5.4 : Fineness Modulus

Consider a sample of fine aggregates being sieved through a standard set of sieves. Note the weight of aggregates retained on each sieve.

Calculate the cumulative weight of aggregates retained on each sieve and express it as a percentage of the total sample weight.

If, for instance, all the particles are retained on or above a particular sieve, and nothing passes through it, the cumulative percentage retained for that sieve and those stacked underneath it is entered as 100.

The fineness modulus is calculated by summing the cumulative percentage retained on each sieve and dividing the total by 100.

The fineness modulus is a numerical index that represents the grading of aggregates.

When aggregates from the same source are used, slight variations in the gradation of fine aggregates are less visually obvious than with coarse aggregates.

These differences will be reflected in the fineness modulus value, which will be more insightful for fine aggregates than coarse aggregates.

Typically, the value of the fineness modulus for fine aggregates ranges from 2.3 to 3.1; the higher the value, the coarser the aggregates.