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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. It also increases the
rate of hardening of binders which causes 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.
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