Applications
The task of corrugated sheaths with bonded tensioners in prestressed concrete is to provide a cavity in the structural concrete which allows movement of the tendons
at a low rate of friction.
at a low rate of friction.
Leakage Resistance
Sheaths have to guarantee that
- no laitance intrudes into the prestressing duct during
concreting,
- no mixing water is squeezed out during grouting since this
would cause segregation of the intrusion mortar components
and clogging,
- no leakage occurs even under various types of stress in harsh
con struction-site conditions,
- the sheath is free of buckling or indentations.
Bending Behaviour
On the one hand, sheaths have to be sufficiently rigid to
prevent their sagging between the support points, on the
other hand, they have to be sufficiently flexible to adapt
themselves to the course of the tendon in the structure.
Wherever sheaths are laid without internal stiffening and
the tendons are inserted after the concrete has hardened,
longitudinal stiffness comes to the fore as a decisive
criterion. Flexibility is required whenever tendons are
manufactured in a factory and are supplied to the
construction site on drums, as rings or in loops.
Resistance to Transversal Stress, Tensile Strength
Before being laid in structural concrete, sheaths are
subject to various types of mechanical stress. The wall
thickness and the shape of the profile are decisive factors
in avoiding damage which will affect the proper function
of the sheaths, for example when the tendons are
inserted into the sheath, when the sheath is installed in
the structure. In addition to these types of stress sheaths
are also subject to tensile stress. The tensile strength
therefore is another important quality and testing criterion.
Corrosion Protection and Bonding
Profile shape, pitch and leakage resistance influence the
flowing process of the intrusion mortar and reduce the
danger of irregular protrusions. The profile shape has to
provide sufficient space for the collection of air bubbles
and water pockets in the corrugation crests in order to
keep them away from the prestressing wires. The pitch
guarantees an optimum enclosing of the prestressing
wires in the protecting mortar. The leakage resistance
prevents the segregation of intrusion mortar components
due to the squeezing out of mixing water.
The interior surface of the sheaths have to be free of oil
and grease films which are insoluble in water in order to
ensure a good bonding quality.
Sheaths have to guarantee that
- no laitance intrudes into the prestressing duct during
concreting,
- no mixing water is squeezed out during grouting since this
would cause segregation of the intrusion mortar components
and clogging,
- no leakage occurs even under various types of stress in harsh
con struction-site conditions,
- the sheath is free of buckling or indentations.
Bending Behaviour
On the one hand, sheaths have to be sufficiently rigid to
prevent their sagging between the support points, on the
other hand, they have to be sufficiently flexible to adapt
themselves to the course of the tendon in the structure.
Wherever sheaths are laid without internal stiffening and
the tendons are inserted after the concrete has hardened,
longitudinal stiffness comes to the fore as a decisive
criterion. Flexibility is required whenever tendons are
manufactured in a factory and are supplied to the
construction site on drums, as rings or in loops.
Resistance to Transversal Stress, Tensile Strength
Before being laid in structural concrete, sheaths are
subject to various types of mechanical stress. The wall
thickness and the shape of the profile are decisive factors
in avoiding damage which will affect the proper function
of the sheaths, for example when the tendons are
inserted into the sheath, when the sheath is installed in
the structure. In addition to these types of stress sheaths
are also subject to tensile stress. The tensile strength
therefore is another important quality and testing criterion.
Corrosion Protection and Bonding
Profile shape, pitch and leakage resistance influence the
flowing process of the intrusion mortar and reduce the
danger of irregular protrusions. The profile shape has to
provide sufficient space for the collection of air bubbles
and water pockets in the corrugation crests in order to
keep them away from the prestressing wires. The pitch
guarantees an optimum enclosing of the prestressing
wires in the protecting mortar. The leakage resistance
prevents the segregation of intrusion mortar components
due to the squeezing out of mixing water.
The interior surface of the sheaths have to be free of oil
and grease films which are insoluble in water in order to
ensure a good bonding quality.