Concrete specifications for pole building

[Egon]

Concrete water content is measured by "slump".

On industrial projects slump will be one of the concrete specifications. Later when core samples are tested the additional water will show up as reduced failure strengths. Depending on situation it may mean a reduction in payment or replacement.

And if it is to stiff to work you will end up with a big pile

If thats the case its out of spec or the placement crew is inexperienced, slow or too small.

 

[Gary Fowler]

Slump is only an indication of WC ratio. The only true measure is controlling the amount of water added. Check the batch ticket and see if they allowed for additional water to be added at site. Some do unless prohibited by the client specifications. Michigan Iron has a unique way of checking slump that I never heard of. If you can drop a shovel of concrete from knee high and have a 6" slump it is likely too stiff to place. A slump cone for testing per ASTM standards is approx 6" diameter on bottom and 4 inchs on top, concrete is layered in 3 lifts and consolidated with a round nosed rod by plunging the rod in at least 25 times for each layer and penetrating the previous layer by at least 2 inches. It is then raised carefully and slowly and the slump measured by inverting the cone and measureing down to the concrete pile. 4-6" slump is usually considered acceptable for standard concrete without any plasticizer added. Plasticizer is a chemical that gives the concrete properties of higher water cement ratio without adding the water and the effect usually last for only a couple of hours before fading away.

 

[Egon]

Good information!

Unfortunately I'm many years out of date to when we had the driver add water before coming on site. In this case our major payment issue was depth.

 

[smfcpacfp]

You guys are getting too technical for me. I am having it done and I am taking the warning and advice here. I am going with 6" of 4,000 PSI concrete with mesh and rebar. The additional depth cost about $900.

I just hope I get lucky and it isn't below freezing too much of the day at the end of October when they do the job.

 

[sixdogs]

I have poured concrete in two barns with no problems and very heavy equip. The first was in gravel-based soil in Maine and was 36 X 48. I dug the sides deeper with gravel and went rebar on 20" (I think) spacing and 6" of high pressure concrete @ 5 1/2" think. Had a few cracks but NO expansion cuts. To this day, I don't remember why.
The second was in Ohio clay with a crushed rock base, wire mesh and 5 1/2" of high pressure concrete on a 42 X 60 size with good expansion cuts. Lots of heavy equip and I can't even find a crack on the joints. For me, the few extra $$ for concrete or steel is a good way to spend money. And, of mention, you can never have a barn too big.
This is a good thread with wise info.

 

[Normanc]

I read with interest offer my comments as I have some experience with placing concrete for both floors in a building/garage and for a driveway. The first and foremost item is to have a good drainage layer beneath your slab. Keep the top of your finished floor a minimum of 6" above the surounding ground so as to promote positive drainage away and not into your building. I would recommend a minimum of 12" of crushed rock or good gravel underneath the slab. Thicken the slab around the permineter. If you are placing a 5" slab consider using 2" x 8"'s to form the perimeter. This allows you to backfill around the slab and gives you additional thickness should some washing from the drip from your roof occur. Place a layer of plastic (6 mil) on top of the gravel to prevent moisture from coming up into the building afterwards. Next I would place 8 x 8 x 6/6 welded wire mesh (that is, 8 gauge wire in 6" squares) over the entire area keeping it about 1/3 of the thickness of the slab off the ground. I supplimented the mesh with 1/2" rebars around the perimeter of the slab and at 4' on center. Keep the rebar at the bottom 1/3 level as well. You may still have some cracking in the floor due to shrinkage in the drying process but the adjacent concrete should not move vertically in relation to one another. Use 4000 psi concrete with 6% air entrainment (the concrete supplier knows all about this). This concrete mix will resist the freeze/thaw that we experience up hear in the north east. Yes, only use the minimal amount of water in the mix to make it workable. Power trowel the surface to a smooth finish. As mentioned in an earlier reply, form and place a concrete apron at all door locations. There surfaces should have a broom finish for traction, sloped away from the building and they make a great work area.

 

[Builder]

I went 6", rebar and remesh not the rolls.

I doubt there would be a problem with an RV on 4". I was concerned with backhoes, dozers etc that have some really heavy point loads.

I would at least go up to 4000 psi concrete, you are probably getting speced 3500

Problem with putting rebar in 4" concrete is it sometimes creates a weak point in itself if it get's to close top or bottom. If you think about it, 4" concrete is usually only 3 1/2" then put a 1/2" piece of rebar in there and you have 1.5" on each side if it is perfectly centered. 6" gives you a little more leeway to work with.

This is what I ended up with, not sure it is right, but nobody said it was not enough, and plenty said it was too much, but the only downside I heard was the extra money I "wasted". I figure if it cracks and comes apart now, I will feel I did everything reasonable. If I had done less, it would eat me up.

I think you have a nice layout there, but why space the rebar so far apart? It really won't do much with that kind of spacing. I go max 2' square spacing.
Been doing that for decades and no call backs. In fact, one of my customers stores MACK 10 wheelers on a floor I poured for him that way over 15 years ago. 5" thick, rebar on 2' centers and no cracks!

 

[whistlepig]

I have had two pole barns built. One with 4" of concrete and wire mesh and one with 6" of concrete and rebar. The barn with 4" of concrete and mesh always sounded like I was walking on something that was hollow. 6" of concrete and rebar sounds like walking on solid granite. Also the 4" floor had pea gravel under it. With the 6" floor I went to "Chip's and Dust" and packed it before pouring.

 

[crbr]

Several months ago, I started a thread about having a pole building built. It is going to be a Cleary building (30 by 48 by 14 feet) and appropriate for the kinds of snow loads (20 to 30 feet per year) we get in the UP of Michigan, and they will build it during the last week of October.

The proposed contract calls for 4" of concrete with wire mesh. I was wondering what you guys thought of this. The soil is pure beach sand, thus there is no heaving in the winter. I read somewhere that you should have 5 to 6" thick concrete if you are going to have heavy vehicles like the RV that will be stored in it.

As someone said either here, or elsewhere, it is cheaper to get concrete right the first time, than to redo it. So what would you guys want for concrete specifications?

Rebar and a 6" placement. Wire mesh is useless. Expansion joints-a-plenty then fill in with self-leveling filler. Air-entrainment admixture and fiber admixture. 4000# mix.

 

[Duffster]

I have had two pole barns built. One with 4" of concrete and wire mesh and one with 6" of concrete and rebar. The barn with 4" of concrete and mesh always sounded like I was walking on something that was hollow.

the 4" floor had pea gravel under it

That is part of the reason right there.