“Fourteen Points” of Good Concrete.

Progress, Volume XV, Issue 2, 1 October 1919, Page 621

“Fourteen Points” of Good Concrete.

1. With the same concrete, materials the quantity of mixing water used determines the strength of the concrete, so long as the mix is of workable plasticity. N 2. The sieve analysis furnishes the only basis for proportioning aggregates in concrete mixtures. 3. The sieve analysis curve of the aggregate may be widely different in form without exerting any influence on the concrete strength. 4. Aggregate of the same concrete-making qualities may be produced by any number of different", gradings of a given material. 5. Aggregates of the same concrete-making qualities may be produced from materials of widely different size and grading. . 6. Fine and coarse aggregates of widely different size or grading can be combined in such a manner as to produce similar results in concrete. 7. The grading which produces the strongest concrete is not that giving the maximum density or lowest voids. A coarser grading than, that giving maximum density is necessary for the highest strength. 8. The richer the mix, the coarser the grading should be for an aggregate of given maximum size. 9. The shape of the particle and the quality of the aggregate have less influence on the strength of the concrete than previously supposed. 10. A simple method of measuring effective size and grading of an aggregate has been developed. This gives rise to a function known as the “fineness modulus of the aggregate. 11. The fineness modulus of the agregate furnishes a rational method for combining materials of different size for concrete strength. 12. The quantity of water required is governed by the following factors :— ' ■ v (a) The plasticity of the concrete to be used; (b) The normal consistency of the cement; (c) The sile and grading of the aggregate as measured by the fineness modulus;

(d) The mix or relative volumes of cement and aggregate; (e) The absorption of the aggregate; (f) The contained Avater in the aggregate. 13. There is a close relation between the grading of the aggregate and the quantity of Avater required to produce a workable concrete. 14. The water content of a concrete mix is best considered in terms of the volume of the cement or Avater-ratio. i