## 3 Results and Discussion
### Mechanical Tests of PET Bottles and Blocks
#### 3.2.2 Compression Tests of Building Blocks Composed of PET Bottles  
The tests showed that the average maximum compressive load was approximately 14.7 kN when applied to the bottles in the upright position. When the blocks were composed of bottles in the horizontal position, the load increased to 29.4 kN. Figure 4a-d shows the compression setup before and after compression. In Figure 4b, the block tested with bottles in the vertical position had more and larger fractures than in the horizontal case. The above is not necessarily related to the compression tests of single bottles, which had higher compressive strength when tested horizontally. The compressive loads on the blocks were supported mainly by the concrete, and, as a result, the PET bottles had low deformation before the block cracked. The fractures propagated along the border between the PET bottles and the concrete in the vertical case.  
We identified serious limitations in the use of blocks composed of PET bottles/concrete for building the prototype room. Three main findings were identified, which finally prevented their use for construction: (1) the mechanical properties diminished when using the bottles since fractures propagated along their interface with the concrete; (2) they required more concrete than commonly used hollow commercial blocks; and (3) they were heavy and difficult to prepare, which increased the difficulty of moving the blocks to upper areas by one or two persons. The preparation of a large number of blocks for building a room would require work, material, time, and higher costs than for commercial blocks and would have a larger environmental impact. Due to the above disadvantages, evidenced by preparing and testing the blocks incorporating PET bottles, we decided not to use them in the prototype room-building process.  
The reason to choose a \(5\times 4\) configuration for the bottles was associated with the work and time required for making each piece. By having a fewer number of bottles and more concrete, the results of the load test were better, such as using \(4\times 4\) or \(4\times 3\) bottles per row. The main concern was that the bottle surfaces acted as crack pathways. In addition, the net avoided having collapses of the pieces but did not change the fissures in the concrete. Nonetheless, much time, concrete, and work are required for making small pieces.  
Mechanically, the blocks showed low strength at the junction points of the bottles. As such, even light loads caused fractures. Some areas lacked concrete, which were always weak zones. The block mechanical properties were dependent on the position of the bottles; in the horizontal position, their strength was higher than in the vertical position. This was not associated with the behavior of single bottles under compression tests since the bottles did not change shape. Instead, the vertical position favored the propagation of cracks along the PET/concrete interface.  
On the basis of the above results obtained by testing trapezoidal building blocks incorporating PET bottles, they were not used for the room prototype; instead, a configuration of confined stacks of PET bottles between concrete columns and metallic nets was chosen. The bottles were alternated between each row to maintain balance and improve the stability of the wall. The blocks were not a suitable option whether considering their structural characteristics or other factors, such as cost, weight, handling, preparation time, etc. Nonetheless, the results are included as a valuable negative outcome worthy of sharing, which support the proposed alternative.