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The durability of any material is determined by its resistance to the damaging effects of an influence such as extreme temperature, ultra-violet radiation, exposure to aggressive chemicals, stress cycles, etc. Durability is assessed by measuring an appropriate material property such as strength, modulus, etc., before and after exposure to one or more such influence for a period of time under prescribed conditions. A high level of property retention is consistent with high (good) durability. In this respect, the "lifetime" of a material may be identified with the time of exposure that results in a particular property remaining above a certain level.
Composite materials have been used successfully over the past 50 years in a wide range of applications in the marine and civil engineering sectors in a diverse range of applications that include pipes, tanks, slabs, walkways, bridge decks, gratings, column reinforcing wraps and reinforcing bars for concrete. In many of these applications composites are exposed to one or more of the influences noted earlier.
All composite materials are durable inasmuch as they are water resistant, thermally stable and cannot rust. Applications such as those listed are predicated on more stringent measures of durability. In this respect, particular grades of high durability (5-20 year lifetime) composite materials are available for particular applications. For example, composites for concrete re-bars incorporate alkali resistant glass fibres in order to resist fibre attack by pore water, while composites for marine applications incorporate a chemical bond at the fibre /matrix interface in order to resist water penetration.
In almost all applications, the durability of a composite material may be enhanced by imposing a conservative safety factor (2-4) on the design, and in many such cases additional durability may be achieved by the use of a protective coating and/or the incorporation of light stabilisers and antioxidants.
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