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close this bookAppropriate Building Materials: a Catalogue of Potential Solutions (SKAT, 1988, 430 p.)
close this folderExamples of wall materials
View the documentStone masonry blocks walls
View the documentRammed earth walls
View the documentCompressed soil blocks walls
View the documentBamboo reinforced earth walls
View the documentBurnt clay brick walls
View the documentConcrete hollow block walls
View the documentBamboo walls
View the documentTimber panel walls
View the documentSulphur concrete walls
View the documentWalls from agro-waste

Rammed earth walls

KEYWORDS:

Special properties

Good impact resistance and durability

Economical aspects

Low cost

Stability

Good

Skills required

Experience in earth construction

Equipment required

Formwork, rammer

Resistance to earthquake

Low to medium

Resistance to hurricane

Good

Resistance to rain

Medium

Resistance to insects

Medium

Climatic suitability

Hot dry climates, upland climates

Stage of experience

Traditional

SHORT DESCRIPTION:

· This method of construction has been used for centuries in various parts of the world and is commonly known by its French name "Pise".

· Earth is filled into formwork in layers of up to 10 cm and thoroughly compacted to a thickness of 6 - 7 cm with a ramming tool. When the formwork is full, it is dismantled and moved (usually horizontally) to the next position, fixing it firmly over a previously completed row. In this way the building goes up gradually, layer by layer, row by row.

· Other than patching up cracks, holes and damaged edges immediately after removing the formwork, no surface treatment is normally required.

· To a large extent, the choice of formwork and ramming device influences the speed, cost and quality of construction, so that experience and/or several trials with alternative equipment is necessary. As far as possible, the use of stabitizing agents (eg cement, time, etc.) should be avoided, as they complicate the whole procedure. However, this is only possible with optimum soil qualities and good building design.

· Rammed earth is a natural material, constructed with only a small fraction of the energy input required for other materials to produce structures of similar strength and durability. It also causes no wastage or pollution, and when demolished, soils that contain no stabilizer can be reused over again. Further information: Bibl. 02.06, 02.19, 02.28, 02.32.

Soil

· The most appropriate soil for rammed earth construction contains: 50 to 75 % fine gravel and sand; 15 to 30 % silt (pulverized sand) and 10 to 20 % clay (cohesive particles).

Formwork

· The formwork must be more rigid than standard concrete shuttering, because of the high outward pressure of compacted earth;

· it must be light and easy to dismantle and assemble, so that the work does not become too tiring and time-consuming;

· it should be the largest size that can be reasonably handled, in order to reduce the number of moves;

· and it should permit the wall thickness to be varied.

· Different types of formwork are illustrated. The formwork is normally moved horizontally after each section is completed. In order to avoid the horizontal cracks that tend to develop between successive rows of rammed earth (since each row dries out separately), a climbing formwork was developed at the Kassel College of Technology, Federal Republic of Germany (Bibl. 02.28, Vol. 2).

· The length of formwork can range between 150 and 300 cm, the height between 50 and 100 cm. As the ratio of wall thickness to wall height should be between 1: 8 and 1: 12 (the latter requiring good quality control), rammed earth walls can be as thin as 30cm. However, foreman to stand between the two sides of the form to compact the soil, a minimum of 40 cm is recommended.


Test to determine optimum sand and clay content

Rammers

· Manual rammers consist of a wooden or steel rod with a heavy wooden or metal striking head. The heavier it is, the better the compaction, but the more tiring for the user.

· Pneumatic rammers imitate the manual rammers, but achieve much higher impact frequencies, thus reducing construction time. The main drawback is their high cost.

· An alternative is a small vibrating plate, developed at the Kassel College of Technology. An electric motor with an eccentric rotating mass transmits vibrations to the plate, thus causing the machine to move. An automatic switch makes it move back and forth in the formwork, without manual guidance.


FIGURE

Construction

· A stone, burnt brick or concrete foundation and base course (at least 30 cm above ground level and exactly as wide as the earth wall) are required to start with. The top surface must be horizontal (requiring steps on sloping sites) and should never project beyond the external face of the Barth wall. A damp proof course between the footing and wall is recommended in moist environments.

· The sides of the formwork should overlap the wall section below by at least 10 cm to stand firmly. The work should always begin at a corner.

· The soil is filled in the formwork in layers of not more than 10 cm. The person who rams the soil stands on it or on the top edges of the formwork, and strikes the soil systematically, first along the sides and then in the centre. The operation is completed, when the sound of each stroke of the rammer changes from a dull to a solid clear sound. Once the formwork is moved to the next section, the previous section should be covered with an appropriate material (grass, leaves, cloth, plastic sheets) for protection against rain, wind or direct sunshine.

· Care must be taken to stagger the joints between each row (just as in masonry work) and wall junctions should be made to interlock connecting walls. Wall anchors and reinforcements (eg at corners) made of metal scrips or rods, strong twigs, split bamboo or rope, can be placed in these junctions and building corners during compaction.

Openings

· These should be well planned so that their sides correspond to the ends of formwork sections, their height is in line with the top of the last layer, and the ring beam substitutes the lintel. It is also possible to insert the window and door frames within the formwork and attach anchors, so that the frames are rigidly fixed to the wall. Small openings can also be easily cut into the finished wall by means of a pise saw (a length of barbed wire with handles at each end) used by two men.

Surface Treatment

It is important for the durability of the wall that broken edges, cracks and holes are filled and compacted, immediately after removing the formwork, as the patching material does not bond with partially dried up walls.


Illustration adapted from Vorhauer, 1979 (Bibl. 22.09)


FIGURE