A Self-Learning Manual - Institution of Engineers Mauritius

A Self-Learning Manual
Mastering Different Fields of Civil Engineering Works (VC-Q&A Method) Vincent T. H. CHU
machine. The compacting effort increases with the period of contact
and larger machine weight.
(ii) Compaction is brought about by the generation of shear stress between
the compressed bituminous material under the machine and the
adjacent uncompressed bitumen.
15. What is the significance of bleeding in bituminous pavement? (C3)
Bleeding occurs in bituminous pavement when a film of asphalt binder
appears on road surface. Insufficient air void is a cause of bleeding in
which there is insufficient room for asphalt to expand in hot weather and it
forces its way to expand to pavement surface. Too much asphalt binder in
bituminous material is also a common cause of bleeding. Bleeding is an
irreversible process (the bleeded asphalt on pavement surface would not
withdraw in winter) so that the amount of asphalt binder on pavement
surface increases with time.
16. 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.
17. What is the function of prime coat in bituminous pavement? (C4)
The principal function of prime coat in bituminous pavement is to protect
the subgrade from moisture and weathering. Since the presence of
moisture affects the strength of subgrade, the prevention of water entry
during construction is essential to avoid the failure of the pavement. In cold
countries, by getting rid of moisture from subgrade, the danger of frost
heave can be minimized.
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