A numerical algorithm for the ITZ area fraction in concrete with elliptical aggregate particles

Abstract

In view of the importance of the interfacial transition zone (ITZ) to the macro-properties of concrete, it is essential to determine the ITZ area fraction in concrete. Once the ITZ area fraction is known, the physicomechanical properties of concrete can be predicted based on the three-phase composite model. The intention of the present paper is to develop a numerical algorithm for the ITZ area fraction in concrete with elliptical aggregate particles. By introducing a contact function for two ellipses, the elliptical aggregate particles with various sizes are distributed within a square element with periodic boundary conditions. The Monte Carlo method is then adopted to evaluate the ITZ area fraction. After verifying the developed numerical algorithm with the analytical solution for the ITZ area fraction in concrete with circular aggregate particles, the effects of key factors that affect the ITZ area fraction are examined in a quantitative manner. It is found in the paper that the ITZ area fraction increases with the increase of the ITZ thickness, but decreases with the increase of the maximum aggregate diameter and the ratio between the major and minor axes of elliptical aggregate particles. It is also found that the aggregate gradation has a significant influence on the ITZ area fraction. The paper concludes that the numerical algorithm presented in the paper can predict the ITZ area fraction with reasonable accuracy.

An overlapping detection algorithm for random sequential packing of elliptical particles

“…9(d). Apparently, the stability of the overlapping detection algorithm is fine and the packing fraction realized by the current model is higher than that (0.60) by Zheng et al [24].…”

“…Recently, employing the Perram contact function [21] to check elliptical aggregates overlapping, Zheng et al [24] also simulated the random sequential packing of elliptical aggregates with periodic boundary conditions, and revealed that the maximal random packing fraction reached 0.60 for polydispersed ellipses.…”

A 2D elliptical model of random packing for aggregates in concrete

“…Thus, if ellipses slightly deviate from circles, the wattle effect will disappear at once [13] . Due to the maximal packing fraction of random packing is higher than that of 0.55 in Bezrukov et al [8] and that of 0.60 in Zheng et al [9] , this 2D elliptical model of random packing is very efficient. In addition, the result of the simulation for random packing of ellipse particles with increasing aspect ratios is that the packing fraction firstly increases and then drops down with increasing aspect ratio.…”

“…For example, Bezrukov et al [8] applied a force-biased algorithm for the simulation of a broad spectrum of dense random packing of spheroids and the maximum packing fraction was 0.55. Zheng et al [9] employed Perram contact function [10] to simulate random packing of 2D ellipses in the periodic boundary condition and the maximum packing fraction reached 0.60.…”

Multi-scale analytical theory of the diffusivity of concrete subjected to mechanical stress

“…This theory was also applied by Garboczi and Bentz [5] and Du et al [11]. Moreover, Zheng et al [30] adopted the Monte Carlo method to evaluate the ITZ area fractions. Herein the present study, it is assumed that the ITZ layers of aggregate particles are independent of each other, namely, they do not overlap just as that Fig.…”