## 3 Results
### Embodied Carbon  
Cement is the factor with the greatest carbon impact. On the other hand, sand, used as a fine aggregate, although less impactful than cement, also contributes to CO\({}_{2}\) emissions through its extraction and transportation. Wash fines, considered in this study as a partial substitute for cement, are by-products of concrete plant cleaning operations, the use of which reduces the demand for Portland cement and, therefore, the emissions associated with its production.  
To assess the carbon impact of mortar manufacturing, several assumptions were made. Firstly, it was assumed that the integrated carbon emissions for each raw material were taken from the ICE (Inventory of Carbon and Energy) database [39]. Secondly, washing powder was dried for 8 hours in a laboratory oven, followed by sieving. As the product is sinterable, no grinding was required. To assess the carbon impact of this process, it is essential to analyze the energy consumption of production stages.  
Carbon impact calculations for each kg of powder produced have taken into account two key stages in the process: drying the waste in an oven and sieving. These two operations require specific energy consumption, which varies according to production parameters and depending on the type of energy source used (low-carbon electricity or coal-based electricity).  
1. Energy consumption: * [label=.] * Oven drying: For a batch of 50 kg of powder, a laboratory oven consuming 1000 W [40] was used for 8 h. The total energy consumption for this stage was 8 kWh for 50 kg, or 0.16 kWh per kg of powder. * Sieving: Each kilogram of powder was then sieved using a sieve shaker consuming 360 W [41] for 20 min. The energy consumption for this stage is 0.12 kWh per kg. * The total energy consumption to prepare fine wash is 0.28 kWh per kg.
2. CO\({}_{2}\) emissions: CO\({}_{2}\) emissions vary according to the source of electricity used [42]: * With low-carbon electricity (e.g., nuclear in France, 50 g CO\({}_{2}\)/kWh), the total carbon footprint is 14 g CO\({}_{2}\) per kg of powder. * With coal-based electricity (1000 g CO\({}_{2}\)/kWh), the total carbon footprint is 280 g CO\({}_{2}\) per kg of powder. * As this study was located in France, it is estimated that 1 kg of fine washing causes an emission equivalent to 14 g of CO\({}_{2}\).  
These results cover the energy consumed in drying and screening the waste but do not include the transport of raw materials or finished products. With regard to transport distance, it was assumed that all mortar constituents are located within 30 miles of the manufacturing plant, thus minimizing the carbon impact associated with transport. These assumptions make it possible to standardize the calculation conditions and provide a consistent estimate of the carbon footprint of different mortar formulations.  
The results in Figure 5 show a significant reduction in carbon footprint with the gradual incorporation of washing fines. Mortar formulations L10, L20 and L30, with 10%, 20% and 30% cement substitution by washing fines, respectively, show carbon footprint reductions of 9%, 19% and 28% compared to the reference formulation (Ref), whose integrated carbon is 436 kg CO\({}_{2}\)/m\({}^{3}\). Thus, integrated carbon values decrease to 395 kg CO\({}_{2}\)/m\({}^{3}\), 355 kg CO\({}_{2}\)/m\({}^{3}\) and 313 kg CO\({}_{2}\)/m\({}^{3}\), respectively, for L10, L20 and L30 formulations.  
This reduction is due to the lower quantity of cement required, with the cement saved translating into a significant reduction in CO\({}_{2}\) emissions. Consequently, using wash fines as a cement substitute in mortar manufacture is an effective strategy for reducing carbon impact by valorizing an industrial by-product while reducing dependence on Portland cement. This approach not only reduces overall CO\({}_{2}\) emissions but also promotes a more sustainable, environmentally friendly construction industry.