Will this Concrete Mix Work?

[robertwhite]

I am building a shop on my barn and I need to level it out first.

The builder will be using a crushed stone mix (like item 4) for the initial leveling, then once level will be pouring 4 inches of concrete. He will be pouring a 3600psi full fiber (?) mix and where the 2 post lift (10K capacity) will be going, he will be adding rebar in a checkerboard pattern before it is poured.

So I guess the question is will a rebar reinforced 3600psi mix allow for my 10K two post lift?

And, can I drill after the pour to install the lift or do I need to put anchors in during the pour? I am undecided as to exactly which lift, so I don't know how I could do the latter.

 

[jkeyser14]

This is just my opinion, but if it were me I would ask him to pour 6" thick in a 2'x 2' area where I was planning to put each lift post. It wouldn't be a lot of extra cost since it's a minimal amount of concrete and it will give you extra piece of mind.

 

[robertwhite]

This is just my opinion, but if it were me I would ask him to pour 6" thick in a 2'x 2' area where I was planning to put each lift post. It wouldn't be a lot of extra cost since it's a minimal amount of concrete and it will give you extra piece of mind.

I should have mentioned that the slab will be poured over existing 4-6 inch old pad. The whole thing slants (on purpose) as it was used for hog wash drainage years ago. That is why I am re-doing it so its level.

Guess I should also ask if I need to do anything to the old pad to ensure bonding where old meets new if no crushed stone is needed in spots.

 

[tatra]

i would be more concerned about adhesion to the old pad.......what is he doing to prep for this ?.............

 

[stafford]

Gravity

 

[rwhite692]

This is just my opinion, but if it were me I would ask him to pour 6" thick in a 2'x 2' area where I was planning to put each lift post. It wouldn't be a lot of extra cost since it's a minimal amount of concrete and it will give you extra piece of mind.

I would go 6" for the whole slab. When I did my shop, based on my intended use, contractor recommended 6" throughout and used a 4.5K PSI mix.

 

[contactme_11]

I would not go less than 4000 psi for concrete that will have the weight of cars on it.

 

[ddawg16]

I agree with Contact.....4000 PSI....it's just a little bit more portland....

So, if we understand this correctly....you have an existing slab...that your going to be putting about 4" of gravel/sand on......then rebar along with another 4" of cement?

If the bottom existing slab is in good shape....no huge cracks...not likely to move....then I think you will be fine....the gravel layer will provide enough 'coushion' and give to prevent the upper from cracking.

But I would still go 4000....and the fiber and the rebar.....

 

[robertwhite]

i would be more concerned about adhesion to the old pad.......what is he doing to prep for this ?.............

Anywhere new concrete will meet old, he is planning on drilling holes and using pieces of rebar as a nail protruding up as a kind of anchor. There are also about a dozen 4x4 post holes (that the posts have been removed) that the concrete will be allowed to fill in acting as further anchor sites so the floor can't shift.

So, if we understand this correctly....you have an existing slab...that your going to be putting about 4" of gravel/sand on......then rebar along with another 4" of cement?

Its kind of odd so try and picture this.............Area is 25' x 90'. The entire length (90') is higher on the left side and then gradually slopes gradually down about 12" once you get to the other edge (25' wide). It used to be a hog barn and the floor is poured that way to allow for easy washdown as the water/**** would run off to the lower side.

So if I have explained well enough, you should now have a picture in your head.

The new floor will be crushed stone over the entire length at a sufficient height to level the whole slab (12" at the outer edge up to almost nothing at the other edge). Once leveled, the concrete will then be poured and reinforced.

The existing concrete is many years old and in good shape. It was also fairly rough poured and is in no way smooth like a garage floor would be.

In the end, I would imagine the entire floor, whether almost all concrete at one edge or concrete plus stone, plus concrete again, will be a total thickness of anywhere from 7 or 8 inches to 18 inches depending on which side of the floor we are looking at.

If I up the psi and keep the full fiber plus rebar pins all over, plus rebar crosshatch under the lift, I would imagine this would be sufficient, no?

 

[1320stang]

I think the concrete at the lift location should go all the way down to the existing slab with no gravel between, and a higher PSI mix.

 

[Herb]

Ok, instead of paying for the materials and labor to level the area for new concrete, why not just pour extra concrete directly on top of the old stuff? It would be interesting to calculate the cost for the extra yardage vs. fill +labor.

 

[robertwhite]

Ok, instead of paying for the materials and labor to level the area for new concrete, why not just pour extra concrete directly on top of the old stuff? It would be interesting to calculate the cost for the extra yardage vs. fill +labor.

Interesting thought, but I would imagine the concrete alone would be way higher. It is 12" difference at one side. Multiply that by the 90' long building and say it goes 20 feet wide or so before it is reasonably the same level and that would get pretty expensive. There is also about a 25' x 12' section at the end of the building in which there is nothing but dirt, so that would be even more than 12" plus the 4" of new concrete.

I am going to get a better idea of how many yards of fill is needed tomorrow.

 

[folgers]

Anywhere new concrete will meet old, he is planning on drilling holes and using pieces of rebar as a nail protruding up as a kind of anchor. There are also about a dozen 4x4 post holes (that the posts have been removed) that the concrete will be allowed to fill in acting as further anchor sites so the floor can't shift.

I don't like the idea of tying into the old slab. Concrete will shrink as it cures. You would be anchoring one part of your new slab while other parts of it try to pull and move away. You'd be better off to fully float the new slab with at least a couple of inches of sand or fine gravel covering the high spots of the old slab.

Fiber is not a replacement for reinforcement in concrete. 4 inches of 4000lbs mix with re-bar or wire mesh throughout the slab is strong enough for light trucks and cars.