Rammed Earth Tests

Hi everyone,
   Well since our stick frame chicken coop was flipped over and ransacked by a bear last week I decided to start investigating rammed earth as a building material for some of our basic infrastructure like another chicken coop and maybe a greenhouse if things work out. Our county limits buildings to 200 square feet unless you have a permit so these structures will be within that size.

   Our soil is entirely decomposed granite, not the best for rammed earth or eath blocks or so I have been told. After doing some research I began making the first test pieces to determine what stabilizers or additives would be necessary to make our soil work.

  After the first test block it has some inherit strength, but the edges are very crumbly and I can easily pick it apart. I will let it cure a little longer and then try some basic strength tests like the pick test and a drop test to see how it holds up.

Without a laboratory to test it with compression and other tools, how do we know if the strength is good enough for basic building? I know sand, fly ash, etc. can be used as additives but I would love to keep the recipe as simple as possible as our location is quite remote so transporting more non native materials is the least appealing option.

I will update with more test blocks and findings in the future...

Are you sure that 20% is clay, it looks more like soil.
Is it slippery between your fingers?
You will need roughly 50/50 clay and sand etc.
Your mix has too many larger bits in it.
Another test is to wait until it dries out.
If it stays together it may be ok, but its my guess it will break apart when it dries.

hink about Rammed eath into tyres.
If you screw he tyres together as well, it may work.
Rammd tyres do not need clay at all, I have used empty bottles to fill tyre walls with a clay cap to keep water out

Any test is a good test.
What did you compress it with? Or ram, if you like.

Would this be dry stack or will you use something to bond the bricks?

I can relate to your bear problem, sometimes bunnies nest in the engine compartments of cars I'm not using.
Grrrr

Thank you for the replies and suggestions, it is correct that the first batch was far too crumbly, however it did stay together better then initially expected. These will not be used as building blocks but rather monolithic rammed earth walls (12"-18" wide), the blocks are only for testing and seemed like a convenient size to work with (a 4' pine board made two sets of wood formers to produce blocks roughly 7"x7"x3"). These tests are just for our extremely granitic soil type and obtaining a baseline on which to improve upon but hopefully this can help with anyone else and their soils as well.  

Using the corner of a speed square triangle I tapped it quite hard until it split directly into two chunks. I then held it at shoulder level and dropped it onto concrete pavement at which point it continued to break into smaller chunks.

To improve on the mixture I went from 9:1 earth to portland ratio, to an 8:1:1 earth, sand, and portland.

Next I made another block of 7:2:1 earth, sand, and portland.

I am now letting them dry from 24 hours to 72-96 hours before 'pick' and shoulder drop testing again. Already the additon of sand has made it feel much harder around the edges compared to the initial crumbly block, and they are virtually impervious to trying to dig a finger nail into it to scratch it away. If they are substantiall stronger as I imagine I will subject them to varioius water test (spraying pressurized water and soaking one in a bucket).

While looking for ways to test different mixes with or without added materials, I found this video which gave me a lot of ideas how to test at home.  


Sand Castle Holds Up A Car! - Mechanically Stabilized Earth

When I was thinking about using sandy soil in earthbags and didn't want to risk wearing and tearing, I looked for screen materials as mentioned after the 4:00 minute mark in the video above.  (That homework led to finding basalt materials formed as rebar, mesh, fabric, rope for various purposes.  I may use a basalt mesh or fabric for a project.)

Your area being low in clay, might produce the effect you're looking for by making a thicker wall by layering something suitable about every foot or two.  If you try dropping different shapes of heavy weights on the test bricks, that might help find a way to combine materials to achieve the strength you're looking for.

Forgive the lack of tech jargon.  I'm nowhere near being an engineer, and learn by seeing what goes boom or not :)

Catherine Windrose wrote:While looking for ways to test different mixes with or without added materials, I found this video which gave me a lot of ideas how to test at home.  

https://www.youtube.com/watch?v=0olpSN6_TCc
Sand Castle Holds Up A Car! - Mechanically Stabilized Earth

When I was thinking about using sandy soil in earthbags and didn't want to risk wearing and tearing, I looked for screen materials as mentioned after the 4:00 minute mark in the video above.  (That homework led to finding basalt materials formed as rebar, mesh, fabric, rope for various purposes.  I may use a basalt mesh or fabric for a project.)

Your area being low in clay, might produce the effect you're looking for by making a thicker wall by layering something suitable about every foot or two.  If you try dropping different shapes of heavy weights on the test bricks, that might help find a way to combine materials to achieve the strength you're looking for.

Forgive the lack of tech jargon.  I'm nowhere near being an engineer, and learn by seeing what goes boom or not :)

Wow that video was just amazing thank you very much for sharing that!!!

I see exactly what you mean in adding a reinforcing material now, we have a ton of sheep fence wire that had to be torn down (basically a 6x6" grid work of metal), I wonder if layering this into the earth works would be beneficial or if a tighter mesh like the screen and even t-shirt example provided. I recall a film on ancient building techniques where they layed straw width-wise inbetween rammed earth lifts/layers and the straw stems worked in wicking moisture out of the inner workings of the wall. I imagine their foremost thought was adding strength as seen in the video though now.

I know their is basalt rock but have never heard of materials such as you mention being made from it before, is it a material that is easy to acquire or a bit of a specialy item? Being in the mountains I am neary a few quarries so if it is available I would love to know more about it as a material.

Thank you for your reply!

The first link is from a company outside the US, however it has a ton of useful information about basalt materials.  The other links were useful for guestimating cost although I have since found less expensive.  Still learning what the cost differences imply.  May be a little price gouging.  Or may be a quality difference.  Perhaps with temperature or heat ratings?  I haven't yet learned enough to come to a satisfactory conclusion.

http://compositegroupworld.com/produktsiya/bazaltoplastikovaya-armatura.html

https://www.forconstructionpros.com/concrete/equipment-products/article/12184173/basalt-fiber-reinforced-rebar

https://basalt-rebar.com/

https://basalt-mesh.com/

Example of a dome with basalt material:  https://www.youtube.com/watch?v=N18HcPfKv1E

Also just read that the strongest bears can lift about 400lbs to 600lbs (Malaysian Sun Bear).  If you feel there isn't enough mass, maybe 1' or 2' thick walls with a couple slight buttresses on each side so the building cannot be tipped or pushed over?

While I love mechanically stabilized earth, and actual teach farmers how to build a low cost, effective way to farm in my sheep farming classes, I do not think you would need to go through all that for your situation.

If I was you I would try testing how well screw in anchors would hold. They are often called dog tie outs here, and are about $1 per anchor. If you put a few on your buildings, I seriously doubt a bear could flip over the chicken coop then.

But I have also made my own anchors, welding them out of steel, and it tethered a 2000 pound bull running at full tilt. Again, I seriously doubt a bear could move a building secured like that.

An even easier method would be to just dig some holes, and then bury dead-men into the holes and run cables around your building to help hold it down.

The amount of time doing any of these things is going to be a lot less time doing it than rammed earth, and net you the same result.

You may be testing the bricks too soon. Concrete which is made from cement , sand and stnes gains it maximum strength is 28 days, and perhaps 90 % strength in 7days.
If you wait longer you may get better results.
also, a water test with a pressurised hose nozzle will show if the soil is soluable.