# Strength Development of Metakaolin-Based Alkalial-Activated Cement
## 2 Materials and Methods
### Sample Preparation  
Cement slurries were prepared by mixing suitable amounts of the solid precursors with liquid activators, where metakaolin type MKB was used as the main precursor in all experiments, while MKF and GGBFS were also investigated as co-binders. Samples consisting of both MKB and MKF were denoted as \"Bx Py\", where x and y is the percentage  
\begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline \multicolumn{3}{c}{**Physical Properties**} & \multicolumn{6}{c}{**Main Oxide Composition (\%)**} \\ \hline  & **d50** & **Specific Gravity** & & & & & & & \\  & **(\(\mu\)m)** & **(g/cm\({}^{3}\))** & **SiO\({}_{2}\)** & **Al\({}_{2}\)O\({}_{3}\)** & **CaO** & **Fe\({}_{2}\)O\({}_{3}\)** & **TiO\({}_{2}\)** & **MgO** & **K\({}_{2}\)O** \\ \hline MKB & 25.3 & 2.6 & 70.3 & 23.4 & 0.1 & 1.6 & 1.7 & 0.1 & 0.3 \\ MKF & 6.29 & 2.4 & 51.4 & 43.6 & 0.1 & - & 5 & - & - \\ GGBFS & 10.0 & 2.9 & 35.8 & 12.7 & 33.7 & 0.2 & 2.2 & 12.8 & 0.8 \\ MS & 0.15 & 0.6 & 95.5 & 0.7 & 0.4 & 0.3 & - & 0.5 & 1.0 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Chemical composition and physical properties of metakaolin samples MKB and MKF, as well as Ground Granulated Blast Furnace Slag (GGBFS) and MicroSilica (MS) samples. Chemical composition was provided by the respective suppliers.  
Figure 1: Overview of experimental procedure to determine solubility of Si and Al of metakaolin samples.  
of MKB and MKF, respectively. Several samples of varying Si/Al ratios were prepared, where both potassium silicate and MicroSilica (MS) were used to adjust the Si/Al ratio. MicroSilica consists of amorphous silica particles of sub-micron sizes and are thus easily dissolvable. Estimations of the Si/Al ratio in the slurry were based upon the assumption that only the metakaolin part of the MKB samples dissolved, and that the quartz part remained inert. Increasing Si amounts in the slurry were obtained by increasing the ratio of potassium silicate/KOH in the activator, as well as the addition of MicroSilica in increasing amounts. Furthermore, several samples of varying KOH concentrations were prepared, where the increased KOH concentration was obtained by adjusting the amount of 12 M KOH vs. distilled water in the mixture. All samples were prepared with a solid/water ratio of 0.55.  
The cement slurries were mixed in an OFITE model 25 constant speed blender according to the mixing procedure described in API 10B-2 [31], where the solid precursors were added to the liquid activator solution for 15 s at 4000 rpm, and the slurry was subsequently mixed at 12,000 rpm for 35 s. After mixing, the slurry was poured into 5 cm cubic molds, and cured in sealed conditions at room temperature (20 \({}^{\circ}\)C). It should be noted that 20 \({}^{\circ}\)C is a quite low temperature for most downhole applications, but this temperature was selected as it is relevant for tophole well sections. Room temperature is also relevant for civil engineering applications. The samples were de-molded after 1 day and the cubes were placed in sealed plastic bags and left to cure until designated time for UCS testing. Two replicates were tested for each sample, where the reported results are the average of these two measurements. Figure 2 illustrates the sample preparation procedure.