*2.4. Characterization of Engineered Stone Plates*

To perform the physical indices test, 18 specimens of 30 × 30 × 30 mm were cut from the ENS plates. The apparent density, water absorption, and apparent porosity were determined in accordance with Annex B of the ABNT/NBR 155845-2 [23], responsible for classifying stone materials for applications such as coatings in civil construction.

The dilatometry test aims to identify dimensional variations of the specimen under heating conditions. The test was performed on the Netzsch DIL402PC equipment under a heating rate of 10 ◦C/min and a temperature range of 30–1000 ◦C.

The 3-point bend test was performed according to the Annex F of ABNT/NBR 155845- 6 [24] Brazilian standard and UNE-EN 14617-2 Spanish standard [25]. Six (6) specimens of 10 × 25 × 100 mm were tested on the Instron branded universal mechanical testing machine, model 5582, under a 0.25 mm/min loading rate, 100 KN load cell, and 80 mm two-point distance, to evaluate the maximum bending stress, as well as the standard deviation.

Abrasive wear tests were performed according to the ABNT/NBR 12042 Brazilian standard [26], using 2 samples of 70 × 70 × 30 mm, which had their thicknesses measured before and after abrasive wearing suffered in 500 and 1000 m track in a MAQTEST Amsler equipment.

The chemical attack resistance was determined according to an adaptation of Annex H of the standard ABNT/NBR ISO 10545-13 [27]. The attack was performed on 16 specimens with dimensions of 50 × 50 × 10 mm, representing 4 specimens for each one of the 4 attack agents. The specimens were under chemical attack by ammonium chloride and citric acid for 24 h and by hydrochloric acid and potassium hydroxide for 96 h.

The stain resistance was performed on ENS-15 according to an adaptation of the guidelines described in Annex G of ABNT/NBR ISO 10545-14 [28], in addition to the staining agents already listed in the standard, namely penetrating agents (Cr2O<sup>3</sup> green and Fe2O<sup>3</sup> red), the oxidizing agent (iodine), and the film-forming agent (olive oil). Common household products were also used: grape juice, ketchup, mustard, and coffee. For each staining agent, 5 polished ENS specimens of approximately 40 × 20 × 10 mm had half of their face covered with the staining agents for 24 h, and the material was then classified according to ease of stain removal.

The salt crystallization test was performed on ENS-15 according to an adaptation of the guidelines described in ABNT/NBR 8.094 [29]. Five 50 × 50 mm specimens were prepared, washed, and dried in an oven at 70 ◦C for 24 h. The specimens were identified, weighed, measured, and subsequently submerged in a sodium chloride solution for 6 h and oven-dried for 18 h, totaling a 24 h cycle. The process was repeated until 50 cycles were completed.

In the 10th, 30th, and 50th cycles, the samples were analyzed using the Olympus LEXT OLS400 confocal microscope to observe possible surface changes due to exposure to the sodium chloride solution.

The ENS pore characteristics before and after the salt crystallization test were obtained in an automatic mercury injection porosimeter, model Autopore IV 9500, from Micromeritics Instrument Company of America, in 6 × 6 × 6 mm samples. Mercury intrusion and extrusion were investigated under pressures between 0 and 33,000 Psi, which equates to approximately 228 MPa, with pore diameters reading between 0.005 µm and 360 µm.

The ENS fractured surface regions subjected to bending tests were observed through SHIMADZU's Super Scan SSX-550 scanning electron microscope (SEM) for microstructural analysis, at 20 kV of secondary electrons. The samples were prepared using an adhesive carbon tape enveloped by a gold surf. The microstructural analysis is important to determine the quality of the adhesion between the particles and the epoxy resin, as well as the presence of voids.
