CEB Bricks

What is most important in the strength and durability of CEB? The kind of materials used in the bricks? The ratio of these materials? The amount of pressure used to squeeze them?

It depends... Mostly on what they are trying to sell you.

There is not one right answer. My opinion is consistency and protection from the elements matters most long term. If one block is harder or softer than the next, that causes problems.

Thanks! I should probably back up and share the "root" of my questions. I have read a lot about "green" technologies for constructing buildings but many of the technologies do not seem to get well developed because there is not much money in them, as there is for deforesting land to build stick houses, etc. What do I mean by "well developed"? As an example...I wish that a university with a respected civil engineering department would undertake a study of CEB, using a variety of ingredients, mixtures, pressure, etc and test the results. The ideal outcome would be a computer model that would allow for up to 6 variables, (pressure, time, size, ingredient 1, ingredient 2, ingredient 3) With this construction technique more well documented, it might make it easier to get it approved so that building permits could be issued, buildings could be insured, and the idea as a whole would be more well accepted. The goal would be to help people make stronger bricks that are more uniform, rather than less. I know that places in India and Africa as using CEB more extensively but I have never heard of or seen any test results. I have done some searching online to no avail - it is always possible that I am not using the right search terms.

Those tests have been done. By some Germans (who else? ).

Here's the book you want, free to download:

https://archive.org/details/Gernot_Minke-Building_With_Earth
(The download link is rather inconspicuous, on the left of the page.)


They discuss strength on pp26-51, and here's a very surprising quote to whet your appetite (bold added):

Preparation
The compressive strength of a mix is affected
by the type and amount of preparation,
as well as by the proportion of water used
in the preparation, a fact that is neither well-known
nor well-researched.
At the Institute for Building Technology of
the Swiss Federal Institute of Technology in
Zurich and at the BRL, it was proven that a
slightly moist loam, when free from lumps
and compacted in a soil block press, usually
has a smaller compressive strength than the
same loam combined with sufficient water,
mixed by hand, and then simply thrown into
a mould (as is done when making adobes).
In one experiment at the BRL, handmade
adobes had, on an average, a compressive
strength 19% higher than if produced in a
soil block press which imparted a pressure
of 20 kg/cm2 to the material. The belief of
many researchers and practitioners that
pressing in a soil block press leads to an
increase of compressive strength may only
be true for limited cases. As a rule, it is not.
The “secret” of loam lies in the lamellar
structure of the various clay minerals and
their internal electrical attraction, which is
activated only by water and movement. This
means that by kneading loam in a plastic
state, the clay minerals are able to come
together in a denser, parallel layered packing,
achieving greater binding force, and
when dry, higher tensile and compressive
strength.

Adobes stronger the CEBs? Not what I expected, either.
Read the whole book, it's invaluable.

Thanks! I love this forum That will be very useful reading.

Mike Cantrell wrote:Those tests have been done. By some Germans (who else? ).

Here's the book you want, free to download:

https://archive.org/details/Gernot_Minke-Building_With_Earth
(The download link is rather inconspicuous, on the left of the page.)


They discuss strength on pp26-51, and here's a very surprising quote to whet your appetite (bold added):

Preparation
The compressive strength of a mix is affected
by the type and amount of preparation,
as well as by the proportion of water used
in the preparation, a fact that is neither well-known
nor well-researched.
At the Institute for Building Technology of
the Swiss Federal Institute of Technology in
Zurich and at the BRL, it was proven that a
slightly moist loam, when free from lumps
and compacted in a soil block press, usually
has a smaller compressive strength than the
same loam combined with sufficient water,
mixed by hand, and then simply thrown into
a mould (as is done when making adobes).
In one experiment at the BRL, handmade
adobes had, on an average, a compressive
strength 19% higher than if produced in a
soil block press which imparted a pressure
of 20 kg/cm2 to the material. The belief of
many researchers and practitioners that
pressing in a soil block press leads to an
increase of compressive strength may only
be true for limited cases. As a rule, it is not.
The “secret” of loam lies in the lamellar
structure of the various clay minerals and
their internal electrical attraction, which is
activated only by water and movement. This
means that by kneading loam in a plastic
state, the clay minerals are able to come
together in a denser, parallel layered packing,
achieving greater binding force, and
when dry, higher tensile and compressive
strength.

Adobes stronger the CEBs? Not what I expected, either.
Read the whole book, it's invaluable.