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Sulphate Attack

Sulphate attack can develop at the surfaces of concrete in contact with ground containing sulphates. Damage results from reactions between sulphates in the ground and the cement hydrates and the expansive growth of compounds such as gypsum or ettringite in the cement paste. In the presence of a source of carbonate ions, sulphate attack can also result in the formation of thaumasite. Sulphate-related damage is often superficial but in some cases can result in the complete disintegration of several centimetres depth of concrete.

Geomaterials has extensive experience in the petrographic and electron microprobe examination of foundation concrete affected by the thaumasite form of sulphate attack. Mike Eden of Geomaterials contributed to the Report of the Thaumasite Expert Group. Further details of the laboratory investigation of concrete affected by the thaumasite form of sulphate attack are given in a recent paper published by Mike Eden in Cement and Concrete Composites.

During the investigation of foundation concrete in highway structures throughout the UK, extensive use has been made of the petrographic and electron microprobe procedures employed by Geomaterials. These techniques can be applied to provide the following types of information:

  • An identification of the type of sulphate minerals present
  • Measurement of the maximum depth of deteriorated concrete
  • Determination of the type of cement
  • Determination of the composition of the concrete including water/cement ratio and cement content
  • Identification of the type of aggregate and classification of its carbonate range