Fracture Behavior of Notched Concrete Cylinder

Even after more than 20 years of research in the field of fracture mechanics applied to concrete, the influence of notch length on specimen behavior and fracture toughness, $K_{\mathrm{Iq}}\text{,}$ based on the experimental evidence, is not clear. In an effort to study this influence, we have employed a notched cylinder specimen geometry. Observed failure modes of portland cement concrete cylinders are reported and discussed, and $K_{\mathrm{Iq}}$ as calculated from both the maximum load and from the load at the end of the linear part of the load versus crack mouth opening displacement (CMOD) plots are compared. Values of $K_{\mathrm{Iq}}$ have been found to increase with increasing initial notch length. It is concluded that this is a consequence of the more ductile behavior due to increased microcracking of specimens with longer notches relative to those with shorter ones. Maximum linear load and initial notch length yield $K_{\mathrm{Iq}}$ values less dependent on initial notch length, thus suggesting that the notched cylinder may provide a good standard fracture mechanics specimen to measure the fracture toughness associated with the onset of microcracking ahead of a macrocrack.