# Reactivity Assessment of Modified Ferro Silicate Slag by R\({}^{3}\) Method
## 3 Results and Discussion
### Reactivity Assessment of \(R^{3}\) Model Paste
#### 3.2.2 Isothermal Calorimetry  
Figure 1 shows the calorimetric data of the R\({}^{3}\) model paste containing MFS slag, GGBFS, FA, and quartz filler expressed per g of SCM. GGBFS shows a higher heat production rate than MFS, FA, and quartz. The following observations can be made on their reactivity:  
1. GGBFS paste is prone to dissolve by itself in H\({}_{2}\)O and can synthesize more binder such as C-S-H or C-A-S-H, AFm, and AFt, which results in a strong exothermic heat release. Bound water analysis of GGBFS explained in Section 3.2.1 also showed that GGBFS possessed a high amount of hydrates.
2. MFS slag paste shows increased heat release in comparison to FA. This behavior is attributed to the presence of a higher content of reactive amorphous phase (as shown in Table 4), possibly suggesting faster dissolution of the reactive phase and formation of binder.
3. As the MFS slag has released substantially more heat compared to inert filler, this indicates that extra heat release is probably due to the pozzolanic reaction (Figure 1b).  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**R\({}^{3}\) Model Paste**} & \multicolumn{2}{c}{**CH Consumption (g/100 g SCM)**} & \multicolumn{2}{c}{**Bound Water (g/100 g SCM)**} \\ \cline{2-5}  & **Mean** & **Std.dev.** & **Mean** & **Std.dev.** \\ \hline MFS & 55 & 8 & 5.3 & 1.2 \\ FA & 72 & 7 & 3.5 & 0.8 \\ GGBFS & 48 & 6 & 7.4 & 1.9 \\ Quartz & 5 & 2 & 0.3 & 0.2 \\ \hline \hline \end{tabular}
\end{table}
Table 6: Reactivity assessment of R\({}^{3}\) model paste—CH consumption calculated from ThermoGravimetric Analysis (TGA) analysis and Bound water calculated by oven method.  
4. The inert quartz filler proved to be a comprehensive inert material to investigate the filler effect due to its limited heat production attributed to its CH consumption observed in Figure 1a).  
From Figure 2, the heat production rate of the R\({}^{3}\) model paste can be categorized into two regions: (1) Initial heat release up to 2 h, likely due to the dissolution of reactive ions such as SO\({}_{4}\)\({}^{2-}\), Al\({}^{3+}\), and CO\({}_{3}\)\({}^{2-}\), (2) later heat release until 10 h, likely attributed to the gradual dissolution of the amorphous phase and the formation of binder phases such as C-S-H or C-A-S-H, AFt, and AFm. This heat release intensity tends to differ for FA due to the increased presence of crystalline phases (25 wt.%) which act as a barrier for the dissolution of the amorphous phase. For instance, [PERSON] et al. [38] characterized the amorphous and crystalline phases of the FA class F and showed that the amorphous phase was partially surrounded by crystalline phases such as quartz, mullite, and maghemite, thus limiting the dissolution and reaction towards formation of binder. Heat release till 10 h is only seen with MFS slag, GGBFS, FA, and not with inert filler, suggesting that this relates  
Figure 1: Calorimetric analysis of the R\({}^{3}\) model paste: (**a**) Heat production rate in J/(h-g scm) vs. hydration time (h); (**b**) cumulative heat production in J/(g scm) vs. hydration time (h).  
Figure 2: Calorimetric analysis of the R\({}^{3}\) model paste for initial 10 h.  
to the dissolution of amorphous (glassy) phases to form hydrates. Moreover, R\({}^{3}\) model paste incorporating MFS slag showed an increased heat release in the period between 4 to 6 h. This heat release can possibly be attributed to the dissolution of Zn\({}^{2+}\) ions present in the MFS slag. For instance, ZnO present in the glassy structure of the MFS slag could potentially tend to dissolve and influence the hydration mechanism.