Rammed in Kenya 2
Strength and rain test
Rammed earth in Kenya part 2
: Ramming earth has been a method of construction used for centuries in various parts of the world,
and is commonly known by its French name 'Pise'. Earth is extracted from the ground and compacted
in layers inside specially constructed formwork. After compaction the formwork is released and moved
along to a new position in the wall or upwards to the next layer. In this way slip forming is formed.
This technique can produce buildings that are strong, durable safe and desirable. Above all, because
earth is an abundant and cheap resource, rammed earth buildings are very economical; in addition
the majority of the investment goes directly into the local economy. The method has an essential
simplicity, and with its unskilled labour intensity, rammed earth can be seen as a valuable tool in the
generation of low-cost housing in developing countries in both urban and rural areas.
The compressive strength of rammed earth is less than that of concrete but more than strong enough
for use in domestic buildings. Costs will also, in most cases, be highly competitive. It must be
remembered, though, that 'earth' varies in quality just as bricks or concrete blocks do. Standards of
comparison are needed.
Optimum moisture content OMC
The OMC is important because it has a direct bearing on the strength of the finished wall. With too
little water the soil cannot be properly squeezed, with too much it becomes too wet and the water
itself resists compaction. The ideal amount of water will vary from one soil mix to another. Fortunately,
once some experience in ramming has been gained, it becomes quickly obvious when the soil is too
wet or dry. The mix of materials for use in rammed earth structures should have the 'optimum
moisture content', according to the 'drop' test
Suitability of soils for ramming
Natural soils for earth building shall be taken from subsoil layers found beneath organic
topsoil layers, which are typically 100 to 300 mm thick.
Soil used to form rammed earth structures shall be free from organic material and other non-
soil substances, such as rubbish, deleterious material, etc. While this requirement is the optimum
requirement, soils low in organic content not exceeding 2% to 4% are considered suitable for rammed
earth construction [1–4].
More information on our part 3
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