Soil Materials In Building

Many parts of Europe do not have easy access to gravel and sand as a building material - not necessarily because the resources are not there, but because extraction would have too much impact on the local environment. Certain types of clay, e.g. clay used for ceramic tiles, can also be limited in some regions. Otherwise, deposits of argillaceous materials are very large and well-distributed. Their use, however, is limited - in fact, this material is an almost unused resource. It will continue to be available as a valuable resource in the future.

Extraction of soil materials for use in the building industry requires low energy consumption. Drilling and explosives are unnecessary. It often takes place in quarries, and if these are large they can damage

The use of sand, gravel and stones for building.

Table 8.4 Material pollution from the production of materials from soils

Raw materials/basic materials

Polluting substances

Sand and gravel

Dust (possibly containing quartz)

DC

Earth for construction purposes

Dust

< A

Fired clay products with low lime content

Carbon dioxide, sulphur dioxide, fluorine compounds, dust, possibly chromium

IL

Fired clay products with 15-20% lime content

Carbon dioxide, possibly chromium, dust

groundwater and local biotopes. The most suitable clay for the production of bricks and ceramic tiles is usually in the 4-5 metres nearest the surface.

A large amount of water is used in brick manufacture and also in the production of expanded clay pellets and ceramic tiles when grinding the clay. The ceramics industry in Italy has developed an efficient re-circulating system with a simple filter for the waste sludge. In this way they have reduced the quantity of water used and kept the sludge effluent to a minimum.

The energy consumption for firing clay products is very high (see Table 8.5). Fossil oil is the usual source of energy, but wood, peat or a combination of electricity and coal can also be used. When oil alone is used large amounts of greenhouse gas carbon dioxide, acidic sulphur dioxide and nitrogen oxides are released. The brick industry has become increasingly more centralized in Europe. This has resulted in heavier energy consumption for transport and distribution.

Heated clay emits pollutants such as sulphur and fluorine compounds. These can be neutralized by adding 15-20% lime to the clay. The firing process at high temperatures can transform a largely silicate clay with a relative low intrinsic health hazard into forms of crystalline silica, which as dust is hazardous if inhaled (Curwell etal., 2002).

The building of an earth house causes minimal pollution. Vibrations from the ramming machines (see 'Pisé', page 210) can cause physical

Table 8.5 Embodied energy in soil materials

Products

Temperature required in production C)

Embodied energy (MJ/kg)

Sand and gravel -

0.5

Earth, compressed -

0.5

Vitrified bricks

1050-1300

3.5

Well-fired bricks

800-1050

3.0

Medium-fired bricks

500-800

2.5

Low-fired bricks

350-500

2.0

Cellular bricks

1000 (approx)

3.5

Ceramic tiles

1100 (approx)

8.0

Expanded clay pellets

1150 (approx)

3.0

Zytan

1200 (approx)

4.0

harm to the operator. As far as locally built houses are concerned, there is probably no other technique that can compete with the earth house in terms of the lack of environmental impact. The most common building techniques use earth that is dug out of the ground on the site itself. As the volume of material is large, transporting earth long distances is not normally economically viable.

The use of fired or unfired clay products in building causes no problems. In many cases they also improve indoor climate by regulating moisture levels.

Clay building waste is inert, and depositing both fired and unfired products has no detrimental effects on the environment. Exceptions are brick or ceramic tiles that are coloured with pigments containing heavy metals, fire-proof bricks that contain soluble chrome, and bricks from sooty chimneys which have absorbed large amounts of aromatic hydrocarbons during their lifespan. These products have to be separated and disposed of specially.

Bricks have proven to be considerably more effective than concrete in resisting the effects of modern air pollution. They are usually considered to be maintenance-free and have very high durability. However, all brick has a degree of porosity that makes bricks susceptible to frost damage. Such damage is likely to increase in northern Europe with global warming, but to decrease farther south.

Roof tiles and brick can usually be re-used, the latter depending upon the strength of mortar used - Portland cement mortar is much more difficult to remove from the bricks. Other fired clay products, such as ceramic tiles and expanded clay pellets, are seldom recycled and are more usually downcycled to become filler materials. Roof tiles and bricks can be broken up and used as aggregate in concrete.

When an earth house is demolished, the earth is physically and chemically intact in its original form. It can therefore be easily returned to the earth. To demolish a house of rammed earth, either the roof can be taken off and the rain allowed to wash it away, or it can be hosed down with water.

0 0

Post a comment