Alkali release from feldspars into pore solutions

For many years, the possibility that alkalis may be released from feldspars and other alkali-bearing aggregate components directly into concrete pore solutions has been explored by various mostly indirect methods. In this study, we demonstrate this effect unambiguously by direct measurements of the concentrations of alkalis in pore solutions expressed from mortars with and without such aggregates. Mortars with three different alkali-bearing feldspar minerals all released significant amounts of alkali ions. This evidence confirms the indications provided by others who monitored the release of alkalis into external solutions of calcium hydroxide or alkali hydroxide. It was also found that when both feldspar and a reactive aggregate (calcined flint) were present, some of the released alkali ions were taken up into ASR reaction products. These findings lend further emphasis to the likely importance of alkali release in many practical ASR problems.