In the CEMHYD3D hydration model, solid grains (cement, fly ash, fillers, etc.) are represented by digitized spherical particles whose diameter is an odd integer number of pixels. This representation allows one to easily locate each grain knowing its radius and the position of its central pixel. In the model, MSWI fly ash particles are similarly represented by digitized spherical particles.
The scale chosen for the model is 1 µm per pixel; this provides a satisfactory representation of the microstructure of cement pastes [5]. 1 µm cubic pixels allow one to represent the size of the capillary pores, and of the cement, fly ash, and filler particles. The calculation volume used in the model is a cube 100 pixels on a side (i.e. 100 µm). The maximum radius of the particles has been limited to one fifth of the side of the calculation volume so that the maximum diameter of the particles is 41 pixels for a 100 pixel x 100 pixel x 100 pixel microstructure.
However, laser granulometric analysis of the MSWI fly ash has shown that the greatest part of the particles have sizes between 50 µm and 500 µm (the finest grains are smaller than 1 µm). The granulometry of the ash introduced into the model (diameter limited to a maximum of 41 µm) is therefore quite different from the experimental granulometry. The difference between experimental granulometry and granulometry of the digitized particles in the model is much smaller for the cement grains (as 82 % of the grains are smaller than 41 µm).