For advice on decorative surface aggregates see [[Stone]]
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<li>Granite is generally recommended over limestone for all drainage applications. Granite is both more chemically stable, and more resistant to crushing over time. </li>
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<li>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].</li>
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*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],
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<li>The 20 mm clear crushed aggregate permits the use of an overlaid layer of high performance bedding (HPB) as a choker layer.</li>
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*The 20 mm clear crushed aggregate permits the use of an overlaid layer of high performance bedding (HPB) as a choker layer,
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<li>The void space ratio should be > 0.35 (or > 35%)</li>
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*The void space ratio should be > 0.35 (or > 35%)
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</ul>
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All gravel should meet the following criteria:
All gravel should meet the following criteria:
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<ul>
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*Maximum wash loss of 0.5%
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<li>Maximum wash loss of 0.5%</li>
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*Minimum durability index of 35
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<li>Minimum durability index of 35</li>
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*Maximum abrasion of 10% for 100 revolutions and maximum of 50% for 500 revolutions
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<li>Maximum abrasion of 10% for 100 revolutions and maximum of 50% for 500 revolutions</li>