Rough roads

BAD roads make for unsafe driving. Now,researchers at the University of Newcastle upon Tyne in the UK think that theycan relieve the problem of worn- outroads by using a longer-lasting surfacemade of concrete instead of asphalt (NewScientist, Vol 146, No 1980).

Each time a heavy vehicle passes overan asphalt road, the surface tends todeform slightly. The deformation,although small, is permanent and makesthe surface uneven, causing it eventuallyto break up. Though concrete has oftenbeen suggested as a workable substitute,it has failed to catch the imagination ofscientists because it gives drivers a noisy,bumpy ride. This is because conventional concrete roads are built in sectionsconnected by steel reinforcing rods andthe joints between the sections causevibrations and noise in moving vehicles.

A team-led by John Knapton, professor of structural engineering atNewcastle, has solved the problem byemploying steel fibres and a machinecalled the Laser Screed, which uses laserbeams to measure the evenness of a concrete surface and automatically adjustsits hydraulic arms to give the required smooth finish.

Knapton has adapted the machine toproduce cambered surface needed forthe roads. The machine lays the concretein a continuous section, thus eliminatingjoints which produce noise and vibrations. Further, the concrete is reinforcedusing steel strips, spread in randomdirections throughout the mix.

To prevent the concrete road fromcracking - due to expansion or contraction that temperature changes cause -notches are etched across the surfaceevery few metres. According to Knapton,these grooves are so narrow that they canhardly be felt by people in the movingvehicles. He believes that a concrete roadcould last up to 40 years without needingrepairs, while asphalt roads last for amaximurn-of 20 years and also require atleast 3 resurfings during the period.