KINEMATICS OF CRACK FORMATION IN CEMENTITIOUS COMPOSITES BY FIBER OPTICS

Assessment of fracture characteristics for cementitious composites subjected to impact loading is important in prediction of structural response and residual capacity under dynamic loading conditions. In the study reported herein, three-point-bena fiber-reinforced-concrete (FRC) specimens were tested under an impact velocity of 1.1 m/s (43 in./s). The range of specimens tested in this study included plain concrete as well as FRC reinforced with 0.5%, 1.0%, and 1.5% by volume of straight steel fibers. A new fiber-optic sensor is introduced, by which it is possible to directly measure the displacements associated with opening of cracks in cementitious composites, if their locations are known a priori. Hence, such sensors are most suited for experimental determination of crack tip opening displacements (CTOD) in notched specimens. The development and calibration of this fiber-optic sensor for use in cementitious composites is described. Crack tip opening displacements are measured at the tip of notched FRC specimens by embedment of fiber-optic sensors in the specimens during mixing. The fiber-optic sensor developed in the present study can be employed in experiments involving both static and dynamic loads.