Alkali–carbonate reaction

The alkali–carbonate reaction is a process suspected for the degradation of concrete containing dolomite aggregate.

Alkali from the cement might react with the dolomite crystals present in the aggregate inducing the production of brucite, (MgOH)₂, and calcite (CaCO₃). This mechanism was tentatively proposed by Swenson and Gillott (1950) and may be written as follows:

CaMg(CO₃)₂ + 2 NaOH → CaCO₃ + Na₂CO₃ + Mg(OH)₂

Brucite (Mg(OH)₂), could be responsible for the volumetric expansion after de-dolomotisation of the aggregate, due to absorption of water.

See also

• Alkali–aggregate reaction
• Alkali–silica reaction
• Pozzolanic reaction

External links

• Cement.org | Alkali-aggregate reaction

References

1. Swenson, E.G. (1957) A reactive aggregate undetected by ASTM test. ASTM Bulletin No. 226, pp. 48–50.
2. Swenson, E.G. (1957) Cement-aggregate reaction in concrete of a Canadian bridge. ASTM Proceedings, 57: 1043–1056.