Academic literature on the topic 'Soil–Lime–Sulfate Reactions'

Reactions between lime, alumina released from clay during pozzolanic reactions, and sulfates present in some soils, have been responsible for the deterioration and ultimate failure, by expansion, of several lime stabilization projects, by causing the formation of the highly expansive crystalline mineral ettringite. Based on an extensive literature review, the mechanisms for these reactions were hypothesized, and a laboratory research program using both artificial and natural lime-treated soil specimens was designed and undertaken. The strength, swelling, pH, compositional, and micromorphological characteristics of the treated specimens were determined following different curing times and soaking conditions. Swell development in some of the specimens prepared, in relation with pertinent strength, pH, composition, and micromorphological data obtained, allowed the delineation of the underlying mechanisms leading to heave and deterioration. It was found that the amount of heave following ettringite hydration and growth is a function of the amount and rate of release of alumina into solution. The amount and type of sulfates present, and the amount and type of lime used are also important factors in the development of heave. Moreover, temperature and relative humidity fluctuations were also found to play an important role in the overall ettringite-related heave mechanism, as they affect reaction rates, solubilities of species, and the overall stability fields of a soil system’s components. Finally, the present study was successful in developing a soil pretreatment method that would ensure safe performance of lime-stabilization applications in sulfate-bearing soils. Pretreatment of the artificial lime-treated soil mixes with barium compounds was effective in eliminating ettringite formation. Further research is needed to assess the effectiveness and the required levels of barium pretreatment in field applications. This pretreatment method, upon appropriate modifications, could be potentially applied in other sulfate-related deterioration problems.

The use of lime to stabilize expansive soils has been the preferred technique for many years. However, heaving and premature pavement failures in lime-treated expansive subgrades containing sulfates led to the search for alternative stabilization techniques. Of the several techniques developed, precompaction mellowing has the potential to be effective in stabilizing sulfate-bearing soils. Yet this method needs experimental evaluation. In the current study, an attempt was made to assess the stabilization effectiveness of precompaction mellowing on high-sulfate soils. For this task, six natural expansive soils from Texas, with sulfate contents varying from 200 to 44,000 ppm, were collected. Soils with low-sulfate contents were spiked with additional sulfates to make them high-sulfate soils. Basic classification and chemical tests were performed to establish the clay mineralogy of the soils. Three mellowing periods (0, 3, and 7 days) were studied. The test soils were treated with lime and allowed to mellow for the specified periods. Following the mellowing, the samples were subjected to three-dimensional tests for volumetric swell, shrinkage, and unconfined compressive strength (UCS). To study the consumptions of alumina and silica during sulfate–soil–lime reactions, reactive alumina and silica measurements were also attempted. The authors observed that shrinkage was of no concern in treated soils because the shrinkage invariably reduced with lime treatment. In four of the six soils, precompaction mellowing reduced sulfate-induced swell to a level below the natural expansive swelling. The UCS strengths of treated soils decreased slightly with mellowing. Reasons for the anomaly in UCS strengths and ineffectiveness of precompaction mellowing in two soils were explained.

Soil acidity or aluminum (Al) toxicity is a major limitation to crop production. In this paper, we examine the effects of surface-applied lime and gypsum on soil profile chemical properties that affect Al toxicity in short-term (1 year), medium-term (2 years and 8 months) and long-term (10 years) experiments. Sulfate applied to the soil surface as gypsum was leached rapidly to a depth of 40 cm in the short-term despite relatively low amounts (279 mm) of rainfall. In the medium and long-term experiments, 28–54% of the sulfate applied as gypsum was retained in the 0–50 cm soil layer due to adsorption and precipitation reactions. The combined application of lime and gypsum increased soil calcium, to a depth of 30 cm in the short-term and to a depth of 50 cm in the medium and long-terms. Increases in soil sulfate and calcium were associated with greater electrical conductivity to a depth of 50 cm for all sampling times. Application of lime alone had no impact on soil Al, pH, and calcium in the soil layers below 10 cm in the short and medium terms. In the long-term, increasing the rate of lime application from 2 to 8 t L ha−1 increased soil pH in the 10–20 cm soil layer while soil Al decreased to a depth of 30 cm. The combined use of lime and gypsum decreased soil Al in the 30–50 cm soil layer in the medium-term and the 20–30 cm soil layer in the long-term which was more than when only lime was applied. Hence, we recommend the use of lime plus gypsum for treating soils with subsoil Al toxicity. Additionally, soil Al measurements are a more sensitive measurement of the impact of surface application lime and lime plus gypsum than soil pH.

Stabilized soil is widely used as road base and sub-base materials, and is sometimes used as covering for waste matter in China. In soil stabilization, the property of a locally available soil are usually modified though chemical stabilization[1]. Cement stabilization and lime stabilization are the two most commonly used methods. Lime-fly ash stabilized soil has been widely applied in road engineering due to its good integrity, great bearing capacity, high stiffness, and water-proofing quality[2-4]. One disadvantage of lime-fly ash stabilized soil is that without any additives, its inherent low initial strength makes it inappropriate for use under low-temperature conditions. Researchers have found that the pozzolanic reactivity among lime, fly ash, and soil contributes to the strength of lime-fly ash stabilized soil. To increase the initial strength of lime-fly ash stabilized soil, many approaches have been used to accelerate the pozzolanic reaction. Sulfate activation is one of the methods that has been widely investigated, specifically, Na2SO4 and CaSO4[5]. PG, another sulfate, has also been investigated. However, existing studies have limited to the investigation of the development of strength of the stabilized soil as road base and sub-base materials. The effect of PG on the durability of stabilized soil has rarely been implicated. This work aims to study the effect of thermally treated PG (400°C) on the properties of durability, in addition to other aspects, of lime-fly ash stabilized soil. Lime-fly ash stabilized soil with different proportions of calcined PG were prepared and cured at normal conditions for 7 d and 28 d. Mass loss and strength loss under different treatments were determined. X-ray diffraction(XRD) patterns and scanning electron microscopy(SEM) photos were examined to gauge whether improvements in the performances of the stabilized soil can be obtained by use of thermally treated PG.

Several roads, airfield pavements, and parking lots in Texas and other states in the western United States have suffered severe pavement damage due to expansive minerals formed from the reactions of calcium-based materials used to stabilize sulfate-bearing soils. Remediation costs for projects that suffer sulfate-induced heave damage are very high, because often the entire pavement may have to be removed and reconstructed. Observations from several projects are described to illustrate the phenomenon of sulfate-induced heave and the current methods to predict the problem. Two recent projects described include one using cement as a replacement for lime and a second using a double application of lime. The discussion also includes limitations of the present methods for determining the so-called soluble sulfate levels in soils. The practice of a double application of lime and several other alternative methods and their limitations are discussed. Although research has clearly identified the expansive minerals as being calcium bearing, no published investigations of non-calcium-based stabilizers that could effectively stabilize sulfate-bearing soils were found.

Expansive sulfate-bearing soils are frequently encountered in transportation and construction practices. These soils are often treated with a lime or cement stabilizer to improve the relevant qualities. However, the reaction between sulfate and alumina in soils and calcium of lime or cement can lead to the formation of ettringite, an expansive sulfate mineral resulting in soil swelling or heaving. The underlying mechanisms often involve intricate interactions between chemical processes and mechanical responses. The present study explores a chemo–mechanical approach in an attempt to quantify several mechanisms potentially responsible for the volume expansion, including the geochemical formation of ettringite, crystallization pressure, and osmosis-induced swelling. The geochemical reaction leading to ettringite formation is examined with a specific focus on the circumstances under which it may lead to volume change. The crystallization pressure developed during the ettringite formation may also play a significant role in the soil expansion and is investigated in the present study based on thermodynamic formulations, and the resulting volume expansion is simulated. The osmosis-induced swelling is studied within the context of the chemo–mechanical framework, and its kinetics is also explored. Numerical simulations are performed in the present study to examine different scenarios driven by distinct predominant mechanisms. In particular, the interplay between ettringite formation and osmosis swelling as interpreted from some recently-reported experimental studies shows that these mechanisms can all contribute to the observed expansion processes, and overall, the modeling results are consistent with the experimental findings.

Analysis of acid sulfate soils (ASS) under sugarcane cropping at a site on the Tweed River, north-eastern New South Wales, showed that the majority of the acidity and higher valence ions generated through pyrite oxidation was retained within an individual caneblock. It appears that the oxidation products generated >1 m away from the field drain edge primarily remain where they were formed, and are not exported to the adjacent field drain. Capillary rise and diffusion control the transfer of oxidation products within this area. Leaching and mass movement dominate the transport of ionic species in the topsoil and close to the field drain edge (~1 m). Soluble ion movement within the unsaturated zone also appears to be influenced by nutrient uptake of the growing sugarcane, adsorption and exchange reactions, and convective/dispersive forces. The almost ubiquitous degree and depth of oxidation of ASS profiles along most of the coast, even where no artificial drainage has occurred, leads us to propose natural hydrological and pedogenic processes as the cause. While artificial drainage systems may not have caused the acidity that is stored in backswamps, they do provide the conduit for acidity export. Therefore, management regimes should focus on maximising the retention of acidity in the backswamp and treating that which is exported. Whilst a reduction in the drain frequency appears a logical solution to a reduction in the acidity export from the site, consideration must be given to the benefits field drainage provides before any subsequent changes can be made. An integrated approach of drain minimisation, laser levelling, and active watertable control would appear to be the most appropriate policy in containing the acidity within the soil profile. This approach, combined with the strategic application of lime, offers a means for minimising acid export from the sampled site.

The aim of the work was a comprehensive study of the soils (pH, EC, SOC, NT, ST), surface waters (pH, EC, Ca2+ Mg2+, Na+, NO3−, SO42−, Cl−, HCO3−), and reactions of trees and herbaceous plants in the restored forest ecosystem of a former sulfur mine. Common birch and Scots pine growth reaction, vitality (according to IUFRO standards- International Union of Forest Research Organizations), nutrient supply (Na, K, P, Ca, Mg, K), and Calamagrostis epigejos (L.) Roth chemical composition (Na, K, P, Ca, Mg, K) were assayed. The chemistry dynamics (pH, EC, DOC, NT, Ca, Mg, and S at the beginning and end of the experiment) of soil leaching and the sulfur load leached from the sulfur-contaminated soil substrates were evaluated. The remediation effects of birch and pine litter were assayed in an experiment under controlled conditions. It was found that reclamation was effective in the majority of the post-mining site; however, hotspots with sulfur contamination reaching even 45,000 mg kg−1, pH < 2.0 and electrical conductivity (EC) of 6500 µS cm−1 were reported. Surface waters typically displayed elevated concentrations of sulfate ions (average 935.13 mg L−1), calcium ions (up to 434 mg L−1), and high EC (average 1797 µS cm−1), which was related both to sulfur contamination and the sludge lime that was used in neutralization. Calamagrostis epigejos was found to be a species that adapted well to the conditions of elevated soil salinity and sulfur concentration. It was observed that the application of organic matter had a significant beneficial impact on the chemistry of soil solutions, but did not show a remediation effect by increased sulfur leaching in a short-term study.

After treatment to dissolve and to extract uranium, tailings from Ranger Uranium Mine had a low pH of about 1.8. However, this rose rapidly during initial stages of aging in the laboratory, due to the neutralizing effect of chloritic minerals present in the ore. Within two weeks at 22�C, the pH had reached 3.1, and it continued to rise with time and increasing temperature. The maximum value observed was 5.4 after six weeks at 70�C. Associated with (and acting against) the rise of pH was precipitation of iron, aluminium and silicon oxyhydroxides and hydroxy-sulfates from pore solution into the solid phase. These compounds acted as scavengers to reduce the concentrations of potentially toxic elements copper, zinc, cobalt, nickel, cadmium and lead in porewaters to levels which eventually became comparable to those in limed tailings. Concentrations of radionuclides were also reduced by sorption/coprecipitation reactions with these scavengers, but levels in solution were continually replenished by slow dissolution of a residual uranium mineral, probably brannerite. As a result, radioactivity in porewaters after prolonged aging was appreciably higher than that in limed tailings. Salt concentrations were high, being composed essentially of magnesium, ammonium and manganous sulfates. Ionic strengths were nominally of the order of 1.5 M, but in reality were close to that of seawater (0.7 M) if complex ion formation was taken into account. Concentrations of the major ions magnesium, ammonium, manganous and sulfate, as well as those of calcium and sodium, did not change appreciably during aging at the various temperatures. In general, porewater compositions of limed tailings were similar to those of aged acidic tailings, but the solid phase of limed tailings contained much more gypsum. Also, there appeared to be differences in the behaviour of iron and aluminium hydroxy compounds in the two systems, probably because the hydroxy compounds were precipitated very rapidly during liming and recrystallized into less hydroxylated forms with time. Porewaters from tailings neutralized with magnesium oxide rather than lime had higher total salt concentrations, because, unlike calcium, magnesium salts did not precipitate unless porewaters were further concentrated by evaporation. Manganese precipitated from porewaters at about pH 8.5, and this precipitate also helped to retain heavy metals and radioelements within the solid phase.

To solve the difficult problems of large-scale utilization of solid waste soda residue (SR) as a resource and reduce the cost of road building materials, the technical idea of using SR instead of part of lime to prepare lime soil of pavement base was put forward. Through laboratory tests, the basic characteristics of SR and the optimum moisture content and maximum dry density of soda residue lime soil (SRLS) under different proportioning conditions were tested. The test results showed that (1) with the change of SR content in the range of 0%–12%, the optimum moisture content of SRLS showed the change law of first increasing and then decreasing, but the change range was small; (2) the UCS of SRLS gradually increased with the extension of curing age, with the strength increasing faster in the early stage and slower in the later stage. The UCS of SRLS with SR content in the range of 0%–12% shows the law of first increasing and then decreasing, and the UCS value was the highest when the content of SR is 3%. Compared to the control group, the increase in the amplitude of UCS is as high as 34.6%; (3) appropriate content of SR will increase the gelation of C-S-H and N-A-S-H, and at the same time generated hydrated calcium sulfate and other cementitious materials, enhancing the cementation and strength of SRLS. However, when the content of SR is too much, the excess SR will not participate in hydration reaction even reduce the strength of lime soil. The cost of road materials per kilometer in the test section of SRLS base can be saved by 164,000 yuan, and the treatment cost per ton of SR in alkali factory can be reduced by about 80 yuan. The research results have remarkable economic, technical, and social benefits, which can provide technical reference for large-scale recycling of solid waste SR.

Soil stabilisation is a useful civil engineering technique that enables the insitu material to be used as part of an engineered structure. Stabilised layers are used in road foundation; working platforms and for slope stabilisation and sea defences. Chemical stabilisation involves the use of a hydraulic binder (and sometimes additional pozzolans). Commonly, quicklime (CaO) or slaked-lime (Ca(OH)2) is used. On mixing into the ground, this reacts with the aluminosilicates of the clay fraction, reducing its overall water content and plasticity. Further additions increase the insitu pH. Above pH 10.4, the aluminosilicates become soluble in the pore solution. They are then able to form a range of insoluble mineral hydrates which constitute a cementitious matrix. This results in both an increase in mechanical strength and a decrease in dimensional stability. If the insitu material contains sulfur bearing mineralogies, these can react with the hydraulic binder and the aluminosilicates to form expansive minerals. If this occurs after the initial setting and hardening of the stabilised layer has occurred, it can lead to severe dimensional instability and mechanical weakening. This is termed sulfate heave and the principal agent of this heave is a hydrous calcium sulfoaluminate hydrate, ettringite (AFt). The fundamental processes of ettringite formation and associated expansion are little understood in stabilised soils. This research used a range of artificial sulfate bearing, lime stabilised blended soil samples subject to two immersion tests used for material suitability assessment in the UK. The physicochemical response (in terms of dimensional heave and mechanical weakening) was assessed as a function of soil composition and the environmental conditions imposed by the two immersion tests. The fundamental microstructure and phase composition was characterised using a range of analytical techniques (XRD, SEM-EDX, dTGA). The relationship between the observed macro-physical properties and underlying chemical environment and microstructure was explored. Key findings include that the mechanism of ettringite formation and expansion was found to be governed by the fundamental structure of the bulk clay. This explained the greater swell response of the kaolin based soils compared to those of the montmorillonite. The SEM-EDX analysis identified a primitive, Ca-rich, AFt phase termed ‘ball ettringite’, in stabilised soils. This has only relatively recently been reported in studies of cement mortars. Also, small amounts of sulfate in the bulk soil actually increase soil strength. It was suggested that the preferential formation of monosulfate (AFm) plays an important role in this mechanism. The introduction of water to the pore solution is key to the formation of ettringite. This was evidenced by X-Ray CT of the damage caused to soil specimens on immersion, as well as low angle XRD studies of the principal AFt peak. Based on the limited testing undertaken one of the immersion tests (European accelerated volumetic swell test, EN13286-49), appears to be more onerous than the other (UK CBR linear swell test, BS1924-2).

Solos que contem sulfatos apresentam complicações no seu comportamento quando são tratados com estabilizadores à base de cálcio como a cal. Quando um solo que contem sulfatos reage com cal, formam-se minerais expansivos como a etringita e a taumasita que são responsáveis pela deterioração e falha de vários projetos de solos estabilizados. Tem-se bem demostrado sob ensaios de laboratório que a relação vazios/(agente cimentante) é um parâmetro adequado para a avaliação e previsão de comportamentos mecânicos, como a resistência à compressão simples de vários tipos de solos cimentados artificialmente. Este trabalho pretende encontrar se as previsões da relação vazios/cal na resistência à compressão simples são efetivas para dimensionar misturas de solos sulfatados estabilizados com cal construídas em campo. Para lograr esse objetivo executou-se um programa experimental de ensaios de laboratório em conjunto com a construção de trechos experimentais de solo-cal. Os ensaios de laboratório ajudaram comprender o comportamento de solos sulfatados estabilizados com cal, e demostraram que a relação vazios/cal controla a resistência à compressão simples desses solos estabilizados evidenciando uma relação coerente com os resultados das resistências de campo, encontrando-se que as resistências de campo e laboratório são controladas por essa relação e que podem ser previstas pela mesma Ensaios de Difração de Raios X (DRX) e Microscopia Eletrônica de Varredura (MEV) identificaram minerais expansivos (etringita) nas amostras estabilizadas com cal e cinza-cal. Finalmente em laboratório foram testadas algumas soluções recomendadas na literatura para melhorar a estabilização de solos sulfatados mediante um projeto experimental demostrando que a estabilização com cinza volante e cal melhoram consideravelmente a resistência, a durabilidade e a estabilidade volumétrica de solos sulfatados enquanto que a técnica do mellowing mostrou melhoras apenas na estabilidade volumétrica do material.
Sulfate rich soils present complications in their behavior when are treated with calcium-based stabilizers such as lime. When a soil containing sulfates reacts with lime, expansive minerals such as ettringite and thaumasite are formed which are responsible for the deterioration and failure of various stabilized soil projects. It has been well demonstrated under laboratory tests that the relationship porosity/cementing agent ratio is an appropriate parameter for the evaluation and prediction of mechanical behavior, such as the unconfined compression strength of various types of artificially cemented soils. This work intends to find out if the predictions of the relation porosity/lime in the unconfined compression strength are effective to design lime stabilized soils mixtures built in field. In order to achieve this objective an experimental program of laboratory tests was carried out together with experimental road sections of lime stabilized soils were built. The laboratory tests helped to understand the behavior of lime stabilized sulfate soils, and demonstrated that the void/lime ratio controls the unconfined compression strength of these stabilized soils and that exist a consistent relationship with the field unconfined compression strength results, finding that both, field and laboratory strengths are controlled and can be predicted by this ratio X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM) tests were performed to identify expansive minerals (ettringite) on soils samples stabilized whit lime and fly ash-lime. Finally, some solutions recommended in the literature have been tested in laboratory to improve the stabilization of sulfate rich soils through an experimental design, showing that the fly ash-lime stabilization improve considerably the strength, durability and volumetric stability of the sulfate rich soils whereas that for the mellowing the improve was observed only on the volumetric stability of the material.

Stabilization of expansive soils with various calcium–based stabilizers (lime and cement) directly or in combinations with other solid waste materials such as fly ash and ground granulated blast furnace slag (GGBS) etc. is common approach by many foundation engineers to improve the properties, and conquer the distress caused by undesirable swell–shrink in the soil. Several researches have also been dedicated to understanding the complex ionic reactions and their products, and the mechanisms by which they affect the behaviour of expansive soils. Also, protocol for the lime stabilization of soil is established for the determination of optimum lime content (OLC) based essentially on the compressive strength test. The mechanism of lime treatment works mainly through cementation of flocculated matrix caused by the reduction in repulsion between soil particles with pozzolanic reaction compounds. However, no detailed studies have been carried out to establish the relation between change in fabric and its influence on the properties of expansive soil. It is also not clear whether the optimum lime content will be the same to improve different properties viz., strength and volume change. Hence, the research is directed to address these issues by performing elaborate experimental investigations on geotechnical properties and understanding the mechanism in improvement through fundamental physico–chemical and micro–analytical studies. There are several cases documented in literatures where recent heaving and premature failures of structures constructed on lime and cement–treated soils containing sulfates exhibits, leading to question the validity of calcium-based stabilization. The failures in sulfate bearing soils are attributed to the formation and growth of ettringite/thaumasite minerals in certain environmental regime. It is Stabilization of expansive soils with various calcium–based stabilizers (lime and cement) directly or in combinations with other solid waste materials such as fly ash and ground granulated blast furnace slag (GGBS) etc. is common approach by many foundation engineers to improve the properties, and conquer the distress caused by undesirable swell–shrink in the soil. Several researches have also been dedicated to understand the complex ionic reactions and their products, and the mechanisms by which they affect the behaviour of expansive soils. Also, protocol for the lime stabilization of soil is established for the determination of optimum lime content (OLC) based essentially on the compressive strength test. The mechanism of lime treatment works mainly through cementation of flocculated matrix caused by the reduction in repulsion between soil particles with pozzolanic reaction compounds. However, no detailed studies have been carried out to establish the relation between change in fabric and its influence on the properties of expansive soil. It is also not clear whether the optimum lime content will be the same to improve different properties viz., strength and volume change. Hence, the research is directed to address these issues by performing elaborate experimental investigations on geotechnical properties and understanding the mechanism in improvement through fundamental physico–chemical and micro–analytical studies. There are several cases documented in literatures where recent heaving and premature failures of structures constructed on lime and cement–treated soils containing sulfates exhibits, leading to question the validity of calcium-based stabilization. The failures in sulfate bearing soils are attributed to the formation and growth of ettringite/thaumasite minerals in certain environmental regime. It is reported that this swell is either by crystal growth or, expansion by hydration of the new minerals formed. Research findings contradict the swell mechanism caused by ettringite and it is still a matter of active current research. Further, the mechanism related to strength behaviour of lime treated sulfate containing soil is not well understood. Among several factors influencing ettringite formation, sources and form of sulfate and availability of water play a key role to induce the expansion in lime treated soil which is often termed as “Sulfate Induced Heave” and soil as “Manmade Expansive Soil”. Gypsum is the main source of sulfate in the soil and soil containing gypsum is termed as gypseous soil. Gypsum is an unpredictable material due to its property of changing the chemical structure under certain temperature–pressure and situations where water exists, and hence gypseous soils are not preferred as construction material. Therefore, prior to investigation of sulfate induced heave in lime treated soil, the role of gypsum in the geotechnical behaviour of soil needs to be investigated to make clear the inconsistencies and contradictions in the research findings of different investigations. Hence, the study has been taken up to investigate the impact of varying gypsum content on behaviour of lime treated expansive soil after curing for different period. The mechanism of changes in strength and volume change behaviour of lime treated soil in the presence of gypsum has been elucidated through detailed micro–mechanistic analytical study. Several remedial measures are adopted to control the sulfate induced heave in lime treated soil. Fly ash is often used to suppress this undesirable heave. Utilization of fly ash supplies additional pozzolans (silica and aluminium) with collection of adequate divalent and trivalent cations (Ca2+, Al3+, Fe3+, etc.). However, the effect of additional aluminium supplied by the fly ash on ionic reactions, particularly with ettringite formation in lime treated gypseous soil is not well understood. It is interesting to know that gypsum is frequently used as an accelerating agent to improve properties of fly ash with lime. Hence, an attempt has been made to understand the role of fly ash on the properties of expansive soil treated with varying lime content and the same combination by using diminutive amount of gypsum with a view to find a solution to overcome the adverse effect of sulfate, particularly in the form of gypsum. Mechanism of the strength and volume change behaviour of soil treated with varying lime content in the presence of diminutive gypsum content are investigated and explained. Though, fly ash has been recommended to control the sulfate induced heave in lime treated soil, no particular attention is given to quantify the amount of fly ash to suppress the heave. Also, the effect of intrusion of additional ions (silica and alumina), which are known to affect mineralogy and microstructure, altering the particle size by fly ash to soil is not understood. Hence, work is extended to compare and explore the effect of varying fly ash content on the behaviour of soil, lime treated soil and lime treated gypseous soil and deduce the mechanism through physico–chemical and micro–analyses studies.

Civil engineers are at times required to stabilize sulfate bearing clay soils with calcium based stabilizers. Deleterious heaving in these stabilized soils may result over time. This dissertation addresses critical questions regarding the consequences of treating sulfate laden soils with calcium-based stabilizers. The use of a differential scanning calorimeter was introduced in this research as a tool to quantify the amount of ettringite formed in stabilized soils. The first part of this dissertation provides a case history analysis of the expansion history compared to the ettringite growth history of three controlled low strength mixtures containing fly ash with relatively high sulfate contents. Ettringite growth and measurable volume changes were monitored simultaneously for mixtures subjected to different environmental conditions. The observations verified the role of water in causing expansion when ettringite mineral is present. Sorption of water by the ettringite molecule was found to be a part of the reason for expansion. The second part of this dissertation evaluates the existence of threshold sulfate levels in soils as well as the role of soil mineralogy in defining the sensitivity of soils to sulfate-induced damage. A differential scanning calorimeter and thermodynamics based phase diagram approach are used to evaluate the role of soil minerals. The observations substantiated the difference in sensitivity of soils to ettringite formation, and also verified the existence of a threshold level of soluble sulfates in soils that can trigger substantial ettringite growth. The third part of this dissertation identifies alternative, probable mechanisms of swelling when sulfate laden soils are stabilized with lime. The swelling distress observed in stabilized soils is found to be due to one or a combination of three separate mechanisms: (1) volumetric expansion during ettringite formation, (2) water movement triggered by a high osmotic suction caused by sulfate salts, and (3) the ability of the ettringite mineral to absorb water and contribute to the swelling process.

Soil Chemical Methods – Australasia describes over 200 laboratory and field chemical tests relevant to Australasia and beyond. The information and methodology provided across 20 chapters is comprehensive, systematic, uniquely coded, up-to-date and designed to promote chemical measurement quality. There is guidance on the choice and application of analytical methods from soil sampling through to the reporting of results. In many cases, optional analytical ‘finishes’ are provided, such as flow-injection analysis, electro-chemistry, multiple flame technologies, and alternatives to chemical testing offered by near-range and mid-range infrared diffuse reflectance spectroscopy. The book supersedes and updates the soil chemical testing section of the 1992 Australian Laboratory Handbook of Soil and Water Chemical Methods of Rayment and Higginson, while retaining method codes and other strengths of that Handbook. Chapters cover soil sampling, sample preparation and moisture content; electrical conductivity and redox potential; soil pH; chloride; carbon; nitrogen; phosphorus; sulphur; gypsum; micronutrients; extractable iron, aluminium and silicon; saturation extracts; ion-exchange properties; lime requirements; total miscellaneous elements; miscellaneous extractable elements; alkaline earth carbonates and acid sulfate soils. In addition, there are informative Appendices, including information on the accuracy and precision of selected methods. This book targets practising analysts, laboratory managers, students, academics, researchers, consultants and advisors involved in the analysis, use and management of soils for fertility assessments, land use surveys, environmental studies and for natural resource management.

This chapter addresses a case study of long-term assessment of a field application of environmental nanotechnology. Dense Non-Aqueous Phase Liquid (DNAPL) contaminants such as Tetrachloroethene (PCE) and Trichloroethene (TCE) are a type of recalcitrant compounds commonly found at contaminated sites. Recent research has focused on their remediation using environmental nanotechnology in which nanomaterials such as nanoscale Emulsified Zerovalent Iron (EZVI) are added to the subsurface environment to enhance contaminant degradation. Such nanoremediation approach may be mostly applicable to the source zone where the contaminant mass is the greatest and source removal is a critical step in controlling the further spreading of the groundwater plume. Compared to micro-scale and granular counterparts, NZVI exhibits greater degradation rates due to its greater surface area and reactivity from its faster corrosion. While NZVI shows promise in both laboratory and field tests, limited information is available about the long-term effectiveness of nanoremediation because previous field tests are mostly less than two years. Here an update is provided for a six-year performance evaluation of EZVI for treating PCE and its daughter products at a Superfund site at Parris Island, South Carolina, USA. The field test consisted of two side-by-side treatment plots to remedy a shallow PCE source zone (less than 6 m below ground surface) using pneumatic injection and direct injection, separately in October 2006. For the pneumatic injections, a two-step injection procedure was used. First, the formation was fluidized by the injection of nitrogen gas alone, followed by injection of the EZVI with nitrogen gas as the carrier. In the pneumatic injection plot, 2,180 liters of EZVI containing 225 kg of iron (Toda RNIP-10DS), 856 kg of corn oil, and 22.5 kg of surfactant were injected to remedy an estimated 38 kg of chlorinated volatile compounds (CVOC)s. Direct injections were performed using a direct push rig. In the direct injection plot, 572 liters of EZVI were injected to treat an estimated 0.155 kg of CVOCs. Visual inspection of collected soil cores before and after EZVI injections shows that the travel distance of EZVI was dependent on the method of delivery with pneumatic injection achieving a greater distance of 2.1 m than did direct injection reaching a distance of 0.89 m. Significant decreases in PCE and TCE concentrations were observed in downgradient wells with corresponding increases in degradation products including significant increases in ethene. In the pneumatic injection plot, there were significant reductions in the downgradient groundwater mass flux values for chlorinated ethenes (>58%) and a significant increase in the mass flux of ethene (628%). There were significant reductions in total CVOCs mass (78%), which was less than an estimated 86% decrease in total CVOCs made at 2.5 years due to variations in soil cores collected for CVOCs extraction and determination; an estimated reduction of 23% (vs.63% at 2.5 years) in the sorbed and dissolved phases and 95% (vs. 93% at 2.5 years) reduction in the PCE DNAPL mass. Significant increases in dissolved sulfide, volatile fatty acids (VFA), and total organic carbon (TOC) were observed and dissolved sulfate and pH decreased in many monitoring wells. The apparent effective destruction of CVOC was accomplished by a combination of abiotic dechlorination by nanoiron and biological reductive dechlorination stimulated by the oil in the emulsion. No adverse effects of EZVI were observed for the microbes. In contrast, populations of dehalococcoides showed an increase up to 10,000 fold after EZVI injection. The dechlorination reactions were sustained for the six-year period from a single EZVI delivery. Repeated EZVI injections four to six years apart may be cost-effective to more completely remove the source zone contaminant mass. Overall, the advantages of the EZVI technology include an effective “one-two punch” of rapid abiotic dechlorination followed by a sustained biodegradation; contaminants are destroyed rather than transferred to another medium; ability to treat both DNAPL source zones and dissolved-phase contaminants to contain plume migration; ability to deliver reactants to targeted zones not readily accessible by conventional permeable reactive barriers; and potential for lower overall costs relative to alternative technologies such as groundwater pump-and-treat with high operation and maintenance costs or thermal technologies with high capital costs. The main limitations of the EZVI technology are difficulty in effectively distributing the viscous EZVI to all areas impacted with DNAPL; potential decrease in hydraulic conductivity due to iron corrosion products buildup or biofouling; potential to adversely impact secondary groundwater quality through mobilization of metals and production of sulfides or methane; injection of EZVI may displace DNAPL away from the injection point; and repeated injections may be required to completely destroy the contaminants.