# Concrete with Organic Waste Materials as Aggregate Replacement
## 2 Materials and Methods
### LCA Methodology  
#### 2.4.1 Goal and Scope  
An LCA comparison was conducted to assess the environmental impact associated with the utilization of organic waste materials as alternatives to sand in concrete production. The LCA was performed using inventory data from the ecoinvent database v3.9.1 [31], with the results calculated using the open-source framework brightway2.5 [32; 33].  
The impact assessment was performed following the core rules for construction products included in the standard EN 15804 [34]. The impact assessment method considered was EF v3.1 EN15804, which includes 16 impact categories. For the climate change impact, the impacts are divided into 4 categories: biogenic, fossil, land use, and land use change. Investigating the biogenic flows was particularly helpful in our case to assess the carbon uptake from the use of bio-based materials. The process of carbon uptake is also known as sequestration and consists of the capture of CO\({}_{2}\) from the atmosphere during the growth of biomass through photosynthesis [35]. It is worth noting that the default configuration of brightway25 does not account for regionalized biosphere flows. This is especially relevant for the water use impact category, which assesses the potential impact of water consumption on water availability. The reason for this is that the characterization factors can differ based on the specific location where a natural resource is consumed or an environmental flow is emitted. For instance, the characterization factor for the biosphere flow \"Water, natural resource\" can range from 0 for Greenland to 100 for Aruba. Therefore, for this impact category, we considered the characterization factor specific to Great Britain (3.5 m\({}^{3}\)-eq/m\({}^{3}\)), assuming that the entire supply chain of the materials included in the concrete takes place in this country.  
As for the unit used for the comparison, we first compared the impact of the different mixes on a mere volume basis, using 1 m\({}^{3}\) as the declared unit (DU). Then, in order to include the main function of concrete (i.e., to withstand compressive forces) in the unit used for the comparison, the impacts were normalized for the compressive strength of the different concrete mixes [10; 36; 37]. Therefore, the considered functional unit (FU) is 1 m\({}^{3}\)/MPa.  
The system boundaries of the system analyzed are presented in Figure 3. The boundaries included the production of Portland cement, the extraction of sand, the collection of organic wastes, and the production of concrete mixes. Moreover, the extraction and processing of raw materials, energy generation and supply, the utilization of natural resources throughout each stage of the life cycle, and the transportation services required for the concrete ingredients were also taken into consideration. The considered system boundary corresponds to a cradle-to-gate scenario.  
The end-of-life stage was not included in this study. Concrete at the end-of-life can be crushed and recycled into new concrete [38; 39]; therefore, the biogenic carbon stored in the material does not go back into the atmosphere. However, according to the EN15804 standard, biogenic carbon storage shall not be included in the computation of the climatechange impact, even if it is stored permanently [34]. Yet, since one of the goals of this study was to assess the amount of carbon that can be stored in the concrete, depending on the organic waste considered, we decided to include this part in the computation and to assess the biogenic carbon separately. Nevertheless, the carbon content of the materials was included in the datasets developed for the waste. In this way, the potential climate impact of the carbon uptake of the material could be assessed. The carbon contents of the organic waste materials considered are reported in Table 2.