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Sub-base
Sub-base materials comprise natural sand, gravel, laterite, brick metal,
crushed stone or combinations thereof meeting the prescribed grading and
physical requirements.
The sub-base material should have a minimum CBR of 20 % and 30 % for traffic
upto 2 msa and traffic exceeding 2 msa respectively.
Sub-base usually consist of granular or WBM and the thickness should not be
less than 150 mm for design traffic less than 10 msa and 200 mm for design
traffic of 1:0 msa and above.
Base
The recommended designs are for unbounded granular bases which comprise
conventional water bound macadam (WBM) or wet mix macadam (WMM) or equivalent
confirming to MOST specifications.
The materials should be of good quality with minimum thickness of 225 mm for
traffic up to 2 msa an 150 mm for traffic exceeding 2 msa.
Bituminous surfacing
The surfacing consists of a wearing course or a binder course plus wearing
course.
The most commonly used wearing courses are surface dressing, open graded premix
carpet, mix seal surfacing, semi-dense bituminous concrete and bituminous
concrete.
For binder course, MOST specifies, it is desirable to use bituminous macadam
(BM) for traffic upto o 5 msa and dense bituminous macadam (DBM) for traffic
more than 5 msa.
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