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
Level One (Core FAQs)
Part I: Bituminous Road
1. What are the differences in function between roadbase and
basecourse in flexible carriageway? (RS1)
Roadbase is the most important structural layer in bituminous pavement. It
is designed to take up the function of distributing the traffic loads so as not
to exceed the bearing capacity of subgrade. In addition, it helps to provide
sufficient resistance to fatigue under cyclic loads and to offer a higher
stiffness for the pavement structure.
However, the basecourse is normally provided to give a well-prepared and
even surface for the laying on wearing course. Regarding the load
distribution function, it also helps to spread traffic loads to roadbase but this
is not the major function of basecourse.
2. What are “mortar mechanism” and “stone contact mechanism” in
bituminous materials? (RS4)
“Stone contact mechanism” applies to well graded aggregates coated with
bitumen (e.g. dense bitumen macadam) where the traffic loads on
bituminous roads are resisted by stone-to-stone contact and by interlocking
and frictional forces between the aggregates. It is essential to adopt
aggregates with a high crushing strength. The bitumen coatings on the
surface of aggregates merely serve to cement the aggregates together.
“Mortar mechanism” involves the distribution of loads within the mortar for
gap-graded aggregates (e.g. hot rolled asphalt). The mortar has to
possess high stiffness to prevent excessive deformation under severe
traffic loads. It is common practice to introduce some filler to stiffen the
bitumen.
3. What is the importance of friction course to expressways and high
speed roads? (RS2)
Friction course, which is known as porous asphalt, is often used as surface
material in high speed roads and expressway. It is porous in nature which
allows for speedy drainage of surface water. Road safety can be improved
because it reduces the chance of hydroplaning/aquaplaning (i.e. there is a
layer of water between the tires of the vehicle and the road surface. It may
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