Saturday, May 19, 2012

21 - Mixing soil for compacted earth blocks (CEB)

Compacted Earth Blocks (CEB) are some of the best construction materials we can find. They are and have been used in many parts of the world for many centuries and have proved to be worth a lot more consideration than we sometimes give them.

As the name indicates they are made out of soil that is compacted in a simple press and cured in the sun. They are not fired and are more resilient than adobe blocks. It is much easier to build with CEBs than to build with rammed earth.  

They are often manufactured in the location where the dwelling will be built. CEBs can be made with soil components only. But they can be stabilized with lime or cement to be more durable.
Since they do not consume fuel for the firing process CEBs do not contribute to climate change and deforestation. The manufacturing process uses 5 to 15 times less energy and is about 8 times less polluting than other types of blocks and bricks.

All these factors contribute to a lower production cost when compared to the available alternatives.
The CEB manufacturing process and the many construction methods using CEBs are well documented in many languages. For that reason we will only cover here some basic points on how to get the right soil mixture.
Raw materials
The basic raw material is soil with a good mix of gravel, sand, silt and clay. This type of soil can be found in many locations around us. These locations are well known in all communities and there is always someone who knows where they are.

This good soil is found under the ground layer of topsoil. Topsoil is where plants grow and will always contain a large amount of plant and animal matter. The soil in topsoil is not good for what we need. We need the more reddish soil as shown in the picture above.
Soil identification
To identify the type of soil we have we use the same identification method we used to make adobe blocks.

The above picture shows some examples of the type of results we may get. The percentages always refer to the total amount of soil in the sample. The water used and left after the test has no impact on the results.

The right soil mixture

A good soil mix for CEBs has the composition shown in the picture below. If the soil collected from the local source does no have this mix we need to add more of one of the other component until we do. It is important that our soil sample does not contain rocks or organic material such as found in the topsoil.
First we need to make sure that our soil is well ground up and has no lumps. Then we mix all the components well without water. Only then do we mix water until we get a humidity level that will allow us to make a ball in our hands. But our hands should not be wet after making the ball.
When we drop the ball from waist height the ball should break in pieces like the example in the middle of the picture above. At that point we have a good mix to make our CEBs in the press.
We may add about 5% of lime or cement to obtain a good stabilization. This makes our CEBs more resistant to breakage and more durable. Stabilized CEBs need to cure in air for about four weeks.

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