## 3 Results and Discussion
### Mechanical Tests of PET Bottles and Blocks  
#### 3.2.1 Compression Tests of PET Bottles  
We had various primary aims for developing the prototype room described here. The prototype was primarily intended for people with low incomes, allowing self-construction practices and upcycling of widely available waste materials in their original form and without further processing. Some of the above-described sustainable housing concepts were incorporated. The construction of the prototype includes waste materials and more upcycling than recycling, since the bottles were not cut, painted, or reprocessed, minimizing the use of energy and time. In the case of PET, recycling involves mixing with pure materials since its polymeric chains are partitioned in the recycling process, necessitating the addition of new PET. Conversely, glass conserves its properties when recycled, but the recycling process involves energy consumption to transform raw materials into products. Intending to use entire PET bottles, these were tested as conforming blocks and individually filled with widely available materials of different particle sizes. Figure 1 shows the compression tests of individual PET bottles, both horizontal and vertical. Initially, the deformations for the vertical position were consistently wrinkles around the neck and, subsequently, open fractures that exposed the filler. The horizontal position tests usually did not show shedding of the filler and consisted of axial fractures or occasional cuts around the cylinder compression area. Figure 1 shows the bottleneck as the weak point in the bottles tested in the vertical position. The main difference in the vertical position tests was that the shape changed twice from narrow to wide along the axis. The force lines had a component directed to the axis in the narrow areas and the outside in the wide areas. Proportionally, the force lines were more concentrated, corresponding to the size of the area. This was the reason for the first deformation around the bottleneck, which had a wrinkle directed to the interior. Usually, the necks of the bottles were reduced to approximately 15% of their height. The final fracture appeared in the middle of the wide area of the bottle, directed outside and spilling the filler. The data collected from the tests, shown in Table 1, indicated that the bottles more strongly resisted compression in a horizontal position, regardless of the filler material used. Nevertheless, the bottle changed during the horizontal test from round to flat. The contact area increased from punctual to very wide, with an estimated surface of 78 cm\({}^{2}\), which was similar at both the top and bottom. The contact area remained almost unchanged during the vertical compression test, except for a small deformation at the bottom. The upper areas of contact were estimated to be approximately 6.6 cm\({}^{2}\). The bottom areas usually had five contact circles of similar radii of 0.85 cm and an approximate area of 11.35 cm\({}^{2}\). In general, a comparison between horizontal and vertical positions still favored the former. Table 1 shows the maximum load of a PET bottle under compression for the vertical and horizontal positions. Six main combinations of fillers were tested: air, dry sand, sand/water, sand/gravel, sand/tezontle (locally available construction material of light volcanic rocks), and fly ash. In the vertical position, two load charges were registered, i.e., one corresponding to the first deformation of the bottlenecks and the other for the fracture that spilled the filler. The test related to sand/water was intended to fill the voids, which was not ultimately achieved, even after 24 h of immersion of an uncapped bottle. The voids remained, but the sand became wet. During the tests with sand/gravel, sharp points of the gravel drilled the bottles, causing premature failures. In contrast, drilling did not occur during the sand/tezontle tests, since the volcanic rocks did not have sharp points, resulting in the best performance.