The workability of concrete

Abstract

Summary An analysis is made of a large number of tests for workability as measured by the compacting factor, in order to determine how workability is related to the grading and shape of aggregate, the mix proportions and the water/cement ratio. An index is developed which takes account of the influence of particle size on workability, and largely overcomes the limitations of the fineness modulus and surface area coefficients. Similarly, an angularity index is introduced which is based on a test on the aggregate and is shown to take account of its shape. The relation between workability and mix proportions is assessed. It is established that a proportion of the water, equivalent to a water/cement ratio of about 0·25, is required to wet the cement, and that any additional water may be regarded as available to make the mix workable. An approximate relation is given for the calculation of compacting factors, and a worked example illustrates the use of this relation for mix design.