Civil Engineering Reference
In-Depth Information
5
Water and air
Water and air are needed for all life and therefore for all animal and vegetable
products; they are the constituents of many materials. Water can dissolve more
chemical compounds than any other solvent and is used a great deal in the paint-
ing industry. When casting concrete, water is always part of the mixture, even if
it evaporates as part of the setting process. Air is also an important component
in the chemical processes required for the setting of concrete. The majority of
industrial processes also use great amounts of water for cooling, cleaning etc.
Clean air and pure water are very limited resources in many places, especially
dense industrial areas. During recent years large areas of the European continent
have experienced drastic disturbances in the ground water situation, including
widespread pollution of ground water.
Water
Water is seldom just water. It nearly always contains other substances to some
degree such as calcium, humus, aluminium, nitrates etc. The quality of water is
important, not only for drinking, but also as a constituent in building materials.
Water with a high humus content produces bad concrete, for example, as the
humus acids corrode the concrete.
The terms 'hard' and 'soft' water are well known. Hard water contains larger
amounts of calcium and magnesium, 180-300 mg/l, than soft water, which con-
tains approximately 40-80 mg/l. Very soft water will have a dissolving effect on
concrete.
Water also has different levels of acidity which is expressed in a so-called pH-
scale with values from 0-14. The lower the pH value, the more acidic the water.
A pH value of 6.5-5.5 has a slightly aggressive effect on concrete and materials
containing lime, while a pH value under 4.5 is very aggressive. Marsh water
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