In situ double torsion fracture studies of cement mortar and cement paste inside a scanning electron microscope

Abstract

The characteristics of microcracking in cement and high strength mortar have been investigated by fracture experiments of small (33×11×1.1mm) double torsion (DT) type specimens, inside the specimen chamber of a conventional scanning electron microscope. The control of incremental crack growth, at less than a micron, is finer than has been reported before. The cracking path is tortuous and quite branched both around and through fine aggregate particles, thus absorbing significantly more energy than a corresponding straight crack. In the vicinity of the main crack tip a zone of diffuse microcracking was observed which may be regarded as a “process zone”. These two observations suggest that fracture mechanics models utilising discrete straight single cracks should only be used with circumspection. In cement paste there also appeared to be a transition from predominantly intergranular to transgranular fracture with increased age of hydration.