Aggregate swelling and shrinkage

Shrinkage of clay-rich particles is very common although they do not usually form a large proportion of an aggregate. Some clay types are particularly prone to expansion on wetting and shrinkage on drying. The clay can be a contaminant of the aggregate or a natural part of it. Aggregate swelling will lead to pop-outs on the surface and the formation of ‘Isle of Man’ cracks, i.e. three-legged cracks radiating out from a point.