Deep mixing technique to reinforce Loire levees are currently used. The techniques were implement... more Deep mixing technique to reinforce Loire levees are currently used. The techniques were implemented with dedicated trench-cutting equipment rotating so that cut-off wall could be continuous in the levee structure and its foundation. It resulted in a mixture between the soil in place, a hydraulic binder and water. Several formulations are tested for the soils of the levees and their foundation. Indeed, hardening issues appeared locally, on part of Orleans levee, linked to the presence of organic soils. It led to experiment several lime-cement formulations in the laboratory. Subsequently, the best soil-fitted formulation was tested in the lab and applied on site to validate the implementation. This included testing new control timeframes in terms of permeability and mechanical resistance. The properties of the deep mixing material were assessed by testing clay-cement materials, treated at different cement and water contents. Permeability and strength parameters were confronted to their physico-chemical and microstructural characteristics in order to explain the variations of the mechanical properties and better understand the behaviour of natural soils treated with this technique. In addition, differences appear between mixture built on site and in the laboratory in terms of hydraulic and mechanical properties but also in terms of soil inclusions.
Journal of Colloid and Interface Science, Jun 1, 2006
The sorption of selenite from aqueous solutions onto hematite was investigated as a function of p... more The sorption of selenite from aqueous solutions onto hematite was investigated as a function of pH (2-12), ionic strength (0.01-0.1 M), and concentration of selenium (10 -7 -10 -2 M). The sorption may proceed according to two processes: surface complexation, followed by the precipitation of ferric selenite starting at approximate [Se] = 4 Ă— 10 -4 M (surface coverage > ca. 2 at nm -2 ). The sorption isotherms have been fitted by a Tempkin equation. A surface complexation model (2-pK/Constant Capacitance Model) was used to fit the sorption data. The nature of the surface species of selenite cannot be determined by modeling since monodentate >FeO-Se(O)O -or >FeO-Se(O)OH and bidentate (>FeO) 2 SeO surface complexes are both able to fit the experimental data. The reversibility and kinetics of sorption were also studied. The affinity of selenite ions toward hematite, expressed as the distribution coefficient with respect to the surface area (K D in L m -2 ), was compared with results published for other ferric oxides (goethite and amorphous ferric oxide). It was found that the reactivity toward selenite is similar, contrary to acid-base properties which depend on the nature of the oxide and its level of purity.
The impact of the dissolved quantity of aluminum on the calculation of surface charge from titrat... more The impact of the dissolved quantity of aluminum on the calculation of surface charge from titration experiments of hydrated gamma-alumina was investigated. Two methods were developed to correct this effect: direct determination of aluminum in solution in batch titration experiments and application of a dissolution rate model in continuous titration experiments. There is a large effect of dissolution on surface charge determination for pH>10 and pH < 4.5. Application of these correction methods to these pH ranges lead to apparent saturation surface charges of 1.3 and 2.3 at nm(-2), respectively. The last value seems to be the real proton-active site density, while the hydroxyl-active site density cannot be reached for easily achievable basic pH values.
Acid-base properties of metal oxy-hydroxides are derived from their ability to gain or loose prot... more Acid-base properties of metal oxy-hydroxides are derived from their ability to gain or loose protons in aqueous solution in which they are immersed. According to the surface complexation theories, fixing or releasing protons induces variation of the surface charge of the solid. Acid-base properties and surface charge can be determined by several methods. Measurement of the mobility of particles in an electrolyte subjected to an electric field is associated with the ζ potential (zetametry). The accuracy on surface charge and on acid-base parameters depends greatly on the accuracy of pH measurements. An important step is the measurement of the “blank” or titration of the indifferent electrolyte without solid, because the amount of protons sorbed is the difference between the titration of the solid suspension and the blank. The chapter examines the errors associated with pH measurement and also discusses the different errors related to the physicochemical properties of the solid—kinetics of proton sorption, hydration and phase evolution, solubility of the solid, influence of impurities. A titration experiment consists in measuring the pH after successive additions of aliquots of an acid or a base of known concentration to a solid suspension of fixed concentration in an electrolyte.
Journal of Colloid and Interface Science, Aug 1, 2006
The present work addresses the protolytic charge of montmorillonite, which occurs on the broken-b... more The present work addresses the protolytic charge of montmorillonite, which occurs on the broken-bond sites at the particle edges. The purpose is to overcome the general difficulty arising in potentiometric titration due to coupled side reactions, which severely impede the titrant budget (partial dissolution of the clay and of secondary phases, hydrolysis and readsorption of dissolved species, cation exchange). Batch potentiometric titrations were carried out on the montmorillonite fractions extracted from two bentonites (MX80 and SWy2) to quantify their protolytic charge. The effects of equilibration time (24 h and 7 days), pH from 4 to 10, and ionic strength (0.1 and 0.01 mol L(-1)) were extensively studied for the MX80 sample. Quantification of dissolution was achieved by analysis of the equilibrium solutions for dissolved species and by La(3+) exchange of the readsorbed species. The results clearly show that secondary phases such as iron- or silica-rich minerals contribute to the dissolved species, according to the nature of the raw bentonite. Furthermore, readsorption affects significant amounts of dissolved species. The overconsumption of proton/hydroxide due to dissolution, readsorption, and hydrolysis of dissolved species was evaluated using a self-consistent thermodynamic calculation. The ability of such calculation to correct the raw titration curves in order to extract the titrable surface charge of montmorillonite was evaluated by comparison with the continuous titration procedure. Especially in the alkaline domain, correcting the raw batch titration curves for the measured side reactions failed to reproduce the continuous titration curves. These observations demonstrate the limitations of the batch titration method and the superiority of fast, continuous methods for quantifying the dissociable surface charge of clays.
Journal of Colloid and Interface Science, Sep 1, 2005
Measuring and modeling the surface charge of clays, and more especially smectites, has become an ... more Measuring and modeling the surface charge of clays, and more especially smectites, has become an important issue in the use of bentonites as a waste confinement material aimed at retarding migration of water and solutes. Therefore, many studies of the acid-base properties of montmorillonite have appeared recently in the literature, following older studies principally devoted to cation exchange. It is striking that beyond the consensus about the complex nature of the surface charge of clays, there are many discrepancies, especially concerning the dissociable charge, that prevents intercomparison among the published data. However, a general trend is observed regarding the absence of common intersection point on raw titration curves at different ionic strengths. Analysis of the literature shows that these discrepancies originate from the experimental procedures for the preparation of the clays and for the quantification of their surface charge. The present work is an attempt to understand how these procedures can impact the final results. Three critical operations can be identified as having significant effects on the surface properties of the studied clays. The first one is the preparation of purified clay from the raw material: the use of acid or chelation treatments, and the repeated washings in deionized water result in partial dissolution of the clays. Then storage of the purified clay in dry or wet conditions strongly influences the equilibria in the subsequent experiments respectively by precipitation or enhanced dissolution. The third critical operation is the quantification of the surface charge by potentiometric titration, which requires the use of strong acids and bases. As a consequence, besides dissociation of surface sites, many secondary titrant consuming reactions were described in the literature, such as cation exchange, dissolution, hydrolysis, or precipitation. The cumulated effects make it difficult to derive proper dissociation constants, and to build adequate models. The inadequation of the classical surface complexation models to describe the acid-base behavior of clays is illustrated by the electrokinetic behavior of smectites, which is independent from the pH and the ionic strength. Therefore, there is still a need on one hand for accurate data recorded in controlled conditions, and on the other hand for new models taking into account the complex nature of the charge of clays.
Case Studies in Construction Materials, Dec 1, 2021
Abstract Swelling clays characterized by their shrinkage and swelling phenomenon are known to be ... more Abstract Swelling clays characterized by their shrinkage and swelling phenomenon are known to be the main cause of cracking of paved roads. So, the road construction on swelling soils require knowledge and specific techniques, including the chemical stabilization with lime or cement addition. This technique favors the sustainable development by avoiding waste production especially soils. Indeed a maximum reuse of materials located in the building project area allows reaching the "zero loan, zero deposit" objective. In this paper, the efficiency of mixed treatment with lime and cement was tested on swelling karal-type soils collected at Pitoa in the North Cameroon region. The soil samples were characterized by applying microstructural and geotechnical tests (XRD, SEM, Particle Size Analysis, Atterberg Limits, Modified Proctor, CBR test, and Unconfined Compressive Strength (UCS)). The results showed that the mixed treatment of karal soils using a 2% of hydrated lime mixed with CaO or a 3% of low carbonated hydrated lime and 3, 5 or 7% of cement, reduced drastically the soil volume variation under water content change and improved the soil physico-mechanical properties. Finally, soils after treatment reached the minimum characteristics required for recovery in road construction.
Deep mixing technique to reinforce Loire levees are currently used. The techniques were implement... more Deep mixing technique to reinforce Loire levees are currently used. The techniques were implemented with dedicated trench-cutting equipment rotating so that cut-off wall could be continuous in the levee structure and its foundation. It resulted in a mixture between the soil in place, a hydraulic binder and water. Several formulations are tested for the soils of the levees and their foundation. Indeed, hardening issues appeared locally, on part of Orleans levee, linked to the presence of organic soils. It led to experiment several lime-cement formulations in the laboratory. Subsequently, the best soil-fitted formulation was tested in the lab and applied on site to validate the implementation. This included testing new control timeframes in terms of permeability and mechanical resistance. The properties of the deep mixing material were assessed by testing clay-cement materials, treated at different cement and water contents. Permeability and strength parameters were confronted to their physico-chemical and microstructural characteristics in order to explain the variations of the mechanical properties and better understand the behaviour of natural soils treated with this technique. In addition, differences appear between mixture built on site and in the laboratory in terms of hydraulic and mechanical properties but also in terms of soil inclusions.
Journal of Colloid and Interface Science, Jun 1, 2006
The sorption of selenite from aqueous solutions onto hematite was investigated as a function of p... more The sorption of selenite from aqueous solutions onto hematite was investigated as a function of pH (2-12), ionic strength (0.01-0.1 M), and concentration of selenium (10 -7 -10 -2 M). The sorption may proceed according to two processes: surface complexation, followed by the precipitation of ferric selenite starting at approximate [Se] = 4 Ă— 10 -4 M (surface coverage > ca. 2 at nm -2 ). The sorption isotherms have been fitted by a Tempkin equation. A surface complexation model (2-pK/Constant Capacitance Model) was used to fit the sorption data. The nature of the surface species of selenite cannot be determined by modeling since monodentate >FeO-Se(O)O -or >FeO-Se(O)OH and bidentate (>FeO) 2 SeO surface complexes are both able to fit the experimental data. The reversibility and kinetics of sorption were also studied. The affinity of selenite ions toward hematite, expressed as the distribution coefficient with respect to the surface area (K D in L m -2 ), was compared with results published for other ferric oxides (goethite and amorphous ferric oxide). It was found that the reactivity toward selenite is similar, contrary to acid-base properties which depend on the nature of the oxide and its level of purity.
The impact of the dissolved quantity of aluminum on the calculation of surface charge from titrat... more The impact of the dissolved quantity of aluminum on the calculation of surface charge from titration experiments of hydrated gamma-alumina was investigated. Two methods were developed to correct this effect: direct determination of aluminum in solution in batch titration experiments and application of a dissolution rate model in continuous titration experiments. There is a large effect of dissolution on surface charge determination for pH>10 and pH < 4.5. Application of these correction methods to these pH ranges lead to apparent saturation surface charges of 1.3 and 2.3 at nm(-2), respectively. The last value seems to be the real proton-active site density, while the hydroxyl-active site density cannot be reached for easily achievable basic pH values.
Acid-base properties of metal oxy-hydroxides are derived from their ability to gain or loose prot... more Acid-base properties of metal oxy-hydroxides are derived from their ability to gain or loose protons in aqueous solution in which they are immersed. According to the surface complexation theories, fixing or releasing protons induces variation of the surface charge of the solid. Acid-base properties and surface charge can be determined by several methods. Measurement of the mobility of particles in an electrolyte subjected to an electric field is associated with the ζ potential (zetametry). The accuracy on surface charge and on acid-base parameters depends greatly on the accuracy of pH measurements. An important step is the measurement of the “blank” or titration of the indifferent electrolyte without solid, because the amount of protons sorbed is the difference between the titration of the solid suspension and the blank. The chapter examines the errors associated with pH measurement and also discusses the different errors related to the physicochemical properties of the solid—kinetics of proton sorption, hydration and phase evolution, solubility of the solid, influence of impurities. A titration experiment consists in measuring the pH after successive additions of aliquots of an acid or a base of known concentration to a solid suspension of fixed concentration in an electrolyte.
Journal of Colloid and Interface Science, Aug 1, 2006
The present work addresses the protolytic charge of montmorillonite, which occurs on the broken-b... more The present work addresses the protolytic charge of montmorillonite, which occurs on the broken-bond sites at the particle edges. The purpose is to overcome the general difficulty arising in potentiometric titration due to coupled side reactions, which severely impede the titrant budget (partial dissolution of the clay and of secondary phases, hydrolysis and readsorption of dissolved species, cation exchange). Batch potentiometric titrations were carried out on the montmorillonite fractions extracted from two bentonites (MX80 and SWy2) to quantify their protolytic charge. The effects of equilibration time (24 h and 7 days), pH from 4 to 10, and ionic strength (0.1 and 0.01 mol L(-1)) were extensively studied for the MX80 sample. Quantification of dissolution was achieved by analysis of the equilibrium solutions for dissolved species and by La(3+) exchange of the readsorbed species. The results clearly show that secondary phases such as iron- or silica-rich minerals contribute to the dissolved species, according to the nature of the raw bentonite. Furthermore, readsorption affects significant amounts of dissolved species. The overconsumption of proton/hydroxide due to dissolution, readsorption, and hydrolysis of dissolved species was evaluated using a self-consistent thermodynamic calculation. The ability of such calculation to correct the raw titration curves in order to extract the titrable surface charge of montmorillonite was evaluated by comparison with the continuous titration procedure. Especially in the alkaline domain, correcting the raw batch titration curves for the measured side reactions failed to reproduce the continuous titration curves. These observations demonstrate the limitations of the batch titration method and the superiority of fast, continuous methods for quantifying the dissociable surface charge of clays.
Journal of Colloid and Interface Science, Sep 1, 2005
Measuring and modeling the surface charge of clays, and more especially smectites, has become an ... more Measuring and modeling the surface charge of clays, and more especially smectites, has become an important issue in the use of bentonites as a waste confinement material aimed at retarding migration of water and solutes. Therefore, many studies of the acid-base properties of montmorillonite have appeared recently in the literature, following older studies principally devoted to cation exchange. It is striking that beyond the consensus about the complex nature of the surface charge of clays, there are many discrepancies, especially concerning the dissociable charge, that prevents intercomparison among the published data. However, a general trend is observed regarding the absence of common intersection point on raw titration curves at different ionic strengths. Analysis of the literature shows that these discrepancies originate from the experimental procedures for the preparation of the clays and for the quantification of their surface charge. The present work is an attempt to understand how these procedures can impact the final results. Three critical operations can be identified as having significant effects on the surface properties of the studied clays. The first one is the preparation of purified clay from the raw material: the use of acid or chelation treatments, and the repeated washings in deionized water result in partial dissolution of the clays. Then storage of the purified clay in dry or wet conditions strongly influences the equilibria in the subsequent experiments respectively by precipitation or enhanced dissolution. The third critical operation is the quantification of the surface charge by potentiometric titration, which requires the use of strong acids and bases. As a consequence, besides dissociation of surface sites, many secondary titrant consuming reactions were described in the literature, such as cation exchange, dissolution, hydrolysis, or precipitation. The cumulated effects make it difficult to derive proper dissociation constants, and to build adequate models. The inadequation of the classical surface complexation models to describe the acid-base behavior of clays is illustrated by the electrokinetic behavior of smectites, which is independent from the pH and the ionic strength. Therefore, there is still a need on one hand for accurate data recorded in controlled conditions, and on the other hand for new models taking into account the complex nature of the charge of clays.
Case Studies in Construction Materials, Dec 1, 2021
Abstract Swelling clays characterized by their shrinkage and swelling phenomenon are known to be ... more Abstract Swelling clays characterized by their shrinkage and swelling phenomenon are known to be the main cause of cracking of paved roads. So, the road construction on swelling soils require knowledge and specific techniques, including the chemical stabilization with lime or cement addition. This technique favors the sustainable development by avoiding waste production especially soils. Indeed a maximum reuse of materials located in the building project area allows reaching the "zero loan, zero deposit" objective. In this paper, the efficiency of mixed treatment with lime and cement was tested on swelling karal-type soils collected at Pitoa in the North Cameroon region. The soil samples were characterized by applying microstructural and geotechnical tests (XRD, SEM, Particle Size Analysis, Atterberg Limits, Modified Proctor, CBR test, and Unconfined Compressive Strength (UCS)). The results showed that the mixed treatment of karal soils using a 2% of hydrated lime mixed with CaO or a 3% of low carbonated hydrated lime and 3, 5 or 7% of cement, reduced drastically the soil volume variation under water content change and improved the soil physico-mechanical properties. Finally, soils after treatment reached the minimum characteristics required for recovery in road construction.
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