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For advice on decorative surface aggregates see '''[[Stone]]'''
*Granular material for underdrains should be clear crushed 20 or 50 mm diameter stone graded in accordance with [https://www.astm.org/Standards/D2940.htm ASTM D 2940],
*The 20 mm clear crushed aggregate permits the use of an overlaid layer of high performance bedding (HPB) as a choker layer,
*The void space ratio should be > 0.35 (or > 35%)
All gravel should meet the following criteria:
*Maximum wash loss of 0.5%
*Minimum durability index of 35
*Maximum abrasion of 10% for 100 revolutions and maximum of 50% for 500 revolutions
[[Category:materials]]
Did you want an article on [[Reservoir gravel]] or [[choking layer|finer gravel]]?