# The Incorporation of Steel Slag into Belite-Sulfoaluminate Cement Clinkers
## 3 Results  
### Clinkers  
#### 3.1.1 X-ray Powder Diffraction  
The phase composition of cement clinkers KMO1 and KMO2, sintered at different temperatures, was determined by Rietveld refinement (Table 5). In both types of clinker, the overall content of the main clinker phases was closest to the targeted values following sintering at 1250 \({}^{\circ}\)C (Table 5). The most abundant phase was C\({}_{2}\)S, which was mainly presented in beta form. During cooling, less than 1 wt.% of the beta C\({}_{2}\)S was transformed into gamma modification in both KMO1 and KMO2 (Table 5). The amount of belite did not significantly vary between clinkers sintered at 1200, 1250, and 1300 \({}^{\circ}\)C (Table 5). The second most abundant phase was C\({}_{4}\)A\({}_{3}\)S, which presented in orthorhombic and cubic form. The orthorhombic modification dominated in both clinkers at all sintering temperatures (Table 5). The highest amount of C\({}_{4}\)A\({}_{3}\)S developed at 1250 \({}^{\circ}\)C in both KMO1 and KMO2 clinkers (Table 5). With regards to the C\({}_{4}\)AF phase, the targeted amount was reached at all three sintering temperatures in KMO1, while the amount of C\({}_{4}\)AF detected in KMO2 was much lower than the value predicted, only reaching around 2 wt.% (Table 5). The amount of ferrite remained constant between 1250 and 1300 \({}^{\circ}\)C, and then increased slightly between 1200 and 1250 \({}^{\circ}\)C (Table 5). However, perovskite was present in both clinkers, with less than 1 wt.% detected in KMO1, compared to more than 5 wt.% in KMO2 (Table 5). Ferrite is the artificial equivalent of natural mineral browmillerite, having a structure similar to perovskite, which allows the substitution of various cations [31]. However, Ti was mainly incorporated into the raw clinker mixtures as a result of the presence of bauxite (Table 1), meaning the higher amount of perovskite in KMO2 can be explained by the larger amount of bauxite used in the KMO2 mixture (Table 3). Among the minor phases, mayenite and pericase were detected in both clinkers. The amount of mayenite was higher in the KMO2 sample due to an increased content of the calcium sulfoaluminate phase. In both KMO1 and KMO2, the highest amount of mayenite was detected in samples sintered at 1200 \({}^{\circ}\)C, when the C\({}_{4}\)A\({}_{3}\)S was forming, while the lowest amount of C\({}_{4}\)A\({}_{3}\)S occurred at 1250 \({}^{\circ}\)C, which corresponds to the optimal \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & \multicolumn{3}{c}{**KMO1**} & \multicolumn{3}{c}{**KMO2**} \\ \cline{2-7}  & **1200 \({}^{\circ}\)C** & **1250 \({}^{\circ}\)C** & **1300 \({}^{\circ}\)C** & **1200 \({}^{\circ}\)C** & **1250 \({}^{\circ}\)C** & **1300 \({}^{\circ}\)C** \\ \hline \hline
**C\({}_{4}\)A\({}_{3}\)S - orthorhombic** & 11.5 & 13.0 & 12.3 & 21.7 & 23.2 & 20.5 \\
**C\({}_{4}\)A\({}_{3}\)S - cubic** & 4.2 & 6.7 & 5.3 & 10.6 & 14.6 & 15.1 \\ \(\sum\) C\({}_{4}\)A\({}_{3}\)S & 15.7 & 19.7 & 17.6 & 32.3 & 37.8 & 35.6 \\
**C\({}_{2}\)S-beta** & 64.6 & 63.8 & 64.5 & 51.8 & 49.2 & 50.9 \\
**C\({}_{2}\)S-gamma** & 0.1 & 0.7 & 0.7 & 0.1 & 0.7 & 0.7 \\ \(\sum\) C\({}_{2}\)S & 64.7 & 64.5 & 65.2 & 51.9 & 49.9 & 51.6 \\
**C\({}_{4}\)AF** & 9.9 & 9.9 & 9.6 & 2.0 & 2.2 & 3.0 \\
**Perovskite** & 1.1 & 0.8 & 0.7 & 3.9 & 5.2 & 4.2 \\
**Mayerite** & 5.3 & 1.8 & 2.7 & 7.4 & 2.6 & 3.3 \\
**Perilcase** & 2.4 & 2.5 & 2.3 & 2.2 & 2.3 & 2.3 \\
**Apthitalite** & 0.6 & 0.3 & 0.8 & 0.3 & - & - \\
**Langbeinite** & 0.3 & 0.3 & 0.4 & - & - & - \\
**Arcanite** & - & 0.2 & 0.7 & - & - & - \\
**Total** & 100.0 & 100.0 & 100.0 & 100.0 & 100.0 & 100.0 \\
**R\({}_{\rm wp}\)** & 2.5 & 2.5 & 2.8 & 3.5 & 3.0 & 3.1 \\
**GoF** & 2.2 & 2.2 & 2.4 & 3.0 & 2.6 & 2.7 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Phase composition of cement clinkers KMO1 and KMO2, sintered at different temperatures, as determined by Rietveld refinement (wt. %). R\({}_{\rm wp}\) presents the weighted profile R-factor and GoF represents the goodness of fit.