China's Refractories

Abstract: Two kinds of pure calcium aluminate cement (CAC) prepared by the sintering method and the electric melting method, respectively were analyzed in terms of the particle size, XRD patterns and hydration characteristics; and their effects on the hydration heat and construction performance of the cement-based castables were discussed. It is found that (1) the electric fused CAC contains 50.67% CA and 44.89% CA₂, while the sintered CAC contains 74.57% CA and 22.97% CA₂; in addition, compared to the sintered CAC, the electric fused CAC contains more C₃A, C₁₂A₇, and a small amount of amorphous phase; (2) the electric fused CAC (d₅₀ of 7.93 μm) has much smaller particle size than the sintered CAC (d₅₀ of 12.51 μm); (3) in the early stage of hydration, the exothermic peak of the electric fused CAC appears earlier and the heat flow rate is higher than that of the sintered CAC; the dormant period of the sintered CAC is relatively short and the main exothermic peak appears earlier than that of the electric fused CAC; (4) for cement-based castables, there is no obvious exothermic peak in the early hydration stage, but the temperature of the castables slightly increases; among them, the initial hydration temperature of the electric fused CAC-based castable is higher; and the main exothermic peak of the sintered CAC-based castable appears later than that of the electric fused CAC-based castable; (5) the exothermic heating on-site occurrs earlier, which is related to the higher environmental temperature (about 30 °C); the on-site electric fused CAC-based castable begins to show more cracks during the exothermic peak stage.

Key words: pure calcium aluminate cement, sintering method, electric melting method, hydration exothermic peak