Civil Engineering Reference
In-Depth Information
Earth does not have a particularly high
thermal insulation value - slightly better than
concrete, but more like brick. By adding dif-
ferent organic fibres the insulation value can
be improved; dwellings cannot be built with-
out extra insulation on the walls. Solid earth
walls, possibly with fibre mixed in, are best
for buildings with low internal temperatures
or with external two-leaf walls containing a
cavity. An exception to this is 'leichtlehm', or
light clay (see p. 289).
Earth can only be used locally, as trans-
porting it for building or rammed earth
blocks over distances is uneconomical and
ecologically unsound.
Suitable types of earth
For pisé construction earth must be dry
enough for the shuttering to be lifted directly
after ramming without damaging the wall.
Shrinkage needs to be as little as possible to
avoid small cracks. A well-graded earth with
about 12 per cent clay is the best type,
although even an earth mixture with up to 30
per cent clay is usable, but will be harder to form. If a mixture is less than 12 per
cent clay, fine silt can be added. These types of earth need more preparation
before ramming. Sand can be mixed with earth that has too much clay, and clay
can be added to earth that has too little. This can be a very labour intensive and
uneconomical task.
For adobe blocks a much more fatty earth with up to 40 per cent clay (or even
more in blocks mixed with straw) can be used.
Figure 13.17: A six storey earth building erected in
Weilburg (Germany) in 1827.
Stabilizing aggregate and other additives
In certain situations it may be necessary to add stabilizers. These usually have
three functions:
•
To bind the earth particles together strongly
. These are substances such as lime,
Portland cement, pozzolana cement and natural fibres. These strengtheners
