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concrete floor in barn
Sounds like what you are most interested in is shear srength from concentrated loads. Shear strength is around .45 compressive strength, which governs puncture shear. Believe it or not, the compressive strength of the subgrade is more important than the shear strength of the concrete. The crushed stone backfill will probably develop 2500 to 4000 lbs/sq ft compressive strength if properly installed over good soil. To keep the slab from experiencing bending, which you are not reinforcing for, you don't want to exceed the bearing capacity of the soil. With a 6" slab, with just temperature reinforcing, and 2500lb/sq ft subgrade, you have a load capacity on the slab of 10,000 lbs per square foot ( with a 6" slab, the bearing area is 2' x 2' at the subgrade). You would gain more from a thicker slab than by going to high stregth concrete. This is due to the 45 degree distribution of the load through the slab, which increases the bearing area on the subgrade.
Use regular concrete, have a well compacted subgrade, and thicken the slab to achieve the bearing capacity you want. The other option is to design a reinforced slab for bending to increase the bearing area at the subgrade, but that would get pretty expensive.
Hope this helps you.
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concrete floor in barn
Just some other thoughts to assure a quality slab:
No more than 6" slump when placed.
Don't allow over troweling, it softens the top of the slab.
Saw cut at 15' intervals 2-3 days after placement.
Wet the subgrade before pouring.
Stay away from high-ealy concrete, too many shrinkage stresses.
Make sure you have a Ratwall. You'll be sorry if you don't.
Avoid cold joints.
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concrete floor in barn
Rat wall and frost wall are essentially the same thing. Sometimes called rat wall because not only does it help control movement of the slab edge, it keeps critters from habitating under the slab. The exposed edge of the slab from the outside is a perfect place for rodents and small mammals to dig under the slab for a home. The "rat wall" prevents that. Also keep in mind that if you aren't heating the building, the subgrade will freeze everywhere under the slab. The best way to prevent frost heave is to keep water drained away from the building, and have good drained soil under the slab. The frost wall won't help keep the interior of the slab from heaving if you don't have drainage.
Insulating the comcrete in an un-heated barn isn't necessary. If you plan to heat it in the future, you probably want to consider it now, along with a good vapor barrier. If you use a compressable insulation, you will greatly reduce the bearing capacity of the slab. The location for rebar placement in the slab cross section, and the total area of steel in the cross section are critical if you are trying to increase the bearing capacity of the slab through bending. If temperature stability is what you are after, you need to consider that steel and concrete have very different coefficients of expansion, meaning that too much steel can be worse than not enough. It is recommended that for temperature reinforcement, steel should be about 1.5% of the cross section. As the concrete cures, it shrinks, developing compressive stresses in the steel reinforcing, with the subsequent tensile stresses in the concrete. Temperature changes add to these effects in cold weather as the slab shrinks further. If you have too much reinf steel, the tensile stresses in the concrete will lead to cracking.
The balance between the two materials is inportant.
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concrete floor in barn
Vapor barriers can be usefull, but it is the warm air that causes moisture to travel. If you don't have any heat in the barn, there really isn't anything to cause the moisture to move. The temperature inside the barn is going to be whatever the outside temperature is if you don't heat it. Insulation is only useful to stop heat transfer. If you don't have heat, there isn't anything to insulate. All the insulation is iseful for is to help keep the barn floor warm if you heat it. The ground under the floor will freeze if the barn isn't heated continuously, insulated or not.
Compressable insulation will reduce the bearing capacity of the slab. The best thing you can have under your floor is a well compacted granular fill, with plenty of drainage.
I don't have insulation or a plastic vapor barrier under my floor. I heat it only when I use it in the winter. I have a couple feet of compacted sand and gravel under the slab, and have no moisture problems. With a well draining fill, there isn't any moisture to move.
Most modern industrial plant floors are fiber-reinforced comcrete over 12"-18" of engineered fill.
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concrete floor in barn
Thanks, I am going to try it. I have another shed planned for next year that I would love to have options to use on the floor. Any organic material in the soil does create heat as it decays. I've though about adding organics to the soil under a floor to create heat during the winter, but have never tried it.
Sometimes being an engineer can be a handicap if you don't listen to practical solutions. I'm not too to old (yet) to listen. Just don't tell my wife. She thinks I'm just a brick headed Italian who happens to be an engineer.
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concrete floor in barn
Thanks for the article grinder. Interesting stuff for home building. I think it's important to note that the article discusses heated structures. The introduction of heat to the system changes the design requirements, and how you want and need the structure to act.
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