The Potential Use of Clay-Fly Ash Geopolymer in the Design of Active-Passive Liners: A Review

Abstract

AbstractBecause long-term leachate migration through a hydraulic barrier is inevitable, compacted clay and cementitious liners are commonly used as ‘active-passive’ liners to attenuate percolated leachate. The scarcity of suitable clay and because of the CO2 emitted during the production of Portland cement as well as drying shrinkage, flow rate due to consolidation, limited attenuation capacity, and chemical instability may mean that these are not the best choices of materials to use for this purpose. An environmentally friendly method to improve the properties of local clay and provision for a long-term physical and chemical containment are essential. Geopolymers can be environmentally friendly substitutes for Portland cement to improve soil properties, not just because of the reduced carbon dioxide emission, but also because of its superior physical and chemical properties, as well as significant early strength, reduced shrinkage, freeze-thaw resistance, long-term durability, and attenuation capacity. According to previous studies, class-F fly ash-based geopolymers activated with NaOH exhibit superior attenuation capacity and long-term durability. The presence of silica, alumina, and iron oxides and the lack of calcium oxide play pivotal roles in the acceptable attenuation capacity and chemical stability of class-F fly ash. Accordingly, a clay-fly ash geopolymer may also work as a sustainable liner with appropriate physical and chemical performance. Clay can also participate in the geopolymerization process as an alumino-silicate precursor. All components of clay-fly ash geopolymers possess acceptable adsorption capacity. The type and percentage of the constituent raw materials control the attenuation capacity and physical properties of final products, however. The porosity and conductivity of typical geopolymers are related to the activator type and concentration, water content, and curing condition. Furthermore, the properties of liner materials can be adjusted with respect to the target contaminants. The present study aimed to present a comprehensive review of the relevant studies to highlight the properties required.