Alkali–aggregate reaction

For more information on this subject, please, refer to the main article named alkali–silica reaction. The present page is aimed to reorient you to a particular and more appropriate topic.

Alkali–aggregate reaction is a term mainly referring to a reaction which occurs over time in concrete between the highly alkaline cement paste and non-crystalline silicon dioxide, which is found in many common aggregates. This reaction can cause expansion of the altered aggregate, leading to spalling and loss of strength of the concrete.

More accurate terminology

The alkali–aggregate reaction is a general, but relatively vague, expression which can lead to confusion. Actually, it is recommended to refer to a more precise definition such as one of the following:

1. Alkali–silica reaction (ASR, main article to read first);
2. Alkali–silicate reaction, and;
3. Alkali–carbonate reaction.

The alkali–silica reaction is the most common form of alkali–aggregate reaction.
Two other types are:

• the alkali–silicate reaction, in which layer silicate minerals (clay minerals), sometimes present as impurities, are attacked, and ;
• the alkali–carbonate reaction, which is an uncommon attack on certain argillaceous dolomitic limestones, likely involving the expansion of the mineral Brucite (Mg(OH)₂.

The Pozzolanic reaction which occurs in the setting of the mixture of slaked lime and pozzolanic materials has also features similar to the alkali–silica reaction, mainly the formation of calcium silicate hydrate (CSH).

See also

• Pozzolanic reaction

External links

• Cement.org | Alkali-aggregate reaction
• Alkali-Aggregate Reactions (AAR) – International Centre of Research and Applied Technology

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