Suitable Materials
See also British Standards Page
The materials used to construct a sub-base are chosen for their inherent load-spreading capabilities when correctly laid. Two different types of material are considered here...
Unbound Granular Material
Cement Bound Material
Unbound materials are defined as those aggregates which are loose and do not bond or adhere to their neighbours when laid and compacted, but rely on the natural interlocking of adjacent particles. An unbound sub-base material can be loosened and removed quite easily.
Bound materials are, therefore, those which do bond with their neighbouring particles by means of a "binder". The two most common binders are Bitumen (tar) and Cement. Hence, 'tarmac/bitmac' is actually a Bitumen Bound Material and 'concrete' is a Cement Bound Material (CBM). Bound materials 'set' and are consequently more difficult to loosen and remove.
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