Alkali content of concrete

Alkali content of concrete

Hydroxides present in the alkaline cement paste of concrete (whether innate or absorbed from an external source) have been found in some circumstances to react deleteriously with forms of silica within aggregate causing serious expansion and cracking, possibly resulting in a lack of integrity of a structure.  Alkali-silica reaction (ASR) is the most common form of this alkali-aggregate reaction.

For ASR to occur three conditions are necessary:

  • A sufficiently high alkali content
  • Reactive aggregate
  • Moisture in the concrete

When a potential for ASR exists, it is accepted that a limit of 3.0kg/m3 equivalent sodium oxide should apply.  Testing can be carried out on concrete dust or lump/core samples, results provided in tabular form.

The alkali content of concrete is determined in accordance with BS1881:Part 124:1988 and is covered by our *UKAS accreditation.