Quasi-brittle behavior of cementitious matrix composites

Observations on crack interactions with bridging sites during in situ crack propagation in steel microfiber reinforced cementitious composites are presented. The loading fixture used for identifying the toughening mechanisms is briefly described. The loading fixture can be placed under an optical microscope, inside a Scanning Electron Microscope (SEM) or inside the Environmental Electron Microscope (ESEM). Controlled displacements are applied to compact tension specimens through a piezoelectric translator which is driven by a high voltage amplifier. The in situ crack propagation measurements reveal energy absorbing mechanisms in the vicinity of fiber and aggregate bridging sites which are contributing to the strength and toughness enhancement observed in these composites.