Editing Concrete (section)

===Prestressed ===
{{Main|Prestressed concrete}}
[[File:Scott System cacti.jpg|thumb|Stylized cacti decorate a sound/retaining wall in [[Scottsdale, Arizona]]]]

[[Prestressed concrete]] is a form of reinforced concrete that builds in [[compressive stress]]es during construction to oppose tensile stresses experienced in use. This can greatly reduce the weight of beams or slabs, by
better distributing the stresses in the structure to make optimal use of the reinforcement. For example, a horizontal beam tends to sag. Prestressed reinforcement along the bottom of the beam counteracts this.
In pre-tensioned concrete, the prestressing is achieved by using steel or polymer tendons or bars that are subjected to a tensile force prior to casting, or for post-tensioned concrete, after casting.

There are two different systems being used:<ref name="Claisse-2016" />

* [[Prestressed concrete|Pretensioned concrete]] is almost always precast, and contains steel wires (tendons) that are held in tension while the concrete is placed and sets around them.
* [[Prestressed concrete|Post-tensioned concrete]] has ducts through it. After the concrete has gained strength, tendons are pulled through the ducts and stressed. The ducts are then filled with grout. Bridges built in this way have experienced considerable corrosion of the tendons, so external post-tensioning may now be used in which the tendons run along the outer surface of the concrete.

More than {{convert|55000|mi|km}} of highways in the United States are paved with this material. [[Reinforced concrete]], [[prestressed concrete]] and [[precast concrete]] are the most widely used [[types of concrete]] functional extensions in modern days. For more information see [[Brutalist architecture]].