Swelling behaviours of compacted lime-softening sludge for application in landfill liners

The objective of this study was to investigate the swelling potential of compacted lime-softening sludge for application in landfill liners. The study involved the assessment of the effect of compaction and moulding moisture content (30-40%), corresponding to the Proctor standard compaction test. One-dimensional oedometer swell tests were conducted using distilled water, tap water, and municipal landfill leachate, resulting in the determination of the expansion indices. Moreover, changes in the moisture content and dry density during the swelling process were investigated. The expansion index was significantly influenced by the initial moisture content and liquid chemistry. 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. An increase in the sludge moulding moisture content, limited swelling in all liquids used. The highest expansion, dry density, and moisture content changes due to swelling were identified for leachate at w < w_opt. It should be underlined that the effect of liquid on the swelling potential faded away along with a further increase in the moisture content w > w_opt. 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 lime-softening sludge non-swelling moisture content was defined as w_non ≈ (w_opt + 4.0%) - (w_opt + 4.5%). 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.