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Well technically I'll be pouring concrete over 2" rigid foam, the millings would be compacted under that.
in structural fills such as your proposing the structural part of the fill is the angular stone interacting with adjacent angular stone, voids are normally stabilized by the fines...the "oil" in the mix needs to be light or thin enough to not cushion that stone to stone interaction...ie stone needs to touch stone to truly achieve compaction which may be difficult since you will be working the millings cold....you can also purchase a product to spray on the millings to allow the "oil" to soften enough to allow for true stone to stone compaction....vibratory compaction helps fines move to voids and forces stone to stone contact .....cold oil will not move to the voids with vibration and requires weight,heat or a chemical softening agent to consolodate properly.........how this applies to your specific application is for your consideration.....but i certainly would not use millings underslab unless you have a good structural substrate under the millings or you have adequate means to fully consolidate the materials
 

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And I stand corrected
 

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Depends on what kind of rock is in the millings. Remember asphalt is basically gravel sprayed with hot tar and put through a big tumbler with a giant torch hearing it up.

ATB is asphalt treated base. It’s typically the first layer they put down. It’s made of more course 1 1/4” stones with a few fines in it and less asphalt (the asphalt part is the hot tar). It usually gets put on a good road base and then rolled. Once it cools, HMA is put on top (hot mix asphalt). The top coat. It’s made of finer stones and fines and has more asphalt in it. Sometimes the millings will be a mixture of both seeing how they layered them together using a tack coat to adhere them. This all breaks down over time and pressure, friction and your left with the rocks themselves.
Your rock, millings are only as good as your base so if it’s been sitting there a while without any mushy spots or settling I’d say your good to use it as a base for a driveway.

As far as highways putting asphalt down under their concrete theyuse the same method of ATB. Asphalt treated base is very strong stuff and once cured, whatever you put on top of it will have the same uniform thickness. They use the big concrete screeds on highways and smearing outthousands of tons of unruly mix can disturb the subgrade creating undulations in it leading to thin spots in the poor. Hence the solid base gleaning a correct thickness
 

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My drive is crushed asphalt and has been down since 1998. It is at least 8" everywhere and I can't think of anything that would be a better base for concrete. I'm planning on concreting my 1/4 mile drive and I will pour over the asphalt.
 

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Kenny, It starts with your local codes and what they say is acceptable. In all my years in commercial
construction building big buildings and stadiums, Mile High and miles of concrete sidewalks we
never used ashphalt millings. Couldn't meet the compaction requiments. We always used crushed concrete with lots of fines in it to hold moisture while compacting it. Or 1/2 inch to 3/4 gravel with the fines from gravel pits. We would use the asphalt millings for roads to access jobsites. Even those would get hard but compaction on them was always a issue.

You might be alright because you are putting foam bt the 2...curious to see how it turns out!

Good luck!
WB 🚜🇺🇲
 

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I assume when you refer to millings you mean asphalt that has been torn out and ground to a gravel texture. I have never heard of problems where asphalt harms concrete. In fact, it is a common practice to lay asphalt over a concrete roadway when the concrete gets too rough as a means to extend the life of the road for another 5-10 years before a complete tearout is necessary.

My driveway has concrete curbs and aprons which abut the asphalt. Under all of it are 8-10" of reclaimed asphalt. Years past some asphalt companies required the gravel used for the based be class 5 (crushed limestone). Conbit (reprocessed concrete and asphalt) could fail. It would fail because the ground concrete could continue to degrade and cause soft spots. As long as you use ground asphalt and compact it correctly it is the base of choice for both concrete and asphalt installers in Minnesota. I have a pile siting in my yard now for more concrete work that will start in a few weeks. In a prior life I have built several commercial buildings, both slab on grade and multi story with tilt up concrete walls. Without exception, the common base for the concrete has been reclaimed asphalt. Construction was always subject to engineer inspections and testing before concrete was poured, and never was the use of ground asphalt an issue of concern.

If it can handle the freeze/thaw of MN winters it should work anywhere. Like any base material, adequate depth and compaction are essential. Skimp on either and you will have a failure in due time.
 

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Wow, such a contrast in opinions :unsure:
This might be the new "Oil" brand / synthetic vrs non / diesel fuel treatment brand type "debate board"........... :unsure: ;)
 

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I'd go for it if you do not have a drainage issue. Where you are located I'm pretty sure you don't have any big long freeze issues.
I would make sure the ground is well compacted or virgin ground. I might also go more than 4" (3.5") of concrete with wire. FWIW I don't care for thin floors, at least in our area.
IMO, if the ground is very well compacted you could pour right on the dirt.
 

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My humble opinion. Do not cut costs on the base under concrete. All vegetative soils should be removed and the base should be constructed of fractured stone that can lock together to provide strength. A certain amount of fines are required to make this work. There are engineered base course materials for this specific use. Bite the bullet, use those and be sure they are correctly installed. If doing so doesn’t fit the current budget modify the size of the project or delay the project until it does. I strongly suggest not going with the “I use this all the time” product.
For What It’s Worth.
Always fun to have a new project on the horizon. Enjoy. Ken
 

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Ken, you got a bunch of opinions here, some from practical professional users. In my opinion; To get the answer you are looking for as I tell anyone who has those type questions for me, I would contact an engineer who is familiar with differing materials and their uses. Code does not tell me it's ok to use millings under cement, doesn't address that question, it addresses gravel base and soils analysis. There are cement companies who have an on-board engineer that can answer that question in a second. I would start with your local redi-mix plant and it will be free to ask the question, just take a ride over, don't do it on the phone. I would love to know that answer as I've never seen it done here and the question has never been asked to me personally..
Jeff
 

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When we doubled the size of our house three years ago it was a real circus when the concrete contractor had trucks scheduled for the next day and he couldn't get the fill he wanted to finish forming (slab on grade). I had a guy that was hauling crushed pink granite for me for my internal roads (drives) so I asked the slab guys if the granite would work as fill - yes it will. I have no idea if they knew anything about using crushed granite but I suspect they were grabbing at straws to get the slab poured.

Crushed granite when dried out is extremely hard but when the surface gets wet, the fines become a bit soupy. So we deal with the occasional pink soup when it rains. The other choice is chip seal but that's ugly compared to the granite.
 

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Discussion Starter · #33 ·
Here is the the VERY short version:
-We are expanding our pole building, adding a 24x52 addition.
-The area will be excavated down to 10-12" below the existing floor's hight, this will be virgin soil.
-We will place some sort of compacted base (the purpose of this thread)
-Vapor barier
-2" rigid foam
-PEX pipe for radiant floor heating
-Rebar on chairs
-4-5" concrete that will end up ~2.5" below existing floor level
-Finally, a company is coming in to install "clinker" tile, it's made in Germany and used in many high end auto shops and other facility's. This is vibrated into a 2" bed "grout" or "mortar" of sand and Portland so they can control the level perfectly.




The intent of this thread topic was not to "cheap out" or do anything half-a$$ed, it was merely educational since as I stated I can get the millings readily and cheaply if it would work. I will use them (again) for the driveway base for sure.

Thanks to all those who've responded so far, I really appreciate it.
 

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I'm missing the issue of using it vs. stone or gravel. What I have in my driveway is at least 80% gravel. I've had it for almost 25 years, concrete trucks, tractors and tractor trailers have been on it constantly without it ever moving. I think it's really good stuff and i wouldn't think twice about pouring over the top of it.
 
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As someone who works in asphalt / heavy highway construction, I can tell you that every major airport with concrete runways are sitting on cement treated base, then several layers of asphalt, then 2' or so of concrete thick. And to this date, we build new bridges on rural routes with concrete beams and cover the deck with asphalt as a wearing surface. No they do not "react" to each other. Funny thing is the reason why more people do not use millings under concrete or for any project here in NC is because you can get washed stone cheaper than the millings! BUT, given the current administrations stance on emissions, millings may become much cheaper if the asphalt plants are limited to less of the % millings allowed/permitted into new asphalt. Currently you can get away with 20-30% of millings into the new asphalt. However by using millings, the VOCs that are created is higher than using all new raw materials. Bottom line, use the millings if you can get them cheaper than stone.
 

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I think this is all about economics AND availability! Too me, if the base soil is WELL compacted, then millings, in several lifts/layers, compacted, the foam and then concrete, it'll be fine. Bob
 

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I see three critical items: how well each layer is compacted, the placement/height of the chairs, and the size of the rebar. Do your homework on chairs & rebar! Bob
 
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If you use it, make sure to compact the living he** out of it doing very short lifts. You're using foam so that's much better than just pouring directly over base material. Whoever does the foam, get SUPER fussy. Make that base as flat as a pancake so that the foam sits completely flat and is supported over 100 percent of the foam board. This can be a PIA and takes time with a screed. Watch my Youtube vid on how I did mine.. I'm no pro but it worked out well for me. If you're contracting out the foam board walk over every inch of it after it's put down, you'll instantly tell how well they did. Good luck!
 

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Discussion Starter · #39 ·
If you use it, make sure to compact the living he** out of it doing very short lifts. You're using foam so that's much better than just pouring directly over base material. Whoever does the foam, get SUPER fussy. Make that base as flat as a pancake so that the foam sits completely flat and is supported over 100 percent of the foam board. This can be a PIA and takes time with a screed. Watch my Youtube vid on how I did mine.. I'm no pro but it worked out well for me. If you're contracting out the foam board walk over every inch of it after it's put down, you'll instantly tell how well they did. Good luck!
Thanks, I have watched your video and learned some things.
I'm doing the sub-base, foam, piping, and rebar myself.
 
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