## 3 Results and Discussion  
### Hydration Kinetics of Slag-Blended System  
The reacted and unreacted slag of the paste specimens at different ages were determined based on the EDTA dissolution method. The hydration degrees of the slag, defined as the ratio of the reacted slag over the total slag and as a function of age, are provided in Figure 1. The three curves exhibit similar trends, regardless of the slag replacement level. In general, high reactivity of the ultrafine slag can be found and its hydration degree was above 21% for the paste specimen incorporating 25% slag, even on the first day of hydration. The rapid reaction of the slag proceeded until the end of 14 days. Afterwards, the slag continued to hydrate, but its reactivity seems to have decreased gradually. After 28 days, the hydration degree of the slag tended to be slowly increased as time elapsed. It is worthwhile to note that a higher slag content led to an obvious decrease in the hydration degree of slag. The content of calcium hydroxide CH, which acted as a necessary activator, largely controlled the reaction of the slag. The CH was produced in the process of the OPC hydration, and its content was lower for the specimens with a lower amount of OPC (namely, a higher amount of slag) in the binder mixture, as will be proved later in the present work. The hydration degree of slag as a function of age can be well described using [PERSON]'s equation (Equation (3)), as referred to by [PERSON] [15]. The results by using Equation (3) to fit the experimental data of the 85% slag binder are shown as a green dotted line in Figure 1.  
\[\alpha=1-\exp(-kt^{n}), \tag{3}\]  
where \(\alpha\) represents the hydration degree of the slag, and \(k\) and \(n\) are constants. The curve-fitting values of \(k\) and \(n\), as well as the correlation coefficient \(\mathbb{R}^{2}\), were derived and are given in Table 2.  
The mass losses of various hydrates in the slag-blended paste specimens with elevated temperatures were quantified by TGA. The derivations (DTG) of the specimens at 28 days, as a representative result, are shown in Figure 2. The components are somewhat similar, as expected. A consistent mass loss of all specimens below 100 \({}^{\circ}\)C was observed, which partly resulted from the evaporation of free water and loosely bound water. The first main \begin{table}
\begin{tabular}{c c c c} \hline
**Mixture** & \(k\) & \(n\) & \(\mathbb{R}^{2}\) \\ \hline
25\% slag & 0.22 & 0.27 & 0.97 \\
65\% slag & 0.16 & 0.32 & 0.97 \\
85\% slag & 0.10 & 0.36 & 0.98 \\ \hline \end{tabular}
\end{table} 
Table 2: Values of fitting parameters in [PERSON]’s equation. Figure 1: Hydration degree of ultrafine slag in paste specimens of different ages. peak at around 70 \({}^{\circ}\)C can be ascribed to the decomposition of ettrinigite (AFt). Losses of interlayer water in the main hydrates, C-S-H, took place at 50 \({}^{\circ}\)C. The dehydroxylation of C-S-H started at approximately 100 \({}^{\circ}\)C [15; 25], and continuous loss of chemically bound water up to 800 \({}^{\circ}\)C was reported [26]. The decomposition in the temperature range of 140-400 \({}^{\circ}\)C is attributable to the series of AFm phases, which should include hemicarbonate or monocarbonate, owing to the presence of CO3\({}^{2-}\) in the raw materials [27]. The two small peaks at about 300 \({}^{\circ}\)C and 380 \({}^{\circ}\)C can be related to the two-step dehydration of the lamellar hydrotalcite (Ht), which contains aluminum and magnesium [28]. The sharp peak between 400 and 500 \({}^{\circ}\)C corresponds to the dehydration of the crystal CH phase, followed by a small peak between 600 and 700 \({}^{\circ}\)C related to calcite (CC) decomposition. With quantitative analysis, it is clear that a higher AFt content was found when OPC was partially replaced by 25% slag, as seen in Figure 2. The AFt content decreased by increasing the substitution from 25 to 65%, while it increased again with a further rise in the replacement level by 85% slag. The CH content decreased with an increase in the slag content.