5.1 : Unsoundness of Aggregate due to Volume Change

Unsoundness in aggregates due to volume changes is primarily caused by the physical alterations aggregates undergo, such as freezing and thawing, thermal changes, and wetting and drying. Unsound aggregates, when subjected to these changes, result in volume change upon disintegration. This, in turn, contributes to the deterioration of concrete, including scaling, pop-outs, and cracking. Particular types of aggregates, such as porous flints, cherts, and those containing clay minerals, are especially susceptible to these changes.

To evaluate the potential for such detrimental changes, several standardized tests have been established, such as exposing aggregates to magnesium sulfate solution and drying cycles. These procedures aim to simulate the formation of salt crystals and the consequent disruption of particle structures through repeated expansion and shrinking. Furthermore, the frost susceptibility of aggregates is specifically analyzed by focusing on the aggregates' reaction to freezing and thawing cycles. These tests are performed solely on aggregates or concrete specimens embedding aggregates.

The shape and continuity of the aggregate pores, which influence the rate and amount of water absorbed and released by the aggregate, are often more critical than the total volume of pores in determining the aggregate's durability in varying environmental conditions.