Utilization of bagasse in brickmaking
Practical Action
Clay was dug in the evenings, using hoes, from a depth of 0.5 to 1.5m. To the pile of clay, 20
buckets (each bucket weighing 20 kg) of loose mature bagasse, which needed no further
processing, were added followed by a suitable amount of water. Mixing was carried out and the
mix was sprinkled with more water and left to mature overnight. Early the following day the
contents were remixed, using bare feet, adding more water if needed, till a workable plasticity
was reached. Slop-moulding of bricks was then started using double metal moulds (each
compartment measuring 25 x 12 x 7 cm).
Five labourers moulded one pile of clay weighing 11 000 -13500 kg per day. Two labourers
brought clay from the pit to the moulder on the moulding table and the other two carried away
the green bricks for drying. Each pile of clay produced 3500 to 4000 green bricks. As soon as
moulding was completed, the following day's clay pile was prepared.
Drying was done on flattened ground, bricks being turned for even drying. After two days bricks
were dry enough to be piled in a honeycomb manner for airing.
This continued for seven days and then the bricks were loaded into kilns. At the time of loading
average weight of a brick was 2.31 kg. All production stages were manual.
Fuels and Brick Firing
The 118000 green bricks were loaded into two clamp kilns (see table 1 below for number of
bricks loaded into each kiln). The two kilns were plastered with mud and their tunnels were filled
with miskit wood for fire ignition. Each kiln required 4 labourers.
The first kiln (Kiln 1) was fired using miskit wood only. Firing continued for 26 hours using a
total of 5827 kg of wood.
The second kiln (Kiln 2), after igniting with wood, was fired with bagasse blocks for 23 hours. It
consumed 1439 kg of wood and 3524.5 kg of bagasse blocks. Bagasse blocks can be fed into
tunnels every 3 to 4 hours compared to every 0.5 to 1.5 hours with wood.
Sets of Buller's bars were put into each kiln at different heights. Each set was viewed through
spy-holes. Each set contained bars numbered 11, 13, 15 and 17 as indicators of temperatures
845, 890, 940 and 990°C respectively. Firing was stopped in each kiln after melting of every
number 17 bar. By then physical indicators of complete firing were visible. These were a drop in
height of the kiln, appearance of whitish colour on the uppermost layer, ending of the emission
oI white smoke and blackening mud cracking of the mud plaster layer.
The kilns were cooled for seven days and then off-loaded.
Firing Results
These are summarised in Table (1).
Grade 1 refers to well burnt bricks while grade 2 means a lower firing bond. Grade 3 bricks are
those from the outer-most layers in the kiln and therefore underfired.
Kiln 2 (bagasse blocks) yielded proportionally more grade 1 and less other grade bricks than kiln
1. Kiln 2 also produced a higher percentage of saleable bricks i.e. the sum of grades 1 and 2.
Additionally, compared with using cow dung as a clay additive, bagasse was found to be easier to
work with. Bagasse is fine and its smell, when wet, is more tolerable. Dung is found in hard lump
form, which does not break up easily and leaves voids in bricks when fired. In contrast clays
mixed with bagasse result in bricks with a smooth surface finish, as the green mix quite
homogenous.
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