Mode I and mode II fracture toughness and fracture energy of cement concrete containing different percentages of coarse and fine recycled tire rubber granules

The effect of adding recycled tire rubber granules on pure mode I and II fracture behaviors of ordinary cement concrete is investigated using a testing specimen called the Edge Notch Disc Bend (ENDB). Several ENDB samples containing coarse and fine rubber granules with weight percentages of 0, 1, 2, 4, and 12% are tested to obtain the corresponding values of the fracture toughness and fracture energy besides the compressive strength measurement. The results showed the noticeable effects of both granule type (i.e., fine and coarse) and percentage of granules on the fracture characteristics of the tested cement concrete mixtures. The addition of up to 4% coarse grain granules can provide concrete mixtures with acceptable fracture characteristics. However, the greater percentage of rubber granules noticeably reduces the performance of concrete against cracking. The relationships between fracture characteristics (including modes I and II fracture toughnesses and fracture energy values at the onset of peak load and final failure stage) were explored in terms of the common compressive strength index of the tested concrete mixtures. In general, fairly linear correlations were obtained between the cracking resistance indexes and the compressive strength of the tested concrete materials.