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Utilization of Bagasse in Brickmaking

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Otto Ruskulis - for Practical Action said:

Dear Ghali

Clay deposits are common throughout the world. They are formed from the weathering of rock and are laid down where rocks have been eroding or by transportation and deposit of the clay by slow moving streams or in stagnant water. They may be found near or in dried up river beds or old silted up lakes.

Clay minerals are most commonly made up of complex structures of iron and aluminium oxides, although the oxides of some less common metal elements can also form clays. Many clay deposits are suitable for making bricks. For making pottery, decorative tiles and specialist ceramics only relatively few clay deposits are suitable.

The type of oxides in the clay minerals as well as the firing temperature and quantity of air passing through the kiln determine the final colour of the brick. Most fired clay bricks are red in colour because of the iron oxide content. However, they can also be lighter in colour if there is more aluminium oxide present, or yellow, blue or grey.

The most common clay minerals are kaolinites, smectites, illites and chlorites. Deposits that mainly contain kaolinites are most suitable for pottery and generally not used for brickmaking. Where kaolinites exist mixed with other types of clay this can be used for brickmaking. Smectites include some expansive clays such as montmorillonite. A certain amount of expansive clays can be tolerated in the brick, but if this is too high the bricks will crack on drying and firing. Illites are the best clays for brickmaking and can usually be found mixed with smaller amounts of the other types of clay mineral.

Other materials found in clays include limestone and chalk, sand silt, organic matter and other minerals, which may act as fluxes, for example feldspars, or be completely inert. A small amount of limestone (less than five per cent) can be tolerated in the brick if it is finely distributed in the clay and does not occur in nodules. The problem with nodules is that after firing they expand and cause cracking in the brick. Some lime in the brick gives it a lighter colour. A proportion of sand and silt in the clay is necessary to control shrinkage, but is best kept to below 30 per cent to avoid having low strength bricks. The sand might occur naturally inside the clay or can be added separately when the clay is being prepared for moulding and firing. Lumps of organic matter in the clay are not good as they burn out to leave holes in the brick. So, when removing the topsoil to reach the clay it is important to dig down deep enough to where the organic matter of the topsoil is no longer mixed in with the clay. However, very fine organic matter mixed in with the clay is not a problem and can act as an additional fuel when firing. Materials such as sawdust or decayed sugar cane fibres (bagasse) are sometimes added to the clay to save on the use of external fuel. Flux materials, where they occur mixed in with the clay, are very useful as they reduce the temperature at which the formation of ceramic bonds and vitrification occurs in the clay, i.e. when the brick hardens due to firing. They can save on the added fuel by 10 per cent or more.

The analysis of clays is a very specialised task that can be undertaken by a national geological survey organisation or some university chemistry or geology departments. Small to medium-scale brickmakers would not do this analysis. Instead there are a number of less complex physical tests that can be carried out on the unfired clay and then on the finished bricks after test firing. These consider the shrinkage of the clay on drying and firing, the cohesion of the moulded samples, and the strength and appearance of the fired bricks.

For further reading on clay types for brickmaking and assessment and testing of them and the brick products see:- Green Brick Making Manual, by Heinrich Muller and others, VSBK Programme Nepal, 2008, http://www.ecobrick.in/resource_data/KBAS100046.pdf

Commented on: 2014-08-13 15:19:00

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Ghali Mousa said:

What is the typical or optimum chemical composition of the clay bricks that fulfill low production cost with high quality?

Commented on: 2014-08-03 13:53:00

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Ghali Mousa said:

What is the typical or optimum chemical composition of the clay bricks that fulfill low production cost with high quality?

Commented on: 2011-09-08 12:00:00

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Otto Ruskulis - for Practical Action said:

Dear Ghali

Clay deposits are common throughout the world. They are formed from the weathering of rock and are laid down where rocks have been eroding or by transportation and deposit of the clay by slow moving streams or in stagnant water. They may be found near or in dried up river beds or old silted up lakes.

Clay minerals are most commonly made up of complex structures of iron and aluminium oxides, although the oxides of some less common metal elements can also form clays. Many clay deposits are suitable for making bricks. For making pottery, decorative tiles and specialist ceramics only relatively few clay deposits are suitable.

The type of oxides in the clay minerals as well as the firing temperature and quantity of air passing through the kiln determine the final colour of the brick. Most fired clay bricks are red in colour because of the iron oxide content. However, they can also be lighter in colour if there is more aluminium oxide present, or yellow, blue or grey.

The most common clay minerals are kaolinites, smectites, illites and chlorites. Deposits that mainly contain kaolinites are most suitable for pottery and generally not used for brickmaking. Where kaolinites exist mixed with other types of clay this can be used for brickmaking. Smectites include some expansive clays such as montmorillonite. A certain amount of expansive clays can be tolerated in the brick, but if this is too high the bricks will crack on drying and firing. Illites are the best clays for brickmaking and can usually be found mixed with smaller amounts of the other types of clay mineral.

Other materials found in clays include limestone and chalk, sand silt, organic matter and other minerals, which may act as fluxes, for example feldspars, or be completely inert. A small amount of limestone (less than five per cent) can be tolerated in the brick if it is finely distributed in the clay and does not occur in nodules. The problem with nodules is that after firing they expand and cause cracking in the brick. Some lime in the brick gives it a lighter colour. A proportion of sand and silt in the clay is necessary to control shrinkage, but is best kept to below 30 per cent to avoid having low strength bricks. The sand might occur naturally inside the clay or can be added separately when the clay is being prepared for moulding and firing. Lumps of organic matter in the clay are not good as they burn out to leave holes in the brick. So, when removing the topsoil to reach the clay it is important to dig down deep enough to where the organic matter of the topsoil is no longer mixed in with the clay. However, very fine organic matter mixed in with the clay is not a problem and can act as an additional fuel when firing. Materials such as sawdust or decayed sugar cane fibres (bagasse) are sometimes added to the clay to save on the use of external fuel. Flux materials, where they occur mixed in with the clay, are very useful as they reduce the temperature at which the formation of ceramic bonds and vitrification occurs in the clay, i.e. when the brick hardens due to firing. They can save on the added fuel by 10 per cent or more.

The analysis of clays is a very specialised task that can be undertaken by a national geological survey organisation or some university chemistry or geology departments. Small to medium-scale brickmakers would not do this analysis. Instead there are a number of less complex physical tests that can be carried out on the unfired clay and then on the finished bricks after test firing. These consider the shrinkage of the clay on drying and firing, the cohesion of the moulded samples, and the strength and appearance of the fired bricks.

For further reading on clay types for brickmaking and assessment and testing of them and the brick products see:- Green Brick Making Manual, by Heinrich Muller and others, VSBK Programme Nepal, 2008, http://www.ecobrick.in/resource_data/KBAS100046.pdf

Commented on: 2011-09-08 12:00:00

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