# Analysis of Life Cycle Environmental Impact of Recycled Aggregate
## 6 Conclusions  
By observing the ISO 14044 (LCA) standard, this study assessed the life cycle environmental impact of matter discharged in the production (dry/wet) of recycled aggregate on GWP, AP, EP, ODP, ADP, and POCP.  
The environmental impact of recycled aggregate (wet) was up to 16%(EP)\(\sim\)40%(AP) higher compared with recycled aggregate (dry); the amount of energy used by impact crushers while producing wet recycled aggregate was the main cause for this result.  
Comparing the methods of production, while the environmental impact of the recycled aggregate produced by the wet method is somewhat high, the wet method remains the most practical method, and is beneficial in terms of the aggregate quality attained due to the high fine-powder-removal effect achieved by washing with water. The recycled aggregate produced by the dry method has a simpler production process and a lower production cost, but its quality requires improvement because the impurity and adhesive mortar removal efficiency is low.  
The environmental impact of using recycled aggregate was found to be up to twice as high as that of using natural aggregate, largely due to the greater simplicity of production of natural aggregate requiring less energy. However, ADP was approximately 20 times higher in the use of natural aggregate because doing so depletes natural resources, whereas recycled aggregate is recycled from existing construction waste.  
Among the life cycle impacts assessment of recycled aggregate, GWP was lower than for artificial light-weight aggregate but greater than for slag aggregate. This is because energy use, such as electricity, LNG, and coal in the mixing, molding, and frit sealing process during the production of artificial light-weight aggregate was higher than the amount of energy used in the production of recycled aggregate. However, in the environmental impact of recycled aggregate, AP, EP, ODP, POCP, and ADP were lower by 37% to 93% than that of artificial light-weight aggregate and slag aggregate. Although the concrete into which recycled aggregate was substituted exhibited a somewhat higher environmental impact than natural aggregate in terms of GWP, it was found to be more environmentally friendly in terms of ADP.  
The results drawn through this study do not represent the environmental impact index of all recycled aggregates, and the range of environmental impact indices must be assessed through more analyses in the future.  
Author contributions: Author contributions for this research article are as follows; conceptualization, W-J.P.; methodology and investigation, S.-J.R.; data curation, R.-H.K.; writing--original draft preparation, T.-H.K.; writing and editing, W.-J.P.; review and editing, T.-H.K.  
Figure 4: Comparison of environmental impact by recycled aggregate mixing ratio. (**a**) GWP: Global Warming Potential; (**b**) ADP: Abiotic Depletion Potential  
**Funding:** This work was supported by both a grant (19 CTAP-C141186-02) from Technology Advancement Research Program (TARP) funded by Ministry of Land, Infrastructure and Transport of Korean Government and the National Research Foundation of Korea (NRF) grant (No. NRF-2018R1D1A3B07045700) funded by the Korea government.  
**Conflicts of Interest:** The authors declare no conflict of interest.