Chapter 46 Unbound aggregates

Unbound materials in highways and airfield pavements may be naturally occurring, recycled or artificial aggregates, which are not held together using cementitious, bituminous or other binders. Their uses include earthworks, capping, sub-bases and/or other layers in the construction of roads and related civil engineering applications. They may also be used in railway beds as track ballast or similar.

The function of unbound materials may be to provide all, or some of the following: a working platform for the construction and its plant; a structural layer to spread traffic loading; a non-frost susceptible sub-grade replacement; drainage characteristics.

Testing of unbound aggregates is carried out to determine geometric, chemical, mechanical and physical, thermal and weathering and other such properties. The test methods employed are designated in the requirements laid down in European and national standards or a supplier's factory production control system and can also be subject to obsolete testing protocols as laid down for specific local authority circumstances.

The reasons for using each test and any weaknesses of the tests will be discussed along with comparisons of previous methods for determining similar properties.