A Numerical Investigation on Effective Diffusion in Cement-Based Composites: The Role of Aggregate Shape

Diffusive behaviour is the fundamental mechanism of ionic-induced corrosion in cement–granular composites. Aggregate characteristics, including shape anisotropy, spatial orientation, and size distribution, significantly influence effective diffusivity. However, influences of all such types of aggregate irregularity have rarely been systematically quantified, and most of the representative aggregate shapes in numerical simulations are convex than realistic concave. In this study, we apply the finite element method (FEM) to investigate diffusion behaviour of 2D cement-based composites. Realistic multi-scale aggregate shapes, characterised by fractal dimension ( F d ) and relative roughness ( R r ), are generated to highlight the influence of aggregate morphology on the effective diffusivity. The spatial distribution is evaluated by the disorder index. From numerical results, samples with a larger disorder index, indicating a broader throat size distribution, show smaller effective diffusivities. Meanwhile, aggregate shape irregularity causes much smaller effective diffusivities, highlighting the necessity of the realistic concave particle shapes in numerical simulations. Sensitivity studies show F d and R r are more related to the effective diffusivity than other single-scale classical shape parameters. At last, a model with only these two shape parameters is proposed to predict effective diffusivity. This work further improves the understanding of the role of aggregate morphology on the effective diffusivity, towards applications in ionic-induced corrosion in two-phase composites. Highlights Realistic grain shapes in composites are generated using Fourier transformation. Effects of aggregate characteristics on the effective diffusivity are investigated. F d and R r are key geometrical parameters influencing the effective diffusivity.