Vacuum-Cast Refractory Castables

The compressive and modulus of rupture strength data for 2,400○ F. to 3,400○ F. commercial brands of castables and for 1 to 4 and 1 to 6 refractory concretes were investigated. The refractory concrete test specimens were prepared from the same batch of lumnite-lelite and lumnite-calcined flint clay materials. Methods used in the Vacuum Portland Cement Concrete were adapted for this study. The data compares the strengths obtained by the vacuum-casting technique with the strengths obtained by standard-casting methods. Also, the optimum water content was investigated. Porosity, bulk density and unit weights are given for refractory concretes. Nine tables of data including results are given. The most significant result was that the vacuum-casting strengths ranged from 12% to 170% higher than the standard-cast strengths. The optimum water content for 1 to 4 refractory concrete is 7 gal per sack. Increased strengths of vacuum-cast specimens are attributed to the reduced water content, per se, consolidation of mix, and course of hydration. The magnitude of the increased strengths is shown to be dependent on the water content of the raw mix. Other properties are enhanced slightly. The results show or suggest advancements in the technology of refractories.