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 pre sented. The loading fixture used for identifying the toughening mechanisms is briefly described. The loading fixture can be placed under an optical mi croscope, inside a Scanning Electron Microscope (SEM) or inside the Environ mental Electron Microscope (ESEM). Controlled displacements are applied to compact tension specimens through a piezoelectric translator which is drive n by a high voltage amplifier. The in situ crack propagation measurements r eveal energy absorbing mechanisms in the vicinity of fiber and aggregate br idging sites which are contributing to the strength and toughness enhanceme nt observed in these composites. (C) 2000 Elsevier Science S.A. All rights reserved.