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Water Retention Characteristics of Fly Ash–Bentonite Mix

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The use of sand–bentonite mixes as hydraulic barrier in municipal and hazardous landfills are established in the literature. Environmental awareness and stringent rules on river conservation has restricted the free availability of construction sand making it non-viable for massive geo-environmental projects such as waste containment. Following the same philosophy for which sand was used in bentonite, this study propose to replace the former with fly ash. Apart from being an alternate material to sand, this proposition would ensure mass utility of waste fly ash for environmentally advantageous waste containment project. For this purpose, it is important to study the unsaturated characteristics of fly ash–bentonite mix, which is not reported in the literature. This study explores the influence of fly ash properties and its classification on the water retention characteristics curve (WRCC) of fly ash–bentonite mixes. The extent of variability in WRCC attributed to different sources of fly ash were quantified to investigate whether there is a possibility of generalizing the unsaturated behavior of fly ash–bentonite mixes. In addition, the influence of bentonite water content on the WRCC of mixes were studied and compared with the previously published results in the literature. It was found that at high suction (> 105 kPa), all the WRCC of FA–B mixes merges together and is mainly dominated by the water retention of bentonite only. It was also established from this study that any types of fly ashes irrespective of its source can be used in this application if compacted at optimum moisture content.

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Fig. 1
Fig. 2
Fig. 3



Specific gravity




Gravimetric water content

wb :

Bentonite water content

ψm :

Matric suction


Total suction

γd :

Dry unit weight


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Correspondence to Abhijit Deka.

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Deka, A., Sekharan, S. Water Retention Characteristics of Fly Ash–Bentonite Mix. Geotech Geol Eng (2020). https://doi.org/10.1007/s10706-020-01220-w

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  • Fly ash
  • Bentonite
  • Pond ash
  • Water retention characteristic curve (WRCC)
  • Dew point potentiometer