# The Incorporation of Steel Slag into Belite-Sulfoaluminate Cement Clinkers
## 4 Conclusions  
The present study presents the results of an investigation into the use of steel slag in belite-sulfoaluminate cement clinkers.  
For the two clinker phase compositions targeted, it was possible to incorporate between 7.7 and 11.1 wt.% of the steel slag into the raw clinker meal. The results showed  
\begin{table}
\begin{tabular}{c c c} \hline \hline  & **KMO1** & **KMO2** \\ \hline Cumulative heat (f/g) & 176.6 & 223.8 \\ \hline \hline \end{tabular}
\end{table}
Table 6: Cumulative heat of the KMO cements at 7 days of hydration.  
Figure 6: Cumulative heat of hydration in KMO cements for up to 7 days of hydration.  
that it was possible to achieve the targeted phase composition of both types of clinker at a sintering temperature of 1250 \({}^{\circ}\)C. In addition to the main phases of belite, calcium sulfoaluminate, and ferrite, minor phases were also identified. While mayenite, perovskite, and periclase were identified in both clinkers at all temperatures, alkali sulfates were mainly identified in the KMO1 clinker, since it contained more fly ash with enhanced alkalis. Incorporation of the steel slag especially resulted in the formation of periclase in the two clinkers, since it contains elevated levels of MgO. Furthermore, a higher content of Ti-bearing bauxite in the KMO2 clinker raw mixture promoted the formation of perovskite. A higher amount of mayenite was observed at the lowest sintering temperature (1200 \({}^{\circ}\)C) in both clinker mixtures, but it was higher in KMO2 due to a higher amount of the calcium sulfoaluminate phase. As evidenced by SEM/EDS, a clear porosity decrease and clearer phase development were seen in the clinkers with increased sintering temperatures. Furthermore, various foreign ions were incorporated into the main phases.  
The hydration kinetics of the cements prepared by clinkers were influenced by both the major and minor phases. The heat of hydration was higher in the KMO2, which was made from clinker with a higher content of very reactive calcium sulfoaluminate. Similarly, the compressive strength of cement was higher in the KMO2 cement at both 7 and 28 days. The latter also showed a greater increase in compressive strength development compared to KMO1, with a larger proportion of belite.  
The results confirmed that steel slag can be incorporated into belite-sulfoaluminate cement clinkers. The cements showed appropriate hydraulic characteristics and developed a sufficient compressive strength.  
Conceptualization, L.Z. and S.D.; methodology, S.D. and L.Z.; analysis, L.Z., K.S., and M.B.; writing--original draft preparation, L.Z., K.S., M.B., M.L., and S.D.; writing--review and editing, L.Z., M.B., K.S., and S.D.; funding acquisition, S.D. All authors have read and agreed to the published version of the manuscript. The study has received funding from the European Institute of Innovation and Technology (EIT), a body of the European Union, under Horizon 2020, the EU Framework Programme for Research and Innovation (RIS-ALiCE, project no. 18258). Data Availability Statement Data is contained within the article. The Metrology Institute of the Republic of Slovenia is acknowledged for the use of XRF. The authors declare no conflict of interest.