Permeability of Clay-Modified Fly Ash under Thermal Gradients

Abstract

Mixtures of geomaterials and by-products have potential as barriers for containing contaminants. In this investigation, the permeability of fly ash to distilled water was found to decrease due to the addition of pure bentonite. On subjection of the compacted bentonite-modified fly ash to cycles of freeze-thaw action, using a specially designed freeze-thaw permeameter, the permeability of the composite material decreased to a constant value after one cycle. It is postulated here that the observed permeability decrease stems from the dispersion of flocculated clay material that occupies the intergranular regions among the fly-ash particles. The specific results of this study are fitted into a general framework for describing textural changes and deterioration of composite materials under cyclic thermal gradients. In this framework, a comparison of the response of clay-modified fly ash and ash-modified clay to the stresses induced by freeze-thaw action is made. Both class-C and class-F fly ash are examined.