/ Bonded internal prestressing
This is the most common application. It is based on the use of an uncoated strand (bare steel) in a corrugated metal sheath and injected by cement grout.
Depending on project requirements, different configurations can be chosen, such as:
- the use of a corrugated plastic sheath for aggressive environments,
- Liaseal® duct coupler for precast concrete structures,
- full encapsulation systems for electrical isolation.
/ Unbonded internal prestressing
Unbonded prestressing tendons offer multi-layer protection against corrosion. They allow the prestressing force to be measured, adjusted if necessary and the tendons to be de-tensioned or replaced if required.
When using bare strands, the injection material is usually wax.
The use of individually greased and sheathed strands contained in HDPE pipes, which are injected with a cement grout before tensioning, increases the durability of the prestressing tendons.
/ Unbonded external prestressing
External prestressing is well suited to thin concrete structures; it also allows easy inspection of tendons.
The most common application is based on the use of strands placed inside thick sections of HDPE pipes, mirror-welded and injected with cement grout.
To allow tendon removal, the ducts pass through a recess or a double casing at the anchor diaphragms and deviators.
Two solutions are commonly used to increase durability:
- Use of individually greased and sheathed strands placed in a plastic pipe injected with cement grout before tensioning.
- Use of bare strands placed in a plastic pipe injected with wax after tensioning.