Abstract
Although aggregates for use in bituminous materials are required to be `clean, hard and durable', the definition of these terms has been hitherto left to the discretion of the engineer responsible forspecifying, ordering and accepting the materials. In this Report clean, hard and durable, are defined and research is reported to determine quantitative criteria for each of these properties for aggregates used for bitumen macadam roadbase. It is hoped that this will assist both suppliers and users. Finally, some practical considerations are discussed including the need to waive the criteria when there is long experience of satisfactory use of particular local aggregates.