# The Incorporation of Steel Slag into Belite-Sulfoaluminate Cement Clinkers
## 2 Materials and Methods
### Methods  
The phase composition of the cement clinkers was determined using a PANalytical Empyrean X-ray diffractometer (Malvern Panalytical, Malvern, UK) equipped with CuK\(\alpha\) radiation and a PIXcel 1D detector. The samples were ground to a particle size of less than 63 \(\upmu\)m. Samples were manually backloaded into a circular sample holder with a 10 mm diameter in order to mitigate the possible preferred orientation. The samples were measured at 45 kV at a current of 40 mA, in the range of 4 to 70 \({}^{\circ}\) 20, at a step size of 0.026\({}^{\circ}\) 20 with a scan step time of 197 s. Analysis of X-ray diffraction patterns was performed using X'Pert High Score Plus diffraction software v. 4.9 from PANalytical, using PAN ICSD v. 3.4 powder diffraction files. The Rietveld refinement method was conducted using crystal structures by [PERSON] et al. [28]. The structures for cubic and orthorhombic calcium sulfoaluminate were adopted from the work of [PERSON] et al. [29; 30].  
SEM/EDS analysis was performed to study the morphology, size, and distribution of the phases, as well as to assess which minor elements were incorporated into the phases of the clinker. Uncoted polished cross sections of clinker pellets in vertical profiles were examined by a JEOL IT500 LV Scanning Electron Microscope (SEM) equipped with an Energy Dispersive X ray spectrometer (EDS) with a W filament, operated at an accelerating voltage of 15 kV in low vacuum mode at a working distance of 10 mm.  
The hydraulic reactivity of cements prepared from clinkers sintered at 1250 \({}^{\circ}\)C was assessed by isothermal conduction calorimetry using a TAM Air calorimeter (TA Instruments). In total, 12 g of cement (ground to below 0.125 mm) with a water/cement ratio of 0.5 was mixed with an Ultra Turrax tube dispenser for 1 min. Then, 6 g of mixed paste was placed into glass vials and immediately put into the calorimeter. The heat evolution of cement was evaluated for 7 days at 20 \({}^{\circ}\)C.  
To determine the compressive strength of cement prepared from clinkers sintered at 1250 \({}^{\circ}\)C, cement pastes with a water/cement ratio (w/c) of 0.5 were poured into prismatic molds with dimensions of 10 \(\times\) 10 \(\times\) 25 mm. At 24 h, the cement paste samples were demolded and cured in a humidity chamber at a temperature of 20 \(\pm\) 1 \({}^{\circ}\)C and 95% relative humidity until they were tested under laboratory conditions. The compressive strength of cement pastes was determined at 7 and 28 days, using a ToniNORM test device  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Cement** & **KMO1 1250 \({}^{\circ}\)C** & **KMO2 1250 \({}^{\circ}\)C** \\ \hline Specific density (g/cm\({}^{3}\)) & 3.17 & 3.03 \\ Blaine SSA (cm\({}^{2}\)/g) & 4890 & 4930 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Specific density and Blaine specific surface area (SSA) of the belite-sulfoaluminate (BCSA) cements from raw mixtures KMO1 and KMO2 sintered at 1250 \({}^{\circ}\)C (Blaine method, ToniPERM Standard Model 6578, ToniTechnic by Zwick, Ulm, Germany).  
Figure 1: Particle size distribution (PSD) of cements from raw mixtures KMO1 and KMO2 sintered at 1250 \({}^{\circ}\)C, as determined by laser diffraction (Microtrac SYNC Model 5001, Microtrac Retsch GmbH, Haan, Germany; dry operation).  
(ToniTechnic by Zwick) at a load rate of 0.05 kN/s. The results are given as the average of four measurements for each cement mixture.