Experimental study of the effect of micro-silica and limestone powder on the fracture toughness of concrete

Fracture toughness is one of the most important properties of concrete that controls the conditions for crack propagation and ultimately concrete failure. This research uses the Brazilian disk test to prediction of crack propagation and fracture toughness in ordinary concrete samples without micro-silica and lime powder and ordinary concrete samples containing micro-silica and lime powder has been investigated. Micro-silica replaces 10% by weight of cement and limestone powder replaces 5% by weight of cement. The crack propagation process was investigated from pre-existing cracks in the specimens as well as fracture toughness in modes I, II and hybrid mode I-II. Fracture toughness tests have been performed on Brazilian disk specimens at angles of 0, 15, 28.83, 45, 60, 75 and 90 degrees relative to the pre-existing crack direction. After laboratory studies, it was found that the onset of fin cracks at angles less than 60 degrees (0 <α <60) occurs from the pre-existing crack tip and approaches the loading direction by continuing to load and propagate the crack path. However, for angles of 60 degrees or greater, the crack starts at a distance d from the tip of the crack. This distance is more in ordinary concrete samples without micro-silica and limestone powder than in ordinary concrete samples containing micro-silica and limestone powder. Samples containing micro-silica and limestone powder have higher fracture toughness of modes I, II and mixed state (I-II) than samples without micro-silica and limestone powder.