The fracture toughness of concrete

Analytical modeling and experimental testing are used to evaluate the fracture toughness of plain concrete. The analytical modeling of the fracture toughness considers both the opening of the crack due to the applied external loads and the closing of the crack due to the interlock pressure of the aggregate. Superposition in the linear elastic theory is used to find the mode I stress intensity factor for the opening of the crack. A new line integral is developed in this paper to avoid the non-linearity at the crack processing zone due to the closing pressure. The new line of integration is evaluated in conjunction with the plane stress finite element technique. Data from experimental testing of notched beam specimens are used as an input for the analytical modeling. The developed fracturing criterion is shown to be independent of the length of the crack, it is only a function of the aggregate size and gradation. For given aggregate sizes in the concrete mix, the developed criterion is shown to be a material property.