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P-209 Modified Proctor Test Result Help

P-209 Modified Proctor Test Result Help

(OP)
I have recently received the modified proctor lab results for P-209 crushed aggregate base we plan on using as a base for a new taxiway. The sample was collected at the quarry and taken to a construction materials lab for testing. The lab result indicated an uncorrected maximum dry density of 148.5 pcf at an optimum water content of 4.1%. After correcting for the oversized fraction, the oversize corrected density was 151.6 pcf and the oversize corrected moisture was 5.2% (the percent retained on the 3/4" sieve was 28%). The problem - I expected to see a dry density around 148 pcf (4.0% moisture) which is where P-209 from this quarry typically falls. With the corrections added, there is NO WAY to get 100% compaction at that moisture per the specifications given. After approximating the zero air voids curve on the moisture-density curve, the uncorrected moisture-density curve looks good. However, when you apply the correction factor, it is way right of the zero air voids curve which, I assume with little knowledge of the subject, is not possible.

Could someone help me with this??? I am very concerned that something is not right and I do not know the right questions to ask. I have attached the results I received.

RE: P-209 Modified Proctor Test Result Help

For one thing how can you come up with an increased moisture content (corrected) when in all likelihood the plus 3/4" material is saturated surface dry, meaning no free water? For a given amount of water and an increased weight of sample, the moisture content of that total sample is less than the Proctor test percentage not greater. Practically speaking the presence of the larger particles in the field may change the gradation sufficiently to result in no significant change in dry density. With questions like this consider taking a larger mold and apply the same work (ft.pounds per cubic foot) to that larger mold to the total sample, not just a part of it. Also be aware of particle breakdown resulting in the a lab density being greater than a field density which does not have the same kneading action that the lab test provides. Run a gradation on your resulting large compacted sample as compared to an uncompacted sample to see if the lab result is unrealistic.

Looking at that lab report with cook-book text for reporting. Why not ask the writer if that sample was first carried around in the truck for a day or two, if somehow it was then "returned to the lab". How'd it get there to begin with to have to be "returned"? The tech may have returned, but that sample only made the trip to the lab once.

RE: P-209 Modified Proctor Test Result Help

That is an extremely high density for a modified proctor. Can you tell me what the percentage retained on the 1 1/4" was? If there is any cobble-sized materials involved, I've got some advice about the use of a density gauge. If nothing else you can always take a sample from the installed fill right below the gauge after testing. Another method is testing at consecutive right angles to see if you've got the larger particles right below the gauge. A test taken directly above a cobble will give you lower moisture and higher dry density due to the solid nature of the oversized particles. Sort of a tangent there, but let me know if I'm anywhere close.

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