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For advice on decorative surface aggregates see [[Stone]]
<br>Gravel for underdrains and underground infiltration structures should be 20 - 50 mm, uniformly-graded, clean, crushed angular stone that has a void ratio of 0.4 (40%)<ref>Porosity of Structural Backfill, Tech Sheet #1, Stormtech, Nov 2012, http://www.stormtech.com/download_files/pdf/techsheet1.pdf accessed 16 October 2017 </ref>.
Gravel with structural requirements should also meet the following criteria:
*Minimum durability index of 35
*Maximum abrasion of 10% for 100 revolutions and maximum of 50% for 500 revolutions