Hence, proper calculations for landfill liners require an assessment of the swelling properties 11, 12, 13, 14, 15, 16, 17. Furthermore, the swelling behaviour plays a determining role in the assessment of such properties, as unfavourable changes in geotechnical properties caused by the swelling process affect the permeability and mechanical properties. Regarding the material used for landfill liners, not only its permeation properties but also its bearing capacity, trafficability, internal and interface shear strength, compressibility, and resistance to desiccation cracking should be determined 10. The research confirmed that lime-softening sludge compacted at a moisture content higher than the optimum moisture content determined by the Proctor standard compaction test, i.e., w opt + (1–2)% could replace mineral soils in landfill liners because it met the requirements of inert waste landfill liners ( \(k\)≤ 1.0♱0 −7 m/s), irrespective of the leachate pH and hazardous and non-hazardous waste landfill sites (< 1.0♱0 −9 m/s).
Oxygen not included lime series#
Dąbska 9 conducted a series of short-term tap water permeation tests of lime-softening sludge and long-term permeation tests using tap water, distilled water, NaOH solution with pH ≥ 11.0, HCl solution with pH ≤ 3.0, and municipal landfill leachate. All these potential reuse options for lime-softening sludge were confirmed by Fei et al. 6, 7 also demonstrated the potential use of dried lime sludge modified with stabilisers, or mixed with soil, Portland cement, or Class C fly ash as fill material for road construction. Lime-softening sludge has also been successfully applied in wastewater neutralisation 5. Moreover, Glysson 3 and Raghu and Hsieh 4 proposed using lime-softening sludge in ground levelling and ground stabilisation in combination with other wastes. Research on the geotechnical properties of lime-softening sludge was commenced by Glysson 3, who considered the possibility of its reuse in landfill liners. One of the methods for lime-softening sludge management is its application in geotechnics. Moreover, the lime-softening process results in the removal of suspensions and iron and manganese compounds 2. Magnesium hydroxide Mg(OH) 2 precipitates solely as a gel sediment. The resulting calcium carbonate CaCO 3 precipitates in the form of calcite, sometimes with an admixture of unstable forms, i.e., aragonite or vaterite, under lime-softening conditions. The lime process of softening converts calcium and magnesium salts dissolved in water into precipitating insoluble compounds. The most applied method of carbonate hardness removal is water softening by means of adding lime Ca(OH) 2 1. Water occurring in nature is frequently characterised by a high carbonate hardness caused by the presence of dissolved carbonates, bicarbonates, and calcium and magnesium hydroxides, namely, CaCO 3, Ca(HCO 3) 2, Ca(OH) 2, MgCO 3, Mg(HCO 3) 2, and Mg(OH) 2. Lime-softening sludge is a by-product of the process of water treatment for industrial purposes. For practical engineering implications, the moisture content between ( w opt + 2.0%) and ( w opt + 4.0%) was provided for the most suitable sludge application in landfill liners. The lime-softening sludge non-swelling moisture content was defined as w non ≈ ( w opt + 4.0%) − ( w opt + 4.5%). The novelty of the work lies in identifying a significant plunge of the expansion index at w ≈ w opt for the leachate swelling test. The highest expansion, dry density, and moisture content changes due to swelling were identified for leachate at w w opt. An increase in the sludge moulding moisture content, limited swelling in all liquids used. Subsequently, these factors also affected the sludge dry density decrease, and its moisture content increase, whereas the impact of the initial dry density on expansion was of low importance. The expansion index was significantly influenced by the initial moisture content and liquid chemistry. Moreover, changes in the moisture content and dry density during the swelling process were investigated. One-dimensional oedometer swell tests were conducted using distilled water, tap water, and municipal landfill leachate, resulting in the determination of the expansion indices.
The study involved the assessment of the effect of compaction and moulding moisture content (30–40%), corresponding to the Proctor standard compaction test. The objective of this study was to investigate the swelling potential of compacted lime-softening sludge for application in landfill liners.
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