## 2 Materials and Methods
### Methods
#### 2.2.3 Hydration Studies  
For each slag, a full cement hydration study was carried out as follows. The heat evolution (via calorimetry), microstructural development (via SEM imaging), evolution of the phase composition (X-ray diffractometry), thermogravimetric response (TGA) and porous structure (characterised via MIP) were explored on the paste mixtures shown in Table 5. The control mixture (P_PC) was made with 100% Portland cement and a water-to-cement ratio of 0.40. The three test mixtures (i.e., P_TS1, P_TS2 and P_TS3) were made with 70% Portland cement + 30% slag and a water-to-blinder ratio of 0.40. Another reference mixture was produced (P_QP) where 30% of cement was replaced with an inert material (quartz powder). The rationale behind this is to account for the nucleation effects of the slags. Each paste was produced using a high-shear mixer at 1600 \(\pm\) 50 rpm for 2 min. Samples were cast into 12 ml tubes, sealed and placed in a water bath for curing at 23 \(\pm\) 2 \({}^{\circ}\)C. At each age of testing (1, 7, 28 and 91 days), one tube was randomly taken out and the specimen was ejected from the tube and cut into different slices. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Slag (g)** & **Ca(OH)\({}_{2}\) (g)** & **Potassium Solution (g)** & **CaCO\({}_{3}\) (g)** \\ \hline
11.12 & 33.33 & 59.94 & 5.56 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Batched masses of R3 mixtures produced for studying the pozzolanic reactivity of the slags. Two slices were dedicated to XRD measurements. One specimen was tested in its freshly cut state, and the other was tested as a powder. The reason for running the XRD test on both fresh and milled specimens is to increase the accuracy of phase quantification. The hydrated phases can be affected during routine XRD sample preparation steps (i.e., hydration stoppage, drying and milling), which might introduce unwanted biases into the measurements [34]. Such phases can better be measured and quantified when exposed to XRD in the fresh state. As such, the surface of the freshly cut specimen was smoothened using 400 grit sandpaper and then flushed with water. The extra water film was removed from the surface, and the specimen was directly subjected to the test. The test conditions are the same as described in Section 2.1. Another sample was prepared for XRD measurement in the dried and milled state for the purpose of more accurately quantifying anhydrous/clinker phases [34]. To this end, the specimens were crushed into pieces and their hydration was stopped following a solvent-exchange protocol. The solvent was then fully removed from the specimens by storing them in a low-vacuum desiccator. They were then milled below 100 \(\upmu\)m and exposed to the XRD test. The starting crystal structure data were taken from [PERSON] (2016) [34]. All structure parameters of the anhydrous phases were fixed at levels obtained from the XRD analysis of anhydrous slags and the cement powder. Rietveld curve fitting was applied to each diffraction pattern in both fresh and milled cases, and the mass attenuation coefficients were calculated using the compositions of the mixtures, taking into account their water content. In the case of fresh specimens, the water content was assumed to be the same as the batched water-to-binder ratio (0.4), and for the milled specimens, only the chemically bound water (measured via thermogravimetric analysis) was taken into account. The corrected mass proportions of the anhydrous phases were extracted from the Rietveld analysis results of the milled specimens, and the fresh specimen results were used for determining the hydrated phases. The results were then combined to determine the evolution of phase composition of the hydrating pastes over time. The Rietveld analysis results were used to determine the clinker degree of reaction (DoR). This was accomplished by proportioning the starting and current combined mass fractions of C\({}_{3}\)S, C\({}_{2}\)S, C\({}_{3}\)A and C\({}_{4}\)AF.