Concrete floor info

[mpolli]

Would like some advice before I start callin concrete people.

GF needs a concrete floor in one part of her barn. It is about 400 ft^2 maybe. So I figure about 4 yards should do it. You can't get a truck too close. It is about 120 ft down a hallway to this area. So you could pump it or wheelbarrow it. Do I need remesh, or glass fibers? I am thinking about 3.5" thick, it will just be used for storage. What is going to be the cheapest/best way to get it done?

[leathermang]

Ok.. I am going to risk telling you what I would do in that situation knowing some people who have not studied concrete are going to faint when they read it.
This is the best way to get it done. It will cost the same as the other methods but your money will be IN the better materials instead of the labor which will drive off from the site.
I used this for a floor where I only had access through a window... and I know of other people who have used this method...I first read about it being used on the San Francisco BART.
The more you read about concrete working and designing rules the more you will appreciate this.
First it eliminates the really strong forms normally needed. It spreads out the labor so that it can be performed by a few people instead of having a whole trained squad on site at the time of the pour.
It takes advantage of the fact that the least amount of water added when Placing concrete makes the strongest mix. You put in the mixed material DRY.... and tamp it into place...
You use the same amount and placement of rebar and concrete mesh you would have used for wet placement in the same location.
It will take about one third more concrete per cubic filled space.
If you are smart you will keep it wet at least TWO WEEKS... if you read the engineer reports on various concrete mixes you will see they use 28 DAYS as the test time... of the concrete being kept wet to judge what any particular combo is capable of producing in strength...
This means you can place this dry mix and tamp it at your leisure.. get it exactly how you want it... then either infuse water from under neath ... or on top... you may want to protect the surface from footprints and water stream by placing burlap bags over it... anything to keep it in place while you gently add the water.. it can be added slowly but must keep being added and kept wet until the proper time has passed... and I really suggest two weeks minimum....
It has the potential of being several times stronger than any normal field placement you have ever seen ...

[engatwork]

Hmmm, interesting concept which sounds like it should work fine if you are not loading up large operating machinery on it. Have you ever taken a core out and tested it? It would be interesting to see the results.

I have actually taken unopen bags of quickcrete and stacked them up like sand bags to shore up sides of trails in low lying areas. Go back 6 months or so later and they are as hard as if you would have poured it.

[leathermang]

Jim, try thinking about it from the other direction...the physics of pouring wet concrete and maximizing its strength.... and I promise you that whatever you would have put on it.... machinery or power hammers.... are going to be better supported than normal wet placement... due to the physics of concrete....
If you have studied concrete you will not have to have a core drilled...
Your example of dry stacking sackrete bags is a perfect example... many a pond dam has been made stacking them while driving rebar down through them ...
While accidental wetting from being out in the elements will work...
a little effort making sure they stay wet for a few weeks will ensure their potential strength is reached.....
With just normal care you can figure on three times the strength of a normal pour... at the minimum...

[Yak]

Google books, "dry cast concrete" has a popular science article, including the BART reference.

A small area at the end of a hallway doesn't sound like it needs super strength but in Seattle, in a barn, is she looking for "dry" storage on the slab? Prep for the slab base (compacted gravel?) might be needed.

Would a small mixer in the area be possible? I'd think for that small a pour the additional expense of a truck to pump it would be prohibitive.

Any chance of temporarily removing part of the barn wall, assuming the pour is on an exterior section?

[leathermang]

Concrete slabs should always be ' floated ' on sand... at least four inches... and maybe more depending on the soil composition and the freeze line...
Rebar should be placed near the bottom of the slab.... but at least one inch above the bottom.... and the more steel included the better is the rule..

[engatwork]

During forming/pouring in paper mills we also would put a vapor barrier down before putting the rebar/wire mat in place.

I'll read up on the dry concrete approach. It sounds like a good idea to me. On the new shop it did not initially have two roll up doors on the front of the barn I took down so I had to move some dirt in some low spots to build up ramps to the roll up doors. My plans were initially to put crush and run on it after the dirt has been driven over for awhile to compact it and it has been rained on a time or two (I sure wish it would rain). I may go the dry concrete/bagged Quickcrete route on it after a couple months.

Seeing as how the access is limited I believe I would try this approach on the original posters project as long as there is water available that is close by. Do you run a sprinkler on it to keep it wet?

[leathermang]

No sprinkler is needed....
I put 6 mill plastic over the burlap bags spread around and just let the water seep under it...since I was using a soaker hose type tecninque... I had the plastic to make sure all stayed wet after getting wet on the surface.... did it in summer time..... Texas summer.... You can also plan ahead and place plastic pipe into the concrete and let it infuse that way....you can also just wet the sand underneath it.... all are fine methods.... the speed of getting it wet does not matter.. as long as it is a one way function... do not let it dry out until you are satisfied it all has had ' free water' available for the hydration process for the two weeks.. or longer if you can ... tests show that concrete underwater continues to get harder for up to 50 years....
Tamping or using a roller is part of the process..
You are getting it where you want it with the molecules as close as they can be... with water you can not do that... but once placed and the water added... plenty of water for as long as possible... those the the strength rules for concrete... water is only added for pouring so as to be able to ' place ' it... move it around.... but every drop added decreases the strength.... dry packing is the best of all possible worlds particularly for one or two man operations.. as placement can be spread out over weeks if needed....

[leathermang]

Originally Posted by engatwork

During forming/pouring in paper mills we also would put a vapor barrier down before putting the rebar/wire mat in place.

Seeing as how the access is limited I believe I would try this approach on the original posters project as long as there is water available that is close by.

Putting the plastic below a usual concrete pour is another way to help keep it wet for as long as possible... so as to not have the ground wick out the water from below...

They sell very long water hoses.. which can be connected to each other...and re used after this particular project.....LOL
They will sure run down a hall wide enough for the wheelbarrows to go....

[engatwork]

They sell very long water hoses.. which can be connected to each other...and re used after this particular project.....LOL

LOL

Yea, I know. The reason I said that is because where I will be working on the ramps is about 100 yards from the nearest faucet and those faucets are abotu 100 yards from the well/tank. No telling what kinda water pressure I'd get that far away using water hoses.

[leathermang]

You are IN LUCK... you do not need pressure... only water ... so if it will get there it will be fine...

At that distance.... Tractor Supply Co has black plastic pipe pretty cheap....and very good for that sort of thing...one inch... one and a half...

[Hatterasguy]

3-4 inch's is fine if its not a load bearing floor. What really matters is the sub surface, ideally you want 6in of nice crushed stone. I'd also use 4k psi.

Re bar you can use it or leave it out, it will crack either way. Around here everyone started using it about 10 years ago, but half the foundations in the city don't have a rod in them and are fine.

As for getting it their I'd pump it, er well my concrete guys would. Pumper trucks are not cheap, but sometimes you can't avoid it. Around here they are a G note per day, 1 day min.

[MS Fowler]

The trick with dry-placed concrete is providing sufficient water for complete hydration. Cement will attract as much water as it can find. I would suspect you'd need to keep free water on the surface of the slab for a full month to be sure.

One error in your presentation concerns the 28 day strength. That is a practical limit set by convention for concrete strength. Properly cured concrete continues to gain strength in the presence of water for years, or centuries. Also note that concrete to be tested is cured in the presence of an excess of water--either in a humid room with free water on the surface of the concrete, or submerged in a tank of saturated lime water ( so that lime is not leached out of the samples).
Best Practice for the vapor barrier is to place a 6 mil poly sheet and cover it with 4 inches of sand, then the concrete. The reason for this is that concrete curls along the edges where water is only allowed to escape out the top of the slab--as in the situation where the vapor barrier is in contact with the bottom of the concrete. Placing a 4 inch sand layer above the vapor barrier allows drainage in 2 directions and helps to reduce the edge curl.
I'd place #5 bar 2'OC EW on chairs that support it about 1/3 the thickness of the slab.

Then again, for a storage area in a barn, this may all be overkill.

[Chas H]

Concrete contractors have powered carts for transporting concrete from truck to site.
No need for a pumper. I had a mix on site truck pour my barn floor because a flask mixer couldn't/wouldn't drive over lawn. The operator added fiberglass to mix; no other reinforcement was used. After 10 years the floor -1100 sqft- has one small crack. The floor is 3-4 thick & 3000 psi.

[aklim]

Where she lives, what does the city inspector have to say? Mine made us pour a 12X12 footing around the slab for added strength although the heaviest thing going on it would be the riding lawnmower.