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RE: Proctor Tests

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I think you have it backwards.  As I recall, a standard Proctor (ASTM D698) uses a 5.5 lb hammer dropped 12"  with the sample being compacted in three lifts.  The modified Proctor (ASTM D 1557) uses a 10 lb hammer dropped 18" with the sample being compacted in 5 lifts.  The modified Proctor produces a higher compactive effort (56,000 ft-lb/ft3) than the standard Proctor (12,400 ft-lb/ft3).  (OK, I didn't recall all this, I looked it up).  The point is that a modified Proctor will produce a higher maximum density with a lower optimum moisture content than a standard Proctor.  I have heard that as a rule of thumb, 95% of a standard Proctor is close to 90% of a modified Proctor.
Warren Foy
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From: THunt(--nospam--at) [mailto:THunt(--nospam--at)]
Sent: Thursday, January 27, 2005 10:06 AM
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Subject: Re: Proctor Tests


I remember looking into this a long time ago when we called for modified proctors and received standard proctors from the lab.  As I remember, the standard proctor and the modified proctor are very similar laboratory tests with the standard proctor using more energy (a larger or heavier hammer?).  Both can be used however the desired or accepted percent compaction will be different depending on the test method.  I do not believe there is a direct correlation but if I remember right a 90% standard proctor is roughly about the same as a 95% modified proctor.  With this in mind, I seem to also remember that the standard proctor correlates better with field compaction when using very large rollers whereas the modified proctor correlates better when using smaller rollers, plate compactors, and powder-puffs.  As already suggested, best to check with a real geotech.

Thomas Hunt, S.E.
ABS Consulting


01/26/2005 07:47 PM

Please respond to

Proctor Tests

Are there are guidelines for when you should specify a standard Proctor and when you should specify a Modified Proctor?
Is it  based on type or magnitude of loading?
Gail Kelley