Effects of binder type and dosage on the mode I fracture toughness of cemented paste backfill-related structures

Abstract

The mode I fracture toughness, which is an indication of the amount of stress required to propagate a preexisting flaw, is usually used to evaluate the resistance of interlaminar structure to tensile stress. Considering that the cemented paste backfill (CPB) includes various interfaces (e.g. early-age CPB/advanced-age CPB interface and CPB/Rock interface), a thorough understanding of the magnitude/order of the mode I fracture toughness of different CPB-related structures is critical in stability assessment. However, only limited researches have been dedicated to the fracture toughness of CPB so far, and none of them have addressed the effects of different binders on the development of the mode I fracture toughness. Hence, many semi-circular samples prepared with various binders (e.g., Portland cement type I (PCI), a mixture of PCI and Slag (PCI/Slag) or fly ash (PCI/FA), with a ratio of 25/75, 50/50, 75/25) are prepared and subjected to the semi-circular bending test after being cured for certain periods. The findings reveal that the binder has an observable influence on the mode I fracture toughness of different interface structures, and despite the binder types, CPB depicts the highest mode I fracture toughness in comparison with early-age CPB/advanced-age CPB interface and CPB/Rock interface. Furthermore, the samples prepared with PCI/Slag generally experience higher mode I fracture toughness as well. The results can contribute to the cost-effective design and the safety assessment of CPB structures.