Straw Bales as Concrete Void Form for Garage Floor

Does anybody have any thoughts about using straw bales as a "void form" for a concrete garage pad?
Typical garage pads in my area are made on top of a gravel base that is deeper around the edge. This gives a one-piece concrete pad that is "thickened" around the edge for strength. These pads are pretty good, but they are only "thickened" around the edge and can still crack.
I want to dispense with the gravel completely, and use hay bales as a "void" form as follows:
Place bales in a series of solid 8ft x 8ft squares on the ground. Between each set of 8ft squares would be an 8 inch gap. If you can imagine, the concrete is poured over the while thing. The concrete would go down into the 8" gaps, giving an integral concrete "beam" every 8 feet. So instead of a "thickened" edge beam only, this pad would have a matrix of beams every 8 feet. Of course there would be rebar also.
The hay bales are basically there to "save money" on concrete (instead of pouring a 2 foot thick floor). I think this floor would be so strong that you could lift one corner and the whole thing would stay together (no cracking due to frost etc).
I am wondering about these hay bales though. I really don't care if they rot after the concrete sets. Does anybody see any problems? I would probably put plastic on top of the bales to seperate them from the concrete. Do you think I should also put plastic underneath them so they stay dry forever?
I think the cost would be less also. Typically, you need 2 feet of gravel under the floor to raise the grade of the garage floor. With the bales, I automatically get a 2 foot raise in the grade, as well as the extra strength from the beams.
Also, if you really want to go nuts, the beams can be made deeper (or the grade can be raised) with very little cost by stacking bales on top of each other. If you were to stack 2 bales (instead of one), the beams are deeper and it would not take much extra concrete.
I also like the fact that the beams (both in the middle and around the edge) are nice and "square". The "thickened edge" garage pad has a beam around the edge that is formed by the sloping gravel beneath it, giving a "not so pretty" beam.
Thanks.
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I think that by the time you buy,transport,and lug around that much hay you would be better off using concrete with extra rebar. tonyg
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snipped-for-privacy@yahoo.com (Wpg Man) wrote:

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What you are describing is a bad way of making a structural concrete garage pad like a parking ramp construction. Bare in mind that these structures are heavily reinforced with pre-tensioned rebar and high strength concrete. It takes special knowledge and skill to do this. you risk having your car drop 2 feet into a hole when, not if, your floor fails. Stick with gravel and go with a 6" pour instead of the standard 4" and go a good 10" around the perimeter for an integrated footing.
-- Mike D.
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I've seen it used for walls but not floors. If you want to save just backfill with old material.
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- Wpg Man -

- Nehmo - Crushed stone of the type you use under concrete in Kansas City runs about US$25/yard^3 delivered. It's about the cheapest thing there is.
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* Nehmo Sergheyev *
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So what is going to hold the concrete up when the bales decay? Please send pictures when you do this and the failure that will surely happen.
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How much rebar in the (20" deep?) beams and 8'x8' slab, if it supports a 4,000 pound car? How thick would the slab be?
Nick
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Sounds like a carton form slab.
It was suggested as an option on a high plastic index job. We elected to use lime slurry injection as a less expensive option that project.
I never got into the details of designing the bearings for that slab.
Carton forms are usually used to create expansion voids under grade beams. I know that hay was used for this void in the past, so your idea has merit. I would guess you simply need a strong enough slab to span the voids.
Waffle slabs have decks as thin as 2", though I would tend more toward a thicker slab. Post tension might be considered.
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Keep the whole world singing. . . . DanG

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Thanks for the reply, and thanks to all others that replied (even if you think I'm crazy, he he).
Your description of a "waffle" was just what I had imagined. If you were able to look up (from below) it would look like a "coffered" ceiling.
Yes, the biggest concern is the strength of the slab between the beams. Of course that would require an engineer. However, I can't imagine a problem with an 8x8 ft slab. I've seen lots of untensioned 8 foot spans (for example in small "man" tunnels under roadways etc).
As for gravel. A 24x24 garage pad with 2 feet of gravel requires approx $1000 of gravel. If you don't want to break your back tamping every 6" of the stuff, it's gonna cost another grand for the labour. The hay bales would cost almost nothing (less than 100 bux, or you could scrounge some for nothing). I think the labour is less with the bales (still a bit of work though). Even if the cost of gravel were "zero", I hate the results because any settling or frost just cracks the slab. I want that sucker so strong that you could flip it over in one piece.
Mark my words, I will start a revolution in the construction industry. Soon we will see office towers constructed with the "hay bale" method!

----SNIP
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Save your money http://www.coverquest.com/covers/instant_garages/cover-it.php

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- Trai' La Trash-

- Nehmo - For those of you who didn't follow the link, it leads to a site selling metal-frame tents and frameless covers that can be used for garages.
But the way I see, OP can make a box about the size of a bale of hay, with one side angled. The opposite side can also be angled but it would be movable like a piston. Place a bale of hay in the box and use a bottle jack to push the piston and compress the bale. The product would be a bale in a truncated-wedge shape (a cross-section would be an isosceles trapezoid).
With these bales and some regular bales, OP can assemble an entire barrel-arch garage!
--
*********************
* Nehmo Sergheyev *
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Nehmo;
Nice idea but the reality is that straw bales alone are not really a material that is suited to pure compression structures like domes or vaults.
While it is true that straw bales are strong in compression and it is possible to build straw bale vaults, vaults built using bales alone (in the manner you describe) tend to collapse eventually, and in a spectacular fashion.
The problem is perhaps best understood by looking at a masonry arch. As you may be aware, it is possible to erect a masonry arch leaving out the mortar in the lower half of the joints and have the arch remain in the air.
When using bales compressed into trapezoidal wedges, the most highly-compressed portion of the bale is in the zone which would experience next to zero compressive stress. Moreover, as "an arch never sleeps" the portion of the bale under compression will continue to compress, ultimately leading to collapse of the vault or arch.
As mentioned, straw bale vaults have been built and have been approved by the Code authorities in California, most notably the one built for the late musician/composer Lou Harris, by Skillful Means Construction (see www.skillful- means.com ) and one by Mikal Jakubal.
Images of the Jakubal vault can be seen at the SB-r-us Yahoogroups site, in the PHOTOS section.
http://photos.groups.yahoo.com/group/sb-r - us/lst?.dir=/Vaults&.src=gr&.order=&.view=t&.done=http% 3a//photos.groups.yahoo.com/group/sb-r-us/lst%3f%26.dir=/%26.src=gr%26.view=t
and also at
http://www.asis.com/~edexpert/strawbale
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Hi
Again - thanks for all the replies. I'm getting the distinct impression that you guys are not too hot on this idea!
Anyway, I notice a few of the responses refer to the bales not providing enough support. I just want to make it clear that I do not intend for the bales to provide any support. They are simply a void form. A cheap way to displace the concrete while it cures. I wouldn't care if the rotted away (in fact I would prefer it). I was even pondering some method (chemical disolving or fire) to get rid of the junk after the concrete sets. I only see them attracting rodents and moisture later.
------SNIP

-----SNIP
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What ever happened to a good'ol back fill? I'm pouring another slab on block and throw anything solid in the hole. Old lollie poles,scrap block rocks ect.
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On 7 Apr 2004 21:14:29 -0700, snipped-for-privacy@yahoo.com (Wpg Man) wrote:

Why ? Are you in the habit of flipping over concrete garage floor slabs ?

I'm not going to hold my breath waiting.
I think that we'll see Iraqi Saddam Hussein loyalists hugging/kissing Americans before we see any office towers constructed with the "hay bale" method.
However, about 30 years ago in Quebec, the walls of about 20 homes were built using 3"-thick concrete joints (horizontally and vertically) between the straw bales, creating a structural concrete grid of columns and girts. The description of their construction is available from the Canada Mortgage and Housing Corporation. www.cmhc-schl.gc.ca
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I know you've had a load of replies, but I have to agree that incorporating something that decays under concrete is a really bad idea! Generally when pouring concrete you try to remove any organic matter, not add it!
To be honest i am not sure what you are trying to construct, but how about something that doesn't degrade like polystyrene (plus don't forget some mesh reinforecement!
Marc
(Wpg Man) wrote:

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Wpg;
Straw-bale-formed waffle slabs have been used on a number straw bale homes,mostly in Quebec, so it is something that has been done. The intention was that the straw bales would serve as insulation, as an alternative to foamed plastic insulations.
There have also been forensic studies done on the above slabs (when they were about 10 years old) and as you would expect, the straw did show signs of decay so you should not have any expectations for the straw be there permanently.
Without doing any number-crunching, my wild-ass guesstimate would be that the slab between the ribs would need to be at least 200 mm thick, with reinforcement designed for 2-way action (ie Lots of engineering calc time + lots of time placing reinforcement)
I also think that the bottom line would be that an unreinforced thinner slab, (non-waffle) cast on compacted crushed stone fill would likely be more economical and just as serviceable.
On 5 Apr 2004 21:49:07 -0700, snipped-for-privacy@yahoo.com (Wpg Man) wrote:

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