# Analysis of Hydration-Mechanical-Durability Properties of Metakaolin Blended Concrete
## 3 Property Evaluations of MK Blended Concrete
### Results and Discussion
#### 3.2.2 Reaction of Cement-MK Blends  
Based on the reaction degree of MK at different times, the coefficients of the MK reaction model were determined and are presented in Table 2. These reaction rate coefficients did not change with the MK replacement levels. As shown in Figure 3a, when the MK replacement level increased from 10 to 20%, the activation effect of CH became weaker, and the reaction degree of MK decreased [16; 17]. As shown in Figure 3b, for cement-MK blends, both the cement hydration and the MK reaction affected the CH contents. At early stages, the generation of CH from the cement hydration was dominant, and the CH content increased as the curing time progressed. At later stages, the consumption of CH from the MK reaction was dominant, and CH content decreased as curing times developed. At the same curing times, as the MK replacement levels increased, the CH contents decreased. \begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline
**Binders** & \begin{tabular}{c} **SiO2** \\ **(\%)** \\ \end{tabular} & \begin{tabular}{c} **Al2O3** \\ **(\%)** \\ \end{tabular} & \begin{tabular}{c} **Fe2O3** \\ **(\%)** \\ \end{tabular} & \begin{tabular}{c} **CaO** \\ **(\%)** \\ \end{tabular} & \begin{tabular}{c} **MgO** \\ **(\%)** \\ \end{tabular} & \begin{tabular}{c} **Na2O** \\ **(\%)** \\ \end{tabular} & \begin{tabular}{c} **K2O** \\ **(\%)** \\ \end{tabular} & \
\begin{tabular}{c} **SO3** \\ **(\%)** \\ \end{tabular} &
\begin{tabular}{c} **Specific Surface** \\ **Gravity** \\ \end{tabular} \\ \hline cement & 21.0 & 5.9 & 3.4 & 64.7 & 0.9 & - & - & 2.6 & 3.15 & 3520 \\ MK & 53.2 & 43.9 & 0.38 & 0.02 & 0.05 & 0.17 & 0.10 & - & 2.62 & 12,680 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: The chemical and physical properties of cement and metakaolin. Figure 2: Hydration of neat Portland cement. Figure 4 shows the parameter studies on the degree of binder reaction in the MK blended concrete. The effects of water to binder ratios, MK replacement levels, and specific surface on the reaction degree of MK were all considered in the parameter studies. When the MK partially replaced cement, the reaction degree of the cement was enhanced due to the dilution effect, whereas capillary water consumed from the MK reaction (Equation (4)) lowered the reaction degree of the cement. The holistic results on the reaction degree of cement in the MK blended concrete were dependent on the combined actions of the increasing and decreasing factors. Regarding the concrete with a lower water to powder ratio (0.3), as shown in Figure 4a, when the MK replacement level was 10%, the increase in reaction degree of cement was marginal. Similarly, when 10% or 20% MK was used in concrete with a higher water to binder ratio (0.5), the increase in the reaction degree of cement was also marginal. However, for concrete with a water to binder ratio of 0.3% and 20% MK, the increase in the reaction degree of cement was obvious. This was because for concrete with a low water to binder ratio and a high MK content, the dilution effect from the MK addition was dominant. As shown in Figure 4b, when the water to binder ratio rose from 0.3 to 0.5, the usable space for depositing the reaction products increased, as did the reaction degree of the MK [16; 17]. When the MK replacement levels increased from 10% to 20%, the reaction degree of MK decreased significantly. This was because of the increase in available depositing space for the high water to binder ratios mix. Similarly, [PERSON] et al. [22] and [PERSON] et al. [23] also found that for fly ash or slag composite binders, the reaction degree of mineral admixture increased when the water to binder ratio increased or the mineral admixture placement level decreased. As shown in Figure 4c (with a water to binder ratio of 0.3 and MK replacement level of 10%), when the specific surface of MK increased, the reaction degree of MK also increased. Similarly, [PERSON] et al. [23] also found that at the same curing age, the finer slag had a higher reaction degree than the coarser slag.