The current work addresses the role of damage mechanisms such as interfacial debonding, crack deflection, bridging and sliding during fracture of a brittle-matrix fibre-reinforced composite with respect to their energy dissipation capacity and their impact on the pull-out mechanism. The aim of the paper is to explain why fibre failure is preferably concentrated within the matrix environment to give rise to the pull-out mechanism and not within the crack flanks where fibre stress is maximum. Two approaches, mechanics of materials and fracture mechanics, are invoked to demonstrate that pull-out is triggered and dominated primarily by the fibres’ surface flaw distribution rather than by fibre strength. The origins of pull-out are also explained in terms of statistics and the identified failure pattern of fibres in composites is discussed in view of its implications to experimental practice. The implications of the findings are summarized in a current need for a deeper investigation into the micromechanics of reinforcement in composites, the role of surface flaws and the interface as well as in the competing roles of strength and flaw size.

Recent findings have brought forward the potential of carbon nano-species, especially nanotubes and graphene, to impart exceptional multifunctional potential to cement, offering simultaneous enhancement of mechanical, fracture mechanical and electrical properties. While available knowledge on the topic is still limited, there is a complete absence of direct comparisons of the potential of the nano-species to improve strength and toughness and provide multifunctionality to the mortars. The study offers a comprehensive overview of these potentials, for mortars modified with pure graphene nanoplatelets and carbon nanotubes at consistent, directly comparable, concentrations up to 1.2 wt.%. Testing included flexure under pure bending moments, axial compression, electrical resistivity measurements and fracture tests under three point bending configuration; the latter were also independently assessed by acoustic emission. Differences in documented properties and optimal concentrations associated with improved mechanical performance were directly compared and rationalized in terms of nanospecies morphology. Dramatic, statistically consistent improvements in fracture behavior, up to 10-fold of control values, were documented for specific nanofiller concentrations, indicating an excellent potential of the material system for contemporary smart construction applications. An exceptionally favorable comparison of acoustic emission and fracture energy data confirmed that the non-destructive technique can independently assess the fracture performance of mortars with exceptional precision.