Give us a little more detail about what you have in mind. Are these tires going to be staked into the ground in some fashion? Are they laying down or standing up? What kind of soil do you have? If you are in MO, are you in one of those places where you need a pushbroom to dig down to the bedrock?
As far as covering them over, there's lots of ways you can put some lathing wire over them so that you can slap some cob over the whole thing.
The concrete with the rubble under it will act to keep soil moisture coming up into the cob wall. If it's really wet where you are, you might even want to form the footer so that the top of it is a couple of inches above grade.
P.S. Odd what you have to do here to say "bend something into a u-shape".
Cement is a great improvement over burnt lime (which itself requires burning some fuel), and if there is one place you should give a little on your principles, it is with the construction of the footer. A footer doesn't take use that much concrete, but it can markedly improve the stability of the building.
Of course, if there is a granite quarry around and you can get some blocks of granite for a foundation (like I have seen at old ghost towns in Nevada), that would make for a cement-free alternative.
I (as well as a number of traditional "lime masters" from the UK, France and a few other places) could debate that one John...
Cement is a great improvement over burnt lime ...
One of the key differences I point out to folks new to the building arts is some peculiar characteristics of certain construction materials. Some of the foundational elements are the strangest of these, which are often wrapped in hype and misinformation by the industries and normative cultures behind them. First, let me say I am not completely against concrete, though I do prefer the natural cements over most "industrialized portland's" professionally referred to as OP (ordinary portland) cements. One of my main concerns with OP cements is there possible (probable) degradation over time. Think about our failing bridges and highways that are less than 60 years old, compared to the Roman roads of hand set gravel and stone that are still functional today over 2000 year later. Another challenge with OP cements is its inability to breath, stay wet, and promote "moisture issues." The easiest metaphor to use (or comparison) is to think of OP cement as a cotton sweater, and think of lime and clay (cob, adobe, bousillage, bajareque, daubing ) as a fleece or wool sweater, if they get wet, which one do you want to wear, or live in.
Not that I am recommending it, but you can also use "soil cements" with natural cement or lime binders and certain chemical or enzymic additives. Some of these will yield higher psi that OP cement alone, but it will add cost and more technology to the project.
Back to your original question, "do you have to use cement?" Absolutely not, and I would go further to say that the majority of the domestic architecture in the world today and in antiquity is (was) not sitting on any cement at all, but exactly what Frank Lloyd Wright and many other brilliant builders through the ages used...gravel and/or hand packed stone in a trench or pad. The oldest and some of the most tectonically stable buildings in the world sit on stone plinths/footers, with gravel underneath...not OP concretes. Just look at what happened in Haiti in 2010, if you think OP cement is a good way to build, or the "earth structures" in Yemen that once inspected they started finding evidence that many either hand not been properly maintained and/or repaired/modified with OP cement, while others that had been much older, but not modified stood strong.
Dig into some of my info and contacts, develop questions, and I will do the best I can to answer. I have helped with creating some "soil stabilized" projects, but personally like plain old "traditional" methods of construction above any "rethinking" or "reinventing of wheels," but again, I will help where I can. If you read through the attached infor, you will learn much and probably develop some additional ideas, and questions.
Jay C. White Cloud wrote: The easiest metaphor to use (or comparison) is to think of OP cement as a cotton sweater,
Don't you mean polyester, Jay? Cotton is still a natural material, whereas polyester is a product of our modern industrial age, just like OP cements.
I suppose I should edit my previous statement to say that "given proper attention to detail, cement is a great improvement over burnt lime". At one government facility where I worked, it was obvious that little attention to detail had been given when pouring the steps in front of the building -- the concrete was spalling everywhere.
John Elliott wrote:Odd what you have to do here to say "bend something into a u-shape".
Yeah, it's to stop 'text-speak'-there's a bunch you can't use...
It's a bit hard on these forums, where there seem to be a lot of 'u-shaped' things!
As you've noted John, it's fine if it's not on its own.
If you are "pulling my leg" about the cotton vs. Polyester...read no further as it did make me laugh
As for the actual comparison I meant cotton, because even polyester pulls moisture away and dissipates (desorbs) it efficiently for evaporation, the opposite of cotton. Cotton, and concretes in general are very similar in they both act like a sponge, absorbing in water and holding it.
You can think of concrete as highly hydrophilic, and cob and lime as both hydrophobic and hydrophilic.
Wool fibre has a hydrophobic (water repelling) exterior, and hydrophilic (water loving) interior that confer its unique moisture management properties – properties that are not shared by synthetic fibres such as nylon or polyesters which simply wick the moisture away and allow fast evaporation. Clay and lime share very similar characteristics similar to both wool and polyester fleece, unlike concrete which take on (absorbs) moisture and does not release it (disorb), like wool and polyester fleece.
In contrast to most synthetic fibres, wool has the capacity to remove large amounts (up to 35% of its own weight) of moisture from inside a room, before the fibre
even begins to feel wet. Lime and cob behave in a similar fashion vs concrete which not only feels wet but is wet when humidity is above 70%.
Unsealed cob and lime's chemical structure means that it has the ability to actively absorb and desorb moisture and to gain and release heat depending on the external and internal environment – thus buffering a room against environmental changes.
Cob and lime's ability to absorb moisture may result in a reduced propensity for condensation within a room.