In the present study, the effects of structure induced by different binder treatments, namely lime, cement and a fly ash based alkali activated binder, on the mechanical behaviour of a fine-grained soil are experimentally investigated. The addition of chemical agents and the resulting chemo–physical reactions within the soil–water–binder system affect both the arrangement of soil particles and the nature of interparticle bonding, altering the hydro-mechanical response of the treated soil. A comprehensive understanding of these interactions requires a multi-scale experimental approach that links the processes occurring at the particle level with the macroscopic mechanical response. Experimental analyses are conducted to monitor the evolution of the mechanical properties and the microstructural features of the treated soil, interpreted in light of the chemo-physical transformations occurring within the system. Lime modifies the pore water chemistry and promotes pozzolanic reactions with clay minerals, leading to particles aggregation and formation of stable phases responsible for mechanical improvement. Cement and alkali-activated binders, in contrast, mainly produce cementitious compounds that enhance the stiffness and reduce the compressibility of the soil skeleton. The results evidence the strong coupling between chemical evolution, microstructural rearrangement, and mechanical performance, highlighting the effectiveness of multi-scale approaches for understanding the effects of structure on the behaviour of treated soils.

In this paper, a comparative microstructural analysis of systems hydrated beyond 200 days was conducted to explain drastic changes in transport properties, as measured with bulk electrical conductivity measurements. Cement pastes with three types of binders were analysed: an OPC, a Portland Limestone Cement (PLC) comprising 70

Laboratory investigations on the carbonation of lime- and cement-treated soils were mostly conducted by using a carbon dioxide content up to about 10%, which is much higher than atmospheric carbon dioxide (approximate to 0.03%). Therefore, the present study examines the physicochemical, pore structure, and compressive strength evolution of lime- and cement-treated specimens by exposing the top surface of the specimens to 0.3% carbon dioxide content. The study examines carbonation's impact on silty and sandy soils. Specimens treated with 2.5% quicklime, 5% cement, or a mixture of 1% quicklime and 5% cement underwent 28 days of carbonation. The strength obtained was maximum for carbon dioxide-exposed cement-treated soils, followed by combined lime-and-cement-treated soils, and then lime-treated soils. All carbon dioxide-exposed specimens showed comparatively greater strength than the corresponding nonexposed specimens. In addition to calcite deposition, soil suction and cementitious compounds also contributed to this high strength evolution in the carbon dioxide-exposed specimens. Based on physicochemical and pore structure analysis, the combined contribution made by soil suction and calcite precipitation toward strength evolution can be considered almost the same. The significant differences in strength evolution between the carbonated specimens are attributed to the differences in the development of cementitious compounds. This development of cementitious compounds is governed by the soil's mineralogy and the binders added. The exposure condition of soil specimens during the carbonation reaction defines the soil suction evolution. Therefore, the study highlights the importance of reproducing carbon dioxide content and curing conditions close to the in situ situations to accurately assess the strength evolution of carbonated specimens.

In the present work, an investigation on the influence of the chemical environment on the sedimentation behaviour of bentonite suspensions is performed with particular reference to the effect of lime addition on the clay particle arrangement. The role of lime content, cation valence and source of calcium ions is considered in the experimental work. At the microscale, particle interaction is analysed by means of zeta potential measurements. Soil fabric formation during sedimentation and its physical properties are inferred from dynamic light scattering measurements, sedimentation tests and Atterberg limits. The addition of cations to pore water promotes the flocculation of montmorillonite particles favouring the formation of particle aggregates, whose dimension depends on ion valence and concentration. The final height of sediments reflects the combined effect of the mutual interactions among particles and the development of secondary phases due to pozzolanic reactions. The influence of clay mineralogy and its effects on the physical properties of lime-treated bentonite is highlighted by comparison with experimental evidence on lime-treated kaolin.

This study aims at investigating the potential as SCM of palygorskite by comparison of calcination and reactivity with kaolinite. The physico-chemical modifications after calcination were investigated by XRD, 27Al and 29Si MAS NMR analyses, then the reactivity study and mechanical performance measurements were assessed. The results detailed that palygorskite behaves quite differently from kaolinite during calcination. Dehydroxylation kinetics is longer and gradual dehydroxylation is observed for palygorkiste and associated with progessive evolution of Al and Si environment leading to the formation of silica-rich aluminium-poor domains. The study showed a significant increase of mechanical performance on pastes incorporating only 10 % of calcined palygorskite in comparison to the reference which indicates that calcined palygorskite can be a suitable SCM once calcined.

This study focuses on the use of alkali-activated materials and geopolymer grouts in deep soilmixing. Three types of grouts, incorporating metakaolin and/or slag and activated with sodium silicate solution, were characterized at different scales to understand the development of their local structure and macroscopic properties. The performance of the soilmix was assessed by using combinations of the grouts and model soils with different clay contents. Feret’s approach was used to understand the development of compressive strength at different water-to-solid ratios ranging from 0.65 to 1. The results suggested that incorporating calcium reduced the water sensitivity of the materials, which is crucial in soilmixing. Adding soils to grouts resulted in improved mechanical properties, due to the influence of the granular skeleton. Based on strength results, binary soilmix mixtures containing 75% of metakaolin and 25% of slag, with H2O/Na2O ratios ranging from 28 to 42 demonstrated potential use for soilmixing due to the synergistic reactivity of metakaolin and slag. The optimization of compositions is necessary for achieving the desired properties of soil mixtures with higher H2O/Na2O ratios.

In the race to reduce greenhouse gas emissions, the cement industry appears to be a bad pupil and is responsible for non-negligible pollution, particularly due to clinkerization. Calcined clays are among the most promising Supplementary Cementitious Materials (SCMs) and allow a significant reduction in the environmental footprint of cement manufacturing. Many secondary resources, which are considered as waste by the mining industry, contain clay phases, and are therefore potentially recoverable as SCMs once calcined. This study focuses on the calcination and reactivity of two marlstones (MS1 and MS2) from a phosphate mine. The evolution of the phases as well as the physico-chemical modifications induced by calcination and hydration were characterised by X-ray diffraction (XRD) and Solide State Nuclear Magnetic Resonance (MAS NMR). The two materials are relatively similar and mainly composed of dolomite, associated with clay phases (smectite and biotite), quartz and other minority phases. The main difference between the two materials is the occurrence of palygorskite – a particular TOT clay mineral - in the MS1 sample. The calcination of these two materials resulted in a significant dehydroxylation of the clay phases, a dissociation of the dolomite into lime and periclase and the formation of dicalcium silicate. The self-reactivity of the samples in the presence of water was then tested in order to determine the evolution of the reactive phases (lime, periclase, dicalcium silicate) and to test the pozzolanic reactivity of the calcined clay phases. The results show a strong reactivity of the MS1 sample (mainly pozzolanic) while MS2 exhibits a lower reactivity. The presence of palygorskite in the MS1 material improves its reactivity once calcined, it thus seems that this unconventional clay has a promising pozzolanic reactivity, which opens new ways of valorization for this type of secondary resources.

This article focuses on the use of two calcined marlstones as supplementary cementitious materials, one with palygorskite and smectite (MS1) as clay phases and the other with smectite only (MS2). The calcination and the reactivity of these two materials were first analysed by X-ray diffraction (XRD) and Magic Angle Spinning Solid State Nuclear Magnetic Resonance (MAS NMR). The two calcined marlstones were combined with Portland cement to produce mortars and measure compressive strength. The XRD and 27 Al MAS NMR results showed that 800 °C is an optimal calcination temperature and that both calcined marlstones can be used as supplementary cementitious materials. The reactivity of MS1 was found to be higher than that of MS2. This was confirmed with compressive strength measurements which showed superior performance for mortars blended with calcined MS1 rather than calcined MS2. This difference between MS1 and MS2 is due to the presence of palygorskite in MS1, which greatly improves the reactivity and final mechanical performances. Therefore, palygorskite bearing marlstones are suitable for a use as SCM and this suggests that palygorskite exhibits a significant pozzolanic reactivity.

This study focused on the influence of high H2O/Na2O ratios (higher than 20) on the properties of metakaolin-based geopolymers in fresh and hardened states while keeping constant Si/Al and Na/Al atomic ratios. The increase in H2O/Na2O ratio from 21 to 34 resulted in a decrease of 7-day compressive strength from 10 to 0.025 MPa. This can be attributed to the influence of water on the reactivity of the precursor, which was demonstrated by nuclear magnetic resonance (NMR) spectroscopy, and porosity evolution as the water is not chemically bound. Increasing H2O/Na2O ratio did not change the geopolymer structure of reaction products. A correlation was observed between the reaction degree deduced from NMR spectral decomposition and the cumulated released heat obtained using isothermal calorimetry. The maximum loss tangent, obtained using dynamic rheology, was linearly related to strength development.

RÉSUMÉ Une étude a été menée dans le cadre de l’IRSTV (Institut de Recherche en Sciences et Techniques de la Ville) afin de caractériser les retombées atmosphériques et les eaux de ruissellement d’un petit bassin versant séparatif périurbain (31 ha) à Nantes. Les métaux traces, les hydrocarbures aromatiques polycycliques (HAP) et les pesticides ont été mesurés. La caractérisation des retombées atmosphériques montre une grande variabilité des concentrations en métaux, sans lien avec les caractéristiques de la pluie. L’abondance des métaux est la suivante : Zn > Cu > Cr  Ni > Cd. Les polluants organiques sont rarement détectés dans les retombées atmosphériques. Zn et Pb sont les principaux polluants des eaux de ruissellement, tandis que les concentrations en Ni, Cu, Cr, Cd, HAP et pesticides sont généralement faibles. D’une manière générale, les concentrations mesurées se situent dans la fourchette basse des concentrations rapportées dans la littérature. D’après le système d’évaluation de la qualité (SEQ-eau), la qualité des eaux de ruissellement est mauvaise à cause des fortes concentrations en Pb et Zn. Les observations au microscope électronique à balayage (MEB) montrent que les particules des retombées atmosphériques sont similaires à celles des eaux de

Physicochemical and microstructural evolution in lime-treated soil subjected to successive wetting and drying (W-D) cycles was investigated, and the relevance of the laboratory-implemented testing condition with in situ conditions was discussed. Lime-treated soils were exposed to 17 W-D cycles using different testing conditions. Two laboratory testing conditions were operated at laboratory temperature, consisting of W-D duration representing the saturation level close to the one experienced in the in situ soil during rainy and drought periods. The results obtained were interpreted in terms of those obtained using a reference procedure from current standards, which involved oven-drying specimens at 71 degrees C. Drying of lime-treated soil at 71 degrees C reduced the water content from about 20% to 0.85%. This has led to greater contact between soil particles, thus increasing the suction from about 143.5 to 270 MPa. Such a phenomenon increased the unconfined compressive strength (UCS) of the oven-dried soil up to about three times compared with the air-dried specimen, although the available cementitious bonding, reflected by the presence of pores smaller than 3,000 angstrom, was comparatively low in the former compared with the latter. Percentage leaching of calcium components with respect to the initial calcium content of the soil was significantly low during W-D cycles due to greater exposure of only the outer part of the compacted soil structure during wetting. However, the leaching was comparatively higher in the oven-dried soil. The implemented wetting duration and drying temperature influenced the wetting front velocity of water, which significantly affects the duration taken by infiltered water to invade the core of an earthen structure, and hence its durability.

The present study addresses the characterization of long-term and durability properties for employment in road subgrade construction of geopolymer-treated sediments. Four mixtures are presently selected based on a previous study: untreated sediment, sediment treated with 2% hydraulic lime (L) and 7% ordinary Portland cement OPC, and two geopolymer-treated mixtures using 5% and 10% of ground granulated blast furnace slag/sodium silicate-based geopolymers. Long-term properties are investigated through unconfined compressive strength and tensile strength tests. The resistance of designed materials to weathering conditions is tested through freeze-thaw cycles, humidification-drying cycles, and immersion in water. Sediments treated using 10% geopolymer binder are resistant to weathering conditions and showed long-term properties superior to those of sediments treated using an L/OPC mixture.

This article focuses on the study of the self-reactivity of a 800 degrees C calcined palygorskite-bearing marlstone which is a complex multi-phase system (including CaO and MgO) whose reactivity in water must be studied before being used as Supplementary Cementitious Material (SCM). The sample was hydrated (w/s = 0.8) for 7, 14, 28 and 180 days and then investigated using X-ray diffraction (XRD), Solid State Nuclear Magnetic Resonance (MAS NMR), and Scanning Electron Microscope (SEM). Crossing the results of XRD and MAS NMR analyses (in particular the phase quantification by spectral integration of Si-29 MAS NMR spectra) have revealed the reactivity of the calcined clay phases with the portlandite which leads to the formation of C-(A)-S-H. It also highlighted the reactivity of C2S (neoformed during calcination) within 7 days of hydration. Hydration of this sample showed high self-reactivity (mostly pozzolanic) making it a promising sample for use as SCM.

Locally sourced marginal earthfill geomaterials are generally not used in traditional earthfill construction due to their relatively poor mechanical performance. However, if these geomaterials are stabilised, procuring and transporting of materials from borrow sites can be avoided with significant carbon saving. Further carbon saving can be achieved by using industrial waste as binder in place of conventional high-carbon footprint stabilisers such as lime and Ordinary Portland Cement. This paper examines the use of a calcium-rich fly ash from coal combustion activated by a sodium-based alkaline solution for the treatment of non-active clay in view of its use as earthfill geomaterial. To this end, kaolinite clay/fly ash (90/10) samples were compacted, cured for different periods, saturated, and subjected to one-dimensional compression and direct shear tests. The major outcome from 1D compression tests is that stiffness is enhanced significantly even in the very short-term (1 day after alkali activation), i.e. before the binding phase starts to form. This was attributed to the changes in pore-water chemistry (increase in pH and electrolyte concentration) following the addition of the alkaline solution and the formation of aggregates in face-to-face mode. In the long term (curing time > 28 days) stiffness appeared to be further enhanced due to the formation of the binding phase. These effects were more pronounced in the low-intermediate stress range (<-700 kPa) making the alkali activation a good soil treatment for roadway embankments. Peak shear strength also appeared to be significantly enhanced in both short and long term although effects were more pronounced for curing time > 28 days following the formation of the binding phase. Ultimate shear strength is enhanced only in the long term (curing time > 28 days).

The effect of carbonation on a one-year atmospherically exposed lime-treated soil structure is investigated. The investigation involves analyzing the chemical characteristics and pore-structure modifications of several specimens sampled up to 12 cm depth perpendicular to the surface. On comparing the analysis with untreated and lime-treated core-sampled specimens, carbonation is found to have occurred on specimens sampled up to 4.2 cm depth perpendicular to the surface. The decrease in soil pH to a value 9 or lower than that and the presence of carbonates confirmed the carbonation effect. At the pore-structure level, carbonation mechanism is found to increase macropores of diameter 20000–100000 Å, which is missing in the non-carbonated specimens and even greater than the one found at untreated soil. Such an observation confirmed the loss of cementitious compounds due to carbonation, thus, converting the mesopores developed due to lime treatment to macropores of larger pore diameter.

Blending metakaolin with slag in alkali-activated materials represents a promising way to achieve both acceptable engineering properties and durability. Nuclear Magnetic Resonance (NMR) spectroscopy has appeared as a key technique to investigate the structure of alkali-activation products. However, there is not a consensus on the analysis of NMR spectra to identify the phases formed in binary slag-metakaolin mixtures. This paper characterizes the phase composition and the reaction degree of alkali-activated metakaolin-slag blends, with special emphasis on the effect of H2O/Na2O ratio. Different approaches based on the literature are presented and implemented to analyze NMR data. The results suggest the formation of a heterogeneous phase involved in the transformation of 3D network to C-A-S-H. The evaluation of the reaction degree showed that the incorporation of slag in activated metakaolin mixtures resulted in higher reactivity of metakaolin and higher compressive strength.

The effects on hydromechanical performance due to chemical interactions between pore solution and soil components in lime-treated soil are investigated. Static-and kneading-compacted soils are percolated by demineralized water (DW) and a low-ionic strength solution. Kneading action causes aggregate deformation, thus consequently reducing macropores of diameter 105 & ANGS;. This increases the hydraulic tortuosity and lengthens the pore fluid-soil structure contact, which favors the long-term pozzolanic reactions. DW being relatively more aggressive than low-ionic strength solution accelerates the leaching of Calcium, thus negatively impacting the hydromechanical performance. The study shows that the hydromechanical evolution in lime-treated soil is governed by the duration of pore fluid and soil structure contact, depending on the compaction mechanisms implemented. The extent of the effect of pore fluid-soil structure interaction is regulated by the pore solution chemistry and the lime content. Thus, importance should be given to the relevancy of the selected compaction procedure and the permeant solution at the laboratory scale with respect to in-situ compaction mechanism and pore water.

The long-term benefit brought in lime-treated soil can be altered by the nature of the surrounding wetting fluid, thus, affecting its durability. However, studies regarding such impact are limited. In this study, the influence of different wetting fluids on the microstructural, physicochemical modifications, and Unconfined Compressive Strength (UCS) evolution of lime-treated soil is investigated. Lime-treated soils are subjected to wetting and drying cycles using 0.10 M and 0.60 M NaCl solutions, demineralized water, and Methyl Methacrylate. The results show that despite the soil being exposed to several wetting and drying cycles, the UCS evolved positively compared to the reference specimen. However, this evolution varies with the types of wetting fluids the specimens are exposed to. The NaCls-and Methyl Methacrylate-subjected soils showed an increase in UCS up to about 3 times, while the UCS increase is about 2 times in the corresponding demineralized water subjected soil. Similarly, the extent of the variation of the final pH and the cumulative calcium concentrations measured in the effluent is marked by the wetting fluids available in the surrounding medium. At the pore structure level, the presence of NaCl solutions and Methyl Methacrylate solvent as a wetting fluid was observed to enhance the evolution of pores smaller than 3000 angstrom. However, such a phenomenon is less significant in the demineralized water-subjected soil. Thus, the study confirms that the type of wetting fluid plays an important role in the evolution of lime-treated soil during the wetting and drying cycles.

Hydromechanical performances and pore-structure evolution in in situ lime-treated soil is influenced by the implemented methodology of execution. In situ lime-treated soil experiences kneading action during soil compaction; however, little is investigated regarding the contribution of the kneading mechanism towards hydromechanical and pore-structure evolution. This study evaluates the evolution of Unconfined Compressive Strength (UCS), hydraulic conductivity, and pores of different categories in laboratory kneaded soil. The evaluation involves results from lime-treated soil subjected to different curing times and temperatures. The results obtained from laboratory kneaded and cured soils are interpreted with the one obtained from in situ sampled soil of the same configuration after 7 years of atmospheric curing. The obtained interpretation provides an acceptable insight towards the expected long-term hydromechanical and pore-structure evolution of lime-treated soil. Thus, the study highlights the importance of reproducing an implementation mechanism in the laboratory which closely represents the field compaction.