Magnesia-spinel-based zero-cement refractory castables

Two different batches of zero-cement castables composed of 85 wt.% fused MgO-spinel aggregate with 10 wt.% hydratable alumina and 5 wt.% of either kaolin or alumina/silica fine powder mixture were prepared and compared with other two conventional castables of the same composition where hydratable alumina is replaced by high alumina cement. The densification parameters, cold crushing strength as well as refractory properties (thermal shock and creep resistance) were tested. Zero-cement castables, specially those containing kaolin showed a compromise between considerable mechanical properties and good refractory behaviour as compared with the corresponding conventional ones. This behaviour is strongly related to the absence of lime that causes many deleterious effects on the properties of conventional castables.