For advice on decorative surface aggregatesA broad category of particulate material used in construction, including sand, gravel, crushed stone, slag, recycled concrete and geosynthetic aggregates, and available in various particulate size gradations. see Stone
Gravel for underdrains and underground infiltration structures should be 20 - 50 mm, uniformly-graded, clean, crushed angular stone that has a void ratioThe void ratio (e) of a mixture is the ratio of the volume of void-space to the volume of solids. It is closely related to the concept of porosity (n) where porosity is the ratio of the volume of void-space to the total or bulk volume of the mixture. e = Volume of voids/Volume of solids = n/(1-n) of 0.4 (40%).
Gravel with structural requirements should also 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
- Porosity of Structural Backfill, Tech Sheet #1, Stormtech, Nov 2012, http://www.stormtech.com/download_files/pdf/techsheet1.pdf accessed 16 October 2017