- This article or section should be merged with Prestressed concrete
Post-tensioned concrete is the descriptive term for a method of reinforcing concrete by applying compression to poured concrete after the curing process (in situ).
In pre-tensioned concrete high tensile steel bars or cables are tensioned before the concrete is poured. The cured concrete adheres and bonds to the bars and when the tension is released it is transferred to the concrete as compression by static friction. This method is mainly used for smaller pre-fabricated elements such as piles, balconies or lintels.
Traditional reinforced concrete is based on the use of steel reinforcement bars, rebar, inside poured concrete.
A post-tensioned concrete structure has a number of steel rods or cables protected by plastic, steel or aluminium tubing positioned in the concrete formwork, within the volume of the pour. After the concrete has cured, tension is applied to the rods or cables using hydraulic jacks, compressing the concrete structure. When the cables or bars have stretched sufficiently, according to the design specifications (see Hooke's law), they are locked in position and the tubing is filled with grout.
The technique was developed by Eugène Freyssinet in the early part of the 20th Century and has been used in several large constructions - typically concrete bridges.
Post-tensioned concrete is also the predominating construction of concrete floors in high-rise buildings; foundations for residential buildings in soft soil areas; and in the construction of water tanks.
The advantages of post-tensioned concrete include lower construction costs; thinner slabs - especially important in high rise buildings in which floor thickness savings can translate into additional floors for the same (or lower) cost; and fewer joints since the distance that can be spanned by post-tensioned slabs exceeds that of rebar constructions with the same thickness (height). Increasing span lengths increases the usable unincumbered floorspace in buildings; diminishing the number of joints leads to lower maintenance costs over the design life of a building, since joints are the major locus of weakness in concrete buildings.
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