Radiographic imaging for the observation of Modes I and II fracture in fibre reinforced concrete

In this study, radiographic imaging is used to investigate the mechanisms of fracture in fibre reinforced concrete. The investigation looks at the performance of discrete end-hooked and straight fibres crossing a cracking plane at various angles and loaded normal or parallel to the plane. A main finding of the study is that in Mode II fracture, snubbing of fibres in the concrete adjacent to the crack interface provides significant mechanical anchorage. However, the strength benefits of this anchorage come only after significant slip displacement. Further, for acute angled fibres, due to the high anchorage provided by the snubbing, fibre fracture often governs over fibre pullout suggesting an increased brittle response compared to that of fibres subjected to crack opening (Mode I) fracture. Lastly, the tests clearly show that a significant proportion of fibres in Mode II failure pullout from the longer embedded side.