Mean from 5 samples (Lampris et al., 2008)

The demand for higher quality recycled aggregates has seen a significant increase in washing and grading plants in the UK over the past two decades (Soutsos, 2017) (WRAP, 2010).

The process is much like that for primary crushed rock aggregates, where the mixed mineral waste goes through a crushing, screening and washing process in order to separate the desired grades of sand and aggregate and to remove clay and fines material.

The suspended fines material is separated from the wastewater which can be re-used, resulting in a residual filter cake with little commercial application, either utilised as inert fill or disposed of to landfill (Lampris et al., 2008).

Whilst the proportion of fines will depend on the nature and hardness of the material processed, estimates by Soutsos (2017) indicate that from a typical 20-tonne load brought in for processing at a recycled aggregate plant, 16 tonnes will be converted to useful material and 4 tonnes will comprise of fines, equating to 20% of the material input.

The composition of the waste is the combined sum of a wide range of parent materials, including brick, concrete, stone and soil.