Automated Crack Identification for Cement Paste

Abstract

The development of an automated procedure for the identification of microcracks in cementitious materials is described. The degree and nature of microcracking is measured using backscattered electron images obtained with an integrated scanning electron microscope/image analysis system. Multiple images for specimens are analyzed using a computer program developed to identify and measure microcracks within the individual phases of cement paste. The procedure is developed to assist in the determination of the roles played by individual phases in cement paste in the formation and propagation of microcracks. Procedures for specimen testing, preparation, imaging, and crack analysis are described, along with a description of the development of the analysis program. The analysis capabilities of the program are demonstrated. The gray level of epoxy-filled cracks in polished cement paste specimens is affected by the atomic number density of underlying and adjacent phases. As a result, cracks cannot be identified based on gray level alone.Epoxy-filled cracks in polished cement paste specimens can be identified based on local changes in gray level and the application of geometric requirements; and combined procedures that establish the floor of a crack, minimum gradient and 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.