*1.1. Artificial Stone*

Artificial stones are produced by a high percentage of particles agglomerated by a small percentage of polymeric material. Marble, granite, glass crystals, and quartz sand are examples of stones that, when particulate, are considered natural aggregates. Artificial stone's mechanical properties are considered to be higher than those of natural stone because of the artificial stone's lower water absorption and porosity. As such, artificial stone is a more suitable option for demanding work conditions, such as floors and walls [7–10].

These materials are molded by an aggregate mixture, compacted and agglomerated, which is placed into a mold through mechanical pressure and/or vibration, using vacuumassisted or open molding methods. The process currently used by industries for the compact artificial stone production is called "vacuum vibro-compression". In this process, the mineral fillers are mixed with a polymeric resin and, afterwards, the mass is compacted under vibration and vacuum. The materials are generally subjected to a heat treatment at temperatures in the range of 70 to 110 ◦C, in order to promote the final curing of the resin, that is, the interlocking between the polymeric chains [11,12].

Suta et al. [13] used the method of vibration and compaction in a vacuum environment to produce a compact projected stone slab whose main solid components were glass waste and fine granite aggregate. The final product showed <0.02% water absorption and 51 MPa flexural strength, which were higher than those of natural construction slabs. The research results revealed that vibration was the most important processing step to adjust the aggregate orientation to become more compacted.

Lee and Shin [14] reported fiberglass/PET composites produced under the influence of vacuum, mold temperature, and cooling rate. The authors observed that specimens produced without vacuum during the preheating stage registered values of approximately 1.9% porosity, whereas specimens produced with the aid of vacuum recorded much lower values of 0.3–0.4% porosity.

The use of vacuum in manufacturing artificial stone plates is extremely important, since it facilitates the removal of air that, in the process of molding the composite, could be attached to the load and the mass, lowering the plate porosity degree. Once porosity harms the performance of artificial materials, the use of vacuum helps to produce better quality artificial materials [15].
