Dust Ratio

[a3a]

The spec book on my project states backfill material is to have a dust ratio less than 2/3. To find the dust ratio, do you take the percent passing the #200 and just make sure it is less than 66.6 percent (2/3)?

I'm not sure what this spec is all about. I've only worked around crushed material were the percent passing #200 was around 20% tops. If my method of finding the dust ratio is correct, what is the need for specifiying it if the gradation specs outline the maximum percent permitted to pass the #200?

Thanks

 

[BigH]

Dust Ratio defined as %passing #200 sieve (75micron) divided by %passing 425micron.

http://www.gov.mb.ca/tgs/contracts/specmanual/900.pdf

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