Beneficial Reuse of Fly Ashes in Geotechnical Engineering with Physicochemical and Electron Microscopic Methods

The sedimentation behavior of fine grained soil is largely dependent on its pore fluid chemistry. Physicochemical properties of the pore fluid, such as ionic strength and pH, could greatly influence the micro structure of kaolinite which in turn influences the sedimentation behavior. Other than ionic effect, adding fly ash can also cause different sedimentation behaviors due to the change of gradation, increased ionic strength and pozzolanic reactions. There are several tests to characterize the kaolinite micro fabric, such as sedimentation test, grain size distribution test, viscosity test, zeta potential test, and scanning electron microscopy (SEM). The objective of this project was to investigate the influence of ionic concentration and fly ash on the sedimentation behavior of kaolinite. In addition, zeta potential and particle size distribution in supernatant and suspensions were measured and analyzed. The zeta potential of kaolinite was found closely related to the particle size, micro fabric and settling speed. It was found that an increase in the percentage of fly ash in the fly ash soil mixture could cause an increase in the settling speed. The addition of fly ash was found more efficiency than the ionic concentration because the fly ash can not only interact with kaolinite particles but also increase the ionic strength in the dissolution so that the kaolinite could flocculate and aggregate which in turn increases the settling speed.