Floor slabs - Gravel base
Floor slabs - Gravel base
(OP)
Hi, what type of material do you normally use underneath slabs on grade? Open grade gravel or something like base course material for pavements which has some fines for proper compaction? I think that both materials can provide adequate support for the slab but I kind of prefer the later since it can be compacted and tested. What are your opinions?






RE: Floor slabs - Gravel base
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RE: Floor slabs - Gravel base
You want material that will be a capillary barrier so that water/moisture does not rise greatly through the subgrade into the slab on grade. In order to be a capillary barrier, it should have a fineness modulus no less than about 3.0.
That can be a very clean medium sand to fine gravel, but agree that it should be compactable. Also, make sure you specify good grade control. No more than a 1/2" in 5 feet for flatness and no sudden transitions....otherwise expect more cracking.
RE: Floor slabs - Gravel base
Also, could you look at this website (in Japanese) which has photos of different soil material/aggregates and suggest what type of material could be the more appropriate underneath slab on grades?
http://uks.jp/postproductscat/macadam/
I vote for C40, M40, open grade material can also work based on Ron's notes about capillary barrier. (if you choose any material which its name is in Japanese, just copy and paste that name in your response).
BTW, are there any recommendations for the maximum amount of fines for capillary barriers?
RE: Floor slabs - Gravel base
However what we use does NOT technically meet that specification... I'll explain. Limestone quarries sell the specified base course, but they also offer a lower cost product called "ROC" (Run Of Crusher).
To make ROC the quarry starts with the same limestone used for base course.
ROC is crushed with the same equipment that produces base course.
The difference is that ROC is what comes out to the crusher, with no tests performed on it. Without testing or guarantees, ROC is lower cost than base course, but the product is virtually identical.
Large quantities or ROC are use for roads (both paved and unpaved), foundations, building, equipment laydown areas, etc. at our electric generating stations. Soils are typically poor, water table is high, and loads are heavy. ROC is ideal for these applications.
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RE: Floor slabs - Gravel base
Dik
RE: Floor slabs - Gravel base
RE: Floor slabs - Gravel base
RE: Floor slabs - Gravel base
For my house though, I used 4" washed stone and a 15 mil Stego vapor barrier...I spec 10 mil for commercial...so I overkilled the house a little bit...
I will say this though, I personally watched a concrete bucket truck spin tires on a stego 15 mil for 45 minutes and it didn't tear...
RE: Floor slabs - Gravel base
I used stego in my house too. Pretty durable satuff.