Diagnosis and Control of Alkali-Aggregate Reactions in Concrete
Aggregates containing certain constituents can react with alkali hydroxides in concrete. The reactivity is potentially harmful only when it produces significant expansion.(1)** This alkali-aggregate reactivity (AAR) has two forms—alkali-silica reaction (ASR) and alkali-carbonate reaction (ACR, sometimes called alkali-carbonate rock reaction, or ACRR). ASR is of more concern than ACR because the occurrence of aggregates containing reactive silica minerals is more common. Alkali-reactive carbonate aggregates have a specific composition that is not very common. Alkali-silica reactivity has been recognized as a potential source of distress in concrete since the late 1930s.(2,3) Even though potentially reactive aggregates exist throughout North America, ASR distress in structural concrete is not common. There are a number of reasons for this:
Alkali reactivity of dolomitic limestone aggregate
Summary Additional evidence was obtained in support of the hypothesis that excessive expansion in the alkali-carbonate rock reaction is caused by moisture uptake by the previously ‘unwetted clay’ constituent. The dedolomitization reaction is shown to be necessary only to provide access of moisture to the ‘locked-in’ clay. A microscopic method was used to determine the specific surface of the dolomitc, the quantitative nature of which made it possible to define a practical upper limit below which expansion does not occur. It was also shown that relatively small percentages of illitic clay can account for the excessive expansion shown by reactive carbonate rocks. The new techniques used included measurements of dimensional change of thin rock wafers and of compacts of clay and powdered rock.
ALKALI REACTIVITY OF DOLOMITIC CARBONATE ROCKS
THE PERFORMANCE OF THE ALKALI-REACTIVE CARBONATE ROCKS INFIELD AND LABORATORY CONCRETES IS DESCRIBED, AND PREVIOUSLY PUBLISHED AND UNPUBLISHED RESEARCH CONCERNING THE CAUSES AND MECHANISMS OF REACTIVITY IS REVIEWED AND DISCUSSED. KNOWN OCCURRENCES OF POTENTIALLY REACTIVE ROCKS ARE NOTED, RAPID LABORATORY TESTS FOR THE RECOGNITION OF THE REACTIVE ROCKS ARE SUMMARIZED, AND VARIOUS REMEDIAL MEASURES ARE DISCUSSED./AUTHOR/