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Re: Granular Layer over Vapor Retarder

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Lloyd,
 
Why are you concerned that the material above the vapor retarder be free-draining?  This is intended as a "blotter layer" that absorbs excess mixing water from the concrete.  If the mix is free-draining this water is all just going to go through and sit on top of the vapor retarder.  It will provide better curing for the bottom of the slab if some of it is held against the bottom of the slab.
 
In addition, having more smaller particles makes it easier to grade and reduces the subgrade friction.
 
I will admit that I can't comment on the relative compactability of something with 3% fines (minus #200), versus 6% fines, versus 10%,  it all kind of looks a like, but 3% is the limit for concrete aggregate in concrete subject to abrasion per ASTM C 33.  The limit for concrete not subject to abrasion is 5%, but I think even that is probably unnecessary strict for a fill course layer.
 
For those who don't remember elementary soil mechanics,  sieves 3/8 in. and above are identified by the opening size,  sieves with openings smaller than 3/8 in.. are identified by the number of openings per in., each way.  I.e. a #4 sieve has 4 openings each way for a total of 16 openings per square in.;  a number 200 sieve has 200 openings each way, for a total of 40000 openings per in.  A #200 sieve looks like metal cloth. 
 
Something that is truly a silt will, by definition, be non-plastic.  Silt is just very, very miniature rock particles.  Similarly,  the rock dust from crushing will be non-plastic.  Clays are the result of chemical changes that alter the original rock minerals. Some clays are more plastic than others, depending on the mineral composition of the rock they were formed from, and how they were altered.  Most silty soils have some clay in them, so they have some plasticity.
 
Bill, with respect to the gradation you proposed, 
 
 
---------------------------------------------------
Sieve Designation   % Passing (by weight)
 
    1-inch                            100
    No. 4                            30-70
    No. 8 (or No. 10)            20-70
    No. 40                           10-50
    No. 200                          3-15
 

The liquid limit of the material passing the No. 40 sieve shall not exceed 30 and the plasticity index shall not exceed 6."
 
---------------

I am not sure there is an optimal gradation, but I would note that if you have an aggregate with 1 in. stones all the way down to #200,  you are going to end up with a lot of segregation.  When it is stockpiled on the site,  all the large aggregate is going to end up at the bottom on the pile, and when it gets put down,  you'll end up with pockets of large and small aggregate.
 
This is actually the reason concrete aggregate is batched separately as coarse and fine aggregate.  There is no magic to the plus #4 versus minus #4,  you just can't stockpile such a wide range of particle sizes.  I would also be surprised if anyone stocked this as a standard gradation.  What you would be likely to get is crusher fines (minus 3/8 in.) that had some 3/4 in. drain rock thrown in.
 
Also if you can have 70% passing the No. 4 and 70% passing the No. 8,  you may not end up with a well-graded mix. 
 
Another thing, I'm not sure there is any point in confusing anyone by mentioning a No.10 sieve, it's not really a standard sieve size.
 
Size-wise,  it doesn't make much difference whether you specify a No. 30 or a No. 40 sieve,  but a No. 30 is more standard - it is what is used for fine aggregate per ASTM  C 33
 
Lastly, the Atterberg limits (liquid limit, plastic limit, plasticity index) are done on the minus #200 particles.  
Gail Kelley