Title: Microcracking of Plain Concrete and the Shape of the Stress-Strain Curve
Author(s): Thomas T. C. Hsu, Floyd O. Slate, Gerald M. Sturman, and George Winter
Publication: Journal Proceedings
Appears on pages(s): 209-224
Internal cracking of plain concrete observed directly with a microscope and with x-ray photographs is reported. Cylinders were axially loaded in compression to various strains from 0 to 0.0030. Thin slices were made from the strained specimens, and internal cracks examined by newly-developed techniques. Cracks at the interface between coarse aggregate and mortar are widespread even in nonloaded concrete. These bond cracks are preponder-ate at all stages of straining, while mortar cracks begin to increase noticeably, and bridge between bond cracks to form continuous crack patterns at loads of about 70 to 90 percent of ultimate. This condition leads to a descending stress-strain curve and eventual disruptive failure. Correlationwith previous investigations by others is shown. Hypotheses concerning the relation between microcracking and the shape of the stress-strain curve are presented.