*3.1. Determination of the Highest Packaging Mixture and the Minimum Amounf of Resin*

To determine the materials' vibration density, 10 different mixtures from the three granulometric ranges were proposed, as shown in Table 2.


**Table 2.** Results of vibration density.

The mixture with the highest vibration density determined the proportion of the waste's granulometric ranges used to manufacture the artificial stone plates. Higher vibration density means better packing and, therefore, fewer voids, which contributes to improving the mechanical properties of the final product. Therefore, mixture number 8, with 1.93 g/cm<sup>3</sup> , which, according to the mathematical model presented in Figure 1, corresponds to 67% coarse, 17% medium, and 16% of fine particles, was chosen to manufacture the AS plates. With the optimized apparent dry density (composition number 8), the volume of voids for the load studied was calculated, and with this data, the minimum resin content for the resins was used, according to Table 3.

**Table 3.** Resin contents of prepared stones.


*3.2. Water Absorption, Density, and Apparent Porosity*

Table 4 shows the apparent density, water absorption, and apparent porosity values of the artificial stones developed with 85 wt% of quartzite waste and both epoxy resin (EP), 85 wt% of quartzite waste and polyurethane resin (AS-PU), natural stone "Cristallo" (NS), and the commercial stone "Branco Aldan" (CS).


**Table 4.** Physical properties of apparent density, water absorption, and apparent porosity of the artificial stones developed (AS-EP and AS-PU), the commercial stone and the natural stone.

According to the results in Table 4, it can be observed that, as expected, both the artificial stones and the commercial stone had lower density than the natural stone. This is attributed to the artificial stone's composition, consisting of low-density polymers, producing a lighter material and consequently reducing logistical costs [21]. Manufacturers of artificial stones report density varying in the range of 2.4 to 2.5 g/cm<sup>3</sup> [9]. AS-EP and AS-PU densities were below this range probably because of the low densities of the polymer resins, epoxy 1.20 g/cm<sup>3</sup> and polyurethane 1.08 g/cm<sup>3</sup> .

The commercial stone "Branco Alda" has 2.41 g/cm<sup>3</sup> density that is within the range of the artificial stone's manufacturers and superior to that of developed stones. The commercial stone uses a polyester resin with 1.18 g/cm<sup>3</sup> density as a binder, which can be explained by changes in the values in the production process variables [21]. It is worth mentioning that these results were within the range found by Lee et al. [4], in which by varying compression pressure, vacuum, and vibration frequency, obtained an artificial stone with density values ranging from 2.03 to 2.45 g/cm<sup>3</sup> .

The porosity values of the natural stone were above the Chiodi Filho and Rodriguez [27] recommendation, which can be explained by the natural occurrence of flaws and cracks in the material. Consequently, these defects generate a mechanical strength decrease. The commercial stone obtained better values, which is directly related not only to the waste particle variables in the size distribution process but also to the manufacturing processing and to the additive added to the mixture, which promoted better adhesion and modified the resin properties [28,29].

Gomes et al. [20] developed an artificial stone with granite waste and polyurethane resin, using the same technique as the present work, and produced a stone with 0.42% apparent porosity and 0.19% water absorption, relatively higher than those of AS-PU and AS-EP. The artificial stones' low porosity content may have contributed to an excellent adhesion of the granite particles/polymer matrix, with the voids being filled by the resin, forming a material as homogeneous as possible.

Water absorption includes liquids percolation through these voids. Therefore, once the pores are not 100% interconnected through the cracks, water absorption values will always be lower than the apparent porosity ones [30]. For the artificial stones developed, the water absorption values of 0.16% in AS-EP and 0.14% in AS-PU indicate superior properties when compared to natural stone, which justifies the use of the proposed method.

Chiodi Filho and Rodrigues [27] include the water absorption index as one of the three most important technological parameters (flexion, wear, and absorption). All stones obtained water absorption ≤0.4%, a requirement suggested for stone selection, which are considered as stone class A1, for indoor and outdoor environments, with frequent wetting and low to high pedestrian traffic for floors [31]. For applications as coating, the ASTM C615 [32] standard indicates that, for granites and marble, the value must be ≤0.4% while the NBR 15845 [25] standard indicates it must be ≤0.2%.

Borsellino et al. [31], also used epoxy resin in their research and obtained 0.16% water absorption values. Among some works reported, water absorption between 0.04–0.67% is considered an ideal range for building materials for wall and floor coverings [4,10,16,29,33–35].
