2.3.1. Physical Properties

Twenty randomly chosen pellets were used to determine the length (*L*) and the diameter (*d*) of the pellets (mm) using a caliper (precision 1/20 mm). Particle density (ρ*p*) (UNE-EN 15,150) [18] was determined by weighing the individual pellet using a precision digital balance and calculating its volume based on the length and diameter previously determined. The pellet shape was assumed to be cylindrical. Bulk density (ρ*b*) (UNE-EN 15103) [19] was calculated from the volume and weight of pellets using a laboratory balance and a graduated cylinder. Porosity (ε0) was then calculated from particle and bulk density as:

$$
\kappa\_0(-) = 1 - \frac{\rho\_b}{\rho\_p} \tag{1}
$$
