## 2 Materials and Methods
### Materials
#### 2.1.5 Samples Preparation  
The method of treating soils with POFA-based geopolymer was conducted at controlled water content and dry density to simulate the conditions of soil in-situ. In this study, soils were mixed with four dosages of POFA-based geopolymer. These four dosages are based on POFA being 10%, 20%, 30% and 40% of soil's dry weight. Soils were mixed with geopolymer and free water in the same mixer used for preparing the geopolymer for approximately ten minutes until the mixture showed total homogeneity. The free water quantity was varied to allow for the investigation of optimal compaction parameters, as  
\begin{table}
\begin{tabular}{c c c c c} \hline
**Component** & **Soil 1 (CL)** & **Soil 2 (CH)** & **Raw POFA (\% by Mass)** & **Treated POFA (\% by Mass)** \\ \hline Silicon dioxide (SiO\({}_{2}\)) & 36.71 & 42.46 & 39.23 & 43.52 \\ Aluminum oxide (Al\({}_{2}\)O\({}_{3}\)) & 27.18 & 22.65 & 26.2 & 24.7 \\ Calcium oxide (CaO) & 0.04 & 0.13 & 8.64 & 9.73 \\ Magnesium oxide (MgO) & 0.78 & 0.52 & 6.12 & 4.31 \\ Iron oxide (Fe\({}_{2}\)O) & 9.35 & 7.69 & 5.99 & 6.68 \\ Potassium oxide (K\({}_{2}\)O) & 5.32 & 1.66 & 2.27 & 1.56 \\ Sulfur Trioxide (SO\({}_{3}\)) & 0.06 & 0.04 & 1.63 & 5.28 \\ Sodium oxide (Na\({}_{2}\)O) & - & - & 0.89 & 0.18 \\ LOI (\%) & - & - & 8.79 & 1.26 \\ \hline \end{tabular}
\end{table}
Table 2: Chemical composition of CL, CH and POFA.  
will be discussed in Section 2.2.1. UCS and direct shear test specimens were prepared at the moisture content related to the highest dry density from the compaction test. Moreover, to ensure the consistency and representativeness of the tests, three duplicate specimens were prepared for each test and the results were approved if they differed by up to 5% from the average. Table 3 depicts the mixtures design and testing for both types of soils.  
In this study, it was assumed that the density/unit weight of all samples prepared has achieved the same value as observed from the compaction curves. However, the moisture content values of samples after preparation for UCS and direct shear testing were calculated to check the proximity of these values from the moisture content found from the compaction test, as indicated in Table 4. All standard deviation values are less than 5%, which indicates the small deviation of the measured values from the optimum moisture content (OMC) obtained from compaction testing.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Series** & **Test Number** & \multicolumn{2}{c}{**Curing Days**} \\ \cline{3-4}  & & **UCS** & **DST** \\ \hline \multirow{4}{*}{Soil 1} & Untreated CL & 7 \& 28 & - \\  & CL-G10 PA & 7 \& 28 & - \\  & CL-G20 PA & 7 \& 28 & - \\  & CL-G30 PA & 7 \& 28 & - \\  & CL-G40 PA & 7 \& 28 & - \\ \hline \multirow{4}{*}{Soil 2} & Untreated CH & 7 \& 28 & - \\  & CH-G10 PA & 7 \& 28 & - \\ \cline{1-1}  & CH-G20 PA & 7 \& 28 & - \\ \cline{1-1}  & CH-G30 PA & 7 \& 28 & - \\ \cline{1-1}  & CH-G40 PA & 7 \& 28 & - \\ \hline \hline \end{tabular} Note: G10 PA, G20 PA, G30 PA and G40 PA—geopolymer produced from 10%, 20%, 30% and 40% POFA of soil’s dry weight.  
\end{table}
Table 3: Mixing proportions of different tests.  
Figure 2: POFA-based geopolymer before mixing with soil.