Clean Gravel is an angular, crushed, grey colored limestone gravel. Clean gravel is available in both 3/4" (2B) and 3/8" (1B) sizes. Clean gravel is well suited for drainage applications but does not compact well.
2B Clean Gravel is typically the recommended base under a concrete slab or a wooden shed because it allows water to drain away, preventing issues with frost heave and rot respectively.
2B Clean Gravel, lined with a geotextile, is also used when building french drains. Another use is to backfill behind retaining walls which allows water to drain away from the wall and reduce water pressure behind the wall.