Measurement of aggregate size

Abstract

A technique was developed, based on the addition of quartz of different sizes to a mechanically dispersed soil clay, to determine the size of the largest aggregates (agglomerates) stable to both wetting and drying. The technique was based on the assumption that quartz particles larger than the agglomerate cannot be incorporated within it, and thus will act as foci for failure upon wetting and drying. The agglomerate size determined using this technique, approximately 0.2 mm, was in good agreement with estimates from measurements of water stability, dry aggregate stability and aggregate bulk density on pure clay samples. Neither mechanical dispersion nor the addition of quartz appeared to alter the size of the clay agglomerate; aggregates larger than 0.5 mm are apparently formed by amalgamation of agglomerates, and subsequent fragmentation, on drying.