SEM investigations of fracture surfaces using stereo pairs: III fracture surfaces of mortars

Abstract

Fracture surfaces of mortars prepared using previously described materials and fractured in bending using the ISRM Method I protocol have been examined using stereo pairs produced at various magnifications in a scanning electron microscope. “High performance” mortars containing silica fume and high superplasticizer dosages are seen to generate mostly nearly planar surfaces that expose little crushed sand surface. Plain cement paste mortars prepared at the same low water:cement ratio (0.3) show much rougher surfaces at various magnifications, and the details of fracturing are somewhat dependent on the characteristics of the specific sand. Cleavage surfaces may be fairly commonly exposed, especially with crushed granite sand. The presence of air voids locally does not appear to influence significantly the fracture path, and no obvious differences were detected between the slow crack growth zone expected at the beginning of the fracture and the fast fracture zone expected near the end.