# Sustainable Development of Concrete through Aggregates and Innovative Materials: A Review
## 2 Recycled Materials
### Recycled Plastic  
The global production of plastic products has achieved a continuous growth in the last 50 years. For instance, [PERSON] et al. [37] reported that the United States produced 42.0 million tons of plastic waste during 2016. The inadequately recycled and managed plastic waste can affect the ecosystems on the planet. An alternative solution for the recycled of plastic waste can be its use in sustainable concrete. In this context, [PERSON] and [PERSON] [38] proposed to replace Portland cement by recycled plastic in proportions of 1:5 and 1:1, regarding a water-cement ratio of 0.36. The recycled plastic concrete registered a compressive strength similar to asphalt concrete and sometimes similar to Portland cement concrete. However, the recycled plastic concrete had much less thermal sensitivity than the asphalt concrete. [PERSON] et al. [39] studied lightweight aggregate obtained of waste polyethylene terephthalate (PET) bottles and used ground granulated blast-furnace slag (GBFS) to enhance its quality. The bulk density and specific gravity of the lightweight aggregate decreases close to 50% with respect to natural aggregate. The density and compressive strength (at 28-day) of the concrete with lightweight aggregate decreased when the replacement percentage and the water-cement ratio increased. For a replacement percentage of 75% lightweight aggregate, the structural efficiency of this recycled aggregate concrete was 21% lower in comparison with control concrete. [PERSON] et al. [40] presented the effect of PET coarse aggregate on the compressive strength and workability of concrete. The 28 days compressive strength for the concrete with 20% PET aggregate at water-cement ratio of 0.42 achieved 30.3 MPa. It only decreased 9% with respect to the compressive strength of the natural aggregate concrete (NAC). Thus, small replacement percentage of PET can generate concrete with similar compressive strength of NAC. In addition, the workability of PET replaced concrete increased when both the replacement percentage and water-cement ratio increased. [PERSON] et al. [41] evaluated the influence of the aggregates of polyolefin and PET waste on physical and mechanical behavior of six mortars. The recycled plastic aggregates improved the open porosity of the mortars, reducing their compressive and flexural strength. However, these aggregates generated up to 50% lower thermal conductivity of the mortars, which improved their thermal insulation behavior. This insolation behavior is suitable to control heat gain and heat loss from building during summer and winter, respectively. This mortar type can be employed for applications that do not need a structural performance. The use of recycled plastic aggregates in the production of hydraulic mortars can allow the development of ecosustainable building materials and decrease the environmental damage of plastic waste. Based on regression analysis, [PERSON] [42] proposed the following models (linear and power) to estimate the elastic modulus (\(E_{cw}\)), the splitting tensile strength (\(f^{\prime}_{tw}\)) and flexural tensile strength (\(f_{tw}\)) of concrete containing PET waste aggregate with a ratio from 0.4% to 75% as sand replacement. Figure 3: Comparison of tire rubber particles with other aggregates used in concrete mix. Reprinted with permission from [36]. Copyright© 2019, Elsevier B.V.  
For the elastic modulus [42]:  
\[E_{cw}=1.694+0.807f^{\prime}_{cw} \tag{1}\]  
\[E_{cw}=0.229(f^{\prime}_{cw})^{1.4} \tag{2}\]  
where \(E_{cw}\) and \(f^{\prime}_{cw}\) have units of GPa and MPa, respectively. For splitting tensile strength [42]:  
\[f^{\prime}_{tw}=0.713+0.0826f^{\prime}_{cw} \tag{3}\]  
\[f^{\prime}_{tw}=0.246(f^{\prime}_{cw})^{0.75} \tag{4}\]  
For flexural tensile strength [42]:  
\[f_{rw}=1.36+0.11f^{\prime}_{cw} \tag{5}\]  
\[f_{rw}=0.317(f^{\prime}_{cw})^{0.795} \tag{6}\]  
where \(f_{rw}\) and \(f_{cw}\) are measured in MPa.