Types of Aggregate Grading

Aggregate grading signifies the particle size distribution within a sample of aggregate.

Well-graded aggregates contain all the required aggregate size fractions in the proportions necessary to form a dense matrix with minimum voids.

The corresponding gradation curve is a continuous smooth curve, indicating a wide range of particle sizes.

When the majority of the aggregates pass a specific sieve and are retained on the next finer sieve, it signifies that the particles are predominantly of the same size.

This represents a uniform or one-sized graded aggregates, depicted by an almost vertical line on the gradation curve.

Aggregates are gap-graded if approximately the same fractions of aggregates pass two different sieves considerably differing in size, indicating the absence of aggregates in the intermediate size range and is represented by a horizontal line on the gradation curve.

When fine aggregates are absent, the mixture is called open-graded, resulting in large voids between the coarse particles. The corresponding gradation curve is flat and nearly zero in the small size range.