Alkali-carbonate reaction: a type of internal corrosion in cement concrete

The interaction between coarse aggregates derived from certain types of carbonate rocks and the alkaline environment of the mortar matrix in Portland cement concrete, a process accompanied by the development of internal stresses and concrete deterio-ration, is known as the alkali-carbonate reaction (ACR). The alkali-carbonate interac-tion cannot be halted or slowed down. The only reliable preventive measure against ACR is the identification and rejection of aggregates exhibiting this type of reactivity. Such reactivity is typically highest in argillitic dolomite limestones characterized by a porphyritic-like microstructure; this structure consists of rhomb-spar crystals (up to 50 μm in size) embedded in a fine-grained matrix composed of calcite crystals, clay min-erals (such as illite or chlorite), and microcrystalline quartz.

Highly reactive carbonate rocks are not ubiquitous, and their deposits are mostly lo-cal. Consequently, ACR occurs less frequently than the other aggregate-related form of concrete corrosion, the alkali-silica reaction (ASR). While certain regions of Canada and the USA have been most severely affected by ACR, cases have also been re-ported in China, Brazil, Spain, and several other countries. The mechanism of ACR has not yet been fully elucidated, and the precise role played by dedolomitization (the breakdown of dolomite) remains unclear. ACR is often classified as a version of the alkali-silica interaction; however, its specific characteristics, which differ significantly from the typical progression of ASR, justify classifying it as a distinct type of destruc-tive interaction between the aggregate and the alkaline cement matrix.