Acid sulfate soil where the surface exposure includes exposure to acid sulphate soils or to sulfate soils with a magnesium content of less than 1000 ppm; (please refer back to Structure Engineering if more aggressive acid sulfate soil found onsite)
It is common to find more than one chemical in the service environment and the effect of these chemicals may be modified in the presence of others. For example, sulfate ions become aggressive at levels of 600 to 1000 ppm when combined with magnesium or ammonium ions. In the presence of chloride ions, however, attack by sulfate ions generally exhibits little disruptive expansion with the exception of conditions of wetting and extreme drying where crystallization can cause surface fretting of concrete.
Chemical concentrations relate only to the proportion of chemical present that is water soluble.
It is recommended that the cement be Type SR.
It is recommended that a protective coating is used on the concrete surface.
Acidic ground conditions can be caused by dissolved ‘aggressive’ carbon dioxide, pure and very soft waters, organic and mineral acids and bacterial activity. Care is required in assessment of pH underground structure and lifetime conditions since pH can change over the lifetime of the member. Therefore, the pH should not be assessed only on the basis of a present-day test result, rather the ground chemistry should be considered over the design life of the ground structure. Testing for pH should be carried out either in situ or immediately after sampling as there is otherwise a risk of oxidation with time, leading to apparent acidity, which does not correctly represent in situ conditions.
pH alone may be a misleading measure of aggressivity without a full analysis of causes (e.g., still versus running water).
Contamination by the tipping of mineral and domestic wastes or by spillage from mining, processing or manufacturing industries presents special durability risks due to the presence of certain aggressive acids, salts and solvents, which can either chemically attack concrete or lead to a corrosion risk.
