Building with earth - Gernot MINKE (1)

5.9 Electrical ram
(Wacker)
5.10 Pneumatic ram,
Australia
5.11 Pneumatic rams
(Atlas-Copco)
5.12 Vibrating ram
(Heuser)
5.13 Vibrating ram
(Heuser)
5.14 Shrinkage cracks
in a rammed earth
wall, Ecuador
5.15 Slicing rammed
earth directly after the
formwork is dismantled
5.16 The French pisé
technique
5.11
Normally, soil compaction tools of the type
used in road construction are unsuitable for
rammed earthwork, because their frequency
is too high and their lift too low. Tools which
only vibrate might be suitable for sandy
soils, but not for clayey ones.
The pneumatic rams shown in 5.11 are
extremely effective for rammed earthwork.
The Ram II G, produced by the firm Atlas-
Copco, is fairly suitable because a special
feature prevents its head rotating, thus
ensuring that square heads can also be
conveniently used. All the rams illustrated
require a pressure of 6 bar and an air flow
rate of 0.4 to 0.9 m 3 /min. Due to their high
costs and the infrastructure and energy
required to run them, these rams are used
only for larger building projects. An electrical
vibration ram has been developed at the
BRL and manufactured by the firm Heuser
(5.12 and 5.13). Its engine has a frequency
of 1000 to 1200 cycles per minute. The
most important part of this vibrating ram is
its specially shaped base, which allows the
apparatus to move within the formwork by
itself while compacting the earth. It can
compact loose soil in layers 7 cm thick.
5.16
the upper course than in the lower, leading
to horizontal shrinkage cracks at the joint
(5.14). This can be dangerous, since capillary
water can enter this joint and remain, causing
swelling and disintegration. As can be
seen in the same figure, vertical cracks can
also occur in such walls.
With the French pisé technique, this problem
was solved by using a layer of lime mortar
above each course before laying a new one.
A lime mortar cures over several weeks and
remains plastic until the loam has stopped
shrinking; sometimes even the side joint
between sections of the course is made
with mortar at an incline (5.16).
Another method to avoiding horizontal
shrinkage cracks is to ram in a way that the
wall is produced vertically. This is described
in greater detail below.
Shaping of openings
5.12
5.15
55
Method of construction
In nearly all traditional rammed earth techniques,
the formwork is removed and
re-erected horizontally step by step. This
means that earth is rammed in layers from
50 to 80 cm high, forming courses of that
height before the formwork is moved.
When one course is complete, the next
course that is rammed is moister than the
one already in place, which is partially dried
out. Therefore, there is a higher shrinkage in
Rammed earthworks
5.14
The formwork can be dismantled immediately
after ramming is completed. At the
same time, this rammed earth can be
shaped easily by scraping, cutting, scooping
or scratching. Normally, inserts are left in
the formwork to create openings. However,
with rammed earth, the opening can be
cut with much less effort with a knife or a
barbed wire used as a saw. This technique
also allows shaping of jambs and sills, as
shown in 5.15. It should be mentioned that
at this stage rammed earth has already
achieved sufficient strength to grip nails
(they can be driven into the wall without
making a guiding hole with a drill).