Breve descrizione dei contenuti: The use of fused quartz as a reference reactive aggregate for alkali-silica reaction (ASR) studies was investigated on mortar bars made with Portland or blended cement, natural quartzitic sand as a non-reactive aggregate and fused quartz. The quartz glass varied from 0 to 75% by mass of the total aggregate. The expansions of the bars were measured under different storage conditions (exposure at 38°C and 100% relative humidity (RH), immersion in a saturated NaCl solution at 50°C or in a 1M NaOH solution at 80°C). The proportion of fused quartz in the overall aggregate was found to be strongly limited by the high water demand of fused quartz and by its abnormal expansivity with low-alkali cement in mortars stored at 38°C and 100% RH. A 4% dosage of fused quartz appears to be suitable for the preparation of mortar specimens with appropriate characteristics of workability and expansivity (workability requirements as specified in ASTM C227, high expansion with high-alkali Portland cement and insignificant expansion with low-alkali Portland cement in mortars stored at 38°C and 100% RH). This dosage also appears to be appropriate for investigation of the effects of mineral admixtures on ASR in mortars subjected to various storage conditions.