The material and its advantages

Glass-fibre reinforced cement is a composite material consisting of ordinary Portland cement, silica sand and water; mixed with alkali-resistant glass fibres. It has been described by Young (1980) as an 'ideal marriage between brittle materials, cement, sand and glass, to produce a tough composite'. At that time, the most common percentage constitution of the material by weight was as follows:

Portland cement 40%

Later formulations included 0-5 % acrylic polymer

The ultimate strength of glass-fibre-reinforced cement (GRC) is essentially determined by the presence of the fibres, and is therefore dependent upon the glass content, the orientation of the fibres, the degree of cure, and the bonding of the fibres to the cement/sand matrix.

The glass fibre is introduced into the cement mix to carry the tensile forces, thus overcoming the main disadvantage of cement, which is unreliable and has a relatively low tensile strength. The glass content controls the maximum loading that the material can withstand, the impact performance and the durability of the composite.The incorporation of sand into the

Water Sand

Glass fibre

The material and its advantages 71

GRC mix helps to reduce shrinkage during drying out and reduces in-service moisture movement.

When GRC was first developed in the late 1960s, after pioneering studies by Dr A. J. Mujumdar at the Building Research Establishment, it was claimed that it would become a widely used form of building cladding. Metallic claddings were not yet fully developed, and GRC promised to combine the best features of precast with less bulk, lighter weight and tighter tolerances.

These benefits led to early uses on prestigious projects such as UOP Fragrances (architects: Richard Rogers and Renzo Piano) at Tadworth in Surrey (Fig. 4.1). As the use of GRC began to increase, some projects experienced problems with microcracking, surface shadowing and panel tolerances.The industry did not respond positively to these problems, and GRC fell out of favour with British architects, as they became more interested in the development of metal-faced composite cladding.

Thus in the years since the Architects' Journal's detailed coverage of the performance of GRC (Brookes, 1986), UK architects have not used GRC cladding to the extent that was originally predicted. However, GRC continued to be extensively used in continental Europe and in the Middle East, where manufacturers were actively developing their basic formulations, manufacturing methods and cladding systems. European manufacturers include: Dyckerhoff and Widmann in Germany; Besinor CMEG Creabat, Fiberton in France; Dragados y Construcciones in Spain; and Hibex in The Netherlands. UK manufacturers with an active GRC programme include BCM Contracts, Mouldform, Techcrete (Eire) and Graham Precast.

4.1 UOP Fragrances,Tadworth, Surrey (architects: Richard Rogers and Renzo Piano).

By reducing the cement: sand ratio (from 1:3 to 1:1) and by refining the fibre/polymer mix, the amount of daily moisture movement was reduced, resulting in improved surface quality, elimination of microcracking and tighter tolerances. One of the new formulations using Metakaolin pozzolanic aggregate, CemFil 'Star' was marketed by CemFil International Ltd, who claimed that it did not go brittle with age and that it kept its early strength and ductility. Early use of this new formulation includes the Espace Forbin building at Aix en Provence.

As for many new materials, the use of GRC was at first inhibited by lack of experience in use and general rules governing design and adequate codes of practice. At the international congress on glass-fibre-reinforced cement in London, October I 979 (GRCA, I 980), although some speakers complained of the lack of adequate standards, at the same conference M. W. Fordyce and D. Ward described moves towards standard specifications.

A number of major projects have been built using GRC. In the UK, the Credit Lyonnais building in London is still seen as a classic use of GRC moulding, as is the use of composite GRC panels by Richard Rogers at UOP Fragrances Ltd atTadworth in Surrey. More recent examples include the Grosvenor Hotel and Classic Cinema in Glasgow. A large number of projects have also been built in the Middle East, Spain and Japan, and J. B. Ford (GRCA, I 980) has described 12 projects in the USA using GRC wall panels. Stein (1995) shows several projects in the Middle East.

Design guidance is available describing the properties of glass reinforcement cement. Young (1978) describes the properties of GRC and its methods of manufacture, and gives guidance on the specification and design of such factors as finishes, fixings and joints with reference to a number of case studies. Brookes and Ward (1981) cover developments and feedback from practice. Pilkington (1979) produced design guidance on the use of GRC, which included a detailed description of such properties as its creep and stress rupture, fatigue, density, thermal expansion, thermal conductivity and air and water permeance, with methods of design for determining working stresses, loading, thermal, acoustic and fire performance of a particular design. Information was also given on component testing, quality control and typical specifications.

Designers intending to use the material in complicated shapes or in conjunction with composite insulation core materials should seek further advice from the manufacturers involved.They also may wish to review the recent guidance notes on GRC published by Fachvereingung Faserbeton (FVF), the German GRC trade association. A similar guide is published in the UK by the GRCA entitled GRC Architectural Components, and a Guide to Fixings for Glass Reinforced Cement Claddings is also available from GRCA.

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