30 foot by 40 foot concrete slab with bag Quikrete?

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  #1  
Old 08-25-12, 11:45 AM
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30 foot by 40 foot concrete slab with bag Quikrete?

... lol. Now that I have your attention, please hear me out about this project.

We are a non-profit wildlife management organization, and have been given a 150 acre tract of land in Central Texas. The land is rugged and is 1+ mile from paved roads and utilities. However, the property is accessible with SUV type vehicles. We have a donated 40 x 30 metal structure than we'd like to put on the property to store a tractor + use for covered storage of materials and what-not. The building needs to be placed on a slab foundation.

There is no-way to get a concrete truck anywhere near the property. Using 1 cu. yard toters is also out. That leaves sack concrete. We have access to a tractor mounted concrete mixer that can do 8 cu feet at once & we have tons of volunteers. There is a water well on site.

The site is well drained with a slight slope- approx 1 inch per 10 feet. We'd be using crushed limestone (aka road base, 1.25" to dust) for the compacted base. 6mil vapor barrier & rebar and/or wire mesh for reinforcement.

Is there anyway to do this? Any input would be greatly appreciated.
 
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Old 08-25-12, 12:33 PM
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Welcome to the forums! Got my attention. At 3" deep, you will need 11.11 yards of concrete, which converts to 500 each 80 pound bags of mix. At 4" deep you will need 14.81 cu yards of concrete or 667 bags of mix. And you haven't even considered the apron footing around the building bearing points, which will need to be poured at a different depth depending on frost line. Concrete Foundation - Three Types of Concrete Foundations - The Concrete Network. I'd say you are looking at 1000 bags of concrete.
My concern is going to be cold joints where you can't pour it fast enough for a solid pour.
 
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Old 08-25-12, 01:13 PM
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Hi Chandler,

Thanks for the reply. Yeah, we did the math too- and it is daunting:

Without the apron footing we calculated 15 cu yards @ 4" deep. Convert to feet is 397 cu feet. At .5 cu ft per pad that is 800 bags. Add the footing and we are looking at 1000 bags- same number you came up with. 15 yards of concrete goes for $1250 around here. However, at $3.10 a bag we are looking at $2500. I figure we'd need to round that up to at least $3000.

On the flip side: labor is free as is the building which goes for approx $15,000.

Yeah, doing one whole pour isn't going to work no matter how much labor we have- just can't make the concrete fast enough with our hot weather. An option we have been kicking around is doing it in 10x10 sections. Figure 2x6 forms at the edge and then using 2x4s to divide up the interior. Using 2x4s would give clearance for rebar and wire mesh + would allow some concrete to purposefully spill out and create a key-way joint for the next section. We could help the joint via sandblasting and bedding grout, but it'd still be a cold joint.
 
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Old 08-25-12, 02:57 PM
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If you can get fill stone in there and some type of equipment (bobcat? backhoe?) in there to excavate, then why can't you get concrete there? I have done hundreds of jobs that the concrete was either bobcatted in, brought in with a power buggy, or pumped with a concrete pump. If you are going to store a tractor in the barn, you must have a way to get it there.
Concrete trucks are rugged and can certainly go off road. Just get it as close as you can and go from there with the buggy/bobcat/pump.
 
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Old 08-25-12, 04:33 PM
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On Pecos's note, if you can't get a concrete truck in there, how are you going to get 600 bags of concrete there? The ready mix place will likely put 15 yards into two trucks any way, you could even have them split it again in to 3 or 4 trucks for a nominal up charge. You will likely still be cheaper than bags and a lot less hassle.

Another thought is take some picts or have a guy from the ready mix plant come out and show them what the job site looks like.
 
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Old 08-25-12, 05:55 PM
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Why exactly does the building need to be placed on a slab foundation? Perimeter concrete footings would be capable of supporting the building, and require only a fraction of the concrete an entire slab will.

Tractors are perfectly happy, parking on compacted gravel.
 
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Old 08-26-12, 10:32 AM
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Pecos, Tolyn:

Thanks for your replies. The property in question is land-locked, and there is no suitable building site within 4000 feet of a road that can accommodate a concrete truck. We did look into pumping- even if just part way, then using a buggy/bobcat for the rest, but the terrain can't accommodate either machine.

We can get a high clearance 4wd 45 hp tractor to the build site, but it takes time- too long to use it as for fresh concrete transport. However, we can move 1.5 pallets of bagged quikrete per trip with the tractor. As for the fill, I should have clarified: we are going to harvest natural material already on site. Central Texas is limestone country, and there is plenty gavel on the property.

One of our members is a General Contractor, and he had an engineer come out from a ready-mix plant and do a site survey yesterday. His recommendation was to use a helicopter.

I realize this project has a Don Quixote element to it. The reason we are dead set on putting the building up is that we only have a Conservation Easement on the property at the moment, while the title to the land is being held in trust until we reach certain developmental and land remediation milestones. One of those is the construction of a predetermined square footage of enclosed space on the property. This must be done by October 1st, so there is no time for us to develop roads and such. We purchased the easement from another group, which is why the deadline is so tight.

Nice mess we've got ourselves into huh?
 
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Old 08-26-12, 10:42 AM
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Just wondering....around here you can buy giant shopping bags of sand (best description I can give)....and a dump truck full of gravel/stone....then you might be able to just buy portland cement? Might be cheaper...I dunno. If the tractor can transport pallets of concrete...it could transfer the bags of sand.

I guess no way to get a dump truck load or 3 of gravel/stone up there?


Hmmmm....any Army Engineer bases around? Sounds like it would be a great training mission. I've seen them fly bridge parts. The time factor would be the issue.
 
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Old 08-26-12, 10:48 AM
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BridgeMan45 :

This is probably where we are going to end up. However, we still can't do an entire perimeter footing in one pour which means we'll have cold joints.

If we do this how long should be allow each section to cure before pouring the next section? A few hours, a few days, what is best? As for the joint, we are leaning towards a cane-fiber product as an expansion joint. But do we even need a joint at all? In our area freeze heaving is not a concern, so most builds we've seen don't use any material at all between two differently poured slabs.
 
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Old 08-26-12, 11:02 AM
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Gunguy45:

Yes, that is certainly an option for us- we can get the constituent products up there no problem at all. But even if we go that route, we still can't make the concrete fast enough to do one whole slab / footing in a single pour.

Since we've effectively eliminated the possibility of getting "real" concrete to the job site, our main question at this point is if it as at all possible to pour a slab in 10 x 10 sections? Most concrete people we've talked to have said "you probably can, but I've never seen it done".

I guess we'll give it the 'ol college try and see how it turns out. Any tips and or suggestions would be most welcome.
 
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Old 08-26-12, 11:52 AM
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I like Bridge's idea of a poured perimeter to sit the building on and leave the interior. If, at a later date, you decided to have a concrete floor, you could contain it and make the pour. Maybe by then, you will have a 4 lane close by. I don't think I would worry too much about the joints on the footing if your freeze thaw cycle isn't that drastic. I like the helicopter thingy, too.
 
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Old 08-26-12, 11:59 AM
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I would think you could do it in 10x10 sections and maybe put an expansion joint in between. You can mix a lot of bags with a mixer, and if you figure out the water you need (IE: mark it on a bucket) it goes pretty fast. You said you have access to a tractor mounted mixer, so I say give it a shot. Sounds like your slim on other options.

If you can, wait for a cool day. The concrete will set up slower.

Another option: I know a guy that sells chemicals to ready mix companies that can "sleep" concrete to delay it from setting up. You may want to check into that but it will add more cost to your project.
 
  #13  
Old 08-27-12, 04:20 AM
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Slab

The company I worked for built a 40M sq. ft. warehouse and placed the concrete for the floor in alternating sections. The forms were built with key ways to form slots in the edges of the slabs to lock the slabs together. No foreign material was used between the sections.

If you could get the material in to the site, buying the aggregate materials in bulk and mixing on site with cement and water would be cheaper.
 
  #14  
Old 08-27-12, 05:31 PM
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Smile Solution

Hello,

I've got a great solution to this job, Maximizer concrete mix. This site will direct you to a high strength conccrete mix that is light weight (less trips). I have used this product several times and it has never failed me. Great for slabs, posts and pretty much any type of concrete job. It can be purchased at Home Depot, Lowe's or almost any small hardware store.


It doest take more water per 80lb bag but you mentioned water was not an issue.

Let me know how your job turns out.
 

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  #15  
Old 08-27-12, 06:30 PM
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Light-weight concrete with a very high water-cement ratio. Not sure I'd want to go there, as both could result in long-term durability and permeability problems.
 
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