Carbon fixing

 作者:羊舌硎     |      日期:2019-03-08 08:12:08
By Mick Hamer CONCRETE road bridges can be strengthened quickly by bonding a thin sheet of carbon fibre to them, say civil engineers at the University of Surrey. After years of pounding by heavy traffic, concrete bridges can develop small cracks. Water often contains de-icing salt, and when it reaches the steel reinforcing rods it corrodes them and causes them to expand and the surrounding concrete to crumble, weakening the bridge. The standard technique for strengthening these bridges is to bolt and bond a heavy steel plate to the concrete. But this has many drawbacks, says Tony Thorne of the university’s composite structures research unit. The steel, often supplied covered in grease, has to be grease-free for an adhesive to be effective—and it is difficult to achieve the right level of cleanliness on a busy construction site. Drilling holes for bolts is also problematic. “You don’t want to drill through the reinforcing rods and weaken the bridge still further,” he says. The technique also requires heavy lifting equipment to position the steel plates and the bridges have to be partly closed to traffic during the work. In a series of tests the researchers found that bonding a sheet of prestressed carbon fibre, about 1 to 1.5 millimetres thick, to the underside of the concrete is as effective as strengthening the beam with a conventional steel plate 6 millimetres thick. To prestress the fibre, it is clamped at each end and stretched on a rack. There is no need for heavy lifting equipment and you can put the light roll of carbon fibre in the back of a car, says Thorne. The research was part of a wider government-financed project to study ways of strengthening bridges with composite materials. The Highways Agency, which is responsible for major roads in England, is currently working with researchers at the Transport Research Laboratory in Crowthorne, Berkshire,