Study on the flexural fatigue performance and fractal mechanism of concrete with high proportions of ground granulated blast-furnace slag

The flexural fatigue performance of concretes with 50% and 80% proportions of ground granulated blast-furnace slag (ab. ggbs) by mass of total cementitious materials in concrete has been investigated. The effect of different proportions of ggbs on concrete fatigue performance was investigated by experiments and was estimated by the fractal theory from five aspects, i.e. the 1D fractal dimensions of critical surface cracks, the prediction area of fractured profiles, the ratios between the area of debonded coarse aggregates and the Euclidean area of fractured profile, fracture energy modified by fractal theory, and the brittleness index. In order to estimate these fractal parameters on-line, the grey model GM (1, 1) was employed. Those experimental and numerical results show that the brittleness of concrete is impaired by the incorporation of ggbs, which contribute to higher fracture energy and more complicated characteristics on fractured profiles of concrete. Therefore, potential hydration and pozzolanic effect of ggbs in matrix prolong the fatigue life of concrete comparing with those of concrete without them. The fractal theory and grey model are novel approaches to present quantitatively the flexural fatigue performance of concrete.