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Pulaski, TN | I'm putting up 2 grain bins. First one is 28' diameter. Bin should hold about 8500 to 9000 bu. I'm planning on putting wire not rebar in the concrete. I will pour a 30' x 30' pad. How thick should the slab be? The second bin is 20' diameter and will hold about 5000 bu. This pad will also have wire in the concrete and the pad will be 22' x 22'. How thick should this pad be? Thanks!!!! |
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NE SD | <p>Our bin guys won't pour a pad with forms less than 24" and about 10" thick in the center these days. Bins tend to settle a few inches over time, and having the 2' forms allows for some setting but that way a guy can use a straight out sump and still get an auger hopper under it. Four or five years ago they were using 16" and you needed an incline to get much of a hopper under them especially after they settled a few inches. These are on 42' 7-ring bins but they like that 2' equation for anything smaller as well.</p><p> </p><p>My bad, I thought most would naturally understand that it wasn't that thick from edge to edge. Pi$$ poor wording on my part.</p>
Edited by Chad H 2/22/2007 23:31
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| Do you mean that the whole pad is 24" or just that the bottom of the bin be that high above groung level? Seems like we put enough sand/gravel in the center under the bulk of the pad so we had about 6" thick pad but with about 2' at the edges. 24" seems a little over kill for all over thickness and about 3times the concrete expense if not needed for strength. |
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| I would talk to the manufacturer, but 5-6" for the floor with mesh should be adequate. The footings should be 18-24" and around 8" wide, below the anchor bolts, with a rebar cage wire tied.....again check with the manufacturer. |
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Lapel, In | Around here a bin of that size would have a concrete pad of about 6" in depth with a footer a spade wide and a spade deep near the outer edge of the pour. Could be different where Chads lives due to the much deeper ground freezing depth. I would imagine the depth of the pad would also depend on the height and diamater of the bin.Not sure I would waste money on wire.Wire won't keep concrete from cracking.It will only hold it together once it cracks according to an old time concrete company owner that I know. And since a bin pad will have no traffic on it, it should stay in place when it cracks(and it will crack).
Old timers big city contractors will tell you a pea gravel base should be used at least equal in depth as the depth of the concrete.
Edited by msb 2/22/2007 21:59
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NE SD | They move more than ya think though Bob. The bins I was talking about are 42' x 7 ring - about 33,000 bu. I'm sure with the smaller bin you could get away with a thinner pad towards the center by filling up towards the center but those 2' footings are nice for the sumps if nothing else. Digging holes in frozen ground doesn't work real well. They are poured to last at least this we know. Good damn concrete from the Hutterite colony. Grandpa put up 5 8500 bushel bins in the 70's. They were all poured with probably 10" footings and 6" pads. Today only one of them is still on the original concrete. It cracked right around the edges of the bins and they sunk, etc. One of them had a 2" or so crack right through the center of it so they must move more than you think. Rats had about 2 yards of gravel and corn in there under the air floor. Shoulda seen the mess. Every time the loader hit that pad 30+ rats ran out.
Edited by Chad H 2/22/2007 22:06
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| They must have an interest in the local ready mix plant. |
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| Put in a full drying/cooling floor and inclines become a thing of the past. That way the auger tube is above the concrete and you have chance of spoilage on the cement and way better air flow to keep the grain in condition. |
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Ethridge, TN | I've built 4 bins, and have repaired numerous others, with most of those repairs being caused by skimping being done on the concrete work. You want a real fun job, take a 42' - 9 ring bin and have to put it up on jacks, jack hammer out all the concrete, and redo it all. Why do bin foundations break? Because time wasn't taken to put in the proper foundation under the outside edges of these bins. Wire, don't waste your time, you need rebar if you really intend to keep your bin foundation together. That means digging a footer, size depends on bin size, as well as climate conditions, and also back filling. Then you need upright rods, drove in the ground to hold them in place, and then several rounds of rebar, forming a circle in your footing area, and a 16" to 24" cross hatch across the floor that is tied to that circle. I have yet to have a floor/footing crack that I've installed in this manner. The last I did was a 48', 50,000 bushel, bottom of the footer was 24", tappering up to 4', and was 3' deep. The floor was poured 8" deep, and all tied together with rebar, two rounds, 4 bar runs, and the floor was a 16" cross hatch, 1/2" rebar. If you want a bin foundation to last, you have to build it do that. |
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NE SD |  Don't know anyone that would build new without one. |
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WC MN | I agree. |
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Somerville, Indiana | I really think 5/8 rebar wired together every 12 inches is better than thicker concrete. rebar is for strength, concrete is for keeping a smooth surface for bin walls and floor supports. be sure the rebar is bent into the footers also. |
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| If you put your tube in the concrete, make sure you have an incline in the tube to drain moisture to the discharge end of the bin. (outside) It is good to do this even with one above the floor. You want your floor to be level even if you are not putting in a drying floor, as if you decide to install one in the future, your floor is level to make installation of the drying floor simple. I would recommend beveling the edge of your floor outside the sidewall of the bin when you pour your concrete floor to permit drainage outside the sidewall for ice, rain, etc. |
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Somerville, Indiana | sorry, didn't mean to disagree with you. you have a good plan.
also, glad to see the new map dot. hope it works out as good as we both want it to. |
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| Chris, that's pretty much how our last 42'x7 ring bin's foundation was poured. Only difference that I can see the taper was 6' & the balance of the pad was 10". Reinforcement wire was secured to the rebar as well. Plans from the bin dealer called for 45 yds of concrete but about 63 was used. |
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Southwest Illinois | Footings and form height are two different things. A footing is how much concrete you have below the surface of the ground. Form height will determine how high your bin will sit off the ground.
Footings vary depending on location. In south central Illinois most will tell you around 30" deep, w/ rebar, 36" if you need peace of mind. A 8-12" wide footing works for smaller bins, less than 30' in diameter. Once you get to that size you probably need to consider a footing 12-18" wide for 30'-48' diameter. These are considering wide corrugated bins 6-8 rings high.
Form height varies by everyone. I like the 18-24" if you are going with a short aeration floor and a 10" unload. In this case the 10" unload will only be about an inch or two from the concrete floor. If you are going with a tall drying floor and an 8" unload the 12" forms will work as the unload is now more like 8" above the floor. We haven't put drying floors in for some time and go with the short aeration supports with a 10" tube. The 18" forms will work, but the 24" forms are nicer if you try to get a 12" truck auger under them. If you go with a vertical unload then you can get back to the 12" forms and be OK. My advice use the next size taller than you think you need. If you pour rock or sidewalks around the bin you'll be glad you did.
As far as thickness of concrete everyone will have an opinion. If you have a great base down and use 5/8 rebar on 12", 6" deep is plenty on smaller bins(up to 15K), we go 8" on the bigger bins. When I say good base, I mean a clean excavation followed by 6" of clean rock and 6" of pug mill or grade 8 compacted. On bigger bins I'd go 8-12" of rock under your pug or G8. I've seen guys pour concrete 12" thick only to see it crack because they used a poor base. I would also use rebar and not mesh. If you get a crack, water will rust that flimsy mesh apart in 5 years, rebar will hold together much, much longer. Remember, you can replace roof sheets, augers, floors, bolts, etc, but you only get one shot at the concrete. Do it right or hire it done.
Edited by Lookingglass 2/22/2007 23:22
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Rural Valley pa | nt |
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Southwest Illinois | I guess I haven't seen that. What we get comes with a protectant on it that keeps is from rusting, but if you let it set out a few months it will be gone. Have any info? |
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Rural Valley pa | go to any supplier that sales products for highway / bridge construction pretty much guarantee they will have it. if not can get it for you. cost is higher but even with water getting to it will last for a long time. I have used # 4 bar for fence post and the have been in the ground for 14 years and steal haven't rotted off. don't waist you money on epoxy coated bars in the footer put them on the top pad an tie the in to the footer any were the air can get to the bar+water is were you will get corrosion in a footer under ground it will be safe..
Edited by Dave75 2/22/2007 23:52
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Southwest Illinois | Is it the light green looking rebar you see? |
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Rural Valley pa | that's it but take a pocket knife and scratch at it should peal off like plastic coating if it don't its not epoxy just paint.. |
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| Not a concrete expert but you said you were running a 30 by 30 pad. If that means square it has been my experience the corners that are sticking out usually crack off when the bin settles. You can probably make them strong enough not to but I think that is expensive. If you want a clean pad around your bin I would do it after the bin has been filled once and the settling has taken place. |
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Ethridge, TN | I guess I don't see where youu really disagreed with me  On the other, let's say it is going very well. I think Kevin is very happy with how things are going, cause we are actually getting a fair amount done. Still lots to be done tho before the planting rush starts, and that is just around the corner here. We are going to hold you a visit, or............ |
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| I agree, I don't think Interstate 80 is 18" thick and it gets hammered by 80k # trucks all day long at 75 mph, no direct immobile pressure. |
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How Thick Should Concrete Be Under Grain Bin?
