March 30, 2009

Building bridges with fibre-composite materials could be costly but quick

Composite materials have been with us for a long time.

Mixtures of clay, straw and water have been used to make “mud plaster” and adobe bricks for thousands of years. Various substances have been added to iron to produce different kinds of steel. Cement, sand, aggregate and water became concrete.

All composite materials.

We reinforced concrete with steel bars, with fibres of glass, carbon or steel, and got an ever-broadening range of composites.

Construction Corner

Korky Koroluk

Polymer chemists came along with things we could add to concrete — and the family of composites got bigger.

Materials science has quickly became a much broader field than it was, even 30 or 40 years ago. Then nanotechnology came along and opened up a whole new field — engineering materials at a molecular level. Nanoscientists became the new stars of material science, but those dealing in more traditional aspects of material science never stopped looking for specialized concrete mixes, for example, or steels engineered for specific tasks.

Now a young Swedish scientist has come up with a new idea in bridge building.

Peter Harryson says that with new bridge-building materials, industrial production methods and an efficient construction process, it will be possible to start using a bridge just two weeks after construction begins. In fact, he says, it could be done now, were it not for the cost.

The heart of Harryson’s bridge is a new design concept, using longitudinal load-bearing beams with a V-shaped cross section. They would be made of fibreglass and reinforced on their undersides with carbon fibres.

The bridge deck they carry would be thin, and made of extremely high-strength concrete reinforced with steel fibres.

None of these materials is presently used in bridge construction. The beams would be produced on site; the decking would be prefabricated.

The materials are all extremely durable, which would give the bridge a much longer life than is normal.

Despite the anticipation of a longer life cycle, Harryson acknowledges that his bridge “is a construction that projects several years into the future, but study shows that it would be technologically possible to build this bridge today.”

But a lot of investment money would be needed to start production, he adds, and fibre-composite materials are expensive.

Harryson came up with the idea while working with the Swedish Road Administration, and turned it into a doctoral degree from Chalmers University of Technology, in Göteborg, Sweden.

Harryson’s work was done as part of a research program called Road, Bridge, Tunnel, run by Vinnova, the Swedish governmental agency charged with researching and developing innovative systems.

Some back-of-an-envelope costing has been done, and it is thought that Harryson’s bridge would cost more than twice as much as a conventional bridge — if only material costs are considered. But construction time would be much less, resulting in significant savings. And given his prediction of a much longer-lasting structure, the lifecycle cost of his bridge might turn out to be competitive with the cost of a conventional bridge.

No one is going to jump head-first into this kind of construction, but as environmental degradation forces all of us to think about sustainable construction, life-cycle costing (which includes environmental costs) is becoming more and more important.

It is imaginative thinking by people like Harryson that is helping the world to gradually build a sustainable model for construction. What we also need, of course, is an economic sub-set to that model so that the governments who want bridges (or anything else) built can fit them into the total concept of environmental sustainability.

Korky Koroluk is an Ottawa-based freelance writer. Send comments to editor@dailycommercialnews.com

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