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Conversation between Andrew and Brad earthboundbuilders.com
This is a conversation I had with brad about the methods he uses to stabilise CEB's with lime.
Andrew Graham 4/16/14
to brad I just met James Slade who mentioned to me that you have had great success stabilising CEB's with high clay content using lime. Is there any material you have written on how to replicate the process? I am building in a very high rainfall area in northern Australia for myself, and if its possible for something to approach the stability of a 10% CEB brick I would be very interested in doing this instead.
Thanks so much if you could point me in the right direction,
Brad King 4/16/14
to me Hi Andrew, I m attaching a pic of the CEB project We are currently working on. The blocks were stabilized with +/- 12% type S lime (dry hydrate state). '
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Brad King 4/16/14
to me Sorry, I sent that last one accidentally. As I was saying... The percentage of lime needed to effectively stabilize a clay rich subsoil varies dramatically dependent on several characteristics of the soils makeup. I am getting pretty familiar with my local region's subsoils and it is clear that even samples from different locations or depths on the same site can have different reactions to the highly alkali electrolytic solution that lime and water create. When you throw the high pressure/low OMC treatment of hydraulic compression into the mix things get even hazier. The best thing to do is make lots of test samples of varying percentage stabilized blocks, cure them carefully, then subject them to some harsh treatment and document how they perform. Take the best and make another round of tests with minor tweaks both ways. It takes time but you will find a mix that works for you. The blocks in the photo have been getting hammered by Texas's severe temperature swings and record flood producing rains for eight months (several of them without a roof) with no sign of damage even to the surface integrity. A separate company made those blocks onsite for us to lay, we don't own a machine, but I have used Lime as a stabilizer in a variety of clay applications, not just CEB, and I feel it is well worth the extra hassle and yields far superior results when done carefully. Better thermal properties, better working properties, and much less vulnerable to water damage. If you are interested in the technical details of the chemical process I can send you a couple of good resources. I have heard of geo-engineering lab tests that can tell you how much lime is ideal for your clay by analyzing the pH levels, but I've never sought any thing like that out. Hope that helps, feel free to ask questions, I may be slow to respond but I enjoy hearing about other people's projects.
Andrew Graham 4/18/14
to Brad Thanks a lot brad, thats amazing that you could achieve that result. was there a pic I could see in the end? I'm definitely going to explore this. for my first structure I wont have much time to play around and experiment though so I'll run with a 10% cement brick for the first structure. I've realised from reading Gernot Minke's book building with earth that 30% clay would be undesirable with 10% cement, (too much clay) but haven't been able to figure out how much clay I should instead aim for.
I heard also when you use the lime that you are supposed to spread it all out on the soil and mist it, but i've not found any detail on the process...
This is a soil mixer I helped build the other day at Open Source Ecology. https://www.youtube.com/watch?v=GM3Obl3yWts At the moment we need to get more articulation in the tractor before we can use it properly though.
Attachments area Preview YouTube video Open Source Ecology - Soil Mixer Build
Open Source Ecology - Soil Mixer Build
Brad King 4/18/14
to me image.jpeg
We will be going back to do the interior clay plasters mid May. what you see in the pics is the exposed lime-stabilized compressed earth blocks. They even did great without a roof for a few months of abuse. They did have a cap, a concrete bond beam up top, but the only wear is a slight recession of the unstabilized clay slip/mortar we used to lay them. I have some Portland cement stabilized blocks approximately the same age stacked in my yard and they are essentially destroyed now. Just slowly broke themselves apart in wetting/drying cycles. This is a simplification and I'm no chemist, but heres one way to think of it. The Portland only binds the larger silt and sand particles together against the natural expansion and contraction of the clays and colloid fractions in the presence of water. Lime actually changes the chemical water dynamics between clay particles, causing them to clump together and behave more like dense packed sand. there is also a pozzalonic reaction that creates a weak cementitious binder, but with the high pressure/low moisture process of CEB presses, the slow induration of the lime and the afore mentioned clumping (on a very tiny scale) contribute more to keeping the clay from wanting to expand in the presence of water.
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Andrew Graham 7/5/14
to Brad Hey Brad,
I recall James saying that you would spread all your soil out, and cover it in lime, wet it and then press the bricks with it or some such thing... have you written up any method on how this is done? I haven't seen this before but I'm very keen to experiment when I start building in less than a year!
Brad King 7/6/14
to me The layered ground technique you mentioned is traditional in mixing adobe and would work as long as you are sure to mix the soil and lime into a completely homogenous state. Because the moisture level required for CEB production is so low, it is even more important that the lime be VERY well distributed. I have never seen this done well enough without mechanical mixers, but there is no theoretical reason, besides efficiency of course, that it couldn't be done by hand in small batches. The moisture is best added as you mix because again it too must be very well distributed. A stone rake and a lot of patience might work. You will have to do a fair amount of experimenting to dial in the h2o/batch and it will change slightly with local humidity/temperature conditions. I guess I have seen folks mix the lime (and in this case sharp fine sand as well) into the soil using a skid steer, but it didn't look thorough or efficient enough for automated machine block pressing. I actually think small batches in a large cement mixer would be faster than doing it in large batches on the ground with a skid steer, although that would mean a lot more shoveling material. Hope this helps simehow, Brad > <image.jpeg> > <image.jpeg> > <image.jpeg>
Andrew Graham 7/6/14
to Brad Thanks Brad, so do you after its mixed well, and you add the water, do you press immediately after this point? Or do you wait a bit?
Brad King 7/6/14
to me My understanding of the chemistry involved would lead me to believe that with a lime stabilizer, letting it sit damp and well mixed for a few hours would theoretically be advantageous. In practice I have never seen this done with any real intension to control the timing. The only block producer we have worked with professionally mixes it mechanically then simply mists it on its way into the block press hopper. The quality of the blocks he produced using lime and this technique were excellent, but as I mentioned earlier every subsoil is different and not all clays and silts react to lime the same way.
Andrew Graham 7/8/14
to Brad Thanks Brad,
I do find it interesting because I would think that if the lime set before compression, then maybe this wouldn't be as good if it set after compression. if it happenned before i would have though it would break the bonds when it gets compressed.
Brad King 7/9/14
to me Lime has no initial chemical set, at least not in the sense that most binders do. The "set aside" time has to do with cation exchange in the clay and colloid fraction of the subsoil. It gives the clay mecelles time to aggregate into less plastic clumps before compression, microscopic still, but with less interstitial space btw particles. I'm no chemist but I know enough to know that most owner builders are not going to reach a full understanding of the chemistry involved in lime stabilization of clayey subsoils. Even as a professional who works with Lime, it isn't worth the time required to fully grasp the details. If you are interested I would suggest finding a geotechnical engineer, they should be familiar with the chemistry as it is common to use lime as a clay stabilizer in road construction. The chemical induration that turns calcium hydroxide into calcium carbonate through absorption of atmospheric carbon dioxide is what gives lime it's traditional binding characteristics. This is a very slow process, and must be done in tge presence of moisture, hence the need to cure lime stabilized earth blocks under tightly wrapped plastic for a month before laying them.