CRACK-GROWTH MECHANISMS IN 4 DIFFERENT CONCRETES - MICROSCOPIC OBSERVATIONS AND FRACTAL ANALYSIS

Splitting tests have been carried out for evaluating damage in four ty pes of concrete. The concretes contained either river gravel with maxi mum aggregate size equal to 2 and 16 mm, phosphorous-slag aggregates, and Lytag aggregates. Different failure behaviours have been revealed, mainly depending on the aggregate and interface characteristics. The microscopic cracking mechanisms strongly affect strength, toughness, a nd ductility. In addition to mechanical measurements, a high resolutio n optical microscope was adopted for detecting the crack growth. Fract al dimensions of the crack lips and of the complex damage patterns wer e computed. No simple relation exists between fracture energy and frac tal dimension, but relative differences in the material structure affe ct the value of the fractal dimension. This confirmed the peculiar dif ferent behaviours encountered in the tests. (C) 1998 Elsevier Science Ltd.