Key factors concerning a non-rigid base
A non-rigid base can be made very stiff.
Consider a 200 mm DBM roadbase layer with a 50 pen binder. Some texts
would have us believe that this is as stiff as a concrete but a
bituminously bound layer, such as a DBM, is fundamentally viscous and
may deform over time or under fatigue loading.
An unbound aggregate layer can be constructed with a high stiffness but this also may deform over time or under fatigue loading.
When designing a carriageway or pavement, using full setts over a non-rigid base, the depth of the setts is crucially important.
The NBS clauses below may also be used for where a rigid base is present
but the traffic loading is relatively light and the setts are small.
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