# Viability of Cupola Slag as an Alternative Eco-Binder and Filler in Concrete and Mortars
## 2 Materials and Methods
### Characterization of the Materials
#### 2.1.1 Valorization and Properties of the Cupola Slag  
The cupola slag is removed through a spout at a height slightly higher than the dump spout, at the rear of the cupola furnace. This opening is located below the nozzles to avoid possible cooling of the slag, caused by air currents. The separation of the slag and the liquid metal is possible due to the difference in density between the metal and the slag. This, after being extracted, is collected discontinuously on a conveyor belt equipped with trays, as shown in Figure 1a. Due to the small thickness of the deposited slag, its cooling is fast. Finally, it is deposited, by gravity, in small stockpiles, as can be seen in Figure 1b. Slag is produced by reduction of the sulfur content in iron in the foundry. Desulfurization is done with calcium carbide in the production of ductile iron. At this stage of the process, the slag generated can be classified as a waste with a certain hydraulic potential. The slag recovery process was carried out with a specific methodology (Figure 2), which started with previous crushing in a jaw crusher to guarantee the pulverization of the entire load, reducing the maximum particle size to 10 mm. Subsequently, a wet grinding of the material was carried out to turn it into a filler, using an industrial ball mill. The grinding was carried out at a speed of 45 rpm for 8 h, until a maximum particle size of 100 \(\upmu\)m was obtained. Observations were made in a scanning electron microscope (SEM) after different milling times, until the desired maximum size is obtained. Figure 3 shows a micrograph of the cupola slag at 100\(\times\) magnification, when the measurement of the largest  
Figure 1: (**a**) Transport and cooling of cupola slag in trays; (**b**) detail of the stockpile at the plant. particles was made. Irregular shape of the particles and good homogenization of sizes were also observed. After grinding, the material was removed and deposited on metal trays. The crushed slag was decanted into these containers and the water was removed, introducing the tray with the material in a ventilated oven at 110 \(\pm\) 5 \({}^{\circ}\)C, where the material remains until reaching a constant mass (0.1% wt.). Finally, the material is shredded with the help of a spatula or a tamper, obtaining a powdery material that is stored in drums. This recovery process is associated with an energy cost that results in the emission of CO\({}_{2}\) (grinding +  
Figure 3: Determination of the maximum particle size of cupola slag by SEM. Figure 2: Scheme of the recovery process of cupola slag. drying), but much lower than the energy cost derived from the production of cements (grinding + heating to 1450 \({}^{\circ}\)C to achieve clinkerization + grinding); therefore, there is an obvious economic saving and a reduction in CO2 emissions. On the other hand, the cupola slag does not currently have any application, so if it is not recovered, it will be deposited in landfills, with the associated environmental cost. The crystalline composition of the slag was determined by X-ray diffraction. Bruker D2 equipment was used, fitted with a Cu tube that generates X-rays with a wavelength of \(\lambda\) = 1.5418\(\cdot\)10\({}^{-10}\) m, at a working power of 30 kV/10 mA. The samples were previously pulverized, and the spectrum was collected at 20 angles in a range of 6-80\({}^{\circ}\) (\(\Delta\)20 = 0.02\({}^{\circ}\)) at room temperature, with an integration time of 10 seconds per pass. The diffraction of cupola slag is shown in Figure 4.  
The amorphous structure of cupola slag prevents diffraction peaks from being detected. This result is still interesting, because its majority composition corresponds to silica oxide, which, being in an amorphous state, is an indicator of the possible reactivity of the material. To contrast the mineralogical composition obtained by X-ray diffraction, the presence of the compounds in the cupola slag was determined by infrared spectroscopy.