Clay as a binder
Practical Action
The main industrial stabilizers are cement, lime, and bitumen, and comprehensive
information exists about these. Many other synthetic products have been tried but their
performance is questionable, and doubts exist on their cost effectiveness.
Types of clay and soil
The proportions of the different components in a natural soil (clay, silts, sand, gravels and
pebbles) are very variable. Ideally for building, a soil should have a continuous grainsize
distribution.
Another fundamental point is that the quality of the clay obtained can be very variable in
composition and in characteristics.
The three principal types of clay are:
• Kaolinite, which is relatively stable
and has relatively low cohesion;
• Illite, which is of average stability
and cohesion, and;
• Montmorillonite, which is highly
sensitive to water and has high
cohesion.
A soil usually contains a combination of
these clay types.
Although the properties of different soils
vary widely, there are some characteristic
soils
(laterites, terra rossa, black cotton soils,
loess, saline soils, and alluvial soils) the
properties of which are relatively well
known.
Suitability of soils
Some soils are suitable for use without any
additives. Others can be improved (by
addition of inert materials or by physico-
chemical stabilisation of the clays). Finally,
some have to be rejected (mostly soils with
a high clay content or with montmorillonite
clays).
There are some general requirements for
the suitability of a soil for construction, but
other requirements are specific to a
particular construction application.
To get a good building material, strong and
easy to use, the proportion of clay in a soil
should be 15 per cent on average.
However, depending on cohesiveness of the
clay relative to specific surface of the inert
elements, generally 10 to 20 per cent clay
content would be acceptable. The sand
should be 40 to 80 per cent, the gravel 0
to 40 per cent and the silt 10 to 25 per cent.
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