A Closer Look at Prevailing Civil Engineering Practice - European ...

A Closer Look at Prevailing Civil Engineering Practice, What, Why and How
Vincent T. H. CHU
10. What are the causes of longitudinal cracks and transverse cracks
in bituminous pavement
Longitudinal cracks in bituminous pavement are usually caused by fatigue
failure under repeated traffic loading. In thin pavements, cracking starts at
the bottom of the bituminous layer where the tensile stress is the highest
and then it spreads to the surface as one or more longitudinal cracks. In
thick pavements, the cracks usually commence from the top because of
high localized tensile stresses from tire-pavement interaction. After
repeated loading, the longitudinal cracks develop into a pattern similar to
the back of an alligator.
Transverse cracks are usually formed as a result of thermal movement. It
may occur because of shrinkage of the bituminous surface due to low
temperatures or asphalt binder hardening.
11. Which of the following cause much damage to bituminous
pavement
(a) Low usage by heavy vehicles or frequent usage of light
vehicles;
(b) Low speed traffic or high speed traffic
The relationship between axle weight and the associated pavement
damage is not linear but exponential. The pavement damage caused by
one passage of a fully loaded tractor-semi trailer (80kN) is more than 3,000
passages of private cars (9KN). Hence, heavy trucks and buses are
responsible for a majority of pavement damage.
Slow-moving traffic imposes greater damage than fast-moving traffic. Past
studies showed that when the speed is increased from 2km/hr to 24km/hr,
the stress and pavement deflection is reduced by 40%.
12. What are the differences between tensioned corrugated beam and
untensioned corrugated beam
Tensioned corrugated beam is mainly used in high speed road while
untensioned corrugated beam is mainly used in low speed road.
Tensioned corrugated beam is designed mainly for use on central
reservation. When a vehicle crashes into tensioned corrugated beam, the
beam remains in tension while the post gives way to allow for deformation.
Tensioned corrugated beam absorbs impact energy by deflecting as a
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