The percentage voids in compacted gravel as a measure of its angularity

Abstract

Summary The British Standard for concrete aggregates (B.S. 882:1944) distinguishes “rounded” from “angular” aggregates, but gives no method for defining or measuring different degrees of angularity. The present article describes the development of a test for this purpose. A study of the literature was followed by experimental work which showed thar the most suitable method for expressing the degree of angularity of gravels was the measurement of the proportion of voids in the single-sized aggregate when compacted in a prescribed way. This proportion was found to vary from about 33 per cent in a well-rounded beach gravel to about 45 per cent in a very angular crushed rock. The test result is expressed thus:— “Angularity number” = percentage voids — 33. The angularity number of about 100 samples of aggregate ranged from 0 for very rounded gravel to 11 for an angular crushed material, and showed good agreement with personal opinions of the relative angularity of the samples and with the compacting factor of concrete made from some of the aggregates. Full details of the method of test are given in an appendix.