*3.3. Physical Properties*

Table 3 presents the density, water absorption and apparent porosity values of granite and ASPU.

**Table 3.** Physical Properties of granite and ASPU.


The granite and ASPU density were 2.62 <sup>±</sup> 0.01 g/cm<sup>3</sup> and 2.24 <sup>±</sup> 0.01 g/cm<sup>3</sup> , respectively. ASPU presented a density 15% lower than granite, probably due to the polymer in its composition, which is, in general, a low density material among the others, including minerals.

The lower density results in a material with lower weight per square meter, i.e., lighter. The importance of density relies on the fact that the higher its value, the better the adhesion between the particles and the polymeric matrix, which reduces the occurrence of voids [28]. In their work, Lee et al. [29] used glass and PET (polyethylene terephthalate) crystals for the development of artificial stone varying the levels of compression, vacuum and vibration and the density values varied between 2.03 and 2.45 g/cm<sup>3</sup> . Granite and ASPU density, when compared to Lee et al., are within the expected range.

Regarding granite and ASPU water absorption, the values found were respectively 0.38 ± 0.02% and 0.13 ± 0.02%. The artificial stone developed had a result approximately three times lower than the ornamental stone. Lower water absorption levels and an impermeable surface are crucial for artificial stone once this material will be constantly in contact with water. Coating with low water absorption, following the guidelines of Chiodi Filho and Rodriguez [30], must be between 0.1–0.4% of water absorption. Ribeiro et al. [11] in its artificial marble developed with polyester resin obtained 0.19%, while Borsellino et al. [14] developed a 0.25% water absorption artificial marble, but with epoxy resin. With these comparisons, it is verified the good performance of ASPU, confirming the possibility of its use in humid environments.

The apparent porosity value was 0.99 ± 0.06% for granite and 0.31 ± 0.02% for ASPU. The ASPU water absorption was three times lower than that of granite. Chiodi Filho and Rodriguez [30] classify that high quality coating materials must have porosity below 0.5%, denoting the ASPU good performance. ASPU's low porosity can be attributed to the homogeneity of the material, with granite particles well adhered to the polyurethane matrix, ensuring the filling of the voids.
