Glass Reinforced Polyester (GRP) is a light, durable and astonishingly tough constructional material which can be fabricated into all manner of products. It may be translucent, opaque or coloured, flat or shaped, thin or thick. GRP is a composite of a resilient durable resin with an immensely strong fibrous glass. The resin is the main component and is normally a polyester resin. Just as concrete may be reinforced with steel rods, so polyester resins may be reinforced with glass fibres to form GRP. This is the fabrication process, a single surface mould on which is impregnated layers of glass mat with liquid resin until the required thickness has been built up and the laminate is then extracted from the mould. Glass fibre is one of the strongest of all materials (Table 1). The ultimate tensile strength of a freshly drawn single glass filament (diameter 9-15 microns) is about 3.5 GPa. It is made from readily available materials, it is non-combustible and chemically resistant.

The greatest advantage of GRP over conventional materials is the ability to design and build large structures conceived as a whole and not as an assembly of parts which have to be jointed together. Another advantage of GRP is the possibility of varying the thickness of the material locally and of increasing the strength characteristics at any point in any direction simply by making intelligent use of the glass fibre reinforcement.

GENERAL CONCEPTS

The properties of GRP compared with those of the metals it replaces are shown in tables 2 and 3. Both steel and light alloy have been selected because they are widely used. The two principal differences between GRP and metals are in modulus and density. Lack of stiffness is the most distinctive feature of GRP from an engineering design standpoint. Elongation at break is usually between 1 and 2% compared with about 40% for steel. On the other hand the deformation of unidirectional GRP is almost elastic to the point of failure, whereas the elastic point for steel is about 0.2%metals.

One of the design considerations is the expected performance of the product in the environment in which it is to operate in practice. Several tests have been conducted in order to predict the likely performance of our products in most applications. The weather and water resistance of GRP laminates is largely a function of the gel coat since in most applications it is the gel coat surface, which is exposed to attack. The recommended gel coat is used where resistance to water and mild chemicals is required. For optimum chemical resistance combined with high structural performance a resin rich surface is obtained on the face of the moulding, which is exposed to the hostile environment.

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