Understanding defects, testing and inspection - Concrete Repair - page 17

Figure 1.11 ASR-induced cracking on a dam in Canada.
Shrinkable aggregates
Some, mostly igneous, aggregates can contain inclusions of weathered
material in the form of clay minerals. These minerals, in common with the
clays encountered in the ground, swell in the presence of moisture and shrink
as they dry out ( Figure 1.13). They can cause excessive drying shrinkage of the
concrete and can cause a random crack pattern not unlike that encountered
with ASR. The problem was first identified in Scotland, where it is quite
common, but has been observed in the North East of England, Hertfordshire,
Wales and Cornwall. The cracking can pose potential structural problems
but is more likely to cause loss of durability and is frequently associated with
freeze-thaw damage. Figure 1.13 illustrates a severe example accompanied
by pop outs where frost has attacked the porous aggregate.