**
Geometrical Modeling of Concrete Microstructure**

for the Assessment of ITZ Percolation

**
Daniel Rypl
**

Department of Mechanics

Faculty of Civil Engineering

Czech Technical University in Prague

Thákurova 7, 166 29 Prague, Czech Republic

**
Tomáš Bým
**

Golder Associates AB,

Ostgotagatan 12, 116 25 Stockholm, Sweden

### 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 â soft shell model, in which each randomly-placed aggregate particle is surrounded by a shell of constant thickness
representing ITZ.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 â soft shell model, in which each randomly-placed aggregate particle is surrounded by a shell of constant thickness
representing ITZ.