J. J. Chambers and C. J. Burgoyne
Dept of Civil Engineering, Imperial College of Science
and Technology, London, UK
A new material has become available
for prestressing tendons which will free the designer from some of the
constraints which cause problems when using steel tendons. In particular, the
tendons do not corrode, which obviates the necessity of providing cover to the
tendons. The tendons may, therefore, be placed outside the concrete or in
environments where corrosion protection would be difficult to provide.
This article summarises the basic
properties of this new material and describes some of the work in progress at Imperial College to furnish data relevant to
prestressing. The material does not have properties identical to those of cold-drawn
steel wire and if maximum benefit is to be gained from its use then its
properties should be properly understood.
Parafil (for PARAllel FILaments) is
one of a number of ‘Para’ products
manufactured by ICI. It consists of a closely packed, essentially parallel,
core of high-strength continuous synthetic yarns, contained within a
thermoplastic sheath. This sheath maintains the circular profile of the rope,
and protects the core from ultra-violet radiation which could cause
degradation. Otherwise, the sheath serves no structural purpose.
The core can be of a number of
different materials, but those most commonly used are based on polyester yarns
(Type A Parafil), or aramid, eg, Kevlar 29 (Type F) and Kevlar 49 (Type G).
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