Maximum dry density of poorly-graded gravel

[HSIII]

We recently had a gravel material be tested by a soils lab for sieve and proctor. he sieve results classified it as "Poorly-graded gravel w/sand & silt", which does make sense once you compare the grain-size distribution. However, when they ran the proctor, they claimed they came up with an uncorrected value of 155.3 pcf. Now, I know that most engineers when designing with concrete usually take values from 145 pcf to 150 pcf. Looking at these results, I can't help but think that there may have been an error somewhere.

Has anyone ever encountered a material that the maximum dry density tests out heavier than concrete? Is this truly feasable?

Bear in mind this is 1/2" processed material, no reclaimed concrete or asphalt.

Thanks all.

Extras: ASTM D1557 Method C for compaction. ASTM D422 for washed sieve was used.

 

[Ron]

I would suspect these values, as well. Unless the specific gravity of the larger particles is quite high, I would not expect such values...not impossible, but worthy of further investigation.

 

[HSIII]

Good idea Ron...I have the specific gravities in front of me (asked for everything while they were still open).

According to what they have,

Coarse Aggregate SG = 3.20 (granite?? Extremely high for this region, Southern New England)

Fine Aggregate SG = 2.94 (again extremely high for any type of "common" sand around here).

Based on 53% retained on the #4 sieve, the weighed specific gravity turned out to be 3.07.

Still...something seems rather fishy to me, especially having now looked at these specific gravities. What do you think?

 

[cvg]

I would have expected SG of 2.7 or 2.8 max. Very few naturally occuring rocks with SG that high.

http://www.edumine.com/xtoolkit/tables/sgtables.htm

 

[BigH]

When I was in Ontario - maximum dry density (modified Proctor) on the crushed Granular A limestone was typically in the order of 136 to 137pcf (if I remember correctly). When I moved to Vancouver I would see values of 143 to 144 pcf. Mmmm - and in Laos we had values in the order of 150pcf. Gs does make a big difference!

 

[HSIII]

Yeah, but 1/2" processed, with gravel and sand material located in Southern New England? Usually the SG around here is approx. 2.6 to 2.7, maybe 2.8 absolute max. I think I'm going to have them run just the SG again on any remainder of the original sample they may have left.

 

[Ron]

Unless it's an extraordinary material (such as BigH noted), the specific gravity can be guessed as accurately as it can be run! I would look in the 2.7 to 2.8 range as well.

 

[oldestguy]

In my view "poorly graded" means plenty of void space. Thus, your Proctor guys probably broke down some larger pieces and ended up with many of those voids now filled. Which may show a typical Proctor test is not suitable basis for field testing degree of compaction there.

Perhaps some form of lab vibration test is in order instead.

 

[theCorkster]

We have aggregate base (poorly graded sand with gravel (3/4 inch minus) classifies as (SM) and can have maximum impact compacted unit weights (ASTM D1557) as high as 147 pcf. Gs is usually in the 2.75 to 2.85 range. These materials border on poorly and well graded.

Post test gradation will confirm what oldest guy suggests.

Maximum density by vibratory may or may not be greater than impact compaction, but with post test gradation will answer the question of breakdown.

Match the lab test with gradation from samples of field compacted material to select lab method.

 

[HSIII]

Follow-up to the question:

On the retest of the specific gravity, it came up at 2.8 instead of 3.0. I witnessed this second specific gravity get completed, so all steps were correct, and I feel more confident with this new sp. gr.

Also, the new proctor value in relation to this retest became 144.9 uncorrected, with the same exact sieve breakdown as the previous sample.

I want to thank everyone for their responses and say I am very glad I joined this forum site.

 

[dgillette]

If those specific gravities (3.2 and 2.94) are right, 155.3 might not be too crazy. Assuming the same void ratio and sp gr = 2.7, gamma-d max would be 136 pcf, which is not out of line for broadly graded material.