*3.5. Microstructural Analysis*

The tensile stress of granite, ASPU and vegetable polyurethane were respectively 13.50 ± 1.10, 17.31 ± 0.82 and 23.01 ± 5.30 MPa. According to the ABNT NBR 15844 standard [31], which determines the necessary Figure 4 presents SEM micrographs of ASPU (a,b) and granite (c,d) fracture surfaces after thr three-point bending test. *Sustainability* **2022**, *14*, x FOR PEER REVIEW 8 of 11

.

**Figure 4.** (**a**–**d**): Microscopic images of the fracture region obtained through scanning electron microscope (**a**) of the artificial stone ASPU with zoom 400× (**b**) ASPU with zoom 100×; (**c**) of the granite with zoom 400× and (**d**) granite with zoom 100×. **Figure 4.** (**a**–**d**): Microscopic images of the fracture region obtained through scanning electron microscope (**a**) of the artificial stone ASPU with zoom 400× (**b**) ASPU with zoom 100×; (**c**) of the granite with zoom 400× and (**d**) granite with zoom 100×.

Figure 4a,b shows the ASPU's optimal load/matrix interaction. According to Debnath et al. [33], the quality of interfacial interaction is directly related to the improvement of a

Figure 4c,d shows the natural granite micrographs. Comparing granite to ASPU, one can notice that granite stone presented a higher incidence of voids and a greater particle detachment after the bending stress. The SEM micrographs confirmed the results found in porosity tests, with the ASPU presenting three times less porosity than the granite.

 **Wear Thickness Reduction (mm)** 

According to a study carried out by Chiodi Filho and Rodriguez [30] that classified materials to be applied as floors according to the volume of traffic and the wear thickness reduction: high traffic floors must be less than 1.5 mm, medium traffic floors must be less

Therefore, according to this study, granite can be used for high-traffic flooring since it presented a 0.53 mm thickness reduction after a 500 m run and 1.13 mm after 1000 m. However, ASPU can be used for medium traffic flooring considering a 0.97 mm and 1.75

Abrasive wear tests evaluate the material pullout when it undergoes wear friction. The inferior performance of ASPU can be explained by the greater ease of removal of

**Running distance** 500 m 1000 m **Granite** 0.53 1.13 **ASPU** 0.97 1.75

Table 4 presents the results for ASPU and granite abrasive wear tests.

than 3mm and low traffic floors must be less than 6mm.

mm wear after a 500 and 1000 m run, respectively.

granite particles from the polyurethane matrix [34].

means higher adhesive strength.

**Table 4.** Abrasive wear test results.

*3.6. Abrasive Wear* 

Figure 4a,b shows the ASPU's optimal load/matrix interaction. According to Debnath et al. [33], the quality of interfacial interaction is directly related to the improvement of a composite's mechanical strength. This is due to the fact that good interfacial wettability means higher adhesive strength.

Figure 4c,d shows the natural granite micrographs. Comparing granite to ASPU, one can notice that granite stone presented a higher incidence of voids and a greater particle detachment after the bending stress. The SEM micrographs confirmed the results found in porosity tests, with the ASPU presenting three times less porosity than the granite.
