Abstract
The crack growth resistance of the bricks in MgO-C refractory bricks containing 1.5％ C （carbon black） on were investigated based on the principles of fracture mechanics. R-curves were determined and evaluated. R-curves were determined and evaluated based on notch width changes, and the critical stress intensity was calculated from the R-curves. The critical stress intensity factor in the reference sample exhibited the highest value, whereas the sample whose aggregate contents were respectively 1.6 times higher than that in the reference sample exhibited the second highest. The bridging stress, which indicates the bridging effect of the aggregate, clearly increased when the aggregate content was increased. Based on a roughness analysis, it is predicted that the bridging stress will increase when the ratio of aggregate in the refractory increases because more sites for the action of pullout force and frictional force exist on the crack surface. In conclusion, it was predicted that it will be desirable to increase the content of aggregate in the refractory with keeping the higher strength of matrix so as to provide the refractory with excellent resistance for dynamic thermal fatigue..
