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- Water Treatment Sludge as Geotechnical Liner Material: State-of-ArtPublication . Marchiori, Leonardo; Albuquerque, Antonio; Cavaleiro, VictorThe periodical cleaning of the decanters at the plant generates solid wastes called water treatment sludges (WTS), a chemical compound similar to aluminum silicates. WTS’s properties have been studied for geotechnical purpose and it seems to be suitable for producing liner materials for landfills, dams, ponds, and lagoons which store and prevent soil’s infiltration of residues. Liners are usually shaped of soil and geosynthetics, their main properties required are compaction, compressibility and shear strength, chemical compatibility, and hydraulic conductivity. WTS to be considered as a soil substitute, it must be function like a soil, thus, for developing alternative materials, physical, chemical, mechanical, and hydraulic characterization laboratorial parameters are the first step to make viable its reuse. In this sense, the study aims to review the literature over the above-mentioned parameters in order to evaluate WTS as liner material. This review concluded that WTS have high heterogeneity in chemical and mechanical behavior due source of water and treatment processes. WTS’ water affinity affects plasticity behavior, and its incorporation into soils seems to contribute for a composite with pozzolanic characteristics, low specific gravity, finer granulometry, and mechanical stabilization. Although need attention on its chemical compatibility, the influence on shear resistance—increasing internal effective friction angle and decreasing cohesion—and the optimum ratio of introduction within soils for an alternative liner material. Nonetheless, there are lacks in literature over hydraulic conductivity, and long-term behavior, the use of the material in practice must be preceded by pilot tests or experimental landfills.
- Geotechnical Characterization of Water Treatment Sludge for Liner Material Production and Soft Soil ReinforcementPublication . Marchiori, Leonardo; Studart, André; Albuquerque, Antonio; Cavaleiro, Victor; Silva, AbilioA water treatment sludge (WTS) was characterized in order to evaluate if its properties would be suitable for use as liner of earthworks or for strengthening a clay soil. A WTS and a clayey soil was characterized in terms of granulometry, cumulative volumes, specific surface, density, plastic limit, liquid limit, water content, hydraulic conductivity, and characteristics of compaction (optimal water content and dry density). This study aimed to exhibit and evaluate these investigated parameters of WTS, soft soil and mixed proportions between the materials for liners’ material production while evaluating soft soils’ reinforcement feasibility. The results have shown WTS’s contribution with its fine granulometry and compaction characteristics, indicating filling properties and possible feasibility as soft soils additions for liners’ material production while being applicable for soils‘ reinforcements, corroborating with existing literature on the subject. Thus, the currently developed investigation has exposed WTS as a potential addition for these applications while also attending society’s new demands towards a more sustainable future.
- Mechanical and Chemical Behaviour of Water Treatment Sludge and Soft Soil Mixtures for Liner ProductionPublication . Marchiori, Leonardo; Studart, André; Albuquerque, Antonio; Andrade Pais, Luís; Boscov, Maria Eugenia Gimenez; Cavaleiro, VictorBackground: Clay-based and geosynthetic liners are generally used as hydraulic barriers in solid waste disposal facilities, mining tailing ponds, and soil-based wastewater treatment technologies, avoiding the leaching of hazardous compounds into subsoil and groundwater. Water treatment sludge (WTS) is a water treatment plant (WTP) residue which due to hydraulic properties seems to decrease the permeability in WTS:soil mixtures and may become an alternative material to produce sustainable waste-based liners. Objectives: This research aims to characterize and analyse physical, chemical and mechanical parameters of a WTS, a soft soil and four mixtures WTS:soil following 05:95%, 10:90%, 15:85%, 20:80% ratios, Thereby, evaluating the best ratio for producing waste-based liners for civil engineering applications. Methods: The geotechnical characterization was performed for particle size distribution, specific surface, specific gravity, Atterberg limits, and Normal Proctor compaction; chemical composition due to oxides analyses through X-ray fluorescence (XRF), mineralogical description by X-ray diffraction (XRD) and scanning electron microscope (SEM) with energy dispersive spectrometer (EDS) coupled for imaging; and mechanical behavior performing - –oedometric consolidation, consolidated undrained (CU) triaxial, and falling head permeability. Tests were conducted for all mixtures, the soil, and WTS, with pointed-out exceptions. Results and Discussion: The results showed that the fine-grained WTS filled the soil voids but rearranged soil particles, thus, compacted dry unit weight decreased with WTS addition, probably due to its chemical composition with high amounts of aluminium and silica. The compressibility of the compacted mixtures did not differ significantly compared to the soil, while the shear strength analysis demonstrated a reduction in cohesion and an increase in the effective internal friction angle proportional to WTS addition. Hydraulic conductivity increased with WTS until 10% of residue introduction, decreased for 15%, and continued to decrease for 20%, reaching optimum permeability at 15%. Conclusion: The incorporation of WTS can improve or just not interfere with soil’s properties to be used as liner material in solid wastes storage facilities, mining ponds and soil-based wastewater treatment technologies. Furthermore, 15% of WTS (15:85% mixture) incorporation provided the best results meeting the hydraulic conductivity requirement for liner materials, i.e., equal, or lower than 10-9 m/s. The reuse of WTS for this purpose would allow producing a new added-value material in the scope of circular economy.
- Cracking and desiccation of water treatment sludge for incorporation into soils for alternative liner material productionPublication . Marchiori, Leonardo; Morais, Maria Vitoria; Albuquerque, Antonio; Ferreira-Gomes, L.M.; Cavaleiro, VictorCracks may lead to hydraulic failure in soils due to increase of hydraulic conductivity which facilitate water infiltration, impacting negatively for liner materials. Therefore, cracking and desiccation investigation on liner material is advised. Water treatment sludge (WTS) is a by-product resulting from water treatment plants, and it seems to be suitable for geotechnical applications and soil replacement due to hydraulic latent properties, chemical similarities to soils, and mechanical behaviour. In this work WTS samples were incorporated into soil in different ratios – 05%; 10%; 15% and 20% of waste in dried mass of the geocomposites. The four mixtures, a soil sample and a WTS were tested according to the following procedure: two different circular Petri dishes samples were used, 5mm(H5) and 10mm(H10), and two cylindrical compacted samples with 65-70mm of diameter and 20-140mm of height (EDO-TRI, respectively) - dried for 10 days in controlled temperature and humidity. Water release curves (WRC), digital images correlation supported Crack Intensity Factor (CIF) index results were obtained for each material. Cracking behaviour results were compared with the permeability through falling head laboratorial tests, and studies around WTS ratio. Composites with 10% and 15% had the best results, showing no cracks during Petri dishes procedures for H10, in addition, the permeability for these materials reached the maximum for liner production – 10-9 m/s according to European and American directives - making possible the development of an alternative and feasible liner material.