Rice Hull Ash

Today we’re experimenting with rice hull ash and road base. We’re using a small measuring device so we can get about 10% rice hull ash. This is what rice hull ash looks like. It’s hulls from rice that’s been burned. It looks like ash from a forest fire. It’s a natural pozzolan which can make the soil harder. We’re going to start off with about 10%. I’m adding it in thin layers and tamping it. This will simulate an earthbag. Okay, it’s pretty solid, just like you would tamp an earthbag. The idea is to use rice hull ash in replacement of cement. That big bag over there was only $3.60 and, of course, cement is much more expensive. Now we’re making a second test block with no burned rice hulls, no ash, just the road base so we can compare the two blocks. We’re just adding a little earth at a time, the same consistency, the same amount of moisture we put in earthbags. Just spread it out in thin layers. You notice the plastic on the tamper so it doesn’t stick. So here’s our finished rammed earth block with no ash. We’ll see how they compare after they dry. This one had a little more moisture and seems like it’s stronger, but then again this one has ash, which should add some strength, so we’ll see. I noticed this was crumbly when I took it out of the form, which means it probably had a lack of moisture. Some people may think this is just earth, it can’t be strong. But this is rammed earth, which can last thousands of years. You can learn more on our earthbag website. But just this here alone can last thousands of years. It gains its strength from clay. The clay is like a flat platelet, kind of like the shape of my hand. You put the platelets together and under pressure they create a molecular bond that’s very, very strong. Very compact, very dense. So this can last for a very long time. We’ll wait a little while and take it out of the form. Make sure you use very strong forms. And also note, you don’t have to tamp it and you don’t have to make it in blocks. This is just a test. You could build a whole wall in the same way, not individual blocks. So there are many things you can do with this technology. And this plastic – we tested this out – and it works really well. Here are the final blocks. You can see that this one had more moisture. You can see the smooth, solid clay on the top and even on the sides. You can see more pore space here, more small holes between the particles, so I’m guessing that this is going to be stronger even though we put the ash in this one over here to make it stronger. So we’ll see in maybe a week or two. If you do this, I highly recommend metal forms. The wood form is just too fragile, too easy to break. And with a metal form, you could tamp it much harder and get very, very strong blocks.

9 thoughts on “Rice Hull Ash”

  1. Hi!
    Very cool stuff. I am looking for a rice hull ash supplier, and I can only find international sources (mostly india). Where did you find your ash? Looking for a US, or at least North American supplier.

  2. Is it possible to make your own rice hull ash using a low tech oven, or do you need to use higher temperatures? Do you know of any current research being done on replacing cement with rice hull ash in the forming of CEB’s?

    • Search YouTube for how to make carbonized rice hulls. The videos show how to make the burners with recycled materials. But instead of just carbonizing them, you want to completely burn to ash. Carbonized hulls are for agricultural purposes. You want them completely burned for making building materials.

      I’m covering lots of related topics on my new Geopolymer House Blog: http://geopolymerhouses.wordpress.com/

      There are blog posts about bricks made with 100% fly ash. I imagine rice hull ash would also work. I’m pretty sure you’ll have to buy or rent a grinder to create fine powdered ash. The articles I’ve found don’t explain every detail, but they do give you a lot to go on.

  3. We are going to make some blocs tomorrow using clay and rice hull ash. thank you Owen for inspiring us in Nepal. We are also at the initial stage of experimenting with earthen countertops–don’t know how it goes, but will let you know once we have some results.

    • Add a little extra clay to compensate for the ash. The ash reduces the stickiness of the clay, so a little extra clay is needed for strong blocks. (Ours is too crumbly.)


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