Fracture processes of hybrid fiber-reinforced mortar

Subregion Scanning Computer Vision (SSCV), a digital image based method for measuring surface deformation is used to examine the role of the fibers in the fracture process of mortars reinforced with hybrid blends of microfiber (less than 22 gm in diameter) and macrofiber (500 mum in diameter). Closely-spaced microfibers interact with cracks at the microstructural level and hamper the widening of coalesced microcracks, thus encouraging the growth of multiple cracks. The microfibers improved pre-peak mechanical performance and strength by delaying the formation of a through-specimen macrocrack. Macrofibers were most effective at bridging macrocracks and imparting ductility to the composite due to their geometry and greater length. Compared to mortar reinforced with a single fiber type, an increase in strength and toughness was seen with a blend of steel macrofibers and either steel or PVA microfibers. Finally, based on the crack topography observed, the reduction in water permeability of cracked mortar achieved with hybrid fiber-reinforcement, measured directly in a parallel study, was governed by multiple crack development.