Dear reader we have learnt about soundness test of concrete aggregate according to BS 812. Here we will learn about ASTM C88 Test Method for soundness test of aggregate for concrete. Here our main concern is about mechanism of disruption of aggregates during sulfate test for measuring soundness and its relation to frost damage in aggregates.
As in British standard Test for soundness, there also graded sample of aggregates are immersed in sulfate solution. The solution may be magnesium sulfate or sodium sulfate. After immersion this samples are dried in oven.
Under these immersion-drying cycles (several cycles are done) the aggregate get disrupted. Why and how are they disrupted, we will discussed later? The aggregate under disruption get disintegrated which results reduction in aggregate size.
Sieve analysis is done to determine reduction in size which defines how unsound the aggregates are. Now we will learn why aggregates are disrupted?
When immersion-drying cycles are done salt solution remains in pores of aggregate get crystallized while drying in oven. These crystallization and consecutive rehydration of sodium sulfate or magnesium sulfate produce disruptive effects on the aggregates. These actions are similar to action of ice in aggregate and when a aggregate sample shows sufficient resistance to such disruption of salt, it is believed to have adequate resistance to frost action.