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
Binder: cements the whole mixture together and provides waterproofing.
7. What is the importance of air void content in bituminous
pavements? (BM3)
The air void content of bituminous materials is an important control
parameter for the quality of bitumen being laid and compacted. If the air
void content is too high, it allows for intrusion of air and water. Moreover, it
also increases the rate of hardening of binders which produce premature
embrittlement of pavements. In addition, too high a void content will also
lead to differential compaction subject to traffic loads and result in
formation of ruts and grooves along the wheel track.
However, a minimum amount of air void should be maintained to avoid
instability during compaction process and to provide space for bitumen flow
in long-term consolidation under traffic loads. A sufficient amount of air
voids should be designed to make room for expansion of binder in summer
and compaction by road traffic as suggested by National Association of
Australian State Road Authorities (1968), otherwise bleeding and loss of
stability may occur and the pavement will deform readily under severe
loads.
8. In General Specification for Civil Engineering Works (1992 Edition),
it specifies the temperature requirements for bituminous material
during and after mixing. What is the reason behind this? (T1)
Temperature is one of the factors that govern the compaction of bituminous
material and the air void content is found to decrease with an increase in
compaction temperature. This phenomenon is explained by the
viscosity-temperature relations: the higher is the viscosity of binders, the
greater is the resistance to compaction. Therefore, in normal contract for
bituminous laying, the temperature requirements for bituminous material
during and after mixing are specified.
9. How does wearing course provide skid resistance? (RS3)
The skid resistance of wearing course in a bituminous pavement is
contributed by the macrotexture (i.e. the general surface roughness) and
the microtexture (i.e. the protruding from chippings) of the wearing course
[38]. These two factors affect the skid resistance of flexible carriage in
different situations. For instance, when the carriageway is designed as a
high-speed road, the tiny channels among the macrotexture help to drain
245