Calcium aluminate cement source evaluation for Al2O3–MgO refractory castables

Alumina–magnesia refractory castables are commonly bonded with calcium aluminate cements. At temperatures above 1200 °C, these materials present an expansive behavior due to the in situ spinel (MgAl2O4) formation and the CA2 and CA6 ones. One alternative to control the volumetric stability is by replacing the typical cements used (30 wt.% CaO) for another containing less lime (20 wt.% CaO). Nevertheless, when changing the cement sources, the castable's properties would be affected. Among them, the most relevant are the green mechanical strength, the drying behavior, the properties at intermediate and high temperatures, the expansion behavior, the hot modulus of rupture and creep. Considering these aspects, the objective of this work was to evaluate the impact of different cement sources in the processing steps and properties of alumina–magnesia castables. The results pointed out specific behaviors for each cement source during the whole processing stages, highlighting the importance of its proper selection in order to attain the required properties in working conditions.