# Sustainable Concrete with Recycled Aggregate from Plastic Waste: Physical-Mechanical Behavior
## 3 Results
(2022) found that when 5% PET sand was used, the mechanical strength and modulus of elasticity were maintained [20]. Other studies even found that when 10% PET sand was added, the mechanical strength increased by 9% and was maintained by adding 30% PET sand [37]. The above benefits highlight the potential use of RPAs in percentages of about 10% for non-structural applications and could even represent an opportunity in structural applications (if additional studies are carried out, such as on the modulus of elasticity and durability). The results of previous studies and this one demonstrate an opportunity for using sand in non-structural and structural concrete and establish the foundation for exploring the advantages of plastic aggregates in sustainable concrete. Regarding the flexural resistance (Figure 7), it was found that with a replacement of up to 10% PET sand, the resistance decreased by about20%. In comparison, when the replacement was increased to 15%, the resistance increased, with a loss of 13%. Given these fluctuating losses and gains in flexural strength, it is recommended to increase the percentages of PET sand substitution to analyze an adequate trend and infer whether higher percentages lead to gains in this property. This could be attributed to a potential increase in the deformability, which the more ductile nature of PET could provide. Compressive strength losses (Figure 8) were obtained for the TP gravel mixtures, ranging from 13% for PE5 (12.8%) and PE10 (13.8%). Meanwhile, for PE20, a loss of 27% was obtained concerning the conventional mixture. Regarding flexural strength, the TP5 and TP10 mixtures exhibited similar behavior, with a loss of about 21.5% compared to the conventional mixture. Based on these results, their use in non-structural uses is recommended. Hardened thermoplastic paint residues have not been previously explored as a potential RPA in new concrete. Therefore, further research is recommended to evaluate  
Figure 7: Flexural strength of conventional, PE, and TP mixtures. new substitution percentages, durability tests, and other gravel production procedures. In addition, its behavior should be evaluated by incorporating additives or additions that reverse these losses in properties. However, TP gravel is compromised at 50 \({}^{\circ}\)C, so if it is used in infrastructure for active mobility or non-structural concrete, it should be used in temperate or cold climates. The rebound number graph (Figure 9) shows hardness behaviors similar to those of conventional concrete, which increased as the curing age increased. Except for the TP15 and PE14 mixtures, all mixtures exhibited a drop in hardness ranging from 4.6% to 17.5%. Previous studies have found hardness losses of up to 15% with replacements of up to 20% PET sand. In addition, they showed non-linear variations in behavior, with this test presenting the most variations in the mechanical results [20]. In the case of mixtures with TP gravel, as expected, there was a tendency for the rebound number to decrease as the percentage of RPA replacement increased. Meanwhile, as the percentage of PET sand increased, the hardness increased, going from a loss of 17.5% in the PE5 mixture to a gain in surface hardness of 3.5 compared to the reference mixture. The above can be attributed to a rearrangement of particles on the surface as the percentage of PET sand increased, which should be corroborated in future studies with image analysis. Starting at 50 \({}^{\circ}\)C, the TP gravel began to show a decrease in hardness and an increase in plasticity. Therefore, the results of the ASTM C642 tests regarding porosity, absorption, and density were discarded for this methodology. This phenomenon could partly explain why the absorption after immersion was around 1% for all mixtures, which is 85% less than that of the conventional mixture (absorption after immersion: 6.9%).