Concrete aggressiveness

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The term concrete aggressiveness describes the property of groundwater to attack concrete and the steel it may contain . Under the influence of certain substances in the water, these building materials decompose, which can lead to considerable damage to buildings.

features

Soft water contains only a few dissolved ingredients and therefore dissolves lime compounds from concrete. The amount of ingredients dissolved in water is determined by the degree of hardness. With soft water corrosion (<8 degrees German total hardness) calcium hydroxide is dissolved and washed out. The dissolving processes of lime compounds are intensified at pH values ​​<7, as there are also excess hydrogen ions with an acidic effect. The occurrence of lime-dissolving (aggressive) carbonic acid in water also leads to the decomposition of concrete. During the decomposition process, the poorly soluble calcium carbonate (lime) is converted into easily soluble calcium hydrogen carbonate .

When ammonium salts occur , poorly soluble compounds are converted into easily soluble compounds through cation exchange. Another form of concrete decomposition occurs with magnesium chloride as a constituent of water. The magnesium chloride reacts with the calcium hydrate of the concrete to form magnesium hydroxide (gelatinous mass) and the soluble calcium chloride. Sulphates are among the most harmful substances in water to concrete . When sulfates are present, some lime compounds form calcium aluminate sulfates with a considerable increase in volume, which lead to the destruction (bursting) of the concrete (also known as cement bacillus or concrete drift ).

Attack Levels

Logo of the German Institute for Standardization DIN 4030
Area Construction
title Assessment of water, soil and gases attacking concrete - Part 1: Fundamentals and limit values, Part 2: Taking and analyzing water and soil samples
Latest edition 2008-06
ISO

The assessment of the aggressiveness of water in concrete is based on DIN 4030. The following degrees of attack are distinguished:

Exposure classes (concrete aggressiveness) of water according to DIN 4030
Examination parameters XA1 (weak attacking) XA2 (moderately aggressive) XA3 (very strong attack)
PH value 6.5-5.5 5.5-4.5 4.5-4.0
Lime-dissolving carbon dioxide (CO 2 ) in mg / l 15-40 40-100 over 100
Ammonium (NH 4 ) in mg / l 15-30 30-60 60-100
Magnesium (Mg) in mg / l 300-1000 1000-3000 over 3000
Sulphate (SO 4 ) in mg / l 200-600 600-3000 3000-6000

In order to protect concrete from chemical-physical attacks by substances contained in water , particularly low-lime cements (iron portland cement , blast furnace cement , trass cement ) or special sulphate-resistant cements are used in the production of the concrete . Furthermore, the tightness of the concrete is increased in order to improve the resistance to chemical attack.

See also

literature

  • Rita Hermanns: Securing contaminated sites with vertical mineral barrier systems using the two-phase diaphragm wall method. Verlag der Fachvereine Zürich (vdf), Zürich 1993, ISBN 3-7281-1957-1 .
  • K. Krenkler: Chemistry of the building industry. Volume 1 Inorganic Chemistry, Springer Verlag, Berlin / Heidelberg 1980, ISBN 978-3-642-81476-1 .

Web links

Individual evidence

  1. ↑ FW Locher, S. Sprung: The resistance of concrete to lime-dissolving carbonic acid. Online (accessed August 3, 2018).
  2. ↑ Wolfgang R. Roth roof: Handbook of engineering geology and geotechnical engineering. Springer Verlag, Heidelberg 2002, ISBN 3-540-41353-7 , pp. 71-75.
  3. ↑ Effect of the various substances and chemicals on untreated concrete (accessed on August 3, 2018).
  4. ↑ Jörg Dietrich: Influence of building-chemically relevant pollutants on mineral phases and mechanical-hydraulic properties of ready-to-use single-phase cut-off wall compounds. Approved dissertation at Christian-Albrechts-Universität, Kiel 2005, online pp. 3–15.
  5. ↑ Corrosion of cement-bound building materials (accessed on August 3, 2018).