## 3 Results and Discussion
### Mechanical Strength  
Figures 5 and 6 show the flexural maximum load (kN) and the flexural modulus of elasticity (GPa), respectively, based on the three-point test, in accordance with the European Standard EN 12390-5 [22]. Figure 4: Polyester polymer concretes (PPC) densities. Pure resin showed a flexural strength of 22.61 kN, with \(\sigma=0.002\). For all of the PPC combinations, the flexural strength of the samples was lower than the reference. The sand and AF combinations obtained the lowest values, in the range of 9.40-11.02 kN with \(\sigma\) values of 0.255-0.299, and 10.07-10.93 kN with \(\sigma\) values of 0.434-0.961, respectively. On the other hand, the LS samples achieved flexural strength results of 18.57-19.31 kN with \(\sigma\) values of 0.494-1.322. This demonstrated that, based on the resin and the target materials, the flexibility of the samples depends on the resin content. However, these results also show some apparent contradictions, namely: (i) the sand and AF combinations achieved close flexural strength results at different resin dosages; (ii) considering the average results and their uncertainty, not one of the target materials showed a direct relationship between the samples' flexibility and the resin content; and (iii) the LS combinations, containing the same resin dosages as the AF, showed a very different flexural strength. These results highlight the importance of the resin matrix surrounding the target particles, which constitutes the PPC-resistant skeleton, and act as breaking points. The flexural modulus of the elasticity demonstrated the flexibility of the resin structure, which became more rigid with the use of target materials in the PPC combinations. The use of targets increased the resin flexural modulus of the elasticity from 1.36 GPa up to 2.45-2.69 GPa for the sand, 1.82-2.67 GPa for the LS, and 1.36-1.63 GPa for the AF combinations. The sand and LS  
Figure 5: PPC flexural strength. Figure 6: PPC flexural elasticity modulus. samples showed an indirect relationship between the resin content and the flexural modulus of the elasticity mean, while in the case of AF, this relationship was not evident, probably because of the AF-35 combination's larger uncertainty compared with the other samples: The sand combinations' \(\sigma\) value varied in the range of 0.015 and0.106, while AF ranged between 0.042 and0.147, and LS between 0.030 and 0.055. Figures 7 and 8 show the compressive strength and compressive modulus of the tested combinations, respectively. The resin reached 105.31 MPa with a \(\sigma\) value of 4.208. The S-30 combination obtained a very close value of 106.16 MPa, with a \(\sigma\) value of 2.619. For this target, as the resin dosage decreased, the compressive strength also decreased, reaching a value of 93.35 MPa with a \(\sigma\) value of 2.405 for the S-20 combination. The S-25 combination reached an intermediate result of 99.34 MPa, with a \(\sigma\) value of 1.938. On the other hand, the AF combinations showed an apparent decrease of compressive strength as the sample resin content increased, although this indirect relationship cannot accurately be stated, because of the relatively large uncertainties obtained in these target samples. Thus, the combination of AF-35 reached 104.21 MPa with a \(\sigma\) value of 3.852, while AF-40 decreased to 101.61 MPa with a \(\sigma\)  
Figure 8: PPC compressive elasticity modulus. Figure 7: PPC compressive strength. value of 7.285, and AF-45 obtained the lowest compressive strength with 87.42 MPa, with a \(\sigma\) value of 4.282. Finally, the LS combinations obtained compressive strength results that increased by 50% of those obtained with the resin and the other targets samples: the combination LS-35 got 156.67 MPa with a \(\sigma\) value of 1.720, LS-40 obtained 155.60 MPa with a \(\sigma\) value of 3.438, and LS-45 reached the highest compressive strength with 160.48 MPa with a \(\sigma\) value of 1.576.