BAD roads make for unsafe driving. Now,
researchers at the University of Newcastle upon Tyne in the UK think that they
can relieve the problem of worn- out
roads by using a longer-lasting surface
made of concrete instead of asphalt (New
Scientist, Vol 146, No 1980).
Each time a heavy vehicle passes over
an asphalt road, the surface tends to
deform slightly. The deformation,
although small, is permanent and makes
the surface uneven, causing it eventually
to break up. Though concrete has often
been suggested as a workable substitute,
it has failed to catch the imagination of
scientists because it gives drivers a noisy,
bumpy ride. This is because conventional concrete roads are built in sections
connected by steel reinforcing rods and
the joints between the sections cause
vibrations and noise in moving vehicles.
A team-led by John Knapton, professor of structural engineering at
Newcastle, has solved the problem by
employing steel fibres and a machine
called the Laser Screed, which uses laser
beams to measure the evenness of a concrete surface and automatically adjusts
its hydraulic arms to give the required smooth finish.
Knapton has adapted the machine to
produce cambered surface needed for
the roads. The machine lays the concrete
in a continuous section, thus eliminating
joints which produce noise and vibrations. Further, the concrete is reinforced
using steel strips, spread in random
directions throughout the mix.
To prevent the concrete road from
cracking - due to expansion or contraction that temperature changes cause -
notches are etched across the surface
every few metres. According to Knapton,
these grooves are so narrow that they can
hardly be felt by people in the moving
vehicles. He believes that a concrete road
could last up to 40 years without needing
repairs, while asphalt roads last for a
maximurn-of 20 years and also require at
least 3 resurfings during the period.
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