A fractal study of the fracture surfaces of cement pastes and mortars using a stereoscopic SEM method

A stereoscopic scanning electron microscopic (SEM) method, based on surface areas tallied over a much wider range of measurement scales than has been used in the past, was used to evaluate the fractal characteristics of fracture surfaces of cement pastes and mortars. Fracture surfaces of cement pastes exhibit two distinct fractal regimes: a regime of low fractal dimension (ca. 2.02) at low magnification scales and a significantly higher fractal dimension (ca. 2.12) at higher magnifications. The crossover occurs at a scale dimension slightly greater than 1 μm2. Neither water/binder (w/b) ratio nor the presence of silica fume appears to influence these fractal characteristics. Cement paste areas exposed on mortar fracture surfaces are identical with those of cement paste specimens. In contrast to the paste areas, areas of crushed sand exposed on mortar fracture surfaces display a single fractal domain of significantly higher fractal dimension, around 2.20.