Excerpt from Design of Concrete Mixtures During the past three years a large number of investigations have been under way at the Structural Materials Research Laboratory, Lewis Institute, Chicago, which throw considerable new light on the subject of proportioning concrete. These investigations are being carried out through the cooperation of the Institute and the Portland Cement Association.- These studies have covered an investigation of the inter-relation of the following factors: 1. The consistency (quantity of mixingwater). 2. The size and grading of aggregates. 3. The mix (proportion of cement). Any comprehensive study of proportioning concrete must take into account all of these factors. During this period about 50,000 tests have been carried out which have a bearing on this subject. These tests have been largely confined to compression tests of concrete and mortars. These investigations have given us a new insight into the factors which underlie the correct proportioning of concrete mixtures and show the limitations of older methods. Certain phases of these investigations are still under way. The following may be mentioned as among the most important principles which have been established with reference to the design of concrete mixtures. In a brief report of this kind it is impracticable to present more than an outline of the methods of applying the principles to practical problems. In only a few instances are experimental data given on which these conclusions are based. 1. With given concrete materials and conditions of test the quantity of mixing water used determines the strength of the concrete, so long as the mix is of a workable plasticity. 2. The sieve analysis furnishes the only correct basis for proportioning aggregates in concrete mixtures. 3. A simple method of measuring the effective size and grading of an aggregate has been developed. This gives rise to a function known as the "fineness modulus" of the aggregate. 4. The fineness modulus of the aggregate furnishes a rational method for combining materials of different size for concrete mixtures. 5. The sieve analysis curve of the aggregate may be widely different in form without exerting any influence on the concrete strength. 6. Aggregate of equivalent concrete-making qualities may be produced by an infinite number of different gradings of a given material. 7. Aggregates of equivalent concrete-making qualities may be produced materials of widely different size and grading. 8. In general, fine and coarse aggregates of widely different size or grading can be combined in such a manner as to produce similar results in concrete. 9. The aggregate grading which produces the strongest concrete is not that giving the maximum density (lowest voids). A grading coarser than that giving maximum density is necessary for highest concrete strength. 10. The richer the mix, the coarser the grading should be for an aggregate of given maximum size; hence, the greater the discrepancy between maximum density and best grading. About the Publisher Forgotten Books publishes hundreds of thousands of rare and classic books. Find more at www.forgottenbooks.com This book is a reproduction of an important historical work. Forgotten Books uses state-of-the-art technology to digitally reconstruct the work, preserving the original format whilst repairing imperfections present in the aged copy. In rare cases, an imperfection in the original, such as a blemish or missing page, may be replicated in our edition. We do, however, repair the vast majority of imperfections successfully; any imperfections that remain are intentionally left to preserve the state of such historical works.