Armourstone

Broken stone (very course aggregate) used in hydraulic engineering

Armourstone is a generic term for broken stone with stone masses between 100 and 10,000 kilograms that is suitable for use in hydraulic engineering. Dimensions and characteristics for armourstone are laid down in European Standard EN13383. In the United States, there are a number of different standards and publications setting out different methodologies for classifying armourstone, ranging from weight-based classifications to gradation curves and size-based classifications.

This keyword could refer to multiple things. Here are some suggestions: