The European Committee for Standardisation CEN/TC 154 had planned to replace the essential characteristic "alkali-silica reactivity" in the European harmonized product standard EN 12620 "Aggregates for concrete" by the "releasable alkali content". The requirement "durability against alkalis" of Mandate M/125 was thus to be fulfilled. In the meantime, this plan has been discarded again and the "releasable alkali content" should not appear as an essential characteristic in the future aggregate standard.
Technically, the releasable alkali content of aggregates is nevertheless of interest. For example, there is evidence that certain minerals in aggregates release alkalis and that these can increase the effective alkali content of the pore solution of concrete. This would promote a deleterious alkali-silica reaction (ASR). The alkali contribution could explain why some structures are ASR-damaged even though they were built with a low alkali cement (Na2Oequ ≤ 0.60%) or with less than 3 kg/m³ Na2Oequ (from the cement).
If the releasable alkali contents measured in the laboratory are transferred to a concrete with 1850 kg/m³ aggregates, then aggregates could contribute up to 12.7 kg Na2Oequ/m³ in the worst case (Fig. 2). However, this is only an indicative laboratory result.