Post-tensioning

Post-tensioning is a prestressing method in which steel tendons are stressed after the concrete has hardened, putting the element into compression so that it can resist tensile forces in service. The tendons run through ducts formed in the element and are anchored at the ends; the force is transferred either through those anchorages alone or, in bonded systems, through grout injected into the duct afterwards.

In practice

Post-tensioning suits printed concrete better than most reinforcement methods because it does not interfere with the printing process. Vertical or horizontal ducts can be formed as part of the printed geometry at no extra cost, and the tendons are installed once the element is hard. Keeping the whole section in compression also addresses the weakest feature of a printed element, since the interlayer planes carry far less tension than the material within a bead. The requirements are exacting anchorage detailing, accurately aligned ducts through many layers, and enough compressive strength and section to take the anchorage forces.

Related terms

• Reinforcement strategies — the wider set of options for giving printed concrete tensile capacity.
• Interlayer bond — the weak plane that prestress is intended to keep in compression.