# Effect of Bentonite Addition on the Properties of Fly Ash as a Material for Landfill Sealing Layers
## 2 Materials and Methods
### Methods  
Laboratory tests of the hydraulic conductivity of fly ash, fly ash-bentonite mixture, and cohesive soil were carried out in Rowe-Barden consolidation cell. In this type of apparatus, a sample under conditions of no lateral strain is hydraulically loaded by the membrane with a floating ring, which transfers the load to the rigid porous disk. In the Rowe-Barden cell, the saturation of the sample can be controlled by means of back pressure, constant measurements of vertical displacement and pore water pressure. Specimens, in the form of a disc with 70 mm in diameter and 25 mm in height, were prepared by the compaction using the standard Proctor (SP) method at the optimal moisture content in accordance with the European standard [35]. It must be pointed out here that in order to establish compaction parameters of fly ash and its mixtures, the sample can be compacted only once, the importance of which is emphasized in Zabielska-Adamska [36]. It has been found that re-compaction of fly ash causes crushing of the spherical grains, which are filled by smaller grains, resulting in changes in the physical properties of the fly ash. The maximum dry density of the material compacted several times increases while optimum moisture content decreases. To test the hydraulic conductivity, the required quantity of water was added to the dry fly ash, then the material was thoroughly mixed and placed in an airtight container to keep the moisture content. After 24 h fly ash was mixed with various quantities of bentonite immediately before compaction, then the material was mixed thoroughly. The appropriate mass of each mixture was compacted in the consolidation ring to get its respective maximum dry density at optimum moisture content. The quantity of the mixture used for the test was dependent on the volume of the sample and compaction parameters. The filter paper was then placed on the top and on the bottom of the sample to prevent finer particles from clogging the pores of porous stones. Then, the saturated porous stones \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{3}{*}{**Tested Material**} & \multirow{3}{*}{\
\begin{tabular}{c} **Specific Density \(\rho_{\text{s}}\)** \\ **(Mg/m3)** \\ \end{tabular} } & \multicolumn{3}{c}{**Compaction Parameters**} & \multirow{3}{*}{
\begin{tabular}{c} **Specific Surface Area \(S_{\text{s}}\)** \\ **(m2/g)** \\ \end{tabular} } \\ \cline{3-4}  & & **Optimum** & & **Maximum Dry** \\  & & **Moisture Content** & **Density (MDD)** & \\  & & **(OMC) (\%)** & **(Mg/m3)** & \\ \hline FA & 2.18 & 40.0 & 1.073 & 21.01 \\ FA+5\%B & 2.18 & 39.0 & 1.100 & 42.24 \\ FA+10\%B & 2.22 & 36.3 & 1.118 & 57.90 \\ FA+15\%B & 2.24 & 33.0 & 1.134 & 67.73 \\ sasiCl & 2.68 & 14.0 & 1.950 & 102.58 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Properties of tested materials. were placed and the entire assembly was mounted in the consolidation cell. The cell cover was fitted and the seating pressure (5 kPa) was applied in accordance with British Standard 1377-6:1990 [37]. At first, the sample was saturated and when the saturation stage finished, the load increment was applied to the sample. Saturation of the soil is assessed from the change of pore water pressure \(\Delta u\), which occurs under changes in principal stresses \(\Delta\sigma_{1}\) and \(\Delta\sigma_{3}\), described by [PERSON]'s equation [38]:  
\[\Delta u=B[\Delta\sigma_{3}+A(\Delta\sigma_{1}-\Delta\sigma_{3})] \tag{1}\]  
where \(A\) and \(B\) are pore-pressure coefficients; \(\Delta\sigma_{1}\) and \(\Delta\sigma_{3}\) are changes in principal stresses. Coefficients \(A\) and \(B\) are measured in the undrained triaxial test. Saturation of soil tested under conditions of no lateral strain can be determined based on the value of \(B\) parameter:  
\[B=\frac{\Delta u}{\Delta\sigma} \tag{2}\]  
where \(\Delta u\) is pore water pressure corresponding to an increase of total vertical stress \(\Delta\sigma\). For fully saturated soils \(B=1\), while for dry soils \(B=0\).