Low- and high-alkali cements containing various levels of sulfate were prepared in the laboratory from a Type I clinker by intergrinding with an appropriate sulfate source that included gypsum, calcium langbeinite, and aphthitalite. The cements were hydrated at 23 C, and the amount of aluminate consumed up to 24 hours of hydration was determined using a quantitative X-ray diffraction method. Strength and expansive properties of mortars prepared with these cements were also determined using ASTM standard test methods. It was found that the rate of aluminate consumption during the first hour of cement hydration was about the same for all the cement intergrinds. At 2.4 hours, however, aluminate hydration in high-alkali cements was roughly twice that found in low-alkali cements. To counteract this effect, higher amounts of gypsum were required. Better control of the aluminate hydration up to 24 hours generally resulted in higher 28-day strengths. High-alkali cements showed tolerance for higher gypsum additions without exhibiting excessive expansion. No single optimum S03 level for strength development was evident in this present study; instead, the data seem to suggest that it can vary depending on curing time.
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