The Specification of Concrete Strength. Part I. The Statistical Implications of Some Current Specifications and Codes of Practice

摘要

It is common practice to use the strengths of test specimens made from samples of concrete to judge the quality of the production. This procedure is valid for the judgement of compliance with a strength specification but it is quite inappropriate to the control of the production because of the delay between sampling and the final test result and because the result gives no indication of the adjustment that may be necessary to maintain a uniform well controlled production. The use of the 'proportion defective' to the specified strength is advocated as a suitable meausre of quality and this Report describes the methods available for deriving Operating Characteristic (O-C) curves by means of which the efficiency of different specifications and risks run by the producer and consumer may be compared. A variety of judgement criteria from British and overseas specifications and Codes of Practice are examined and their O-C curves are shown. It is demonstrated that some specifications, although apparently quite strict in their strength requirements, would permit acceptance of a much worse quality of concrete than may have been intended. The requirements of some other specifications however imply that even concrete of the specified standard may not be accepted. (Author)