Effect of alkali release by aggregates on alkali-silica reaction

Mortar and concrete specimens were made using one alkali-bearing reactive aggregate, one alkali-free reactive aggregate and one alkali-free non-reactive aggregate in order to determine the effect of an alkali release by an aggregate into the pore solution on the development of ASR using pore water extraction and direct expansion measurements. The fine fraction of the alkali-bearing reactive aggregate was found to be able to release up to 3 wt% of its total Na2O content (0.73 kg Na2O/m3) into the pore solution of mortar at the age of one year for specimens stored at 60 °C. However, there is no evidence that this sodium release influenced the rate of the development of the expansion. Results on mortar specimens also indicated that the amount of Na2O bounded into ASR gel is approximately proportional to the progress of expansion. The same proportionality is however not observed for potassium ion. For concrete specimens, it is clear that Na2O and K2O ions are bound into ASR reaction products, but there is no evidence that the coarse fraction of the alkali-bearing aggregate released alkalis into the pore solution of concrete after one year of testing completed in this study.