soil lifts and compaction schedule for solid sand under a slab on grade home 4" conc floor?

[schreibs]

Soil lifts and compaction schedule for solid sand under a slab on grade home 4" conc floor? Home will have CMU frost walls.

Building a 2700 sq ft home. Using 4" conc floor and radiant hydronic heat with tubes in the concrete. My spec for the floor is the following, what if anything can or should be changed or is this JUST FINE?!
4" conc floor 4,000 psi mix
4" Type XIV EPS foam insulation, 6 mil PE beneath to prevent R value devaluation (. . . How about above it too??)
4" x 3/4" clean stone
8" compacted ABC class six to native material
6" native material


I copied this spec from another home drawing but it is probably either over or under specified for MY soil.
My soil is almost pure sand. I used a 20" auger on my track loader and got down 4 ft before running out of shaft length. EVERYTHING looked the same-- beautiful clean sand. Location: Sherburne County Minnesota, land is ON the ELK River, home site location on a hill 25 ft above the river plain and 200 yd from river itself.

My excavator questioned the need for the ABC class six. What do you guys think?

 

[oldestguy]

I also question the need for any special base course material. You might spec that the original cut ground is compacted with 3 passes of a vibratory roller and that all sand fill above that meets either 95 percent of Modified Proctor or 70 percent relative density. You don't just say "compacted" if you want to be sure it is done right. I also question only 4 inches of concrete, considering there is heating within it and expansion and contraction is bound to occur with temperature and moisture changes. How are you going to know you have 4,000 psf material? Normally I'd spec a certain bag mix to allow for a high slump, since the placement is likely to be very soupy to get to all locations. High slump concrete also has high tendency to shrink (and crack) in time as moisture is lost.
What will that do to the heating tubes??? Some might spec some reinforcing to resist that. I'd post the concrete question in the Material engineering other" room. They may differ from me.

 

[schreibs]

thanks Oldest guy.
-- Will I have to hire and engin testing company to run density testing then during the compaction work?



-- MISTAKE! I WRONGLY posted the building code as 4000. It is 2500 psi in the case of interior slab. So not a problem for shrinkage probably.

 

[BigH]

is 4" slab a bit thin especially if you are running pipes through it?

 

[oldestguy]

One more comment. Since this is a floor with an occasional post for support of floors above,maybe running testing for compaction is not needed, provided you make sure the sand is as tight as practical. I's also assume it is a uniform sand (nearly all same grain size). In that case it has only a small density value change from loose to dense. With lower strength concrete, and likely high slump, I's guess plenty of shrinkage potential. A 5 bag mix usually will get you 3,000 psi A post in the Materials forum should be done to be sure you do it right. Usually one would cut or form joints every 10 feet or so to let them do the moving instead of random cracks developing. However that may be impossible. With the heating tubes in the concrete, you surely don't want it to fail because of unexpected cracking damage. The more water in the mix the more the higher the shrinkage. A stiff low slump concrete is best. One way to use low slump concrete is to add a fluidifier that temporarily makes it fluid. Again, check with the concrete materials experts.

 

[schreibs]

thanks for the input guys, back to the main question. . . I have concluded that below is an acceptable plan for the subgrade based on this discussion, TRUE??:

4" conc floor(typical for radiant floor, even done with 2")
4" Type XIV EPS foam insulation, 6 mil PE beneath to prevent R value devaluation (. . . How about above it too??)
4" x 3/4" clean stone
8" compacted ABC class six to native material
6" native material, compacted 3x w/ vibratory roller

the Radiant floor subcontractors will be mostly responsible for concrete, reinforcing(wire mesh, fiberglass) and any flow additives. I will spec no curing accelerants.