# Reactivity Assessment of Modified Ferro Silicate Slag by R\({}^{3}\) Method
## 3 Results and Discussion
### Reactivity Assessment of \(R^{3}\) Model Paste
#### 3.2.5 XRD Analysis  
The XRD analysis in Figure 3 shows the presence of hydrated phases in the R\({}^{3}\) paste after 7 days curing. The main hydration products of the R\({}^{3}\) hydrated paste may include C-(A)-S-H, AFt, and AFm phases depending on the chemical composition of the starting SCM. General expected AFm phases are hydroxy-AFm, Al-hemicarbonate (Al-Hc), and Al-monocarbonate (Al-Mc). It has been reported elsewhere [46; 47] that Al-Hc and hydroxy-AFm are unstable with respect to Al-Mc in the presence of CaCO\({}_{3}\), and [48] \begin{table}
\begin{tabular}{c c} \hline \hline
**Element** & **Concentration of Elements (mmol/L)** \\ \hline Zn & 7 \\ Si & 53 \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Elemental concentrations of aqueous pore solution for MFS slag R\({}^{3}\) paste. showed that with rising CO32- ion concentration, hemicarbonate (Hc) is transformed into monocarbonate (Mc). In the FA containing model R3 system, a sharp and distinct peak of ettrinigite (20 = 9.1\({}^{\circ}\)) was observed. Ettrinigite can be synthesised in a system by reacting stoichiometric amounts of Ca2+, SO42-, and Al3+ ions with H2O [49; 50] and formation of ettrinigite in FA is mainly attributed to the high content of Al2O3. However, no presence of AFm phase can be observed in FA due to the fact that FA just reacts so slowly that the SO42- ions were not completely consumed, thus maintaining the saturation index which can stabilise the AFt (ettrinigite) phase [51]. In the GGBFS system, monocarbouluminate (Al-Mc) along with hydrol calcite (HT) can be observed, where the added calcite is the carbonate source to form these AFm phases. Some literature has observed the transformation of hemicarbonate (Hc) to monocarbonate (Mc) happening in the period between 14 to 28 days [46; 52]. However, R3 model paste of GGBFS showed the presence of monocarbouluminate even after 7 days due to the presence of excess CO32- ions with an accelerating curing condition at 40 \(\pm\) 2 \({}^{\circ}\)C. Due to the presence of MgO in GGBFS, Mg2+ ions in the presence of Al3+ and CO32- most likely form hydrol calcite (HT). Due to the poor crystalline nature of C-S-H and the possible incorporation of other ions such as Al3+ when the C-S-H formed, presence of this amorphous C-S-H cannot be validated by XRD analysis. Finally, all crystalline hydrated binder phases discussed are not seen in the quartz based R3 paste, indicating its inert behavior. MFS slag contains around 40 to 41 wt% Fe2O3. During hydration, Fe containing AFm and/or Fe-AFt phases may form [53]. As seen in the XRD analysis around 20 = 10.3\({}^{\circ}\), it is known from literature that Al containing AFm phases (generally Al-Hc) are formed first and later converted to Al-Mc (20 = 11.8\({}^{\circ}\)) with an increase in CO32- content as seen in GGBFS [47]. However, this peak of 20 = 11.8\({}^{\circ}\) has undergone a shift in the MFS slag and it is seen at 20 = 12.2\({}^{\circ}\), possibly indicating that the observed phase could correspond to Fe-Hc and not Al-Mc. However, further experimental research such as Mossbauer and Raman spectroscopy are needed to verify the formation of Fe-Hc. The R3 mix design releases ions such as Ca2+, SO42-, CO32- upon contact with H2O. The released ions dissolve the SCM to form corresponding hydrated binder phases depending on its chemical composition. For instance, SCM possessing FeO/Fe2O3 and SiO2 initially dissolves to release Fe2+/Fe3+ and Si2+ ions, which later react with Ca2+, SO42-, CO32-, OH+ to form C-S-H and Fe-Mc and/or Hc. If the SCM mainly consists of Al2O3 and SiO2 such as, for instance, FA, Al3+ ions react with Ca2+, SO42- to form ettrinigite (AFt), and then the C-S-H can take up remaining Al3+ ions to form C-(A)-S-H. Chemistry of the GGBFS includes oxides of Al, Ca, and Si along with Mg. For instance, Mg2+ in the presence of Al3+ and CO32- ions tends to form hydrol calcite-like phases, and  
Figure 3: XRD analysis R3 model paste after 7 days.