Geometrical Modeling of Concrete Microstructure for the Assessment of ITZ Percolation

Daniel Rypl,Tomáš Bým

doi:10.14311/1674

Abstract

Percolation is considered to be a critical factor affecting the transport properties of multiphase materials. In the case of concrete, the transport properties are strongly dependent on the interfacial transition zone (ITZ), which is a thin layer of cement paste next to aggregate particles. It is not computationally simple to assess ITZ percolation in concrete, as the geometry and topology of this phase is complex. While there are many advanced models that analyze the behavior of concrete, they are mostly based on the use of spherical or ellipsoidal shapes for the geometry of the aggregate inclusions. These simplified shapes may become unsatisfactory in many simulations, including the assessment of ITZ percolation. This paper deals with geometrical modeling of the concrete microstructure using realistic shapes of aggregate particles, the geometry of which is represented in terms of spherical harmonic expansion. The percolation is assessed using the hard core – soft shell model, in which each randomly-placed aggregate particle is surrounded by a shell of constant thickness representing ITZ.

Highlights

Concrete is nowadays a modern composite material
In many practical applications the structure of composite materials evolves in time, so that the percolation transition occurs after an ageing time
In the case of mortar and concrete, the transport properties are strongly dependent on the region of cement paste close to the aggregate particle surface

Summary

Introduction

Concrete is nowadays a modern composite material. It is a multiscale material with length scales from nanometers (C-S-H), via micrometers (cement paste) to millimeters (mortar and concrete). In the case of mortar and concrete, the transport properties are strongly dependent on the region of cement paste close to the aggregate particle surface (typically within 50 micrometers). This region, known as the interfacial transition zone (ITZ), exhibits higher capillary porosity and larger pores than the bulk cement paste matrix [6, 7]. A relatively and robust approach introduced in [14] is employed for describing real three-dimensional aggregate particles This method is based on approximating the particle shape by spherical harmonic functions (the threedimensional equivalent of two-dimensional Fourier analysis).

Geometrical Representation of Aggregate Particles

Packing Algorithm

Assessment of ITZ Percolation

Example