Influence of fine sediments on rheology properties of self-compacting concretes

Environmental, economic and experimental assessment of the valorization of dredged sediment through sand substitution in concrete

The integrated life cycle assessment (LCA), life cycle cost assessment (LCC) and laboratory-based experimental assessment were applied to provide insight for early stage decision-making on the valorization of the dredged sediments. The objective was to find a viable and sustainable solution for the valorization of the dredged sediment in concrete, holding up a certain level of standard concrete performance without compromising in terms of economy and environment. For the sensitivity analysis, parametric life cycle inventories were developed to assess the sensitivity of environmental and economic costs to the rate of sand substitution by sediment, as well as the variations in the concrete components. The workability of fresh concrete and the compressive strength of hardened concrete at 28 days were assigned as the quality indicators to evaluate the influence of sand substitution by sediment on the concrete performance. The compressive strength evaluation in the laboratory demonstrated that a maximum rate of sand substitution in concrete up to 40 % by predominantly sandy sediment could sustain the concrete strength class. However, LCA and LCC negated the rate of sand substitution by sediment higher than 20 %. The integrated environmental, economic, and experimental assessments demonstrated that the substitution of sand by predominantly fine sediment downgrades the strength class of concrete, even in the low rate of incorporation (10 %) and increases the environmental and economic costs. Inferred from the results, the maximum rate of sustainable sand substitution by sediment in concrete could be optimized through a compromise between the expected mechanical strength and workability of the concrete, the economic and environmental impacts of the superplasticiser and the sediment transport. Overall, integrating environmental and economic cost assessments into the laboratory-based assessment of the valorization scenarios would determine the threshold for the sustainable rate of incorporation of sediment in valorization scenarios.

Life cycle assessment of cementitious materials based on calcined sediments from Chorfa II dam for low carbon binders as sustainable building materials

This research was carried out to reuse calcined dredged sediments as a sustainable building material to reduce greenhouse gas emissions, and save significant energy consumption and costs. Moreover, the Life Cycle Assessment (LCA) of cementitious materials (cements, pastes, and mortars) based on calcined sediments was studied in order to quantify its energy consumption and Global Warming Potential (GWP). This study demonstrated that this calcined sediment could be used as a partial cement replacement in the cement industry in Algeria. The potential indicators of climate change for cements based on 0%, 5%, 15%, and 25% of calcined sediments release only 935.10 kg CO₂ eq/T, 901.73 kg CO₂ eq/T, 835 kg CO₂ eq/T and 768.29 kg CO₂ eq/T respectively, which represents a significant reduction of 3.57%, 10.70%, and 17.84%, for cement based on 5%, 15%, and 25% of calcined sediment. The potential indicators of climate change for pastes based on calcined sediments at 0%, 5%, 15%, and 25% rates release only 476.95 kg CO₂ eq/T, 459.79 kg CO₂ eq/T, 425.45 kg CO₂ eq/T, and 391.12 kg CO₂/T respectively, which represents a reduction of 3.6%, 10.80%, and 18%. Indeed, the potential indicators of climate change for mortars based on calcined sediments with 0%, 5%, 15%, and 25% rates release only 436.89 kg CO₂ eq/T, 422.00 kg CO₂ eq/T, 393.07 kg CO₂ eq/T, and 364.40 kg CO₂/T respectively, which represents a reduction of 3.41%, 10.03%, and 16.59%. In conclusion, the LCA of cements, mortars, and pastes with a high substitution rate of calcined sediments offer the best reduction in environmental impacts. These results present prospects for industrializing calcined sediments as green building materials in the cement industry.

Reuse of Untreated Fine Sediments as Filler: Is It More Beneficial than Incorporating Them as Sand?

Large amounts of sediments are dredged each year to ensure navigation. These materials, classified as waste, seem to be promising alternatives to conventional construction materials. Dredging operations, carried out by the Territorial Directorate of the Seine Basin (DTBS), generate an annual volume of sediments of about 150,000 m3, of which nearly 50% are fine sediments (<80 μm). For these fine sediments, it is necessary to look for possible ways of valorisation, knowing that the coarse sediments, sands and gravels are already easily reused in concrete. The valorisation of fine sediments, such as concrete with 30% sand, has already been evaluated. However, it was found to significantly affect concrete performance; it extends setting time from 3 to 18 h, decreases compressive strength by an average of 50% and increases shrinkage deformation up to 200%. This paper seeks to evaluate the effects of ten different fine sediments, used as substitutes for 10% of cement by volume, on physico-chemical and mechanical properties. The experimental results show that fine sediments marginally affect concrete properties. The main peak of the released heat flux is delayed to less than 4 h, the compressive strength is decreased by 8% on average and the increase in shrinkage deformation does not exceed 17%, except for in two fine sediments. This incorporation method also has an environmental advantage over substituting 30% of concrete with sand, as it reduces CO2 emissions by almost 10% (instead of 0.2%).