# Geotechnical Behaviour of Fly Ash-Bentonite Used in Layers
## 2 Materials Used  
### Fly Ash  
The fly ash came from a national thermal power plant in Dadri, India, with an installed capacity of 800 megawatts. The plant generates about 10 million tonnes of bottom ash and 39 million tonnes of fly ash each day. The fly ash is collected in a total of 24 electrostatic precipitator hoppers. To avoid deterioration over time, fly ash was collected in dry form and stored in moisture-proof containers. The results of the research into the chemical composition and physical properties of fly ash are shown in Tables 1 and 2, respectively. It was designated as class F, as defined by ASTM C 618 [19], indicating that it is typically obtained from bituminous and anthracite coals. The intrinsic diversity of fly ashes from different sources as well as from the same source is greater in India than in other nations such as Italy and the United States [20]. The chemical constituents of the Dadri fly ash were found to be within the range of other Indian fly ash chemical compounds. Scanning electron microscope (SEM) and Energy Dispersive X-ray (EDX) were carried out through JEOL, instrument [SM-6510 (Figure 1). The following settings were used to photograph the morphological characteristics of the fly: accelerating voltage = 15 kV, magnification = 3000, spot size = 40, \(\upmu\)m marker = 5, and tilt = 0. The image clearly shows that fly ash is mostly made up of spherical particles of various sizes (Figure 1). Figure 2a shows the EDX of fly ash. \begin{table}
\begin{tabular}{c c} \hline \hline
**Composition** & **Percentage** \\ \hline Silicon dioxide (SiO\({}_{2}\)) & 59.00 \\ Alumina (Al\({}_{2}\)O\({}_{3}\)) & 29.00 \\ Iron oxide (Fe\({}_{2}\)O\({}_{3}\)) & 6.50 \\ Calcium oxide (CaO) & 1.80 \\ Magnesium oxide (MgO) & 1.44 \\ Sodium oxide (Na\({}_{2}\)O) & 0.80 \\ulphur dioxide (SO\({}_{3}\)) & 0.28 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Chemical composition of fly ash. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Properties** & **Fly Ash** & **Bentonite** \\ \hline Specific gravity & 2.19 & 2.73 \\ Optimum moisture content (OMC), \% & 22 & 28 \\ Unit weight, kN/m\({}^{3}\) & 14.39 & 21.5 \\ Maximum dry density (MDD), kN/m\({}^{3}\) & 11.8 & 16.8 \\ Liquid limit (W\({}_{\rm{L}}\)), \% & 24 & 261 \\ Plastic limit (W\({}_{\rm{P}}\)), \% & Non plastic & 38 \\ Plasticity index (P.I), \% & 24 & 223 \\ Coefficient of permeability, (10\({}^{-10}\) m/sec) & 551 & 8.52 \\ Unconfined compression strength, kN/m\({}^{2}\) & 34 & 176 \\ Classification & Class F & CH \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Physical properties of fly ash and bentonite. Figure 1: Scanning electron micrographs of fly ash with different magnification factors: (**a**) 700; (**b**) 3000. Figure 2: Energy-dispersive X-ray spectroscopy (EDS): (**a**) fly ash and (**b**) bentonite. The density bottle method was used to determine the specific gravity of fly ash, which was found to be 2.19 according to IS: 2720-Part 3 [21]. To assess the grain size distribution of the Dadri fly ash, a hydrometer test was performed according to Indian Standard IS 2720-Part 4 [22]. The Atterberg limits were measured according to Indian Standard IS 2720-Part 4 [23]. The liquid limit (W\({}_{\text{L}}\)) of fly ash was found to be 24% and non-plastic in nature. For typical soils, a light compaction standard Proctor test was performed according to Indian Standard IS 2720-Part 10 [24]. The optimal moisture content (OMC), unit weight, and maximum dry density (MDD) were found to be 22%, 14.39 kN/m\({}^{3}\), and 11.8 kN/m\({}^{3}\), respectively. Fly ashes have a lower MDD and a higher OMC than normal soils. This may be attributed to lower specific gravity and the porous nature of the particle. Unconfined compression tests were carried out in accordance with Indian Standard IS 2720-Part 10 [24]. Two specimens were tested, and at 2% axial strain, the failure axial stress was attained, causing the specimens to collapse. The Dadri fly ash specimens had an average unconfined compressive strength of 110 kN/m\({}^{2}\).