Dynamic fracture toughness of fiber-reinforced concrete

The properties of fiber-reinforced concrete (FRC) were investigated at the level of (a) the fiber-matrix interface, (b) crack growth & bridging and (c) as a structural material. To this end, over 300 single fiber pull-out tests, 60 crack growth tests and over 300 flexural tests were carried out. In this program, three drop-weight impact machines and an air-gun driven dynamic pull-out machine were utilized. For the first time, a drop-weight impact machine was configured to conduct fracture studies of Contoured Double Cantilevered FRC beams under impact loading. The thesis reports a complete dynamic analysis, which was performed to identify and account for the inertial effects during crack growth testing. The results reveal that inertial correction was significant in the case of plain and polypropylene fiber reinforced concrete but was negligible when steel fiber was used.; Pull-out of single-fibers reveal that bond stiffening occurred under impact. This was evident through higher peak loads and lower corresponding slip values. Polymeric fibers had higher slip values under static conditions, but under impact, their slip values approached that of steel fibers at all angles of orientation. This capacity of polymeric fibers to approach the behaviour of a higher modulus material such as steel was repeatedly evident in fracture tests as well as flexural tests. The flexural toughness of steel and polypropylene FRC converged at higher drop-heights.; Specimen size-effect on the impact response of FRC has not received adequate attention and hence forms a significant part of this study. The results indicate that, provided the self-weight is ignored, both plain and fiber reinforced concrete exhibit size-effects on their flexural strength under impact. However, the nature of this size-effect was not clear from the present work as the data appeared to fit conflicting empirical models as given by Bažant's Size Effect Law and by the Multifractal Scale Law. Under impact, the flexural toughness with both types of fibers demonstrated size effects, a phenomenon that was not seen during quasi-static tests. Size effect under impact also appeared to intensify with an increase in the drop-height for both plain and fiber reinforced concrete. (Abstract shortened by UMI.)...