Art of glass

Among the most spectacular is a carpet made of blue glass paviours that is set to transform a drab square in Newcastle upon Tyne. Other innovations include the use of structural glass on a bridge by Anthony Hunt Associates, and the development of a glass concrete by Sheffield Hallam University. The £800 000 Newcastle scheme won a 1996 international competition to design a distinctive, visual public space in the centre of the northern city. As conceived by the artist Thomas Heatherwick, the design creates the illusion of a giant azure carpet floating above the square.

This impression is strengthened by the carpet's edges, which appear to curl up as it rests against the surrounding buildings and street furniture, while a row of bicycle racks seems to bend under its weight. Stainless steel bollards pierce the glass, as if the carpet has been dropped onto them, and the illusion that the blue surface is hovering above the square is emphasised by light spilling from chinks below the paviours.

The key to this dramatic scheme is a series of 450 × 150 × 100 mm paviours. Designed by Ron Packman of structural engineer Packman Lucas, who is working alongside Heatherwick, the glass paviours are being made by London-based terrazzo specialist Palam Precast. The company is also making a set of terrazzo benches for the square.

Experimenting with glass grades

Designing paviours using a glass aggregate has been difficult. Packman had to experiment with different concrete mixes and glass sizes to find the right aggregate packing density. The resulting flag design uses a mixture of glass grades, with a maximum aggregate size of 12 mm, sourced from three suppliers, to achieve the correct density. The flags are constructed in two layers. The top, 40 mm thick layer contains the recycled blue glass aggregate (with the edges ground off. This is set into a fine concrete matrix with a 60 mm concrete (grade 30) base below.

Despite being made of small chunks of glass, the surface looks like a continuous, smooth layer, which means there is little chance of pieces being chipped out through wear and tear, says Packman. The carpet of flags will be mounted on a sand/cement bedding course installed to standard highway loadings, allowing cars and light vans to use the square. In all, 35 000 flags will be used, 4000-5000 of which will be designed for edging and fine details.

The flags were not the only design headache for Packman. Beneath the trees, the benches scattered throughout the square will create the illusion of having been peeled back from the glass surface.

To make these elegant seats, Packman has buried stainless steel reinforcement, as well as fibre-optic cables, within the slender bench. The reinforcement and fibre-optics are assembled at Palam's factory before being covered in terrazzo.

The fibre-optics are 2 mm diameter cables set at 30 mm intervals. These punctuate the bench's surface with pinpoints of light fed from a 2000 W light source installed in the pavement below. "By day, the square will sit blue and serene," says Heatherwick, "but at night it will come alive as the hundreds of fibre-optics, cast into the benches' terrazzo, make their surfaces shimmer."

Underground art

Etched, 50 mm thick, toughened clear glass fill the space left in the paviours by the peeled-back seats, and the void beneath is used to exhibit artworks. Heatherwick is also toying with the idea of revealing the gas mains and sewers running beneath the square, or part of the city's historic wall.

For the design team, the pressure is on. Tight funding deadlines – lottery money must be spent by predetermined dates – mean much of the work has to be completed exceptionally early in the programme. The trees have already been planted and the scheme will be completed by September 1999.