Building Materials, Third Edition

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The relative proportions of coarse to fine aggregate, and their distribution into different size
fractions are given by sieve analysis, and plotted as grading curves. Depending upon the
maximum size of aggregate, the workability required, the concentration of reinforcement, the
cross-section of the member, etc. standard ‘ideal’ combined grading curves specifying limits of
size fractions have been prepared by the Road Research Laboratory (RRL), UK and are
reproduced from Road Note No 4, Design of Concrete Mixes. These curves have been prepared for
aggregates of 40 mm and 20 mm maximum size and are widely used as a guide to select
grading for aggregates to obtain a uniform and cohesive mix without segregation, Figs. 11.3
and 11.4 respectively. Similar curves for aggregate of maximum size 10 mm have been prepared
by McIntosh and Entroy, Fig 11.5.
For preparing a mix design of desired workability, attempts should be made to proportion
coarse and fine aggregates of different grading in such a ratio as to obtain the combined
grading conforming to the grading zones as shown in Figs 11.3, 11.4 and 11.5. In general all size
fraction of both types of aggregate should be present in the desired proportions. For example
experience has shown that excess of fine sand results in higher water and cement contents
while excess of coarse sand gives harsh unworkable mixes. For leaner mixes or when small size

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