Fracture and fatigue of CARDIFRCRTM

The flexural fracture and fatigue response of high performance fibre reinforced cementitious composites, designated CARDIFRC , was investigated in this study. CARDIFRC is characterised by high tensile/flexural strength and high energy absorption capacity (i.e. ductility). The special characteristics of CARDIFRC make it particularly suitable for repair, remedial and upgrading activities (i.e. retrofitting) of existing concrete structures. One of the major factors affecting the flexural fracture and fatigue behaviour of CARDIFRC specimens was found to be the distribution of fibres within the mix, and it is on this factor that the greater part of this thesis is focused. An even and proper distribution of fibres can lead to excellent flexural fracture behaviour and an extremely high fatigue life of CARDIFRC specimens. On the other hand, poor fibre distribution results in undesirable performance and failure, well below the designed capacity of the material. In particular, the thesis addresses the following key points. The first point concerns the static flexural behaviour of CARDIFRC specimens and the prediction of their load-displacement behaviour. A nonlinear cracked hinge model has been used for the simulation, and the analytical results were found to be in very good agreement with the test results. In addition, a combined damage/fracture mechanics approach to the description of the flexural behaviour is presented, in which a continuum damage model is used up to the peak load followed by a fracture mechanics approach when the damage has localised along the eventual fracture plane. The second key point concerns the flexural fatigue behaviour of CARDIFRC , subjected to several stress amplitude ranges. Careful preparation of CARDIFRC specimens guarantees an excellent and absolutely consistent fatigue response. The endurance limit of the material is very high, not very often observed in the relevant literature. This is an indication that CARDIFRC has an excellent flaw tolerance. Despite the excellent fatigue performance, some small internal damage was noticed, after a very large number of cycles, but this damage is distributed, without the development of any visible crack on the surface. The last key point concerns the distribution of a large volume of short steel fibres in the mix. A thorough investigation of the fibre distribution was accomplished by image analysis of selected planes of failure, in order to explain the corresponding specimen fatigue behaviour. Moreover, a near linear correlation between the image analysis data and a novel non-destructive technique based on computerised tomography (CT) imaging was observed