If GRC systems have a persistent fault, It tends to lie In relatively unsophisticated detailing between the panels and in the details relating to the panels to adjacent windows, doors, curtain walling and louvre systems. Clearly GRC systems have not kept pace with metal-based cladding systems (see Chapter 6), with their interchangeable panels and sophisticated crossover joints.

The lack of sophisticated detailing explains why, even in continental Europe, GRC systems are predominantly specified on factories, middle market offices, schools and sports facilities, which have a need for the performance characteristics of the material. Architects working on projects that have higher aesthetic requirements have found the detailing unsuitable.

Manufacturers now, however; seem more interested in taking this problem on board, especially in the light of the downturn in the traditional markets experienced over the past ten years. Advances are being made in cutting and forming the edge of the material to allow more sophisticated arrangements. Other opportunities include the inclusion of EPDM or neoprene gaskets mounted within the panel edge. Some manufacturers are developing horizontal panel arrangements as well as a fully integrated system of panels and windows.

Given improvements in GRC technology, which are backed up by a strong track record of successful projects in Europe, the performance advantages of modern GRC may warrant reconsideration. In terms of costs, the installed costs of GRC sandwich constructions average from £80 to £ I 50/m2, which is roughly equivalent to some flat metal sandwich constructions and about twice the cost of corrugated metal constructions. Costs for moulded GRC constructions are 20-30% more expensive than those for equivalent precast concrete, depending on its complexity and the quantities involved. However; GRC may be more cost-effective than precast when savings on superstructure are considered.

It can be seen that the glass fibres constitute only a small percentage by weight of the material, and although, for example, fibres for GRC (Cem-fil) cost twice as much as fibres for GRP (£2000/tin 198 I),the resultant material cost of a total I 2 mm composite is only approximately half that of the material needed for

4.14 Oxford Ice Rink (architects: Nicholas Grimshaw & Partners).

an equivalent GRP composite. Having said that, of course, the material costs represent only a small percentage of the total costs, which will include overheads on production for more complicated panel shapes.

Glass-fibre-reinforced cement can be seen as an alternative to ordinary reinforced concrete in respect to its weather resistance, non-combustibility and low thermal movement. Advantage can be taken of its higher strength-to-weight ratio than those of other cementitious materials to produce strong, fire-resistant yet lightweight claddings. (Its strength-to-weight ratio is, however, less than that of GRP or metals.) Inevitably, though, it is compared with GRP in respect to its

method of manufacture and its resultant ability to be formed into a variety of shapes.

Cement, when reinforced with glass fibre, produces precast elements much thinner - typically 10 mm - than would be possible with traditional steel-reinforced precast concrete, where 30 mm or more concrete cover to the steel is essential as protection against corrosion. Thinner sections are also made possible by the low watercement ratio of the material, the lack of coarse aggregate, and its low permeability. As a result, panels of equal strength and function of precast concrete can be produced with thinner sections and therefore less weight.

In conclusion, it appears that GRC can offer benefits on projects where the physical characteristics of the building can enhance the performance of the building. On very complex projects, which require very

4.15 Cranked panels need supporting to avoid distortion during curing.

End if unsupported will tond to sag in tts Qrasn stfltfi

End if unsupported will tond to sag in tts Qrasn stfltfi

4.15 Cranked panels need supporting to avoid distortion during curing.

sophisticated detailing and integration of many components, GRC is probably unsuitable at present, although promising advances are being pursued.

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