Building with earth - Gernot MINKE (1)

4 Improving the earth’s characteristics by special treatment
or additives
Without
Linseed oil 3%
ISOFLOC 2%
Cellulose 0.5 %
Cellulose 0.75 %
Gelatine 0.5 %
Gelatine/Alum 0.5 %
Starch 1 %
Starch 2 %
Whey 2 %
Whey 4 %
Shrinkage
Compressive strength
Tensile bending strength
Binding force
4.1
4.1 Influence of various
additives on the shrinkage,
binding force, tensile
bending force and compressive
force of a sandy
loam
4.2 Reduction of shrinkage
by adding sand to a
clayey loam
4.3 Reduction of shrinkage
by adding sand to a
silty loam
As a rule, it is only necessary to modify the
characteristics of loam for special applications.
As we can see in 4.1, additives that
improve certain properties might worsen
others. For instance, compressive and bending
strength can be raised by adding starch
and cellulose, but these additives also
reduce the binding force and increase the
shrinkage ratio, which is disadvantageous.
Reduction of shrinkage cracks
Because of increased erosion, shrinkage
cracks in loam surfaces exposed to rain
should be prevented. As described in chapter
2 (p. 22), shrinkage during drying
depends on water content, on the kind and
amount of clay minerals present, and on the
grain size distribution of the aggregates.
Thinning
Addition of sand or larger aggregates to a
loam reduces the relative clay content and
Linear shrinkage (%)
Linear shrinkage (%)
5
2
4.5
1.8
4
3.5
1.6
Sand 1-2
3
1.4
Sand 0-2
2.5
1.2
2
1
1.5
1
0.8
0.5
0.6
0
0 20 40 60 80 100
0.4
Sand content (%)
0.2
Sand 0.25-1 Sand 0-2
0
1/2 1/3 1/4
4.2 4.3
Proportion Loam : Sand (by weight)
hence the shrinkage ratio. The results of this
method are shown in 4.2 and 4.3. In 4.2, a
loam with 50% clay and 50% silt content
was mixed with increasing amounts of sand
until the shrinkage ratio approached zero.
To insure comparability, all samples tested
were of standard stiffness (see chapter 2,
p. 24). Interestingly, a shrinkage ratio of
0.1% is reached at a content of about 90%
sand measuring 0 to 2 mm diameter, while
the same ratio is reached earlier when using
sand having diameters of 0.25 to 1 mm, i.e.
at about 80%. A similar effect can be seen
in 4.3 with silty loam, where the addition
of coarse sand (1 to 2 mm in diameter)
gives a better outcome than normal sand
with grains from 0 to 2 mm in diameter.
Illustration 4.4 shows the influence of different
types of clay: one series thinned with
sand grains of 0 to 2 mm diameter with
90% to 95% pure Kaolinite, the other with
Bentonite, consisting of 71% Montmorillonite
and 16% Illite.
Thinning mediums
In the ceramic industry, fluid thinning
mediums are used to attain higher liquidity,
thereby allowing less water to be used
(in order to reduce shrinkage). Typical thinning
mediums are sodium waterglass
(Na 2 O · 3-4 SiO 2 ), Soda (Na 2 CO 3 ), and
humus acid and tannic acid. Tests conducted
at the BRL at the University of Kassel
showed that these methods were of very
little relevance to earth as a building material.
But tests with whey were successful.
39
Improving the earth