Random non-convex particle model for the fraction of interfacial transition zones (ITZs) in fully-graded concrete

•The fraction of ITZs around non-convex aggregates is studied for the first time.•The effect of fraction of ITZs on CF of aggregates is found for the first time.•A numerical model is developed for fully-graded concrete microstructure (FGCC).•FGCC consists of non-convex aggregates of high packing density, ITZs and matrix.•A robust three-phase random non-convex aggregate model is proposed.

The structural configuration such as the fraction of interfacial transition zones (ITZs) has been found that can seriously impact the whole physico-mechanical properties of concrete. However, the fraction of ITZs is difficultly determined by traditional experimental methods and simple models proposed so far. In this work, a comprehensive numerical framework is devised to statistically obtain the fraction of ITZs around non-convex aggregates in fully-graded concrete. In the numerical framework, the authors generate a three-phase two-dimensional random non-convex particle model consisting of homogeneous cement paste, non-convex aggregates with a specific gradation and ITZs with a constant dimension, through a random sequential addition (RSA) scheme so as to characterize the geometric model of fully-graded concrete at a microscopic sale. The geometric morphology of a non-convex particle is mathematically parameterized in terms of the deformation of an ellipse-based cell. Such the operation can strictly govern the geometric shape of non-convex particle and precisely realize the topological geometry of an interfacial layer with a constant dimension to meet the requirement of the famous core-shell structure. Combining the proposed random non-convex particle model with the one-point probability function, we statistically analyze the fraction of ITZs by the Monte Carlo simulations. Plus, the influences of the geometric characteristics of aggregates including the shape, gradation, fraction and the maximum size and the ITZ dimension on the fraction of ITZs are systematically investigated in fully-graded concrete. Importantly, a quantitative manner on the effects of the geometric shape and gradation of non-convex aggregates is explored for the first time. As a critical ITZ property, the present contribution can be further drawn into assessing physico-mechanical properties of fully-graded concrete.

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