Fractal dimension of concrete incorporating silica fume and its correlations to pore structure, strength and permeability

In this study, we focused on the correlations among the fractal dimension, compressive strength, and permeability of concrete incorporating silica fume. The fractal dimension was calculated from SEM images by using a box-counting method, and the pore structure, compressive strength, and permeability were tested by mercury intrusion, compression and water penetration tests, respectively. Results show that increasing silica fume content improves compressive strength but decreases permeability and fractal dimension. The filling of available space, the promotion of heterogeneous nucleation of cement hydrates and the pozzonlanic reaction of silica fume itself, which densifies and homogenizes concrete microstructures, account for the effects of silica fume on the strength, permeability, and fractal dimensions of concrete. Compressive strength shows no appealing correlations with total porosity, but decreases as median pore size increases. Increasing meso porosity tends to strengthen concrete, whereas coarse pores are always harmful to compressive strength. The relationship between permeability and threshold pore size roughly follows the Katz-Thompson relation. Increasing fractal dimension can linearly depress compressive strength but nonlinearly promote permeability. (C) 2019 Elsevier Ltd. All rights reserved.