prestressed concrete is a type of concrete in which internal stresses are introduced into the structural elements before the application of external loads. These internal stresses are typically induced by tensioning high-strength steel tendons or cables within the concrete element. The purpose of prestressing is to improve the performance of concrete structures by enhancing their strength, durability, and resistance to bending, shear, and other types of structural forces.

The reinforcement used in prestressed concrete typically consists of high-strength steel tendons or cables. These tendons or cables are usually made of high-strength steel alloys such as carbon steel or stainless steel. They are placed in the concrete forms before the concrete is poured and allowed to harden. Once the concrete has gained sufficient strength, the tendons or cables are tensioned using hydraulic jacks or other specialized equipment.

There are two main types of prestressing methods:

Pre-tensioning: In pre-tensioning, the steel tendons or cables are tensioned before the concrete is poured. They are usually anchored at both ends of the concrete formwork, and then the concrete is poured around them. After the concrete has cured to the required strength, the tendons are released from their anchorages, transferring their tension to the concrete, which improves its performance.
Post-tensioning: In post-tensioning, the concrete is first poured without any tensioned tendons. Once the concrete has hardened to a certain degree, ducts or tubes are installed within the concrete forms, and the high-strength steel tendons or cables are inserted through these ducts. Hydraulic jacks are then used to tension the tendons, applying forces that compress the concrete. Once the desired level of prestress is achieved, the tendons are anchored at both ends, and the ducts are filled with grout to protect the tendons from corrosion.

Prestressed concrete is commonly used in a wide range of structural applications, including bridges, buildings, parking structures, railway sleepers, and offshore structures, among others. It offers several advantages over conventional reinforced concrete, including higher load-carrying capacity, longer spans, reduced cracking, and improved durability.