crushing. Coarse aggregates smaller than 20 mm were suggested to be eliminated as they may interrupt the grout flow. Neville proposed the use of coarse aggregates of sizes smaller than 38 mm, with the aggregates being gapgraded and of multiple sizes . Later, the minimum size of coarse aggregates of 10 mm was suggested by Orchard .
Crushed stone, sand, and gravel can all be used as drainage aggregates. Drainage aggregates are either natural or processed, and coarse or fine. Coarse aggregate is typically larger than 5 mm in diameter, while fine aggregates are less than 5 mm. Base Layers. Road and patio base layers can benefit from using both crushed stone and gravel.