Mohamed Boutouil

Trace element mobility in a polluted marine sediment after stabilisation with hydraulic binders.

Abstract The management of dredged marine sediment is an issue for many harbours, particularly when contaminant concentrations prevent disposal at sea. The stabilisation/solidification of the sediments with hydraulic binders for a use in road subgrade layer is a potential alternative solution. However, the environmental acceptability is not yet fully established. This paper presents the results of a case study to comprehensively determine the stabilisation of As, Cd, Cr, Cu, Ni, Pb and Zn. After demonstrating that stabilisation/solidification affects the microstructure of the sediment, a mobility study is realised (single, sequential and kinetic extractions). According to the regulatory/technical guidelines the studied elements do not pose a risk to the environment. However, results from more complex mobility studies reveal that stabilisation in the short term is only effective for Ni while other elements are mobilised after treatment by at least one type of extraction. Stabilisation in the long term is not universally effective.

Influence of chloride and sulfate ions on the geotechnical properties of soils treated with hydraulic binders

The reuse of soils after adding binder agents results in the improvement of their physical and mechanical characteristics, allowing them to be reused in several geotechnical applications. Our ongoing research work is aiming at assessing the influence of chloride and sulfate ions, introduced as NaCl and CaSO4·2H2O, on physical and mechanical properties of treated soils. At 10 g·kg−1 of dry soil, the chloride ions’ presence can affect the stabilisation process of treated soils with hydraulic road binder, but the strengths are still suitable for a reuse in sub-base layer. With the same content, sulfate ions can generate an important swelling, along with losses of strengths during suitability tests. In standard cure, these losses are less severe.

Beneficial reuse of Brest-Harbor (France)-dredged sediment as alternative material in road building: laboratory investigations

ABSTRACT The scarcity of natural aggregates promotes waste reuse as secondary raw material in the field of civil engineering. This article focuses on the beneficial reuse of marine-dredged sediments in road building. Thus, mixtures of raw sediments and dredged sand collected from Brest Harbur (Bretagne, France) were treated with road hydraulic binders. Formulation were prepared and characterized as recommended by the French Technical Guidelines for soil treatment with lime and/or hydraulic binders. Mechanical resistance results are quite similar for both the hydraulic binders, suggesting a similar reactivity with the studied sediment sample. However, some discrepancies can be noted on sustainability parameters. Indeed, water resistance after immersion at 40°C is significantly better for the mixtures treated with cement containing more glass-forming oxides (SiO2 + Al2O3) and fluxing (Fe2O3+CaO + MgO + K2O + Na2O). Moreover, the both hydraulic binders can lead to swelling in the road materials as observed in scanning electron microscopy analyses. Indeed, microscopic observations indicated volumetric swelling of treated samples, which is greatly influenced on the one side by ettringite quantity and on the other hand by the presence of water in pores material.

Geotechnical and mineralogical characterisations of marine-dredged sediments before and after stabilisation to optimise their use as a road material

ABSTRACT Dredging activities to extend, deepen and maintain access to harbours generate significant volumes of waste dredged material. Some ways are investigated to add value to these sediments. One solution described here is their use in road construction following treatment with hydraulic binders. This paper presents the characterisation of four sediments, in their raw state and after 90 days of curing following stabilisation treatment with lime and cement, using a combination of novel and established analytical techniques to investigate subsequent changes in mineralogy. These sediments are classified as fine, moderately to highly organic and highly plastic and their behaviour is linked to the presence of smectite clays. The main minerals found in the sediments using X-ray diffraction (XRD) and automated mineralogy are quartz, calcite, feldspars, aluminium silicates, pyrite and halite. Stabilisation was found to improve the mechanical performances of all the sediments. The formation of cementitious hydrates was not specifically detected using automated mineralogy or XRD. However, a decrease in the percentage volume of aluminium silicates and aluminium-iron silicates and an increase of the percentage volume of feldspars and carbonates was observed.

Geotechnical properties of cement treated sediment: influence of the organic matter and cement contents

Abstract Organic matter (OM) is reported to affect some of the soil properties and hydration processes in case of cementbased treatment. This paper presents investigations on the influence of organic matter on the geotechnical properties of cement-based solidified sediment with naturally high OM content (7%). Moreover, this sediment was treated to provide two other OM content materials: 2 and 5%. Grain size distribution, Atterberg limits, one dimensional compression and microstructure analyses were performed on raw sediment and on sediments treated with 2, 5 and 10% cement. The geotechnical properties appear to be affected by both cement and OM contents. Investigations show an increase in grain size distribution with increasing cement contents. Furthermore, an increase in the OM content is believed to produce an increase in the Atterberg limits of the sediment before and after cement addition. With the same cement content, the developed preconsolidation pressure of treated sediments decreases when the OM content increases. After a 28 days curing period, the preconsolidation pressure σ′p of sediments with OM contents of 2, 5 or 7% reaches 160, 60 and 50kPa, respectively, for a 5% cement treatment and 400, 310 and 210kPa for a 10% cement treatment. Finally, for all OM contents, the compression index Cc increases with increasing cement content. It reaches its maximal value for 5% cement treatment and tends to decrease over. Compared with raw sediment, the compression of cement-treated sediments is characterized by faster primary consolidation.

Trace and major elements’ stabilisation in soils treated with hydraulic binders

Our ongoing research work is aimed at assessing the influence of a treatment of soils with hydraulic binders on the stabilisation of trace elements. For three soils treated according to two standard formulations, the stabilisation of trace (As, Cd, Cr, Cu, Ni, Pb and Zn) and major elements (Al, Ca, Fe, S and Si) is not systematically effective. After 28 days of treatment, an increase of Cu concentrations on the water soluble fraction in soils 1 and 2 is observed. The concentrations in Al, Ca, S, Si also increase: the elements are mobilised in the interstitial solution of soils to form hydrates. After 180 days, the concentrations of Cr, Cu and Ni on the fraction dissolved in water is greater than at 28 days for some mixtures of soils and binders. The concentrations in Si decrease. It could prove a calcium silicate hydrates formation.