Cement Bound Material (CBM)

Those materials that use cement as a binder, i.e., a 'glue' to stick together the individual particles. They are described in the Highways Specification for use in sub-base and road base layers. Mixing is generally carried out centrally, using a forced action or paddle type mixer to ensure correct dispersion of the small quantity of cement used. CBMs are of low cement content and strength compared with structural concretes.

CBM 1 (Clause 1036)

This is the 'weakest' of the CBMs (previously known as 'soil cement') and is normally only permitted for sub-base layers. The aggregate, which can be almost any granular material, is mixed with cement and water and then compacted in place. To control the sulphate and swelling clay content of the aggregate a cracking/swelling test is specified. It is most commonly used as a capping layer or low-grade sub-base beneath flexible pavements.

CBM 2 (Clause 1037)

Very similar to CBM1 except that is is coarser and stronger, with very fine sands and silts excluded. It is also commonly used as a capping layer or low-grade sub-base beneath flexible pavements.