Strength and fracture toughness of silica fume concrete

This paper gives the results of an investigation which assesses the effects of condensed silica fume on the compressive strength and fracture toughness of concrete. The finite element method was used to determine the stress intensity factor for a range of symmetrically notched concrete cubes. Laboratory tests were conducted to determine the loads which cause the specimens to fail by crack propagation in the opening mode offracture. The test specimens were manufactured from concretes in which several levels of partial cement replacement (up to 12%) by silica fume (microsilica) were used. The fracture energy and fracture toughness of the modified concrete were evaluated through the stress intensity factor, and the loads at failure obtained from the laboratory tests. It was found that whereas the increase in the compressive strength for a cement replacement by silica fume of 12% was around 75%, the corresponding increase in the fracture energy was 15–20%.