Coal

Coalmine waste materials are piled up to form enormous slurry heaps; as they naturally contain a certain amount of clay, they have some cohesive power. Several experiments to transfonn this "earth" into blocks intended for building have been successfully carried out.

Glass

An incredible amount of bottles can often be found around small and large towns. Bottles and other glass waste can be ground down into powder, which can in turn be incorporated into earth components, e.g. compressed earth blocks, adobe blocks, etc. Glass powder makes such bricks very hard and virtually impregnable to termite attack. A relatively limited number of blocks used in the footings of a house can effectively protect it from termite attack.

Iron salts

Iron salts are coagulant electrolytes produced by the mining industry. These products can stabilize soil, but this would require very large quantities because of their very slow dissipation. Their use is therefore restricted to mining areas.

Lignosulphate

Lignosulphate is the organic substance which permeates the cells, fibres and vessels of wood and certain plants and which renders them impermeable and non-extensible. For stabilization, one can use lignosulphates or lignosulphites which are by-products of wood processing (as well as straw or alfa) in the paper industry. Lignosulphite, for example, is poured away into the rivers of producing countries at a rate of several million tons a year. Their composition varies very greatly depending on the nature of the basic product used and the chemical reaction; the waste matter can be used as a gluing or dusting agent. But used in this way, they remain almost entirely water soluble. If the lignosulphite solution is mixed (by a process of oxidation) with hexavalent chromium salts, principally potassium bichromate or sodium bichromate, a thick gel is obtained which is an insoluble compound: chromolignin.

When stabilizing a soil with suitable characteristics, 4% lignosulphite and 1% bichromate should be used.

Lignin is found in the following materials:

Lime sucrates

Lime sucrates are not by-products of sugar refinery, but the final products of the transformation of sugar sap during refining. Lime sucrates can be used as a soil stabiliser. They are of particular interest in regions where growing and processing sugar cane are highly developed. These products can not be mixed with cement and may attract termites. Compressive strength is improved and capillary rise is greatly reduced. 5% is effective for sandy soils. When using clayey soils, small quantities of lime need to be added to obtain the equivalent effectiveness.

Molasses

Certain kinds of molasses, which are by-products of plant processing, can be used for stabilization, e.g. wood molasses (see lignin), sugar molasses (see lime sucrates). Sugar aldehydes from dehydrated molasses can be polymerized at high temperatures with phenolic catalysts. The resinous material obtained has characteristics similar to that of a naturally occuring asphalt and synthetic resins.

Phosphogypsum

This kind of gypsum, which is an industrial waste, behaves like plaster. It is an attractive stabilizer for rather sandy soils, but is not recommended for clayey soils. One should not exceed 15% proportion of stabilizer. Because of the danger of rapid setting, the earth must be worked in small quantities. The plaster can be combined with lime in proportions of around 1: 1.

It should never be used in combination with cement, however. Despite a definite stabilizing effect, such products remain vulnerable to damage from water.

Quarry dust

Dust from concrete aggregate quarries is generally considered to be an unusable industrial waste product. Itcan, however, beused to thin soils with too high a clay content, thus making them perfectly suitable for use in the field of building with earth.

Red mud

The raw material for production of aluminium is bauxite. When bauxite is refined, it yields alumina, which in turn is smelted into aluminium. The red or brown mud is a waste product from alumina production and constitutes a considerable environmental problem because there is so much of it - 30-40 million tonnes per year worldwide. Unless disposed of properly, it can contaminate the ground water and spread red dust over wide areas. Even when correctly managed, the unesthetic effect and the mere space requirement of the vast mud ponds motivate the continued search for economic uses.

UNIDO has undertaken a number of technico-economic studies on industrial use of red mud waste. These studies have been used to develop the technology used in China and for similar projects in India and Jamaica.

In Shandong in the People's Republic of China, the traditional local brickmaking factories are able to use a mixture of brown mud from the Shandong alumina plant and fly ash from the neighbouring coal-fired power station to make bricks and tiles.

Rice husk ash

Along-side with the production of rice paddy, are the by-products such as rice straws and husks, which are being disposed of as wastes. When properly burnt (400- 500 'C) the resultant ash can be used as a stabilizer, with pozzolanic properties.

Rubble

The mineral waste products from the demolition of buildings can sometimes be perfectly suited to being mixed with clayey soils which act as natural binding agents. It is in this way that a large area of the centre of Lisbon, that of the Marquis of Pombal, was rebuilt after it had been destroyed in an earthquake,

Shea butter

The shea is a tree (Butyrospermum parkii of the sapotaccae family) which grows in the Sahara, and its seeds provide a fatty substance known locally as "karit‚" butter. The waste materials of the process, which still contain appreciable quantities of oil, can be successfully used in the composition of earth renders intended for earth building production.

Sodium chloride

Sodium chloride is a by-product of the manufacture of sodium carbonate. It can be used successfully with clayey soils to reduce their plastic characteristics. The effect obtained cannot, however, be qualified as stabilization.

Sugar press mud

The sugar will employing carbonation process are producing about 6-8 tons of press mud for every I 00 tons of sugar-cane processed by them. Its disposal is a big problem for the factories. Much useful land in their proximity is being wasted by dumping this material.

Press mud can be added to fine soils with high quantities of clay and/or silt, resulting into dramatic improvements of the characteristics of these soils.

Mortar prepared from this sugar press mud as such and mixed with 3 to 4 % bitumen can be used for rendering walls.

Used engine oil

Used engine oil can be used as a water-proofing agent within the material itself or on the surface. One should bear in mind that such oil will wash out with water. It is not therefore enormously efficient. As surface protection, its must be regularly renewed to achieve viable protection.

Wood shavings

Enormous quantities of wood shavings are produced by our wood industries. In certain specific circumstances, wood shavings can be mixed with earth to form a perfectly stable and durable material, with remarkable insulating properties.

Dozens of other applications for using waste materials certainly exist. Do not hesitate to inform us of your own experiences which you can share with your colleagues through BASIN-News.