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
rainwater to the side of the road and avoid the occurrence of aquaplaning.
In low speed roads the microtexture has particular significance in providing
skid resistance by gripping the car tyres to the road surface.
10. What is the optimum binder content in bituminous pavement?
(BM2)
The amount of binder to be added to a bituminous mixture cannot be too
excessive or too little. The principle of designing the optimum amount of
binder content is to include sufficient amount of binder so that the
aggregates are fully coated with bitumen and the voids within the
bituminous material are sealed up. As such, the durability of the bituminous
pavement can be enhanced by the impermeability achieved. Moreover, a
minimum amount of binder is essential to prevent the aggregates from
being pulled out by the abrasive actions of moving vehicles on the
carriageway.
However, the binder content cannot be too high because it would result in
the instability of the bituminous pavement. In essence, the resistance to
deformation of bituminous pavement under traffic load is reduced by the
inclusion of excessive binder content.
11. How would high temperature affect the laying bituminous
pavement? (T1)
In general, bituminous materials are also broadly classified into two types,
namely bitumen macadams and hot-rolled asphalts. During compaction,
the increase of temperature causes the reduction of viscosity of binder. The
binder acts as a lubricant among aggregates particles because it is mobile
in a fluid state under high temperatures. The internal resistance between
the bituminous materials is drastically reduced resulting in the formation of
a mixture with better aggregate interlock.
Bitumen macadams mainly contain continuously graded aggregates.
Compaction of this type of bituminous material is eased with an increase of
mix temperature as the lubricating effect of reduced viscosity of binder
helps in the rearrangement of aggregates.
The aggregate of hot-rolled asphalt are not well graded. With a rise in
mixing temperature, the binder will stay unset and the mixture has little
resistance to compaction [38].
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