Sulfate Optimization for CCIL Blended Systems

Limestone cements (IL) are becoming commonly available for structural applications. Calcined clays have great effect on performance enhancement of IL systems. Blending of those systems typically occurs in cement plants; however, for markets where blending occurs in concrete ready-mixed facilities, optimization of sulfate content is critical for the successful use of this new ternary blend. Optimum sulfate content for calcined-clay-limestone-cement systems was assessed using isothermal calorimetry, with hemihydrate as a sulfate source. The optimums are determined at 1, 2 and 3 days of hydration using both IL and ordinary portland cement (OPC) with two clay sources. Maximum heat of hydration was found to vary with age as well as the blended material sources. Less sulfate is required to optimize the limestone blended cement system. The replacement level of clay and the sulfate demand in the blended system are also examined. At the same replacement level, the optimum SO₃/Al₂O₃ ratio is similar, irrespective of cement type or clay type.