Behavior of coal ash-bentonite and sand-bentonite mixtures

Abstract

Flexible-wall hydraulic conductivity tests were carried out on bottom ash, fly ash and compacted specimens of sand with additions of O, 3, 6, 9 and 18% of bentonite. ln order to study the effect of bentonite inclusion and particle morphology on the hydraulic conductivity of the admixtures, an investigation was undertaken based on thin section micrographs.  It was found  that, for both  bottom and fly ash admixtures, bentonite addition reduced only one order of magnitude the hydraulic conductivity, from 1.78x10·⁶ m/s to 1.39x10·⁷ m/s. ln the other hand, the sand hydraulic conductivity was reduced five orders of magnitude, from 3.17x10·⁵ m/s to 5.15x l0· ¹⁰ m/s. Amongst several factors that can be responsible for the difficulty in reducing hydraulic conductivity (e.g. grain size distribution  of ash), can also be recalled the high particle voids observed in the ash by means of microscopic analysis. The same is not true with the sand, which has solid particles, without inner voids.