Specifications for sub-bases are based on knowledge that has been gained from past performance of a wide range of aggregates in conjunction with results of tests that define relevant properties. To assess the suitability of an aggregate samples have to be tested but it is extremely difficult to take a truly representative bulk sample of a large batch of material and to prepare that sample for test in a way that entirely excludes errors. This means that in those cases where a material just passes or just fails to meet a specification limit doubts can exist between customers and suppliers as to whether acceptance or rejection is really justified; it is therefore important to be able to make reasonable allowance for the errors likely to arise from deficiencies in sampling and testing. This report describes work done to establish the precision of some of the tests used to assess sub-base aggregates.

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