## 2 Materials and Methods
### Fresh Concrete Washing Fine  
In this study, fresh concrete washing fine comes from a precast concrete plant washing process. Preparation of washing fines for use as supplementary cementing materials  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Data** & **CEM 1 52.5R-SR5 CE** \\ \hline SO\({}_{3}\) & 2.1\% \\ MgO & 0.6\% \\ Na\({}_{2}\)O & \textless{}0.3\% \\ Cl\({}^{-}\) & \textless{}0.04\% \\ Loss on ignition at 950 \({}^{\circ}\)C over time & 1.1\% \\ Compressive strength at 1 day & 21–27 MPa \\ Compressive strength at 2 days & 40–48 MPa \\ Compressive strength at 28 days & 66–76 MPa \\ \hline \hline \end{tabular}
\end{table}
Table 1: Cement characteristics as given in technical sheet.  
Figure 1: Particle size distribution of the used cement.  
(SCMs) begins with their collection from production sites and storage in hermetically sealed containers at room temperature. The fines are then dried at 65 \(\pm\) 5 \({}^{\circ}\)C to a constant mass, ensuring complete dewatering. The dried sludge is then ground by hand to obtain a fine powder, which is sieved to 100 \(\upmu\)m to remove the coarsest particles; see Figure 2. Wash fines can be used without heating, but heating is chosen to make mixing easier.  
To characterize the thermal stability and composition of these washing fines, thermogravimetric analyses (TGA) were carried out. Measurements were carried out in an inert nitrogen atmosphere, varying the temperature from ambient to 1000 \({}^{\circ}\)C, in a Netzsch STA449 F3 Jupiter\({}^{\circledR}\) furnace (Netzsch Geratebau GmbH, Selb, Germany). Several critical phases are revealed at different temperature ranges (see Figure 3). Up to 120 \({}^{\circ}\)C, a decrease in mass is observed, corresponding to the evaporation of residual free water. Between 120 and 600 \({}^{\circ}\)C, another significant mass loss is identified, probably linked to the release of chemically bound water during the decomposition of calcium hydroxide (Ca(OH)2), with a peak between 400 and 500 \({}^{\circ}\)C. Finally, a further decrease in mass occurs between 600 and 1000 \({}^{\circ}\)C, suggesting the release of carbon dioxide (CO2) resulting from the decomposition of calcium carbonate (CaCO3), with a notable peak between 800 and 900 \({}^{\circ}\)C.  
In summary, washing fine TGA reveals mass loss processes associated with three main phenomena: residual free water evaporation up to 120 \({}^{\circ}\)C, chemically bound water release between 120 and 600 \({}^{\circ}\)C (probably related to calcium hydroxide decomposition) and calcium carbonate decomposition between 600 and 1000 \({}^{\circ}\)C with carbon dioxide release. It provides crucial information for understanding the chemical composition and thermal stability of washing fines, guiding the appropriate processing and recovery strategies for these materials.  
In addition, washing fines were examined using laser granulometry. The results in Figure 4 show a distribution similar to that of cement but with certain differences. Wash  
Figure 3: Thermogravimetric analyses of washing fine. TG (Thermogravimetric Analysis, shown in red) and DTG (Derivative Thermogravimetry, shown in green).  
Figure 2: Fine washing powder.  
fines contain finer particles, probably resulting from additions to the concrete mix, such as filler. At the same time, coarser particles are present, originating from the fines in the sand used in the concrete. This particle distribution depends on the nature of the concrete produced. Indeed, a formulation containing more sand, cement or supplementary cementing materials, as well as admixtures, may affect the results. Studies on several sources could be of interest for future work.