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A temperature and stress cycling technique was developed to examine the effects of thermaVstrain history on creep of refractory concrete. Creep of a 90+ % AlzOJ refractory concrete and a high-purity calcium aluminate cement was investigated under stresses of 3.4 to 20.7 MPa at 500" to 1200°C. It was found that on initial heat-up of a cured specimen of either the concrete or cement, the AHc=130 to 170 kJ/mol. After subsequent cycling of the temperature, AH,=620 to 720 kJ/mol. The stress exponent for the initial application of stress was 2.5. It was determined from these and other results that multiple "deformation" processes are acting simultaneously on initial heat-up of the form: i=cAif(Si)u"l expA€Zi/RTThese processes include crystallization, phase changes, sintering, stress-aided sintering, and steady-state creep. Mechanisms of creep and failure are discussed.

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This study compares the grain sizes of dense, equiaxed gadolinia (Gd2O3) specimens as determined by light microscope/polished surface and by scanning electron microscope/fracture surface techniques. The average intercept lengths (AIL) as determined by the two techniques were found to differ only slightly. For Gd2O3 in the grain‐size range studied, a factor of ∼1.10 converts the fracture‐surface AIL to the polished‐surface AIL.