Development of a new alkali-activated binder incorporating dredged sediments

Alkali activated materials (AAMs) are known to be alternative binders to Ordinary Portland Cement (OPC) since the latter has the disadvantage of emitting large amounts of CO2 during its manufacture. Indeed, industrial by-products such as blast furnace slag (BFS) have been the main precursors in the alkali-activation reactions. On the other hand, dredging operations in the marine ports result in the formation of large volumes of sediment. In Europe, 100-200 Mm3 of sediment are dredged annually, and future regulations tend to restrict their immersion at the sea. The valorisation of a part of these sediments as raw materials in the composition of binders would contribute to limit the depletion of natural resources. So the aim of this work is oriented towards the development of a new type of alkali-activated mineral binder, based on blast furnace slag, incorporating dredged sediments. This study aims to assess the effects of sedimentary additions on the properties of the new binder. Parameters affecting the alkali-activation of BFS were fixed (nature of the activator: a solution of Na2SiO3 and NaOH with 5% Na2O and an activator modulus Ms equals to 1.45, while the Water/Solid ratio is set at 0.45). Then, variable percentages of sediments between 0 and 30% were incorporated into the studied formulations of the alkali-activated materials (MAAs), while W/S varied in order to maintain a constant workability. The effects of these sedimentary additions on the properties of the obtained material were studie

Kinetics of lime/bentonite pozzolanic reactions at 20 and 50 °C: Batch tests and modeling

International audienceThe effects of duration (1-100 days) and temperature (20 and 50 °C) were assessed from batch tests for Ca-bentonite mixed with 10 wt.% lime. The pozzolanic processes were monitored over time by 29Si NMR (Cement Concr. Res. 42, 2012), TGA-DTA, XRD and chemical analysis. Modeling considered kinetics and thermodynamics of mineralogical transformations and cation exchange. Kinetic laws were dependent on pH and temperature (Arrhenius energy). Lime hydration occurs within hours, modifying the bentonite exchangeable population and increasing the pH. These alkaline conditions initiate the pozzolanic reactions in a second stage. The rate-limiting step is the dissolution kinetics of the bentonite minerals, i.e. a relatively fast and total consumption of cristobalite in parallel to a long-term slower dissolution of montmorillonite. First C-S-H and then C-A-S-H are formed consequently. Temperature speeds up the pozzolanic reaction kinetics by a factor 5 from 20 to 50 °C, corresponding to an apparent activation energy of 40-50 kJ/mol

Multi-scale analysis on soil improved by alkali activated fly ashes

The development of soil treatment techniques using alkali-activated binders is a relevant issue since the increasing interest into the use of new binders as an alternative solution for geotechnical engineering applications, such as soil improvement. Alkali activated binders are formed by alkaline activation of an aluminosilicate source, containing precursor materials like fly ash, silica fume, steel sludge, which chemically react with an alkaline solution (i.e. sodium hydroxide, sodium silicate) forming a three-dimensional aluminosilicate gel with cementitious properties (Duxon et al. 2007, Provis and van Deventer 2014, Davidovits 1991, Xu and van Deventer 2000, Shi et al. 2006). Recycling of waste materials such as by-product from industrial process to synthesize a new binder favors a closed loop of material use, which minimizes the generation of waste and reduces the costs of production. Alkali activated binders represent a viable sustainable alternative to the use of ordinary binders for soil improvement (Vitale et al. 2017a; Vitale et al. 2017b). In the present study, an insight into the mechanical improvement induced by alkali-activated binders based on the activation of two different type of fly ashes on a clayey soil has been presented. An experimental multiscale analysis on chemo-physical evolution of the systems and its influence on microstructural features of treated soil has been developed highlighting the link between alkaline activation processes and macroscopic evolution of soil properties. Mechanical tests have been performed and interpreted taking into account the chemo-physical evolution of alkali activated fly ashes. Effects of binder content and curing time have been also considered. Addition of alkali-activated binders increases shear strength of the treated samples since the very short term. A reduction of compressibility and an increase of yield stress of treated samples have been also detected, whose extent depends on the curing time and on the binder content. Macroscopic behaviour of treated soil has been linked to the experimental evidences at microscale. Mineralogical and fabric changes induced by alkali-activated binders have been monitored over time by means of X ray diffraction (XRD), thermogravimetric analysis, 29Si NMR spectroscopy and Mercury Intrusion Porosimetry (MIP). Test results showed a high reactivity of alkali activated fly ashes as alumino-silicate source promoting precipitation of new mineralogical phase forming chains and networks with cementitious properties, responsible of the mechanical improvement of the treated soil. The efficiency of treatment has been also highlighted by comparing the mechanical performance induced by alkali-activated binder with the one promoted by ordinary Portland cement. Duxon P., Fernàndez-Jiménez A., Provis J.L., Lukey G.C., Palomo A., van Deventer J.S.J (2007). Geopolymer Technology: The Current State of the Art. Journal of Materials Science 42, 9, 2917-2933. Provis J.L., van Deventer J.S.J (2014). eds. Alkali Activated Materials. Vol.13. RILEM State of the Art Reports. Dordrecht: Springer Netherlands. Davidovits J. (1991). Geopolymers: inorganic polymeric new materials. J Therm Anal, 37,1633-1656. Xu H., van Deventer J.S.J. (2000). The geopolymerisation of alumina-silicate minerals. Int J Miner Process, 59, 247-266. Shi C., Krivenko P.V., Roy D.M. (2006). Alkali-activated Cements and Concretes. Abington, UK, Taylor and Francis. Vitale E., Coudert E., Deneele D., Paris M., Russo G. (2017a). Multiscale analysis on a kaolin improved by an alkali-activated binder. Proceedings of the 2nd Symposium on Coupled Phenomena in Environmental Geotechnics (CPEG2), Leeds, UK. Vitale E., Russo G., Dell’Agli G., Ferone C., Bartolomeo C. (2017b). Mechanical behaviour of soil improved by alkali activated binders. Environments, 4, 80, doi:10.3390/environments4040080

Use of alkali activated high-calcium fly ash binder for kaolin clay soil stabilisation : physicochemical evolution

This study addresses the use of alkali activated high-calcium fly ash-based binder to improve engineering characteristics of soft clay-rich soils as an alternative to common stabilisers. The physico-chemical reaction sequence has been investigated by considering the binder alone and the binder mixed with kaolin. An insight into the reactivity evidenced that calcium-containing phases derived from high-calcium fly ash represent the reactive phases and, hence, pozzolanic activity is the dominant process. New compounds are formed, thenardite Na2SO4 and an amorphous silicate consisting of chains combined with calcium probably incorporating three-dimensional four-fold aluminium environments

Exploration of the phase composition of activated calcined clay-slag mixtures using 27Al and 29Si MAS NMR spectroscopy

Please click Additional Files below to see the full abstract

Influence of pore water chemistry on hydaulic conductivity of kaolinite suspensions

The role of pore water chemistry on particle aggregation and soil formation during sedimentation process has been investigated for a kaolinite clay suspensions. The modification of surfaces charge properties of clay minerals induced by different pore water chemistry rules the particles arrangement. As a consequence, at volume scale the sedimentation behaviour and in turn the physical, mechanical and hydraulic behaviour of the formed soil skeleton are changed. Sedimentation tests on several suspensions showed the influence of different aggregation on settling and self-weight consolidation stages. Hydraulic conductivity of kaolin suspensions has been estimated from the settling velocity recorded in sedimentation tests. Test results showed the relevant dependency of the hydraulic conductivity of the clay suspensions on the particle arrangement induced by the pore water chemistry

Microstructural evolution and mechanical behaviour of alkali activated fly ash binder treated clay

This work focuses on the use of alkali activated fly ash-based binder to enhance engineering characteristics of soft clay-rich soils and as a substitute to standard stabilisers (e.g., lime or cement). Especially, it examines the microstructural evolution of a calcium-rich fly ash from coal combustion-based binder activated by a sodium-based alkaline solution. To this end, the processes generating the microstructure and the evolution of the pore network over time are investigated. A second point addressed by this study is how the presence of kaolin particles affects the microstructural features of the binder. The microstructure has therefore been investigated by considering the binder alone and the binder mixed with kaolin. The effects of microstructural evolution have been observed at macroscopic level by means of one-dimensional compression tests. The combination of completing techniques has been used including Optical microscopy, Scanning Electron Microscopy and Mercury Intrusion Porosimetry in order to gain an overview of the complex pore structure. Microstructural changes occur around calcium-containing phases derived from fly ash which are the reactive phases of the system. Namely, the dissolution of calcium-rich grains leads to the formation of new compounds that first cover the grain surfaces and then further grow into the available space. Furthermore, the evolution of the pore network over time is characterized by a progressive filling of capillary pores by new compounds while small nanometric pores are being formed and associated with the newly formed silicate-calcium chains. Similar tendencies are observed when the binder is mixed with the soil although the general porosity is lesser due to the filling of pores by small-sized kaolinite platelets. Experimental evidences at microscale level have been linked to the macroscopic behaviour of treated soil

Environmental assessment of the behavior of a BOF steel slag used in road construction : the PRECODD-ECLAIR research program

International audienceSteel production generate great amounts of by-products as steel slags. The use of Basic Oxygen Furnace slags (BOF slags) has been restrained due to insufficient volume stability, and due to the lack of environmental regulations. The purpose of the PRECODD-ECLAIR research program is to develop a behavior model based on a multi-scale physico-chemical, mechanical, hydrodynamic and ecotoxicological characterizations of a BOF slag used in a public works scenario. This paper aims at presenting the overall ECLAIR research program, the equipped experimental platform constructed using a BOF steel slag, and the first results of the slag characterization

Caractérisation, simulations expérimentales et thermodynamiques de l'altération de déchets vitreux (les scories de première fusion de plomb et de zinc)

Depuis plus de 50 ans, l'usine Métaleurop de Noyelles-Godault (Nord) produit du plomb, du zinc et des déchets associés (scories, poussières). Stockés en crassier, dispersés dans les sols ou l'atmosphère, ces déchets peuvent relarguer des éléments nocifs (Pb, Zn, Cd) lors de leur altération. Ce travail a porté sur la caractérisation et la simulation expérimentale et thermodynamique de l'altération des scories de première fusion de plomb et de zinc de cette usine. Une caractérisation des scories fraîches (DRX, MEB-EDS, Microsonde électronique, RAMAN) a d'abord été menée. Les scories sont composées d'un verre alumino-silicaté riche en Fe, Ca, Pb, Zn dans lequel sont dispersés des spinelles et des goutelettes de plomb. La scorie de zinc présente également des sulfures et un assemblage à fer métal, sulfures et composés métalliques de As, Sn, Sb, Ni, Cu, Z, et Fe. La nature des minérais, des produits secondaires et des fondants employés ainsi que les différents traitements métallurgiques (grenaillage du laitier) contrôlent les caractères pétrophysiques des scories. L'altération naturelle a ensuite été étudiée sur des scories sur un crassier depuis environ 10 ans. Intense dans la scorie de zinc, elle montre une dissolution des assemblages métalliques, des sulfures et des billes de plomb. L'acidité engendrée par la dissolution des sulfures entraîne localement la dissolution du verre et une mobilisation des métaux. Le fer re-précipite sous forme d'oxy-hydroxydes (x-FeOOH), qui fixent les métaux (Pb, As, Zn) mais aussi les sulfates. Le plomb est contrôlé par la précipitation d'oxydes (litharge, massicot), de carbonates (cérusite et hydrocérusite) et d'oxy-sulfates (xPbO, PbSO4). Des essais de lixiviation de 300 jours pour deux pH acides en système fermé ont simulé expérimentalement l'altération des scories. Pour ces deux pH initiaux, les concentrations en solution sont faibles et les produits ...LILLE1-BU (590092102) / SudocSudocFranceF