usual method using water is problematic,
since the sample dissolves at the joint.
Therefore, the BRL modified the method by
closing the opening of the glass container
with filter paper (see 2.22, right). Results
using this method were comparable to
those using the method given in the Ger-
man standard DIN 52617 (see 2.23).
Stability in static water
Stability in static water can be defined after
the German standard DIN 18952 (Part 2),
as follows: a prismatic sample is immersed
5 cm deep in water and the time it takes for
the submerged part to disintegrate is meas-
ured. According to this standard, samples
that disintegrate in less than 45 minutes are
unsuitable for earth construction. But this
test is unnecessary for earth construction
practices, since earth components would
never be permanently immersed in water
in any case. Significant instead is resistance
to running water.
Resistance to running water
During construction, earth building elements
are often exposed to rain and sensitive to
erosion, especially if still wet. It is important,
hence, to determine their resistance to run-
ning water. To compare the degrees of
resistance of different loam mixtures, the
BRL developed a test apparatus capable of
testing up to six samples simultaneously
(see 2.24). In this apparatus, water jets with
diameters of 4 mm are sprayed onto the
samples from a 45° angle and with a velo-
city of 3.24 m/sec, simulating the worst
driving rain conditions in Europe.
Rain and frost erosion
Illustration 2.25shows two samples: each is
shown prior to testing (left), and after three
years of weathering (right). The earth mix-
ture of the sample on the right contained
40% clay; the one on the left was mixed
with sand, reducing the clay content to
16%. Both mixtures were tested with a mor-
tar consistency in single layers 5 cm in thick-
ness. After drying, large shrinkage cracks
appeared. The clayey mixture showed 11%
shrinkage, the sandy mixture only 3%. After
three years of exposure to the weather, the
clayey soil showed a special kind of scaling
caused by frost. This was due to thin hairline
cracks that appeared during drying, and
through which rainwater was absorbed by
capillary action. When this water freezes, its
volume increases, causing the upper layers
to burst. In areas where no hairline cracks
were found, this effect did not occur. Fur-
thermore, no rain erosion was observed in
these areas. The sample on the left does
not show this type of erosion after three
years. Here we see that some loam is
washed away by rain, so that the horizontal
shrinkage crack is partially filled by these
particles, but no frost erosion is observable.
This is because there were no hairline
cracks, and because the loam contained
pores large enough to allow the freezing
water to expand.
The test resulted in the following conclu-
sions:- sandy loam has little resistance against
rain, but is frost-resistant when free of
cracks; - loam with high clay content tends to
develop hairline cracks, and is therefore sus-
ceptible to frost. If there are no hairline
cracks, it is almost rain-resistant.
The higher the porosity and the larger the
pores, the higher loam’s resistance to frost.
Therefore, extruded common clay bricks
produced in a factory are not frost-resistant
and should not be used on outer exterior
walls in climates with frost. By contrast,
handmade adobes made from sandy loam
are usually frost-resistant.
Drying period
The period during which wet loam reaches
its equilibrium moisture content is called
the “drying period.” The decreasing water
content and increasing shrinkage of a sandy
mud mortar dried in a closed room at a
temperature of 20°C and with a relative
humidity of ambient air of 81% and 44%
respectively is shown in 2.26. With 44%
humidity, the drying took about 14 days,
while with 81% humidity, about 30. Illustra-28 Properties of earthFilter paper
Silicon
Seal2.222.212.23Time t (min)1 Clayey loam, w – value
2 Clayey loam, Karsten
3 Silty loam, w – value
4 Silty loam, Karsten2.21 Modified water
penetration test accor-
ding to BRL
2.22Modified water
penetration test accord-
ing to BRL
2.23Water absorption
according to Karsten and
the German standard
DIN 52617Water absorption w (kg/m^2 )