# Sustainable Concrete with Recycled Aggregate from Plastic Waste: Physical-Mechanical Behavior
## 4 Conclusions  
This work studied the incorporation of recycled plastic aggregates as substitutes for gravel (hardened thermoplastic paint waste) and sand (PET) in new concrete mixtures. Mechanical properties, such as the compressive strength, flexural strength, and rebound number were evaluated, as well as physical properties, such as the porosity, absorption, and density in hardened concrete, and slump in fresh concrete. This study analyzed a previously studied material (PET) and one that has not been previously explored (hardened thermoplastic paint residue), and guidelines and recommendations for its application were established. It should be noted that the most studied plastic to date is PET. It was found that the compressive strength with up to 14% PET sand did not decrease by more than 8%, while for percentages of up to 10% thermoplastic paint gravel, the strength decreased by 14%. The density decreased slightly (less than 2%) for the mixtures with PET. At the same time, the porosity and absorption tended to increase as the percentage of substitution of fine PET aggregate increased compared to the PE5 mixture. When compared to the conventional mixture, the PE5 and PE9 mixtures exhibited lower porosity (\(-8\%\) and \(-5\%\), respectively) and absorption. This suggests that the use of up to 9% PET sand could lead to improvements in the durability properties, and it is recommended to study this in future research. It is concluded that, under the methodology followed, recycled plastic aggregates have the potential to be used in concrete with active mobility infrastructure applications, such as sidewalks, cycle paths, and curbs, which is in line with what has been pointed out by other authors when denoting the relevance of road infrastructure in the achievement of SDGs for a country [2,50]. In addition, new studies should be carried out to replicate these results and to include tests for the elasticity modulus, durability, and microscopy to establish their use in structural concrete. This study could be extended with optical or scanning microscope (SEM) investigations to observe the characteristics of the two materials that influence their chemical compatibility. This work found that FRPAs have the potential to be used in structural concrete with replacement percentages not greater than 10%. Meanwhile, it is recommended that the  
Figure 10: Physical properties of PET mixtures: dry density; wet density; void volume; absorption. use of CRPAs of thermoplastic paint for structural purposes is not ruled out as long as additives or additions are used that reverse the losses in mechanical properties. Establishing a methodology to evaluate the physical properties of thermoplastic aggregates is recommended. Finally, it is recommended that the potential to reduce environmental impacts generated by plastic aggregates in new concrete is evaluated through life cycle analysis [49,50]. Conceptualization, D.C.G.-G., A.J.V.-L, J.G.G.-B. and D.A.S.-G.; methodology, D.A.S.-G., A.J.V.-L., J.G.G.-B. and D.C.G.-G.; validation, H.S.-M. and D.C.G.-G.; formal analysis, D.C.G.-G. and H.S.-M.; investigation, D.C.G.-G., H.S.-M., D.A.S.-G., A.J.V.-L. and J.G.G.-B. ; resources, J.G.G.-B., [PERSON]-G., [PERSON]-M., [PERSON] and [PERSON]-G.; data curation, D.C.G.-G., [PERSON]-L., [PERSON]-G. and [PERSON]-B.; writing--original draft preparation, D.C.G.-G. and H.S.-M.; writing--review and editing, D.C.G.-G. and H.S.-M.; visualization, D.C.G.-G. and H.S.-M.; supervision, D.C.G.-G. and H.S.-M.; project administration, D.C.G.-G. All authors have read and agreed to the published version of the manuscript. This research received no external funding. Not applicable. The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding authors. The authors thank the Civil Engineering Laboratory of the UDEM, Engineer [PERSON], and Architect [PERSON]. The authors declare no conflicts of interest. The following abbreviations are used in this manuscript: