| Abstract
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An experimental investigation was carried out to examine the dependency of fracture parameters on the specimen and aggregate sizes as well as on the crack length in cementitious materials. A total of 73 Compact Tension (CT) concrete and mortar specimens, 3 varying specimen sizes and 5 varying aggregate sizes, were fabricated and tested. In order to gain a more complete and detailed understanding of the fracture properties of cementitious materials, quantitative studies of the fracture surfaces were carried out. A new nondestructive technique to investigate concrete and mortar fracture surface topography was introduced and tested. Fractal geometry concepts were utilized to characterize the roughness of concrete and mortar fracture surfaces. Five different methods were used to evaluate the fractal dimension of the fracture surfaces. To check the validity and applicability of the various methods in evaluating the fractal dimension, synthetic profiles with known dimensions were generated by using the concepts of fractional Brownian motion. Digitized images of the fracture surface via the new technique were found to mimic the actual fracture surface. Actual sectioning of the fracture surfaces, often employed in profilometric methods, was eliminated. In addition, the need for polishing or sectioning the fracture surface, used in the slit island technique, is abolished by introducing two equivalent methods; namely, variable water level and variable threshold level techniques. Results of the analysis suggested that concrete and mortar fracture surfaces exhibit fractal characteristics over the range of scales studied and that fractal geometry provided useful tools in the fracture surface characterization. Fractal dimension D, roughness, monotonically increased with an increase in the maximum aggregate size without being affected by the specimen size. These synthetic profiles showed good visual similarity with the experimental fracture trajectories. The results also suggested that the fracture toughness could be correlated with the fractal dimension of the fracture surface. Two possible correlations were examined, namely, fractal dimension with fracture toughness (G{\rm 1c}) and with fracture energy (G{\rm F}).
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