*3.4. Three-Points Bend Stress*

Figure 3 shows the bending stress vs. strain curves for ASPU, white granite and vegetable polyurethane.

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 requirements for the use of granite as a coating, the 3-point bend strength must not be less than 10 MPa. Even though granite presented an elevated strength (13.5 MPa), its resistance was inferior to ASPU due to its high porosity shown by physical tests results.

Comparing the polyurethane behavior with its derived artificial stone, it is possible to observe that the granite inclusion as a resin filler contributed to increase the material stiffness stiffness. This is an expected behavior, considering that the rigid particles incorporation in a polymer matrix commonly enhances the material's elasticity modulus [32].

According to Chiodi Filho and Rodriguez [30], artificial stones applied as coating are classified as high-strength materials when their ultimate bending strength is between

16–20 MPa, and are considered very high strength materials when this value exceeds 20 MPa. Therefore, ASPU was considered to be a high-strength material for coating, since its bending strength was 17.31 MPa, associated with its little porosity and proving the artificial stones quality performance as a coating. *Sustainability* **2022**, *14*, x FOR PEER REVIEW 7 of 11

**Figure 3.** Stress vs. Strain curves for ASPU, granite and polyurethane (PU). **Figure 3.** Stress vs. Strain curves for ASPU, granite and polyurethane (PU).
