which reduces insulation. The equilibrium
moisture content of rye straw at a relative
humidity of 50% and a temperature of
21°C, for instance, is 13%, whereas under
the same conditions, it is only 0.1% in the
case of expanded clay.Embodied energy
It is often argued that artificially foamed
mineral aggregates like expanded clay
require considerable energy for production.
In this context, one should be aware that
the embodied energy of timber or bricks
used in construction is much higher. The
embodied energy of timber is computed to
be 6 times as high as that of mineral wool,
and twice as high as expanded clay for the
same volume (Turowski, 1977; Weller and
Rehberg, 1979; Elias, 1980; Marmé and See-
berger, 1982).
In making an overall assessment of the con-
struction energy entailed by a given project,
then, we must remember that while it may
be technically true that loams with artificially
expanded minerals use more energy than
those containing other aggregates, this dif-
ference is negligible when compared, for
instance, to the total energy input involved
in the processing, production and trans-
portation of timber.Lightweight cork loam
Expanded cork can be used to form light-
weight loam in place of porous mineral
aggregates. The advantage of expanded
cork is its low density. The disadvantage is
that this material is relatively expensive and
has little compressive strength. Therefore,
bricks made of this mixture break very easily
at their edges.
The German firm Haacke developed a mix-
ture of cork, diatomite, and straw, along
with some cellulose, which can be sprayed
on a wall like an insulating spray plaster.
Density is between 300 and 450 kg/m^3. The
measured k-values are 0.07 to 0.08 W/mK,
measured vapour diffusion resistance
between 4 and 19, and shrinkage ratio
between 1% and 2%.Lightweight wood loam
Sawdust, wood shavings and chips can
also be used as lightweight aggregates to
increase the thermal insulation capacities
of loam. As timber has a higher density
than straw or cork, the thermal insulation
of that mixture is obviously lower. The mini-
mum density that can be achieved is about
500 kg/m^3 , but a dry mix of this density no
longer possesses sufficient rigidity. The dan-
ger of fungus growth and rotting is much
less than with straw, but it still exists.
It is ecologically desirable to use chips made
of branches and portions of trees not other-
wise used in structural work. However,
these contain fairly large quantities of bark,
and are therefore susceptible to fungus
growth and rotting.Foamed loam
In order to foam loam, it has to be free of
sand and gravel, and in a plastic state. As
loam in this consistency needs a long period
to dry, it is hardly possible to foam it using
the regular agents such as those used for
foaming concrete. Therefore, the loam
needs to be given additives which quicken
the drying process, such as the geopoly-
mers described in this chapter, p. 43, in
which clay, quartz and chalk powder are
mixed with waterglass and foamed with
hydrogen peroxide (H 2 O 2 ). This process
produces a foamed loam with a density
of 90 kg/m^3. This material hardens within
two hours at a temperature of 20°C and
in one hour at 50°C. This product, manu-
factured by the German firm Hüls AG, has a
compressive strength of 10 to 20 kg/cm^2 ,
specific heat of 0.2 kJ/kgK, thermal conduc-
tivity of 0.10 to 0.12 W/mK and pH-value
between 9 to 10. It is an ideal material to
form pre-cast earth elements of a large size.
The German company Lorowerk uses a sim-
ilar technique to produce large elements for
thermal insulation. Products with densities
of 300 kg/m^3 reach a thermal conductivity
of 0.08 W/mK. The primary energy input is
only 5 kWh/m^3.51 Improving the earth4.214.21Setting of a light-
weight straw-filled test
element