Aggregate Stability and Size Distribution

In determining aggregate stability, known amounts of some size fraction of aggregates are commonly subjected to a disintegrating force designed to simulate some important field phenomenon. The amount of disintegration is measured by determining the portion (by weight) of the aggregates that is broken down into aggregates and primary particles smaller than some selected size. This determination is usually made by sieving or sedimentation. This chapter discusses the principles underlying the development of methods for measuring aggregate stability and size distribution. Multiple-sieve techniques give data on the amount of aggregates in each of several size groupings. To evaluate treatments or to rank soils, a single parameter to represent a soil sample is necessary. Aggregate size distribution often is measured to gain information on the size of the aggregates as they exist in the mass of soil. This requires a wetting treatment that will cause as little disintegration as possible.