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A contribution to the study of phosphate’s effects on calcareous soils to be stabilized with lime and natural pozzolana
Abstract
When investigating the potential use of lime and natural pozzolana for subgrade soils containing phosphate, especially on agricultural lands, the effectiveness of these traditional binders needs to be assessed because of the possible deleterious effect of phosphates anions. This paper addresses this question using the problematic marly soil of Medea which was deliberately contaminated with a common fertilizer mono ammonium phosphate (0, 2, 4 and 6% by dry weight) and then stabilized with lime and/or natural pozzolana (0, 8%),(0, 20%) by dry weight respectively. Micro and macrostructural changes of these mixtures were studied under X-Ray diffraction test and Scanning electron microscope imaging. Variations of pH levels on a 90 days period, Atterberg limits between 1 to 30 days of curing, normal Proctor parameters, immediate bearing index at optimum moisture were also carried out. Overall, the results indicate that the uncontaminated marly clay soil wasn’t very reactive to lime stabilization even with 8% lime and it required the addition of natural pozzolana with lime to exhibit some improvements. Aside from that, phosphates proved to be deleterious for stabilizing marly clay of Medea producing considerable impact on all the results. It was also shown that calcite present in the soil can interfere with the employed stabilization technique.
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The ever-increasing number of failures of industrial structures due to the heaving of acid-contaminated foundation soils has necessitated a better understanding of soil behavior under changing and extreme environmental conditions. Thus, this paper attempts to micro-mechanistically explain the swelling characteristics of soils contaminated with inorganic acids. Three soils with widely varying physical and chemical properties, namely, natural black cotton soil and commercially available bentonite and kaolin clay, were selected for the investigation. Special Teflon-made oedometer cells, which are entirely non-reactive to acid, were used to assess the swelling behavior. The soils were inundated with two concentrations of sulfuric acid and phosphoric acid and allowed to swell. The results indicate that, in montmorillonitic soils, the type of cation in the exchangeable complex plays a dominant role in governing the swelling behavior of clays during acid contamination. The mineralogical changes due to cation exchange reactions, along with the partial mineral dissolution, resulted in the acid-induced swelling in montmorillonitic soils. In the kaolin clay, the face-to-edge association of the particles due to the adsorption of H⁺ by broken edges led to an increase in swelling along with mineralogical changes.
This paper presents a comparison study between calcium (CaSO4·2H2O) and sodium (Na2SO4) sulphates effects on physico-mechanical properties (pH, plasticity index (PI), unconfined compressive strength (UCS) and shear strength parameters) of both grey and red clayey soils (GS and RS) stabilised with lime (L), natural pozzolana (NP) and their combination (L–NP) in order to recommend adequate mixtures which can be used as building materials for road pavements. In this study, Atterberg limits, pH, UCS and shear strength tests were carried out after different curing periods (1–120 days). Tests results showed that the addition of L as an additive produced a high decrease in the PI of both clayey soils but a considerable increase in UCS, cohesion (C), internal friction angle (φ) and pH was recorded, whereas the NP caused a slight effect. However, when combining both additives, a high decrease in the PI and a further increase in other properties were recorded. Moreover, it was found that the CaSO4·2H2O lowered the PI of both clayey soils whereas the Na2SO4 increased it. Thus, the increase in pH values of all mixtures with sulphate content was more pronounced with the Na2SO4 than with the CaSO4·2H2O. On the other hand, both CaSO4·2H2O and Na2SO4 accelerated the pozzolanic reactions responsible for strength gain. However, at a later stage, the degradation of RS specimens can be explained by the formation of ettringite observed in X-ray diffraction (XRD) patterns. In general, the CaSO4·2H2O developed better effects for soil improvement whereas the presence of Na2SO4 (with a high content) can be classified as a deleterious element for soil stabilisation. From these results, tow tables were given for choosing an adequate mixture for pavement subgrade soil stabilisation.
An experimental investigation was undertaken to study the effects of sodium sulphate (Na2SO4) on the behaviour of two clayey soils stabilised with lime (L), natural pozzolana (NP) and their combination (L–NP). The geotechnical properties investigated are the Atterberg limits and unconfined compressive strength (UCS) on samples cured for 1–120 days curing period. The results show that the L and L–NP reduce the plasticity index (PI) and increase the UCS of two clayey soils. However, the PI of these soils increases when the Na2SO4 is present. In addition, higher UCS values are recorded with 2% Na2SO4. But at later stage, the samples containing 4 and 6% Na2SO4 were completely deteriorated due to the formation of ettringite mineral. In general, the effect of Na2SO4 on the soil stabilisation process depends on the type of additive and its content, the soil nature, the Na2SO4 content and the curing period.
Clayey soils in Syria cover a total area of more than 20,000 km2 of the country, most of which are located in the southwestern region. In many places of the country, the clayey soils caused severe damage to infrastructures. Extensive studies have been carried out on the stabilization of clayey soils using lime. Syria is rich in both lime and natural pozzolana. However, few works have been conducted to investigate the influence of adding natural pozzolana on the geotechnical properties of lime-treated clayey soils. The aim of this paper is to understand the effect of adding natural pozzolana on some geotechnical properties of lime-stabilized clayey soils. Natural pozzolana and lime are added to soil within the range of 0%−20% and 0%−8%, respectively. Consistency, compaction, California bearing ratio (CBR) and linear shrinkage properties are particularly investigated. The test results show that the investigated properties of lime-treated clayey soils can be considerably enhanced when the natural pozzolana is added as a stabilizing agent. Analysis results of scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) show significant changes in the microstructure of the treated clayey soil. A better flocculation of clayey particles and further formation of cementing materials in the natural pozzolana-lime-treated clayey soil are clearly observed.
This chapter reviews the work done with soils and with hydrous oxides of iron and aluminum, with particular reference to mechanisms and structural aspects of anion adsorption. Anion adsorption on clay minerals and calcium carbonate is also discussed. The determination of adsorption isotherms is one of the most useful experimental procedures in the study of the interaction of anions with hydrous oxides or soils. Anion adsorption involves an electrostatic interaction and some chemical interaction between the surface and the ion. The Langmuir model is incomplete in describing this adsorption because it takes no account of charge. The adsorption of anions is dependent on pH, with maximum adsorption usually occurring for fully dissociated ions at low pH where the surface becomes positively charged, owing to protonation of surface M·OH groups. Maximum adsorption of anions of incompletely dissociated acids occurs at a pH value close to the pK of the acid. Anion adsorption reactions in soil are complicated by competition for adsorption sites from anions, including carboxylates, and also by the presence of cations, such as calcium and aluminum.
The large amounts of phosphate fertilizers which are used in agriculture activities in Egypt lead to the contamination of large quantities of soil surrounding the agricultural fields. Also, the use of traditional flood irrigation method makes the problem more worse. An extensive laboratory testing program is carried out to determine the Atterberg limits, compaction characteristics, hydraulic conductivity, and shear strength parameters of clean and contaminated soils. Three types of soils are used including coarse sand, fine to medium sand, and silty clay. Batch tests are used to study the short-term effect of di-ammonium phosphate (DAP) contamination on the soil properties. Contaminated specimens are prepared by mixing the dried soil samples with different di-ammonium phosphate concentrations of 5, 10, and 20 %. The results indicate a significant reduction in Atterberg limits and increase in hydraulic conductivity for silty clay soil with the increase of phosphate concentration. The change that is induced by chemical reaction in the micro-structure of the soil is studied by laser scanning microscope before and after soil contamination. For sand soil, γ
dmax is significantly increased with the increase of DAP concentrations up to 5 % and slightly increased with concentrations from 5 to 20 % which indicates excess phosphate in the soil. However, the general trend of hydraulic conductivity is towards reduction. In addition, the friction angle of two sand samples decreases about 10 % due to the increase of DAP concentration up to 20 %. For silty clay, the reduction in cohesion is about 20 % and the increase of friction angle is about 10 % with the increase of DAP up to 20 %.
Le matériau argileux, dur et cassant lorsqu’il est asséché, présente la particularité de voir sa consistance se modifier en fonction de sa teneur en eau. Un certain degré d’humidité peut le transformer en un matériau plastique et malléable. Ces modifications de consistance peuvent s’accompagner, en fonction de la structure particulière de certains minéraux argileux, de variations de volume plus ou moins conséquentes qui se manifestent soit sous forme d’une forte augmentation de volume (phénomène de gonflement) lorsque la teneur en eau augmente ou de rétrécissement (phénomène de retrait) en période de déficit pluviométrique marqué. Ce comportement est lié essentiellement à certains paramètres environnementaux de ces sols à l’exemple de la géologie et de la lithologie du site, du climat, etc. La prévision du potentiel de gonflement des sols est possible moyennant certaines méthodes empiriques basées sur des paramètres d’identification tels que la plasticité et la granulométrie déterminées lors des campagnes de reconnaissance. Une fois le caractère de gonflement pressenti dans la phase de reconnaissance préliminaire, une estimation de l’amplitude et de la pression de gonflement peut être établie à partir des corrélations, qui tendent à mettre en relation les paramètres de gonflement avec les paramètres géotechniques issus des essais d’identification. C’est dans cet aspect que s’inscrit cet article en traitant le cas d’un site algérien. Les résultats obtenus montrent une concordance entre les méthodes empiriques appliquées. Ces résultats sont aussi comparés avec ceux obtenus des essais de gonflement à l’oedométrique. L’évolution de la structure argileuse au cours de retrait-gonflement est suivie dans l’objectif de comprendre le mécanisme de gonflement.
This paper presents the results of an investigation for the application of alumina filler wastes and coal ash waste for unfired brick production. Mechanical test and durability assessment were carried out on unfired brick test specimens made using marl clay soil and alumina filler waste as a target material, and 70% mix of coal ash waste were used as commercials additive (Portland cement and Lime) replacement. The laboratory results demonstrate that the compressive strength resistance of the unfired bricks reduced as the clay replacement level increased. The unfired brick test specimens made with the blended mixtures containing coal ash waste and lime tended to achieve higher strength values when compared with the coal ash waste and Portland cement blends. The unfired brick test specimens were able to withstand the repeated 48-hour freezing/thawing cycles. The results obtained suggest that there is potential to manufacture unfired bricks from alumina filler waste and coal ash waste.
Soft soil stabilization has been practised for quite some time by mixing additives, such as cement, lime and fly ash to the soil to increase its strength. However, there is a lack of investigations on the use of natural pozzolana alone or combined with lime for ground improvement applications. An experimental programme was undertaken to study the effect of using lime, natural pozzolana or a combination of both on the geotechnical characteristics of soft soils. Lime or natural pozzolana was added to soft soils at ranges of 0–10% and 0–20%, respectively. In addition, combinations of lime–natural pozzolana were added to soft soils at the same ranges. Test specimens were subjected to compaction tests, shear tests and unconfined compression tests. Specimens were cured for 1, 7, 28 and 90 days, after which they were tested for unconfined compression tests. Based on the favourable results obtained, it can be concluded that the soft soils can be successfully stabilized by the combined action of lime and natural pozzolana. Since natural pozzolana is much cheaper than lime, the addition of natural pozzolana in lime–soil mix may particularly become attractive and can result in cost reduction of construction.
Milk and dairy products contain large amounts of calcium phosphate salts that can precipitate. The chemical composition and the crystalline structure of the calcium phosphate precipitates that are formed in dairy industry depend on the physico-chemical conditions, particularly, pH and mineral composition. The objective of this study was to determine, using mineral solutions, the effects of pH and of the concentrations of calcium and phosphate on the quantity and crystalline structure of calcium phosphate precipitates. Experiments were carried out at 20 °C with 20.00 mmol·L−1 phosphate and three Ca/P molar ratios (1.00, 1.50 and 2.00). The initial pH (5.50, 6.70, 7.50, 8.50 and 9.50) were drifting or kept constant during a reaction time of 3 h. After filtration of the suspensions, the mineral compositions of filtrates were quantified. The lyophilized precipitates were characterized using X-ray diffraction, infrared spectroscopy and scanning electron microscopy techniques. At drifting pH (final pH values were between 4.6 and 6.0), the mineral analyses showed that the Ca/P ratio did not influence the amounts of precipitated calcium and phosphate. The analyses of precipitates revealed the formation of brushite as the main crystalline phase. At constant pH, the mineral analyses showed that the Ca/P ratio strongly influenced the precipitation efficiency of calcium phosphate. The analyses of precipitates revealed the formation of poorly crystallized calcium-deficient apatites. A decrease of crystallinity with an increase in initial pH was observed. In conclusion, pH can be a key factor to control the quantity and crystalline structure of calcium phosphates obtained by precipitation. This factor should be considered for the recovery of calcium phosphates from dairy co-products. pH is also important in the fouling phenomena of membranes and heat exchangers caused by calcium phosphate precipitation.
In this note, it is observed that the strength of silty-clayey sand containing a high concentration of metals �like tailings� is increased by mixing of HMP. On the other hand the strength of the kaolinite clay that may be used during the construction of a liner has been reduced by mixing with HMP. In order to study the influence of HMP, soil mixtures with various amount of HMP are prepared to conduct
unconfined compression tests. The strength of the HMP-treated kaolinite specimens is always less than the kaolinite specimens for four weeks. HMP has decreased the strength of silty sand during the first days. However, the cations in the soil �specially Ca and Fe� may lead to precipitation and sorption mechanism to govern and, therefore, the strength increases noticeably up to 740%.
Soil stabilization has been practiced for quite some time by mixing additives, such as cement, lime and fly ash to the soil to increase its strength. However, there is a lack of investigations on the use of natural pozzolana alone or combined with lime for ground improvement applications. In this study, the impact of cyclic wetting and drying on compressive strength behaviour of lime-natural pozzolana stabilized clayey soils has been investigated. Lime or natural pozzolana was added to clayey soils at ranges of 0-8% and 0-20%, respectively. In addition, combinations of lime-natural pozzolana were added to clayey soils at the same ranges. Specimens were cured for 7 and 28 days after which they were tested for unconfined compressive tests and for wetting-drying durability tests. Based on the durability results obtained, it can be concluded that the clayey soils stabilized by the combined action of lime and natural pozzolana exhibits high performance and survive a full 12 cycles of wet-dry testing. On the other hand, the residual compressive strength increases significantly compared to initial compressive strength. Moreover, the results of tests show that the combination lime-natural pozzolana can effectively improve the durability of clayey soils from poor to excellent.
The effect of calcium-based stabilizers such as lime on the geotechnical properties of tropical soils has been reported by many researchers. However, the amount of literature available on the micro-structural, molecular, and leaching characteristics of lime and in particular phosphoric acid-stabilized lateritic clays has been limited. This research was carried out in an attempt to identify the time-dependent soil-chemical reactions. In addition, the possible mechanisms that contributed to the stabilization process were discussed in the light of various spectroscopic and microscopic techniques such as X-ray diffractometry (XRD), energy-dispersive X-ray spectrometry (EDAX), field emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FTIR), and nuclear magnetic resonance spectroscopy (NMR) etc. Based on the results it was found that in lime-treated samples, the coating action of free iron oxides on clay particles imposed inhibitive effects on the dissolution of clay alumina. On the other hand, in phosphoric acid-stabilized soil, due to the increase in solubility of metal oxides and also the subsequent release of clay alumina the formation of cementitious compounds were more feasible. From engineering point of view, the phosphoric acid-stabilized lateritic soil showed the highest degree of improvement with an approximately threefold strength increase in comparison with the natural soil over an 8-month curing period.
The present study aims at studying the effect of initial pH on some geotechnical and geoenvironmental properties of marl soils. For this purpose, marl soils with different initial pHs were prepared by adding 1 M sodium alkali hydroxide (NaOH) and hydrochloric acid (HCl). Changes in geotechnical and geoenvironmental characteristics were investigated by macrostructural experiments (Atterberg Limits, permeability and unconfined compressive strength) as well as microstructural experiments (laser diffraction particle size analysis, XRD, XRF, carbonate percentage determination and SEM images), and the effect of initial soil pH change on marl engineering behavior was investigated. One of the most important results of the present study is changes in the morphology and classification of marl soil with changes in the initial pH. Due to the decrease in initial pH, with the removal of carbonate from the marl soil structure at pH 4, the liquid limit and the plastic limit increased by 19 and 8 units, respectively, and the permeability coefficient (11.7 × 10–9 m/s) decreased by 12 times (0.99 × 10–9 m/s). Also, the unconfined compressive strength reached 0.26 MPa with a 70% reduction at the initial pH of 4. The results of XRD and SEM indicated the stability of palygorskite clay minerals in acidic and alkaline environments. Changing in behavior and classification of marl soil at different initial pHs can be very important in designing geotechnical projects.
The interaction of marly soils and buildings in the town of N'Gaous has led to the appearance of deformations and disturbances that have affected many constructions due to the swelling of the underlying soil. In addition, when these soils are used as construction material, embankments, they are extremely problematic. In this article, three sets of samples, from three different locations, were sampled. Their average carbonate content varies from 14% to 33%.The mineralogical and microsctructural characteristics of these soils are studied by X-ray diffraction (XRD), TG/DTA and SEM analysis. These are mainly smectite clays containing kaolinite and other minor constituents. They all have similar structure, laminar texture with an arrangement of clay particles oriented parallel to the bedding and pores of varying size. These soils are very plastic and have a plasticity index ranging from 41.5 to 54.3%. It was found that the swelling pressure before any treatment ranged from 2.3 to 2.7 bars, after treatment the swelling pressure becomes stable with 5% lime, this behavior has a link with the formation of a cementitious phase of calcium silicate hydrate (CSH) type, as revealed by XRD, ATD/TG and analysis and SEM. In terms of results, it was found that the addition of quicklime has clearly reduced the swelling of the tested samples. It was also found that the presence of carbonates with the above mentioned contents in the studied samples (<50%) does not affect negatively the lime treatment of these soils. However, it promotes the stabilization of swelling, which gives encouraging results.
We studied (i) the pH buffer capacity (pHBC) of calcareous soils varied widely in calcite and texture, (ii) the contribution of soil properties to pHBC and (iii) the significance of using a model based on calcite dissolution to estimate the pHBC of calcareous soils. The pHBC of soils was measured by adding several rates of HCl to soils (100 – 6500 mM H⁺ kg–1), in a 0.01 M CaCl2 background and an equilibration time of 24 h. The pHBC (mM H⁺ kg–1 pH⁻¹) varied from 55 to 3383, with the mean of 1073. The pHBC of the soils was strongly correlated with soil CaCO3 equivalent (calcite) (r = 0.94), sand (r = -0.72), silt (r = 0.60), EC (r = 0.63), pH (r = 0.55), and weakly (r = 0.37) but significantly with clay content. The attained pHBC values indicated that calcite was probably the main buffer system in these soils. The chemical equilibrium model successfully predicted pH titration curves based on calcite dissolution, indicating buffering of acid inputs in the calcareous soils is dominated by calcite dissolution. The model can be used to simulate acidification of calcareous soils and to provide information for making environmental management decisions.
Kew words: pH buffer capacity; acid rain; leaching; calcareous soils; predicting.
Contamination of soils is a critical problem as a result of malfunctioning industries like possible leakage and inferior disposal of wastes. The leakage and spillage of acids infiltrate to the ground and cause swelling of the foundations because of their reaction with the active minerals in the soils. Calcareous soils are widely used in construction. Hence, the carbonate soils are liable to volumetric changes when contaminated with acids. The current work examines the effect of the changes of volume as well as the microstructure of calcareous soils when infiltrated by different concentrations of phosphoric acid. The samples of soil were equipped with molds of acid resistance high-density polyethylene. The volume change was measured by the linear variable differential transformer. The compositional analysis was performed for the acid-contaminated samples. The results indicate there is a volume change with varying the acid concentration, however, silty clayey sand exhibited extensive expansion. This can be attributed to the severe reactions of phosphoric acid and carbonate mineral and the products blocked off the passage for the acid to permeate to the other parts of the soil sample as evidenced by the morphological and compositional analysis of the contaminated samples.
A treatment with hydraulic binders confers to soils enhanced physical and mechanical characteristics that allows their integration in a road section. To gain acceptance of this technique, there is a clear requirement of studies that provide information on success and failures. The aim of this study was to investigate the influence of the salts (i.e. anions and cations) which are present in the soil, on the physical and the mechanical properties of a stabilised soil. Four anions (sulphate, chloride, nitrate, phosphate), associated with sodium or potassium, were added to one soil, using different chemical and concentrations combinations, before treatment. Tests in accelerated curing conditions were used because they are the first realised by the earthworks companies before they undertake further advanced study. The influence of the cationic counter ion and/or salt was also assessed, contrary to the usual recommendations (technical guides) that focused on the anions. The synergistic effects of anions and cations were investigated. For the considered soil, the chloride, nitrate or phosphate ions were less disruptive (important losses of strength or/and volumetric swelling) when associated with sodium than with potassium, while a reverse effect was noticed for sulphate ions. The simultaneous presence of sodium and potassium salts, for each type of anions, except nitrate, induced a significant swelling (up to 24%) and a loss of strength (down to - 75%). Considering stabilisation disturbances, sulphate salts appeared as the most disruptive, the significant swellings associated with ettringite formation causing structural damages. Some technical guides attributed the unsuitability for a soil to a treatment formulation to the presence of some anionic species in soils. This study demonstrated that the unsuitability has to be attributed to a salt, i.e. to the specific combinations of anion and cation. The tests that use simultaneously different salts were innovative and increase the reliability of the usual standard tests. That's why it seems important to reconsider the treatment study methodology used by the companies.
Marly clay was treated with calcitic and Mg-rich lime in order to determine the influence of the clay's high carbonate content on the stabilization effectiveness. The evolution of mineralogical and physical properties over the course of the treatment were studied using XRD, TEM, SEM, elemental analysis, TG, granulometry, and nitrogen sorption and correlated with the marly clay's improved geotechnical behaviour. Only a small portion of smectites and other clay minerals dissolved upon lime treatment. Changes in clay mineralogy had, thus, only very limited influence in the improvement of the material's plasticity and swelling behaviour, which was rather modified by an increase in particle size. This increase was primarily caused by aggregation induced by calcium silicate aluminium hydrate (C-(A)-S-H) formation, whereas flocculation had an only minor effect. After the initial improvement, disaggregation of clay particles occurred which resulted in a particle size decrease, most likely, caused by carbonation of C-(A)-S-H phases. These findings question the effectiveness of lime stabilization for marl using currently applied standard treatment protocols.
The formation and transformation characteristics of ettringite play an extremely important effect on the accelerated hardening and expansion of concrete as well as its long term durability. In alkaline condition, ettringite can be existed stably; but when the alkalinity exceeds a certain value, ettringite can be decomposed into calcium monosulfoaluminate (AFm). In this paper, the stability and its decomposition mechanism of ettringite in alkaline (NH4)2SO4 solution were then investigated. The results show that in alkaline environment, decomposition of ettringite can be occurred and main produces were gypsum and Al(OH)3 as long as the concentration of (NH4)2SO4 reached to a certain extent. Based on experiment data, a kind of NH4⁺ involved decomposition mechanism of ettringite had been proposed by method of quantum mechanics combined with frontier molecular orbital theory and thermodynamic theory.
En géotechnique routière, la technique de la stabilisation des sols à la chaux et aux liants hydrauliques permet la valorisation des sols des déblais. Malgré un encadrement réglementaire strict, cette technique ne donne pas toujours de résultats satisfaisants. Les
entreprises utilisatrices des sols traités et productrices des agents de traitement se sont associées pour lancer des travaux de recherches destinés à comprendre les causes des défaillances.
Cette étude a tout d'abord établi un modèle de l'enchaînement des mécanismes qui conduisent à une stabilisation des sols :
- la chaux permet la floculation des argiles d'où la formation de grumeaux lors du malaxage. Ce grumeau constitue l'entité caractéristique du sol.
- le ciment forme une coque enrobant les grumeaux. Le compactage permet la coalescence de ces pâtes en formant un réseau continu. Le durcissement du ciment permet l'acquisition des caractéristiques mécaniques.
- l'excès de chaux en milieu basique conduit à la formation d'une seconde génération d'hydrates calciques (C-S-H) par réaction pouzzolanique aux dépens des argiles. Le développement des hydrates permet la rigidification du coeur du grumeau et l'augmentation correspondante des résistances mécaniques sur plusieurs années.
Les perturbations rencontrées lors des chantiers peuvent s'interpréter comme des écarts à ce modèle:
- écarts d'ordre microstructural ; dans les sols micacés, le comportement mécanique de ces matériaux est contrôlé par la présence de paillettes de micas dans la coque et de
fragments aplatis de roche au sein des grumeaux.
- écarts d'ordre physico-chimique ; des composés solubles interfèrent avec les liants :
- le soufre favorise le développement d'ettringite selon des faciès qui dépendent de la spéciation du soufre et de la perméabilité du grumeau.
- les matières organiques ralentissent l'hydratation du ciment et piègent les ions calcium et hydroxyle et sont ainsi responsables des résistances mécaniques insuffisantes
Ayant identifié et analysé les mécanismes des perturbations, nous nous sommes attachés à proposer des essais simples et fiables de caractérisation démontrant rapidement la présence de
ces agents perturbateurs au sein des sols :
- par la caractérisation de la morphologie des particules
- par le retard de début de prise de pâtes pures de ciment gâchées avec des jus extraits de sols pour les matières organiques.
A comprehensive series of laboratory tests were conducted on a highly expansive clay soil treated with lime in order to study the lime–soil reaction over a short term and the progression of the pozzolanic reaction over a longer term. Therefore, the results of this study allow determination of the minimal concentration of lime reacting with clay minerals in order to induce a substantial long term improvement in the treated clay soil.
The tests were performed with different percentages of hydrated lime (0–20%) at the room temperature of 20 °C. Plasticity Index, swelling pressure, unconfined compressive strength, wave velocity, pH, electrical conductivity and lime consumption were used to monitor the progression of the lime–clay reactions. X-ray diffraction tests were carried out in an attempt to identify the mineralogical changes and the reaction products formed in the treated soil.
The experimental results indicate that 5% lime is sufficient for a short term reaction involving cation exchange, in this soil. This quantity corresponds to the amount needed for optimum change in soil properties after treatment. The excess of lime added promotes pozzolanic reactions and produces new minerals, such as calcium aluminate hydrates (CAH). This new mineral is identified by X-ray diffraction and its characteristic reflections intensities increase with lime added and curing time. Soil properties continue to be improved with lime addition. Finally, this study shows clearly that lime treatment can be used even for extremely expansive soil.
Field observations suggest that ettringite-induced swell in lime-treated soils may manifest rapidly after placement and compaction or after months or even years after lime treatment. In either case, forensic investigations have identified the presence of the mineral ettringite in distressed sections. However, the time window between the observation of distress and the subsequent forensic evaluations has left room for doubt as to whether the ettringite caused the observed distress or was formed between the time of the observed distress and the time of the forensic investigation. The study focuses on identifying alternative, probable mechanisms of swelling when sulfate-laden soils are stabilized with lime. The research addresses the hypothesis that swelling in sulfate-bearing fine-grained soils results from one or a combination of three mechanisms: (a) volumetric expansion during ettringite formation, (b) water movement triggered by a high osmotic suction caused by sulfate salts, and (c) the ability of the ettringite mineral to absorb water and contribute to the swelling process. The data validate the conclusion that a synergy of the mechanisms discussed contributes to swelling distress. The study also addresses the impact of matrix strength of the stabilized soil on damage potential.
Ground pollution arises from the impact of past and current industrial activity and due to improper disposal of waste generated by society. Geoenvironmental engineering deals with the most important aspects: (a) Soil pollution processes and effect on geotechnical properties, and (b) Waste Management. Soil-pollutants interaction changes soil behaviour and also can lead to various geotechnical problems. Attempts to understand the soil response to various pollutants and available methods to control the same are presented. While the changes in the behaviour of soil contaminated with variety of pollutant in the absence of strong interaction, the behaviour of soil interacted with contaminants leading to mineralogical changes is only getting attention recently. The effect of sulphate on different fine grained soil in alkaline and acidic environment is presented.
Despite the scant quantitative data available in the literature, it has been hypothesized that some chemical compounds can have deleterious effects on soil stabilization with lime and cements (e.g., nitrates, phosphates and chlorides). This study intends to assess their influence on soil stabilization quantitatively. An original experimental procedure was followed. Selected soils were mixed with a potential deleterious compound at a concentration representative of what can be found in the field. The performance of the different mixtures in terms of soil stabilization was then assessed by performing mechanical tests on samples submitted to several curing conditions (temperature and humidity). The results showed that the tested compounds are likely to alter the soil stabilization processes and thus lower the mechanical performance of the stabilized soil. The results also showed that it is not possible to determine a single threshold value for the compounds considered because their influence on soil stabilization is also a function of the nature of the soil (silt or fine sand), the type of cement (CEM I or CEM II) and the curing conditions.
Recent results on synthesis, crystal chemistry, structure and stability of ettringite*, with specific reference to use of this material in hazardous waste immobilization, are presented. Ettringites with selenate, chromate, borate, sulfite and carbonate replacing sulfate have been synthesized and characterized by XRD for phase purity and structure. In X-ray powder diffractograms, selenate and chromate etringites have the normal trigonal P31c ettringite structure, whereas the borate, sulfite and carbonate ettringites can be indexed on a hexagonal unit cell with a halved c parameter. In excess of 95% of the Se and B in solutions spiked with various concentrations of these elements has been removed by precipitation of ettringite. Ettringites appear to be unstable in solutions outside of the approximate pH range 11.0-12.5, and there is a potential for some oxyanion exchange between ettringites and oxyanion-containing solutions. Buffering of pH, and dissolved Ca, Al and sulfate activities by other components of ettringite-based hazardous waste forms, combined with low-reactivity C-S-H matrices, could largely mitigate these concerns.
Marl-rich soils are widely distributed throughout the world. They are generally characterized by a low load-bearing capacity, due to the presence of a clay matrix in them. The stabilization of these types of soils by adding lime or cement is a common practice for increasing their usefulness. This article presents an experimental study of the stabilization of a marl-rich soil based on non-conventional additives, mainly of industrial waste materials. In this way two objectives are achieved: reducing the problems of these types of soils, and in addition enhancing the value of additives and eliminating the economic and environmental cost involved in managing them. From the standpoint of improving their mechanical capacities, CBR and unconfined compression tests were examined, carried out for different curing periods. Thus it was possible not only to determine the improvement of the natural soil, but also to establish the evolution of the increased strength of the soil over time. From a period of 7 days, results were obtained for all combinations of additives that gave an improvement of several times those obtained with the natural material. Results over the course of time showed the formation of pozzolanic reactions in the soil, especially between 14 and 28 days of curing.Research Highlights► We show the potential in using different additives for the treatments of a marl soil. ► The properties of soil stabilized were determined both by laboratory tests. ► The best combinations were lime-RHFA and MgO-RHFA combinations.
This paper focuses attention on the some basic aspects of the role of clay fraction of marly soils including palygorskite and sepiolite upon marl behaviour. The clay fraction of marl is generally dominated by palygorskite and/or sepiolite. It is the performance of these clay soil fractions that are the root cause of many of the problems encountered in the use of such soils as load-bearing materials. This makes it necessary to investigate the role of palygorskite and sepiolite on marly soil's performance. In this paper, some geotechnical and geoenvironmental aspects of marl behaviour is investigated and a new definition and classification of marly soils is presented. This classification focuses attention on the presence of palygorskite or sepiolite as the major fraction of marl, which governs its geoenvironmental and geotechnical behaviour.
Standard Test Method for Laboratory Compaction Characteristics of Soil Using Standard Effort. American society of testing
- Astm D
ASTM D 698-91/98. Standard Test Method for Laboratory Compaction
Characteristics of Soil Using Standard Effort. American society of testing.
DOI: 10.1520/D0698-12E02.
Stabilized materials for civil engineering purposes -Methods of test for cement-stabilized and lime-stabilized materials
BS 1924-2:2018. Stabilized materials for civil engineering purposes -Methods of test for cement-stabilized and lime-stabilized materials.
BRITISH STANDARDS INSTITUTION. London: BSI, 2018.
https://doi.org/10.3403/30355892
Construcción de un terraplén con suelo estabilizado mediante el uso de agentes alternativos en la Autovía del Olivar.Carreteras Revista técnica de la Asociación Española de la Carretera
- C N Ureña
Ureña CN et al (201) Construcción de un terraplén con suelo estabilizado
mediante el uso de agentes alternativos en la Autovía del Olivar.Carreteras
Revista técnica de la Asociación Española de la Carretera, ISSN 0212-6389,
Nº. 203, 2015 Ejemplar dedicado a: Investigación viaria en la Universidad,
págs. 63-72
A study on the use of non-conventional additives for stabilisation of expansive soils
- Ureña Nieto
UREÑA NIETO, Carlos. A study on the use of non-conventional additives for
stabilisation of expansive soils. 2015. Tese (Doutorado em Engenharia Civil) -Universidade de Granada, Granada, 2015. Disponível
em: https://dialnet.unirioja.es/servlet/tesis?codigo=58097. Acesso em: 27 set.
Geotechnical characteristics of Miocene marl in the region of Medea North-South Highway
- Y Yongli
- H Aissa
Y. Yongli, M, H. Aissa. Geotechnical characteristics of Miocene marl in the region
of Medea North-South Highway, Algeria. World Academy of Science,
Engineering and Technology. International Journal of Geological and
Environmental Engineering, v. 10, n. 9 doi.org/10.5281/zenodo.1126746
Etude de l'action des phosphates présents dans l'eau de gâchage sur l'hydratation d'un ciment Portland
- P Benard
BENARD, P. Etude de l'action des phosphates présents dans l'eau de gâchage
sur l'hydratation d'un ciment Portland. 2005. Tese (Doutorado) -University of
Bourgogne. https://doi.org/10.1007/s100649900022. Acesso em: 14 jun. 2024.
Unbound and hydraulically bound mixtures -Test method for the determination of California bearing ratio, immediate bearing index and linear swelling
- Bs En
BS EN 13286-47:2012. Unbound and hydraulically bound mixtures -Test
method for the determination of California bearing ratio, immediate bearing
index and linear swelling. BRITISH STANDARDS INSTITUTION. London:
BSI, 2018. https://doi.org/10.3403/30248456
Effect of industrial wastes on the physical and engineering properties of soils
- S Cyrus
- T G S Kumar
- B M Abraham
- A Sridharan
- B T Jose
Cyrus, S.; Kumar, T. G. S.; Abraham, B. M.; Sridharan, A.; Jose, B. T. Effect of
industrial wastes on the physical and engineering properties of soils. In: INDIAN
GEOTECHNICAL CONFERENCE, 2010, GEO trendz. Proceedings [...].
Physico-chemical properties and engineering behavior of anion adsorbed clay
- R A Sreepada
SREEPADA, R. A. Physico-chemical properties and engineering behavior of
anion adsorbed clay. 1982. Tese (Doutorado) -Indian Institute of Science,
Bangalore.