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<ul>
<ul>
<li>Granular material for underdrains should be clear crushed 50 mm diameter stone graded in accordance with [https://www.astm.org/Standards/D2940.htm| ASTM D 2940].</li>
<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>
<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>
<li>The 20 mm clear crushed aggregate permits the use of an overlaid layer of high performance bedding (HPB) as a choker layer.</li>
<li>The void space ratio should be > 0.35 (or > 35%)</li>
<li>The void space ratio should be > 0.35 (or > 35%)</li>
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<li>Maximum abrasion of 10% for 100 revolutions and maximum of 50% for 500 revolutions</li>
<li>Maximum abrasion of 10% for 100 revolutions and maximum of 50% for 500 revolutions</li>
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[[Category:materials]]
[[Category:materials]]