Influence of cement alkalis on mortar expansion of ASTM C 1260

The main objective of this study was to evaluate the influence of three dosages of cement alkalis, such as 0·42, 0·84 and 1·26% Na₂O_eq, on the alkali–silica reactivity-induced expansion of mortar bars prepared with 14 aggregate groups for 1·0, 0·5 and 0·25 N sodium hydroxide solutions at test durations of 14, 28, 56 and 98 d. For each alkali solution, the percentage contribution of cement alkali, test duration and their interaction to mortar expansion was also evaluated. The study revealed that, regardless of aggregate mineralogy, the influence of cement alkalis on mortar expansion depended mainly on the alkali solution concentration and test duration. The effect was more severe for the reduced concentration of alkali solution and early test duration, whereas the influence was minor for higher concentrations of alkali solution and extended test durations. Elevating cement alkalis resulted in a greater increase in the expansion of reactive aggregates for 0·25 N sodium hydroxide as compared to that of innocuous aggregates.