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Summary Whether considering artificial aggregates or natural aggregates, the most important factor in obtaining optimum utilization is the recognition that ‘quality’ when used as a term in respect of aggregates is relative to the usage to which the material is to be put. There is no such thing as a ‘high quality roadstone’ until one has specified the context of its use in the road. The present paper lists the qualities which are generally considered desirable and relates them to the particular usage. Some important cases of requirements which are conflicting are presented. The paper continues by discussing with reference to case histories the importance and effects of particle degradation on the engineering properties of aggregates in construction materials. The process of degradation is considered in its two principal divisions: physical (disintegration) and chemical (weathering). Mathematical solutions to the degradation phenomena are reviewed and the effects of petrological variation, both in terms of primary and secondary minerals are discussed. Finally various methods of measurement of degradation are considered and an assessment of a suitable technique made.

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