As urban populations grow, the volumes of liquid and solid wastes produced continue to grow, requiring the increased use and performance assessment of waste containment liners (such as landfill liners and water storage pond liners). To comply with regulatory requirements, bentonite (moisture-reactive clay) based hydraulic sealing systems may be required, possibly enhanced using innovative polymer reinforcement. This new bentonite-polymer geomaterial is intended to enhance hydraulic performance, although existing studies often neglect their mechanical behaviour. Due to the low hydraulic conductivity, the testing time for characterisation in the laboratory is long, which makes it difficult for rapid engineering design. Pioneering investigations, as well as new quick hydraulic indexes, are called for.
Accordingly, experimental studies were undertaken on the geomaterials in their higher hydraulic conductivity liquid state, based on rheology and filtration. The literature review highlights the extensive use for bentonite-polymer suspensions, with sound associated theories, but lack correlations with geotechnical parameters. In this present study, the aim was to formulate compatibility and performance indexes for bentonite-polymers geomaterials, while studying their Hydro-Mechanical-Chemical (HMC) behaviour and the physico-chemical interactions involved. Liquid state rheological parameters were then experimentally transposed into solid state soil mechanics parameters (specifically hydraulic conductivity). This methodology was based on test results for various bentonites, fluids (including water and CaCl2), two polymers and sand, for compacted sand-bentonite-polymer mixtures.
One-dimensional test results for solid state bentonite-polymer mixtures showed that the addition of 2% polymer led to low hydraulic conductivity and high swelling geomaterials. This suggested their suitability as sealing liners, and also that high and slow deformations would expected on the field. Classical free swell index tests were proven not to be applicable for bentonite-polymer mixtures. Liquid state testing showed that the chemical fluids deteriorated the suspensions strength parameters, while the polymer reinforced it. The nature of the bentonite also influenced the suspension characteristics, in accordance with the diffuse double theory. Observations from HMC investigations, from the literature, and from rheology and filtration testing, showed compatibility for bentonite-polymer-fluid mixtures over a range of states. Dynamic rheology testing was found to provide the most appropriate parameters to formulate a hydraulic performance index. Two approaches were adopted (gel and swelling), linking the hydraulic conductivity with rheological parameters. Linear correlations were observed, dependent on the fluid chemistry and polymer addition, manifesting the mixing effect and the significance of a liquid-solid continuum.