Large quantities of dredged sediments and recycled concrete materials are generated every year all over the world. The disposal of these large quantities in landfills represents serious environmental ...problems. Furthermore, high-quality raw materials for construction are depleting, and their use cannot be sustained. The valorization of dredged sediments and recycled concrete materials as alternative construction materials has the potential to reduce the impact of these two issues. In this context, this study aims at investigating the feasibility of using dredged sediments and recycled concrete aggregates as alternative raw material for road subgrade construction. Various mix designs were prepared using dredged sediments and recycled concrete aggregates. The mixes were then treated with quicklime and road binder as specified in the French soil treatment guide. Their physical, mechanical, and geotechnical properties confirmed the feasibility of using recycled concrete aggregates and dredged sediments up to a certain percentage in road subgrade construction. Moreover, they showed that the mixes containing 20% of dredged sediments met road subgrade minimum physical and mechanical properties, such as immediate bearing capacity, unconfined compression strength, indirect tensile strength greater, and UCSI/UCS60 ratio. Finally, leaching tests were conducted to ensure the environmental safety of the various mixes. The results showed that the mixes met the thresholds for their use in road subgrade construction. The feasibility of using dredged sediments and recycled concrete aggregates in foundations and base layers will be studied in future projects.
The increase of energy valorization of paper sludge waste and biomass due to their high calorific value by incineration leads to an increase of waste paper fly ash (WPFA) quantities, which are in ...most cases considered as hazardous, and must be dealt with accordingly. The Alternative options for the management of WPFA, such as stabilization/solidification, vitrification or sintering, are not fully developed or either costly. In the present study, accelerated carbonation technology was used to reduce the hazardous nature of WPFA by improving the stabilization of metallic and metalloids trace elements (MMTE), especially Barium (Ba) and Lead (Pb) leaching. The accelerated carbonation of WPFA was found to be optimal at a water/solid ratio of 0.3 L/kg under controlled temperature and humidity conditions. The use of water saturated with 25% sodium bicarbonate (NaHCO3) improved the carbonation of WPFA and the stabilization of Ba and Pb. Batch leaching tests based on thermodynamic equilibrium was used to evaluate the solubility of the MMTE as a function of pH and at the natural pH of non‑carbonated and carbonated WPFA. Thermogravimetry, X-ray diffraction, scanning electron microscopes and energy dispersive spectroscopy analyses were performed to investigate the evolution of carbonation over time and its effect on the chemical and mineralogical properties of WPFA. After 30 days of accelerated carbonation, the leaching concentration of Ba and Pb was below the French legal limit. The leaching concentration of Ba and Pb from carbonated samples decreased 99% and 99.5% respectively. The leaching and release potential behavior of carbonated WPFA were further evaluated using the four-step sequential extraction procedure proposed by the Commission of the European Communities Bureau of Reference (BCR). The speciation of MMTE underwent significant transformation, shifting predominantly from the soluble fraction to the carbonated fraction as a result of the carbonation reaction.
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•Accelerated carbonation with NaHCO3 of WPFA has been performed.•Ba, Pb and Cl leaching concentration decreased effectively after carbonation.•After 15 days of accelerated carbonation, the WPFA becomes inert.•Parameters L/S = 0.3 l/kg, 20 °C/65 °C with NaHCO3 improves carbonation.•Ba and Pb was precipitated as carbonate BaCO3 and PbCO3
In this scientific investigation, we explore the potential of bottom ash from municipal solid waste incineration (MSWI), hereafter referred to as BA-MSWI, as an alternative to natural aggregates in ...epoxy mortar production. BA-MSWI bottom ash represents a prevalent environmental issue due to its excessive production, and its use in sustainable applications could help reduce the demand for natural aggregates. We conducted experiments by replacing natural sand with varying proportions of BA-MSWI (30–100%) and using epoxy resin (15–20%) as a binder. A packing density model was employed to optimize mixture compactness, calculate total porosity, and determine the required amount of resin. The results indicate a decrease in compressive strength and flexural strength when BA-MSWI is incorporated, but they enhance the thermal properties of the mortar. Importantly, the increased proportion of epoxy resin compensates for the loss of strength induced by the addition of BA-MSWI. From an environmental perspective, this research opens up possibilities for the utilization of BA-MSWI in various construction applications.
•Recycled concrete aggregate is evaluated as an additive for cement mixtures.•Various substitution levels are analysed both experimentally and numerically.•Mechanical, microstructural, and chemical ...changes are presented.•Fine powder shows significant potential as a cement additive.
The purpose of this study was to investigate the influence of fine powder (SF fines) obtained from recycled concrete aggregate on the hydration kinetics and mechanical–microstructural properties of hydrated cement through experiments and three-dimensional microstructural modelling using CEMHYD3D. Mixtures prepared with different substitution levels ranging from 0 % to 30 % by volume were examined. The experimental results indicated that the presence of calcite (CaCO3) and residual hydrates in SF powder accelerated the hydration of cement phases, particularly the C3A and C3S phases, at early ages. Increasing the SF fines substitution level led to an increase in the degree of hydration (DoH) of cement compared to that of the reference. The compressive strengths of mortars decreased with SF powder substitution levels; however, a substitution rate of 10 % led to a strength comparable to that of the reference. The modelling results also indicated that increasing the SF fines substitution level increased the DoH of cement. However, at very early ages, the hydration retardation of individual cement phases increased with increasing SF powder substitution levels, particularly for the C3A and C4AF phases. The findings of the study suggest that SF fines can act as fillers, increasing the nucleation zones for cement hydration reactions, and as silico-aluminous sources for pozzolanic reactions.
