3.4.1. Model Geometry and Material Parameters

The plate model developed in the Abaqus/Explicit environment has the dimensions 50 mm × 500 mm (Figure 4). The adopted material parameters of the mortar matrix and aggregate are summarized in Table 1 [17,25]. The calculations were performed for nine models varying in aggregate ratio and aggregate particle size (Table 2). The grading curves for particular models are presented in Figure 5. In all cases, the exponential factor *n* was equal to 0.5. Particles smaller than 4 mm in diameter were not introduced in any model, to avoid the problems with mesh generation.

**Figure 4.** Geometry of numerical models.



The models were developed with the use of four-node plane strain elements with reduced integration (CPE4R). To ensure that the measured signals are dominantly influenced by the concrete mesostructure, a layer of four-node infinite plane strain elements (CINPE4) with a thickness of 50 mm was additionally introduced. The layer of infinite elements allows us to avoid the registering of reflection from the edge of the plate. Moreover, they allow the size of the investigated structure to be reduced. The dimensions of the finite elements were 1 mm × 1 mm and the length of the integration step was to ∆*t* = 10−<sup>8</sup> s. The dimensions of the infinite elements were 1 mm × 50 mm. To visualize the

Δ <sup>−</sup>

differences in aggregate particle concentration, the geometries of three exemplary models are presented in Figure 6. Additionally, Figure 7 shows histograms of the special distribution of the generated particles for three different aggregate ratios. It can be seen that the distribution is more or less uniform, which confirms the random generation of particle placement.


**Table 2.** Parameters of numerical models.

**Figure 5.** Fuller's curves for concrete models considered in the study.

**Figure 6.** Geometry of numerical models varying in aggregate ratio: (**a**) Model A1, (**b**) model A2, and (**c**) model A3.

**Figure 7.** Histograms of the special distribution of the generated particles for model (**a**) A1, (**b**) A2, and (**c**) A3.
