ABSTRACT
Within the last few years, a revolution in concrete making has taken place. The advent of high-strength concrete, and the general introduction of prestressed concrete, has led to greater control over the production of concrete on the site and in the factory. It has long been the complaint of engineers that concrete made in a laboratory could be up to ten times stronger than the same mix when made into concrete on a building site. “Quality control” of concrete is, however, expensive and can only be applied economically to large works: it does, however, produce a concrete of higher and more consistent strength from the same mix than can be achieved by ordinary methods, or will permit the use of a leaner mix to obtain the same strength as a concrete of uncontrolled quality. Very high strength concretes are required for prestressed concrete, and the achievement, under factory conditions and site conditions also, of such high and consistent strengths has led to the introduction, into civil engineers’ specifications, of the concept of “guaranteedstrength concrete”. The strength that the concrete is required to attain in 28 days is specified, and the contractor is allowed to use whatever mix will produce concrete of that required strength. Sometimes, a mix is suggested by the engineer, but the onus rests with the builder. He is free to adapt that mix, or use another. The secrets of such good concrete production are:
To achieve a high-strength concrete the mix should be designed in accordance with the instructions given in Road Research Note No. 4-“The Design of Concrete Mixes (H.M.S.O.). Readers are warned that this implies some familiarity with test procedure and the handling of a few simple scientific instruments.
