(57) In a prestressing strand for use in stressing a concrete structure, having one or
more central core wires and a plurality of outer wires extending helically around
the core wire the surface of at least the core wires is modified in order to increase
the friction resistance to relative movement between the core wire and the outer wires.
This strand is found to give more accurate stressing, where the conduit in the concrete
for the tensioned wire is curved. The outer wires may also have modified surfaces.
The modification may be mechanical indentations or surface conditioning treatment
such as oxidation, etching, coating or deposition.
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