# The Role of Brownmillerite in Preparation of High-Belite Sulfoaluminate Cement Clinker
## 2 Experimental Section
### Preparation  
#### 2.2.1 Mineral Design of Clinker  
Compared to sulfoaluminate cement clinker, whose mineral content is mainly anhydrous calcium sulfoaluminate (above 55 wt%) and a small content of brownmillerite (below 5 wt%), the mineral composition of high-beltite-sulfoaluminate cement (HBSC) clinker containing brownmillerite, as used in this study, is different. Its mineral content is mainly C\({}_{2}\)S (above 45 wt%) and the content of brownmillerite is more than 10 wt%. So, the traditional proportioning rate range and calculation formula cannot be applied, and thus, the mineral composition of HBSC clinker was directly designed, taking into account the increased content of brownmillerite. The chemical composition was calculated by optimizing the Bogue formula [21]. Detailed principles are assumed as follows: (1) all Fe\({}_{2}\)O\({}_{3}\) forms brownmillerite phase 4 CaO-Al\({}_{2}\)O\({}_{3}\)-Fe\({}_{2}\)O\({}_{3}\) (C\({}_{4}\)AF); (2) all Al\({}_{2}\)O\({}_{3}\) forms 4 CaO-3 Al\({}_{2}\)O\({}_{3}\) (C\({}_{4}\)A\({}_{3}\)S) except for the brownmillerite phase; (3) remaining CaSO\({}_{4}\) exists in the form of free CaSO\({}_{4}\) (_f_-CS); (4) all SiO\({}_{2}\) forms 2 CaO-SiO\({}_{2}\) (C\({}_{2}\)S, belite); (5) residual CaO exists in the form of free CaO (_f_-CaO). Based on the above assumptions, the mineral composition of clinker was calculated according to Equations (1)-(4):  
\[w(\text{C}_{4}\text{AF})=3.04\ ^{*}\ w(\text{Fe}_{2}\text{O}_{3}) \tag{1}\]  
\[w(\text{C}_{4}\text{A}_{3}\text{\$}\text{\$}\text{\$})=1.995\ ^{*}\ [w(\text{Al}_{2}\text{O}_{3})-0.641\ ^{*}\ w(\text{Fe}_{2}\text{O}_{3})] \tag{2}\]  
\[w(\text{f}\text{-CS})=1.70\ ^{*}\ [w(\text{SO}_{3})-0.26\ ^{*}\ w(\text{Al}_{2} \text{O}_{3})+0.17\ ^{*}\ w(\text{Fe}_{2}\text{O}_{3})] \tag{3}\]  
\[w(\text{C}_{2}\text{S})=2.87\ ^{*}\ w(\text{SiO}_{2}) \tag{4}\]  
In order to study the influence of brownmillerite upon HBSC, the content of C\({}_{2}\)S and free gypsum in HBSC clinker shall be controlled to be consistent according to the characteristics of the raw materials, and the brownmillerite shall be adjusted to increase by 5.0%. According to the calculation of batching formula, the increase in brownmillerite content will be accompanied by a decrease in anhydrous calcium sulfoaluminate. In order to maintain physical properties, the content of anhydrous calcium sulfoaluminate should not be too low (>10.0 wt%). The mix design of the HBSC raw materials and the theoretical mineral composition of the designed HBSC clinker are shown in Table 3.  
\begin{table}
\begin{tabular}{c c c c c c c c c c} \hline
**Materials** & **Loss** & **SiO\({}_{2}\)** & **Fe\({}_{2}\)O\({}_{3}\)** & **Al\({}_{2}\)O\({}_{3}\)** & **CaO** & **MgO** & **TiO\({}_{2}\)** & **SO\({}_{3}\)** & \(\sum\) \\ \hline LS & 43.37 & 1.03 & 0.16 & 0.26 & 54.13 & 0.44 & - & - & 99.39 \\ AT & 14.06 & 37.20 & 1.88 & 43.15 & 0.57 & 0.41 & - & 0.05 & 97.32 \\ AM & 9.70 & 39.18 & 24.46 & 19.74 & 1.69 & 0.60 & 3.87 & - & 99.24 \\ AH & 8.47 & 4.05 & 1.02 & 0.41 & 33.85 & 5.12 & - & 46.60 & 99.52 \\ \hline \end{tabular}
\end{table}
Table 1: Main chemical compositions of raw materials.  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline
**Materials** & **Cl** & **Cr\({}_{2}\)O\({}_{3}\)** & **MnO** & **NiO** & **CuO** & **ZnO** & **SrO** & **ZrO\({}_{2}\)** & **BaO** \\ \hline LS & 0.004 & 0.010 & 0.082 & 0.015 & 0.028 & 0.022 & 0.019 & 0.143 & 0.065 \\ AT & 0.002 & 0.014 & 0.068 & 0.020 & 0.007 & 0.020 & 0.028 & 0.065 & 0.062 \\ AM & 0.010 & 0.009 & 0.059 & 0.010 & 0.021 & 0.015 & 0.036 & 0.237 & 0.057 \\ AH & 0.006 & 0.003 & 0.000 & 0.004 & 0.005 & 0.003 & 0.408 & 0.000 & 0.020 \\ \hline \end{tabular}
\end{table}
Table 2: Trace elements of raw materials.