# Property Analysis of Slag Composite Concrete Using a Kinetic-Thermodynamic Hydration Model
## 3 Experimental Studies and Modeling
### Modeling  
#### 3.3.1 Kinetic Model  
Equation (6) shows that the hydration heat of blends of cement-slag is dependent on the individual reactions of cement and slag. The Portland cement hydration model can determine the heat release from cement hydration. Thus, using the experimental results for cumulative heat, the reaction coefficients of the reaction model of slag were determined and are shown in Table 4. Figure 4 shows the results of the analysis of the heat of hydration. As a very early age (from mixing to about 5 h), the increase in the cumulative hydration heat was slow because the hydration of the binder was in a period of initial dormancy. From 5 h to about 20 h, the increase in the cumulative hydration heat became quicker because the phase boundary reaction was the controlling process of hydration. After 20 h, the increase in the cumulative hydration heat became much slower because diffusion was the controlling process of hydration. Moreover, as the slag replacement percentage increased, the cumulative heat of the hydration decreased. This was because slag has a much slower reaction rate than cement.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline \(B_{SG}\) (cm/h) & \(C_{SG}\) (cm/h) & \(k_{rSG}\) (cm/h) & \(D_{rSG0}\) (cm\({}^{2}\)/h) \\ \hline \(8.93\times 10^{-9}\) & 0.10 & \(1.0\times 10^{-5}\) & \(1.86\times 10^{-11}\) \\ \hline \hline \end{tabular}
\end{table}
Table 4: Reaction coefficients of the reaction model of slag.  
Figure 4: Analysis results for the cumulative hydration heat.  
Figure 3: Strength of paste.  
Figure 5 shows a parameter study of cement-slag blends. Figure 5a shows that as the slag replacement percentage increased, the hydration degree of cement increased. This was because of the increase in the capillary water concentration from the dilution effect of slag. Figure 5b shows that as the slag replacement percentage increased, the reaction degree of slag decreased. This was due to the weakening of the alkali activation effect of CH for higher volumes of slag. Moreover, the slag reaction degree was much lower than the hydration degree of cement. Figure 5c,d shows the components of hydration heat--i.e., the total hydration heat, the heat from Portland cement hydration, and the heat from the slag chemical reaction. For a 50% slag composite paste at the age of 7 days, about 68% of the heat was from cement hydration. In other words, although the mass fraction of cement was the same as that of slag, the hydration heat from cement hydration was much higher than that from the slag reaction.  
Figure 5 shows the extent of the slag reaction at an early age (from the time of mixing to 7 days). The proposed model can evaluate the reaction degree of slag at various stages, such as at early and late stages. [PERSON] et al. (2018) measured the reaction extent of slag over a longer term using selective dissolution methods. The water/binder ratio of the  
Figure 5: Parameter analysis of the hydration model.  
specimen was 0.5, and the slag replacement percentages were 42% and 67%, respectively. The curing temperature was 20 \({}^{\circ}\)C. The reaction extent of slag was measured from 3 to 91 days. As shown in Figure 5(a),b, the analysis of the reaction extent of slag over a longer term shows agreement with the results of this experiment. In other words, the proposed model is valid for various stages, such as early and late stages. Moreover, as the hydration model considers the interactions between the individual reactions of cement and slag, the coefficients of the reaction model do not change as the mixtures of the specimens change.