In this research the effects of few additives were studied and their influences on the rheological behavior, mechanical, and physical properties of the Alumina-Spinel castables were compared. The used additives were Darvan 7S, TPP, Castament FS20 and Citric Acid. The Samples were formulated using Tabular Alumina, calcined Alumina, Spinel, MgO powder, microsilica and cement, along with additives. Then, the flowability of the castables was measured by using a vibrating flow table immediately after mixing. Then, the mechanical properties were measured and microstructure and formed phases were studied using SEM and XRD. The results showed that the sample A7 (contains the combination of three additives) showed high flow values. The data showed that acid citric as a retarder influences the kinetics of hydration and retards the setting time. The data indicated that the samples with citric acid along with TPP had higher Cold Crushing Strength and cold Modulus Of Rupture (at 110°C & 1500 °C) than castables with Darvan 7S and Castament FS20. At the same time, the result showed that the Alumina-Spinel Castables containing Castament FS20 had high flow values compares with castables including Darvan 7S and TPP. The obtained data in this research showed that the flow value increased up to 80% with the increase of water content, up to 5.3wt% and then decreased to less than 30% when the content of water was less than 4.5wt%. The resultant of microstructure and formed phases in the samples with and without additives, i.e., TPP, Darvan 7S and Castament FS20 were studied and discussed.
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