Breathing Walls

In more and more conventional buildings, the indoorenvironment is provided withfresh air and pollutants are extracted with mechanical ventilation systems. By using hygroscopic materials, the amount of ventilation required can be reduced considerably. The principle for a 'breathing' building is that one uses no mechanical ventilation system at all; all diffusion of gasestakesplacethrough the materials. In a house with hygroscopic materials and a vapour retarder - instead of a vapour barrier - it has been concrete. Much of it is recycled from scrap metal, but it is normal to add at least 10% new steel to improve the strength. Steel reinforcement is in the form of bars of varying dimensions, or fibres of approximately 15 millimetres. The use of fibres can reduce the steel needed to half in concrete floors (Gielen, 1997). The distance between expansion joints can also be increased considerably, therefore reducing the use of plastic joint mastics. Other fibres have been introduced more recently in the form of glass and carbon. With carbon it is also possible to produce a reinforcing wire with far better strength properties than steel bars, reducing the climate impact in production by approximately 60% (Gielen, 1997).

In smaller projects it is also possible to use fibres from plant material, normally in a proportion of 2% in volume. Species with long, strong fibres are well suited. One good candidate is thus hemp fibre. Timber fibres are also used and there have also been experiments with bamboo reinforcement in both the former Soviet Union and France in recent years with good results. Sinarunddinarianitida is a tolerant species of bamboo that can be cultivated in Europe. Thamnecolomus murielae is also a possibility.

Additives

It is quite normal to put a whole range of additives into cement and concrete mixes (see Table 6.10 in Chapter 6). Additives are often organic and more or less volatile, and many of them can cause problems in the indoor climate. Evaporation of irritating substances from residues of oily fluids used on moulds and temporary lathing during concrete casting is a problem in many concrete buildings.

Handling and demolishing concrete can cause a problem with dust including from colouring pigments which can contain heavy metals such as chrome, lead and cobalt. It is possible that the waste process allows seepage into the environment of added tensides, aromatic hydrocarbons, amines, borates, etc. Melamine-based plasticizers can develop poisonous gases during a fire.

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