Yesterday’s video about How the Pyramids Were Built shows how loose limestone can be turned to stone. This method seems easier and simpler than using MICP, don’t you think?

This seems like a good time to experiment with geopolymer cast stone to make the first ever earthbag stone dome. The mountain range near our home is predominantly limestone, so the main material is readily at hand. I recently tracked down a supplier and am in the process of obtaining materials to make some test bags.

The ancients had to make the soil binding materials from scratch using salt, wood ashes, etc. But now the basic ingredients (sodium carbonate and lime) can be purchased off the shelf and mixed with limestone and water. In fact, the process is so simple that I’m surprised more people are not investigating the process.

The end product is actual stone, not just something “hard as rock”. It would be fire and rot proof, bullet resistant (almost bulletproof at some point after it gains hardness), totally waterproof obviously, and could possibly last thousands of years. Not much else can compare to this. Even modern concrete falls way short, because it’s too brittle. Concrete has a lifespan closer to 50-100 years in most cases (I’m talking about lifespans of actual structures, not some theoretical time period). The next closest thing might be Roman concrete that was used to make the Pantheon in Rome, among other structures. More about Roman concrete here.


Comments

Earthbag Stone Dome — 17 Comments

  1. I have done some more digging around and found out that you can make cast stone with natron salt, also known by many other names, and any stone that contains calcium carbonate. Apparently, you don’t have to use all of the ingredients listed in the video.

    There are two US patents, cited below, held by William McNulty that employ this idea. He lists some proportions in the abstracts and explains the process a little bit. On his website http://rosetjau.com he proposes that, in addition to the pyramids, many of the stone objects from Egypt were cast as well.

    Very interesting reading!

    ///////////////////
    http://www.patents.com/us-6264740.html
    Inorganic cementitious material
    Abstract
    A method of producing a new type of cement, hereafter called Conch-krete. Conch-krete is created by adding sodium carbonate (also known as soda ash, natron, etc.) and one or more minerals from the calcium carbonate group (including aragonite, limestone, calcite, marble, dolomite, etc.) and the addition of water to the mix that will harden into a cement-like material. The combination of sodium carbonate and calcium carbonate can be either layered or in a mixed state. An exothermic reaction starts after the addition of water. The composition of Conch-krete can vary between 20% sodium carbonate and 80% calcium carbonate to 80% sodium carbonate and 20% calcium carbonate. Conch-Icrete can be used in a variety of applications not inclusive of forming bricks, interior architecture, table or counter tops, ornaments, repairing damaged cement products, casting and other applications not mentioned above.
    Inventors: McNulty, Jr.; William J. (Provo, TC)
    Appl. No.: 09/456,841
    Filed: December 7, 1999

    Cementitious material
    Abstract
    A combination of compositions, products and methods of producing a new type of cement. The cementitious material is created by adding sodium carbonate (also known as soda ash, trona, natron, sodium carbonate decahydrate, sodium carbonate anhydrous, etc.) and one or more rocks or minerals selected from the following–granite, basalt, sandstone or schist. A new method and product are claimed by combining sodium carbonate and one or more rocks or minerals selected from the following–granite, basalt, sandstone or schist and water. The combination of sodium carbonate and one or more rocks or minerals selected from the granite, basalt, sandstone or schist group can be either layered or mixed in a dry or wet state. An exothermic reaction starts after the addition of water to the cementitious material. The composition of the cementitious material can vary between 10% sodium carbonate and 90% of one or more rocks or minerals selected from the granite, basalt, sandstone or schist group to 90% sodium carbonate and 10% of one or more rocks or minerals selected from the granite, basalt, sandstone or schist group. Organic or inorganic additives may be added to the mixture to enhance the composition and/or the final hardened product. The cementitious material or products can be used in a variety of applications not inclusive of forming bricks, interior architecture, table or counter tops, ornaments, repairing damaged cement products, casting, bioabsorbable devices, extruded products, sprayed products, filler, grout, mortar, gunnite, moulded products, composites, cast stonework, agglomerated stone, concrete, hardened products, electronics, packaging and other applications not mentioned above.
    Inventors: McNulty, Jr.; William J. (Provo, TC)
    Appl. No.: 10/199,079
    Filed: July 22, 2002

  2. In southern Mexico where we are going to live, piedra caliza and caliche are very commonly available. We’ll be arriving in July, during the rainy season so testing various soil mixes will be the first item on my agenda. I’m reasonably sure that the sodium carbonate, lime and kaolin would be available, as well.

    Would you have ANY idea as to a good starting point with the proportions of these ingredients? I wish my father (the chemist who always seemed to have an opinion) were still alive. He’d weigh in on the discussion. :)

    I’ll browse the internet on some cement sites and see what I can find. Maybe I can get a cement research chemist to respond to an email request.

    It seems really amazing to me that the hardening reaction of these ingredients takes place over weeks instead of hours, that you let the mix loll around while the water evaporates, and then pound it into a mold and it hardens. The video said that the “packing operation encourages cohesion”. I can imagine, too, that once you ram the mix into the mold and remove the forms, keeping the block moist might help it to gain strength over time.

    • So you have numerous good materials to choose from. The simplest would be to use caliche. With minimal testing, you could probably use 100% caliche. That saves lots of mixing, time and effort.

      Making geopolymer from scratch will likely take a fair amount of time, research and testing. While I’m still very excited about this possibility, I’ve taken a real pounding at the $300 House design competition. So I’ve offered an alternative to improve my rating. PolyPavement would stabilize the soil and eliminate the concerns people are raising (“too difficult”, “materials may not be available”…).

      Piedra caliza is limestone, so that’s great news. You have the primary material for geopolymer.

      Maybe you could get assistance from a local university. Win them over by explaining how the abundant local resources can be converted into high value products such as stone houses. Try to find a university with a soils testing lab.

      Keep us posted. You’re sitting on top of a wealth of natural building materials and a little effort could go a long way. It would be great to have an example of a geopolymer earthbag house to refer to.

  3. In the video, the ingredients mentioned are sodium carbonate, lime, kaolin, and limestone rubble. He mentions 500 liters of water and 1 ton of limestone rubble. Later, he says that the moistened mixture is 95% limestone aggregates and 5% rock making binder. No actual amounts of sodium carbonate, lime and kaolin are mentioned. Does anyone know what those amounts/proportions are?

    Could you get similar results if you mixed these ingredients into a much smaller amount of water to then combine them with the limestone rubble and lessen the time required for the water to evaporate?

    I’m wondering if you could mix the ingredients into a 1/3 yard concrete mixer (or even mix the ingredients on the ground) and then place the mixture directly into the earthbags, tamp them down and let them cure.

    • Good questions, but I don’t know the answers. The formula has to be determined through testing and then adjusted. That’s probably why he doesn’t give exact amounts.

      The water and soaking time are necessary for the chemical reactions to take place. But some people may not need optimal results. They may be satisfied with rock hard material inside a plastered wall (versus exposed stone). See? They’re showing how to make stone that can withstand rain, etc. for centuries. Your idea might work for some. I hope you try it and post your results.

  4. Very interesting. I wonder how this would dry in a climate such at Canada. If it keeps homes cooler in the summer and warmer in the winter months?

    • Watch for my upcoming blog post on insulated geopolymer walls. You definitely want lots of insulation in Canada.

      Also, I’m working on a blog post about scoria/clay that would work for you.

      Plus, search our site for “insulated earthbag” and “cold climate” for other options.

  5. use this with hyperadobe mesh bags, and you could get an almost monolythic wall. I wonder if it could save on the stucco?

    we don’t have limestone around us, but it would be interesting to try similar techniques with alternative aggregates.

    • It may not need stucco. Sealing the joints may be adequate. This has to be tested.

      Ideas worth trying: Place a piece of 1/4″ rubber tubing near the outside of each course. The next course will compress the rubber, possibly creating a waterproof seal. How long would a rubber seal last inside a stone wall like this??? Or maybe brush some tar or place a bead of silicone in the same location.

      There are different recipes. Search the Geopolymer Institute website. They’re proposing different recipes were used on different historical monuments made of different stone.

    • Seems to me like they set too low of price. $300 would only buy a very small house. (Same is true with whatever building method is used.) Stabilizing the soil to create a stone dome would add to the cost of a typical earthbag home. I’ll give this more thought. Thanks for the heads up.

  6. If I remember correctly one of the earthbag building sites you linked too had a video where they were using crushed limestone. In a later video the people had discovered a problem. It seems, once the bags got wet during winter, they froze and the moisture in the compacted bags expanded. I believe the folks building the house were in Arkansas.

  7. Rammed earth walls looks so much better when you look at it like that.

    Looking forward to see what can be found.

    • It seems like geopolymer walls that turn to actual stone would surpass rammed earth in strength and durability. It would be great to get others input on this.

  8. Pingback: Earthbag Stone Dome (via Earthbag Building Blog) « Seeds-2-Sow LIVE Online

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