The Influence of Vibration, Consistency and Grading of Aggregate Upon the Desing of Concrete
G. W. Hutchinson
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Data supplement those previously published: "Con crete Aggreqate Development on the Claytor Hydr Project (ACI Journal January 1940). They are fror the results of several investigations in the Claytc laboratory of factors affecting the design of concrete which could not be fully reconciled with existing theory. The more important indications: I.-That an optimum gradation exists. for each aggregate or set of aggregates, when of given maximum size and combined with a given paste content, which provides maximum workability in concrete. Gradations of aggregate either finer or coarser than the optimum require additional mixing water to maintain equal workability. 2.-To maintain a given consistency of concrete, a greater water content per unit volume of concrete is required as the paste content is increased. 3.-The compressive strenath and durabilitv of con- crete especially in the mixtures sufficiently dry to re quire placement by vibration, are affected by the consistency of the concrete in a manner not definitely related to the water cement ratio except when the cement content is constant.