Post-tensioning concrete is a technique that strengthens construction durability by preparing the concrete to support its optimal loads.
Concrete is a plant-manufactured material that works well under pressure. This is why pre-tensioning and post-tensioning concrete techniques are used in construction and civil construction, so that the material is subjected to internal loads that improve their final properties. This improves its final quality and life cycle.
While pre-tensioned concrete is tensioned at the plant and is then transported, post-tensioned concrete is tensioned at the construction site, after it is formworked. In both systems, bars, wires or cables are tensioned inside the concrete before it is put into service. The general post-tensioning system is as follows:
- The steel fixings (wire structure) of the future concrete beam are placed where the construction will be built.
- A duct (empty corrugated pipe that is usually made out of galvanized steel) is placed along and inside the steel fixing, in such a way that it follows optimum geometry for the structural work that will be built. It usually functions as a central nerve to reduce swaying.
- It must be kept in mind that, if the beam is very tall and thin, this empty pipe (duct) must be flat instead of circular. That way, the nerve will take up less space in the section.
- It is formworked and the concrete is poured while the post-tensioning cable is threaded through the duct. During this process, the cable can be fixed to one of the sides of the beam (passive anchor) or both can be left free (active).
- When the beam concrete has sufficiently hardened and reached certain properties characteristic of the material, the free sides of the cable — whether there is one or two — are tensioned.
Post-tensioning is especially useful in singular structures such as bridges, viaducts or airports, due to the fact that this type of civil construction makes use of elements of a considerable size that are difficult to transport if they are pre-tensioned. Because of this, post-tensioning technology is being utilized very often at Tecpresa.
A setting where it is frequently used is in bridges or structures where the supports are very far apart from one another, although it is increasingly common to find post-tensioning in slabs for paving and buildings.