# Concrete with Organic Waste Materials as Aggregate Replacement
## 3 Results
### LCA Results per Declared Unit  
As this study aimed to assess the environmental advantages resulting from the partial replacement of sand with organic waste as a fine aggregate in concrete, it is essential to determine the role of sand in the overall environmental impact of the traditional concrete mixture. The traditional concrete results for each impact category of EF 3.1 EN15804 are reported in Figure 5. The main contributor for every impact category, but water use, is the production of Portland cement.  
The impact caused by fine agg is quite limited, with a contribution to the overall impact varying from 3.5% for the impact category metal and mineral resources to 27.4% for water use. Reducing the amount of fine aggregate by 10% can achieve a reduction for the water use impact category of 2.74% and 0.43% for climate change. Nevertheless, when carbon uptake is taken into account, substituting it with organic waste can be a relevant mitigation strategy to further reduce the impact of climate change, thanks to the biogenic carbon stored in this waste. Given that the impact of sand on the overall impact of concrete in all categories is very limited and that no impact is assigned to the waste materials, the focus of the analysis was limited to the climate change category.  
The comparison of the different concrete mixes for the climate change impact category is shown in Figure 6. The results indicated that concrete alternatives incorporating organic waste exhibited lower environmental impacts compared to the traditional mixture per cubic  
Figure 5: LCA results of the traditional concrete: breakdown of the contributions from concrete ingredients in traditional mix.  
meter (i.e., the DU), thanks to their biogenic carbon content. The concretes involving corn-cob and wheat straw demonstrated the most-substantial reduction, achieving a decrease in impact compared to the traditional concrete of 36.5% and 36.2%, respectively. This is due to the higher carbon content of these organic wastes. Moreover, Figure 6 shows, for each concrete sample, the variation in the potential climate change impact as the carbon content changed. A greater variation was associated with wood ash, since the carbon content may vary significantly [16].  
LCA Results per Functional Unit  
For a comprehensive evaluation of the concrete mixes, the climate change impacts were divided by their mechanical strength, considering the results obtained in the compressive test. The outcomes are reported in Figure 7, where the bars represent the compressive test results, while the red line represents the GWP impact at equal compressive strength. The best concrete mix resulted in being the traditional concrete, due to its better mechanical performance. However, the concrete samples including rice husk ash and wood ash had a GWP impact comparable to the one of traditional concrete. The worst results were associated with the concrete mix with corncob due to its poor compressive strength.  
Figure 6: LCA results per functional unit for the climate change impact category. The error bar indicates the variation due to the uncertainty of the carbon content in the organic waste.  
Figure 7: LCA results per functional unit. The bars indicate the compressive strength results, while the red line shows the GWP impact. The error bars display the variation due to the biogenic carbon content of the organic waste.  
It is important to point out that the FU considered does not take into account the specific application the concrete might be used for. For instance, if the application required a compressive strength of only 15 MPa, different results could be obtained.