# Reactivity Assessment of Modified Ferro Silicate Slag by R\({}^{3}\) Method
## 3 Results and Discussion
### Reactivity Assessment of \(R^{3}\) Model Paste  
#### 3.2.1 CH Consumption and Bound Water  
The calculated CH content is shown in Table 6. From this, it can be seen that all SCMs and inert quartz filler consumed CH at a different degree compared to its initial presence. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Component** & **MFS** & **GGBFS** & **FA** & **Quartz** \\ \hline SiO\({}_{2}\) & 32.3 & 35.7 & 54.3 & 99.2 \\ Fe\({}_{2}\)O\({}_{3}\) & 40.9 & 0.9 & 10.2 & - \\ Al\({}_{2}\)O\({}_{3}\) & 11.0 & 11.9 & 22.7 & - \\ CaO & 3.9 & 41.3 & 4.2 & - \\ Others & 11.9 & 10.2 & 8.6 & 0.8 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Chemical composition of the starting materials in wt.%. GGBFS: Ground granulated blast-furnace slag; FA: Fly ash. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Mortar** & **PC** & **MFS** & **Na\({}_{2}\)SO\({}_{4}\)** \\ \hline PC & 100 & 0 & 0 \\
15 M & 85 & 15 & 0 \\
30 M & 70 & 30 & 0 \\
50 M & 50 & 50 & 0 \\
70 M & 69 & 29 & 2 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Binder composition in wt.%. PC: Portland cement; MFS: Modified Ferro Silicate. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Phase** & **MFS** & **GGBFS** & **FA** & **Quartz** \\ \hline Amorphous & 92 & 96.5 & 75 & 3 \\ Crystalline & 8 & 3.5 & 25 & 97 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Amorphous and crystalline content of the starting materials in wt.%. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Starting Materials** & \multicolumn{3}{c}{**Particle Size Distribution**} \\ \cline{2-4}  & **d\({}_{10}\) (\(\mu\)m)** & **d\({}_{50}\) (\(\mu\)m)** & **d\({}_{100}\) (\(\mu\)m)** \\ \hline MFS & 2.9 & 12 & 45.5 \\ GGBFS & 2.8 & 17.2 & 42.5 \\ FA & 2.3 & 18.6 & 81.2 \\ Quartz & 3.7 & 10.9 & 40.2 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Particle size distribution of the starting materials. R\({}^{3}\) paste synthesized from MFS slag has consumed less CH than the well-established pozzolanic source FA. MFS slag has an amorphous phase that is rich in SiO\({}_{2}\) (around 30 wt%). However, although fly ash has lower amorphous content than MFS slag, it contains more SiO\({}_{2}\) (around 50 wt%, assuming all SiO\({}_{2}\) is present in glass phase). Initially, Ca(OH)\({}_{2}\) is dissolved in presence of H\({}_{2}\)O to release Ca\({}^{2+}\) ions which consume the Si\({}^{2+}\) ions (or silicates with different degrees of H dissociation) from MFS slag to produce C-S-H as a result of the pozzolanic mechanism. Furthermore, due to the presence of a minor content of Al\({}_{2}\)O\({}_{3}\) in the MFS slag, C-S-H can take-up aluminate ions to form C-A-S-H.  
GGBFS shows less CH consumption compared to the MFS slag and FA due to the latent hydraulic behavior. Due to the presence of a reactive amorphous phase rich in CaO and SiO\({}_{2}\), GGBFS has the potential to self react with H\({}_{2}\)O to produce C-S-H or C-A-S-H binder phase [32]. Bound water calculated by the oven method also shows that GGBFS paste possessed a high amount of hydrated compounds, which decomposed between 105 and 350 \({}^{\circ}\)C, compared to MFS slag and FA (Table 6). However, by considering this temperature range, certain hydrates such as ettringite cannot be taken into account. Ettrin-gite dehydrates below 100 \({}^{\circ}\)C as mentioned elsewhere [33; 34]. Note that the mechanism governing GGBFS reactivity explained through CH consumption and bound water cannot be considered as decisive, and the results should be interpreted with caution by accounting the results shown in Sections 3.2.2 and 3.2.3. A slight decrease in the CH content compared to the initial presence was observed with the quartz filler material. This indicates that the amorphous phase (around 3 wt.%) of quartz can consume a small amount of CH to produce C-S-H, and this mechanism might be due to the high temperature curing (40 \({}^{\circ}\)C).