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< prev - next > Construction Cement and binders KnO 100090_Lime_production_traditional_Chenkumbi_Malawi (Printable PDF)
Lime has been used in the Malawian building industry for many generations, principally as
the cementing agent in renders and to produce a decorative whitewash. In more recent years,
there has also been a demand for high quality lime from the sugar processing industry and for
soil stabilization in road construction.
The Chenkumbi Hills in Central Southern Malawi, 15 km south of the town of Balaka, is a
traditional lime producing area. It has grown in importance in the 1980s and 1990s due to
the large deposits of calcitic marble of a reasonably high chemical purity.
This case study illustrates the traditional techniques utilized for producing lime hydrate
specifically in the Chenkumbi hills, although they are indicative of methods employed in other
areas of the country. Practical Action has developed improved lime burning and processing
technologies for Chenkumbi in collaboration with local lime producers, since 1986. The
results of this work are described in Malawi lime case study No.2 of this series.
Raw materials and quarrying techniques
The Chenkumbi hills are formed by large deposits of coarse grained, large crystalline marble.
The deposits vary considerably in chemical content from almost pure calcium carbonate to
almost pure dolomite. Only a small portion of the hills has been geologically mapped in
detail, but this mapping alone measured reserves of 3.7 million tonnes of limestone with a
high calcium carbonate content. The Malawian Geological Survey Department has trained the
lime producers in a simple acid reactivity test which helps select the high quality deposits
with a calcium carbonate content (CaCO3) above 95%.
The fuel used for burning the marble is indigenous hardwood, the use of which has led to
considerable deforestation in the vicinity of the hills. The size of the fuelwood logs varies from
30 mm for kindling to 800 mm diameter logs up to 3 m long for the centre of the kiln. Lime
producers experience considerable difficulty in the procurement of suitable fuelwoods,
particularly in the wet season when many rural roads are impassable. Softwoods are not
suitable for the type of kiln used, due to their fast burning characteristics.
Stone is extracted by hand from small surface excavations using picks, crowbars and
hammers. Where large rocks need to be broken, traditional techniques of heating followed by
rapid cooling, using fire and water, are employed. The marble is then broken down by hand
using hammers to a kiln feed size of 50 to l00 mm diameter.
The kiln and firing methods
The kiln is a rectangular box-type kiln with an open top, constructed from rough marble
blocks cemented with a mud/lime mortar. (See figure 1). The internal dimensions of the box
vary but an average-sized kiln would be approximately 6 m long x 4 m wide x 2 m high. The
kiln walls are buttressed, normally with stone abutments, but sometimes with soil forming a
ramped access to the kiln. It has two firing openings at the base on each of the short sides
which lead into two trenches running along the length of the kiln connecting the firing
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