Bentonite-kaolinite mix for barrier systems

Abstract

Due to the shortage of bentonite deposits in Southeast Asia, geosynthetic clay liners need to be imported. Alternatively, a bentonite-kaolinite clay mix can be used if desirable properties are met. Among these are consolidation properties of bentonite-kaolinite mixes, which are presented in this paper. Both compression and swelling indices were found to increase significantly for a small amount of bentonite addition. At least 30% bentonite was needed in the mix to show the same decreasing trend in the coefficient of consolidation as displayed by the pure bentonite. Bentonite-Kaolinite (B:K) mix of 50:50, defined as a threshold mix ratio, behaved almost the same as pure bentonite from the point of view of coefficient of consolidation and deduced coefficient of permeability. Direct permeability tests were performed using four permeants: (1) distilled water (2) 0.25 M calcium chloride (CaCl2) solution (3) 0.1 M hydrochloric acid (HCl) solution and (4) 0.1 M sodium hydroxide (NaOH) solution. When B:K = 50:50 was permeated directly with calcium chloride enriched solution the coefficient of permeability of the mix increased significantly to about 10-9 m/s, whereas the coefficient of permeability with the above acid and alkaline solutions was of the order of 10-11 m/s. Therefore, a 50:50 Bentonite-Kaolinite mix could be an effective barrier in strong acidic and alkaline environments but not in a calcium chloride enriched environment.