## 3 Materials and Methods
### Green Materials  
\"Green materials\" refer to materials that are environmentally friendly in terms of low environmental impact, low carbon emissions, and, above all, recycled materials such as fly ash, granulated and ground blast furnace slag, and marble sludge (MS), which, despite being waste products, are reused.  
The materials considered in this study include Portland cement CEM II/A-LL 42.5 R (CEM) (UNI EN 197-1:2011) [52], fly ash, granulated and ground blast furnace slag, and marble sludge (MS).  
Fly ash is a waste product obtained from coal-based power plants. It is collected in electrostatic precipitators and transferred to silos. The fly ash considered in this study comes from the incineration of municipal solid waste (MSWI-FA), specifically from an incineration plant located in Italy. According to the European Waste Catalogue, this waste is assigned the code 19.01.13* and is classified as hazardous. Ground granulated blast-furnace slag, a by-product of the cast iron production process, results from the iron production process and was provided by RILEM (Research Institute of Liaisons of European Construction). Marble sludge, classified as inert waste according to the current legislative framework with the CER code 10413, is produced by the processing of ornamental stone and was supplied by a plant located in Potenza, Italy. The fly ash, GGBFS, and MS were used as partial substitutes for cement in this study. The use of residual waste from various domestic and industrial sectors leads to significantly lower energy consumption during production, thereby reducing carbon dioxide emissions [53].  
The fly ash improves the strength of the treated material, especially in terms of compressive strength, due to its chemical reactivity that promotes the formation of stable compounds during solidification. Fly ash increases the resistance of the material to aggressive chemicals such as acids (H\({}_{2}\)SO\({}_{4}\), HCI) and salts (Na\({}_{2}\)SO\({}_{4}\), MgSO\({}_{4}\)), enhancing long-term stability, particularly in soils contaminated by chemical agents [54; 55]. In the case of soils contaminated with heavy metals, fly ash, in addition to improving the strength of the treated material, stabilizes the metals through adsorption and complexation, reducing their solubility and availability to plants, particularly for metals such as lead, cadmium, and nickel [40].  
GGBFS was chosen to improve the rheological properties of the mix, facilitating the mixing and application process. Its ability to increase the stability of the treated material is crucial for achieving uniform solidification. GGBFS enhances the compressive strength of the stabilized material, improving its long-term durability [34]. Its ability to reduce the permeability of the treated material helps limit damage from external chemical attacks, such as water ingress and corrosive substances [35]. GGBFS, with its ability to precipitate metals, promotes their transformation into insoluble forms, stabilizing them over the long term, particularly for iron (Fe), chromium (Cr), and manganese (Mn) [56].  
Although there are few studies focusing on marble sludge, the use of this material helps reduce the volume of industrial waste and improve waste material management, making the process an environmentally friendly option [57]. Marble sludge contributes to improving the cohesion and stability of the treated material, reducing permeability, and enhancing both physical and chemical resistance. Additionally, due to its calcium carbonate (CaCO\({}_{3}\)) content, it increases the soil pH, promoting the adsorption of metals such as lead (Pb) and cadmium (Cd), making it particularly useful in acidic soils [58].