Automated crack identification for cement paste

Abstract

The development of an automated procedure for the identification of microcracks in cement paste using backscattered electron images of polished epoxy-impregnated specimens is described. Digitized images are acquired using an integrated scanning electron microscope/image acquisition system. Cracks are identified based on local changes in image intensity (gray level) and feature geometry. The gray level of epoxy-filled cracks is affected by the density of underlying and adjacent phases. As a result, cracks cannot be identified based on gray level alone. Combined procedures that establish the floor of the crack, a minimum gradient in the gray level adjacent to cracks, and minimum differences in gray level between the floor of a crack and adjacent solid phases provide a reproducible and consistent technique for crack identification in cement paste. The crack patterns observed using these procedures show that the denser phases within hydrated cement paste exhibited lower crack density than phases with lower density and that a significant portion of the cracking occurs through the softest phase, undesignated product (UDP), and at the boundary between UDP and other phases.