Mechanical and Thermal Properties of Alumina-Mullite Refractory Castables Incorporating Nigerian Kaolin as a Raw Material

This study develops alumina-mullite refractory castable compositions incorporating kaolin sourced from Kankara, Katsina State, as the primary alumino-silicate component and evaluates their mechanical and thermal properties for application in industrial kiln and furnace linings. The development of refractory materials from Nigerian raw materials is strategic for reducing import dependence in the steel, glass, and cement industries. Kankara kaolin is calcined to metakaolin and further reacted at high temperature to produce mullite as confirmed by XRD. Refractory castable batches are prepared with varied alumina aggregate-kaolin-calcium aluminate cement ratios and water addition levels. Specimens are vibration-cast, cured, and fired at 110, 600, 900, and 1200 degrees Celsius. Cold crushing strength, modulus of rupture, permanent linear change, bulk density, apparent porosity, and thermal conductivity are measured at each firing temperature. Thermal shock resistance is evaluated by water quench cycling from 1000 degrees Celsius. Findings indicate that optimised castable compositions with 60 percent tabular alumina aggregate and 25 percent kaolin-derived mullite achieve cold crushing strength above 50 MPa at 1200 degrees Celsius, comparable to commercial medium-duty castables. Thermal shock resistance is acceptable for 25 quench cycles without cracking. The study provides a formulation pathway for the manufacture of refractory castables from Nigerian raw materials. Keywords: refractory castable, alumina-mullite, kaolin, Katsina State, thermal properties.