Shape and Soundness Test - Testing of aggregates:
For providing a good interlock and strength, the aggregates should be cubical in shape. Elongated and flaky particles lower the strength. Each aggregate particle is passed through standard gauges for determining whether it is flaky or elongated. The combined flakiness and elongation index (i.e. per cent of aggregates which are flaky and elongated) should not be more than 30.
Aggregates for use in bituminous construction should have an affinity to bitumen. The bitumen film should bind firmly on to the aggregate surface and these should be no stripping in the presence of water. The maximum stripping value allowed is 25 per cent.
Under adverse weather conditions, such as alternate wetting and drying or freezing and thawing, aggregates can disintegrate. In the Soundness Test, aggregate are subjected to alternate wetting in a saturated solution of either calcium sulphate or magnesium sulphate. The loss in weight should not exceed 12 per cent (with sodium sulphate) and 18 per cent (with magnesium sulphate).