Gradation

A gradation test is performed on a sample of aggregate in a laboratory. A typical sieve analysis uses a column of sieves with wire mesh screens of graded mesh size. A representative weighed sample is poured into the top sieve which has the largest screen openings. Each lower sieve in the column has smaller openings than the one above. At the base is a pan, called the receiver. The column is typically placed in a mechanical shaker, which shakes the column, usually for a set period, to facilitate exposing all of the material to the screen openings so that particles small enough to fit through the holes can fall through to the next layer. After the shaking is complete the material on each sieve is weighed. The mass of the sample of each sieve is then divided by the total mass to give a percentage retained on each sieve. The size of the average particle on each sieve is then analysed to get a cut-off point or specific size range, which is then captured on a screen.