The thermomechanical behavior of a high-alumina refractory that contains 10 wt% of synthetic spinel has been studied. Results have been correlated with the microstructural and mineralogical evolutions using X-ray diffraction and scanning electron microscopy, as function of the firing temperature. Dry, castable, raw-material mixtures were sieved to <125 mu m, to separate the fraction that is considered as the matrix of this castable. Matrix samples were obtained for thermomechanical characterization, and the results were compared with those corresponding to the entire refractory, The thermal expansion mismatch between coarse grains and the matrix was observed to be responsible for the degradation in mechanical strength that was observed at low firing temperatures. From room temperature to similar to 1000 degrees C, the material exhibited a quasi-brittle behavior, with diffuse and localized damage. The diffuse damage was analyzed by comparison of the load-strain bend curves to a smeared crack model that was calculated using a finite-element method, A good fit was obtained, thereby allowing the parameters of the model to be determined. The localized damage regime was evaluated by recording the strain-energy release rate. Because of the specimen size, an increase in energy was observed, relative to increasing crack size. At temperatures of >1000 degrees C, viscoelasticity-plasticity dominated the mechanical behavior. In this case, the description was initiated by conducting load-relaxation tests, which allowed the behavior to be related to the viscous-phase content.