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Unexpected volume changes manifested in the soil beds due to accidental release of alkalis from industrial establishments has become a major challenge. The neogenic formation that leads to volume changes due to physicochemical reactions between clay minerals and alkalis need to be addressed. The current article focusses on the possibility of using alternate by-products such as ground granulated blast furnace slag (GGBFS) and flyash (FA) for controlling the swell induced in alkali transformed kaolinitic clays, ATKC’s (i.e., red earth and kaolin). Results indicate that ATKC’s exhibited unexpected changes in swelling behavior upon inundation with water and alkali (4N NaOH) solutions. ATKC’s were later amended with FA and GGBFS to address the swelling phenomena. Marked reduction in swelling was noticed in ATKC’s with FA (10% and 20%) and GGBFS (10% and 20%). Reduction of about 40% of overall swelling was noted in alkali transformed red earth (ATR) when treated with 10% FA and 50% reduction with 10% GGBFS. Further, treatment of ATR with 20% FA and 20% GGBFS, decreased swelling to about 82% compared with ATR-4N. In case of alkali transformed kaolin (ATK), 57% and 56% reduction in swelling were observed with addition of 10% FA and 10% GGBFS, respectively. At 20% FA and GGBS content, reduction in ATK-4N swelling was 75% and 90%, respectively. Thermo Gravimetric–Differential Thermal Analysis (TG–DTA), X-ray Diffraction, and Scanning Electron Microscopy (SEM) analysis confirmed the alterations in ATKC are stabilized with FA and GGBFS.

The soils in hazardous waste sites contain heavy metals which would leach into groundwater by various biotic and abiotic processes and eventually pose a threat to human health by contaminating the drinking water. In order to understand pattern of heavy metal leachability, the field conditions can be simulated by adopting various types of sequential extraction methods. In this study, an attempt was made to evaluate the effectiveness and selectivity of a sequential extraction process to determine heavy metal binding mechanisms in soils and soil treated with nano-calcium silicate (NCS). A five-step sequential extraction (SE) procedure was adopted on four soils obtained from a sanitary dumpsite, automobile and battery work units from different localities of Bangalore and a steel plant commissioned at Toranagallu, Bellary, India. The soils were mixed with NCS at varying range of 0.5 to 2% by dry weight of the soil. The NCS-amended soils were spiked with cadmium (Cd2+), nickel (Ni2+) and lead (Pb2+) in concentrations to the tune of 3000 mg/kg. It has been observed that there seems to be a gradual increase in binding ability for the targeted heavy metals when soils were amended with NCS compared to untreated soils. This binding phenomenon was attributed to the presence of exchangeable ions, carbonates, oxides of iron and manganese, organic matter and residual fractions. It was noticed that the residual fractions in soils amended with NCS attenuated maximum quantity of metal ions with Pb2+ at 21.46%, followed by 18.8% for Cd2+ and 9.25% for Ni2+ compared to untreated case. Further, this work highlights the role of residual fraction in enhancing the retention capacity of soils by encapsulation of higher concentrations of contaminants. The current study corroborated the fact that the addition of NCS aids in the better encapsulation of selected heavy metal ions.

Coal gangue is a mine waste generated during the mineral processing phase of coal production. With the surge in demand for coal in thermal power, steel and cement generation industries, the rate of coal gangue generation has reached unprecedented heights. With the realisation of potential threat posed by coal gangue, researchers have made attempts to explore many new avenues of applications for its bulk utilisation. Unfortunately, the implications of coal gangue utilisation on the surrounding environment have not been taken into consideration. In the present study, an attempt has been made to perform carbon footprint analysis on coal gangue to assess the CO2 emissions in utilising it as an embankment material. A similar analysis is done to evaluate the emissions in its disposal process. The results obtained from both the analysis have been compared to assess the feasibility of utilising coal gangue in targeted geotechnical engineering applications. The studies corroborate the fact that the utilisation of coal gangue can lead to a significant decrease in the carbon footprints generation, thus leaving a positive impact on the environment.

This article evaluates the desorption of heavy metals from lime-stabilized, contaminated semi-arid soils under harsh environmental conditions involving chemical extractants, specifically, acetic acid (CH3COOH), nitric acid (HNO3), ethylene diamine tetra-acetic acid (EDTA), and diethylene triamine penta-acetic acid (DTPA). In this study, heavy metals, such as arsenic (As), chromium (Cr), mercury (Hg), and lead (Pb), were spiked with two semi-arid soils (exhibiting different plasticity characteristics) at different load ratios (10–250 mg/kg); they were later stabilized with lime to evaluate the reduction in their mobility. Extensive desorption tests were performed on these soil mixtures to study the efficacy of lime for the in situ fixation of heavy metals. This study revealed that irrespective of the nature and size of the heavy metal, the removal efficiency for the soils was greater than 80%, and EDTA at a concentration of 1 M yielded the maximum removal efficiency. It was found that the cationic metal ions Hg and Pb were desorbed effectively by EDTA, while As was desorbed by HNO3 and Cr by DTPA. The order of desorption for heavy metals was found to be as follows: As > Cr > Hg > Pb. The lime amended soils exhibited lower removal efficiencies (more than 48% retained) due to efficient retention of metals in the soil interstices, making them inert and immobile. There was an improvement of 40% in soils amended with lime compared with virgin soils in the case where soil washing by harsh washing agents was resisted; this proves that the contaminants were embedded in the interstices of the soil calcium interfaces. Therefore, this study asserts the notion that the mobility of heavy metal ions from brownfields can be effectively reduced by in situ lime treatment.

In the design protocols of pavement subgrade layers, the resilient modulus (MR) property assumes importance in evaluating the performance during their life-time under sustainable repeated or dynamics traffic-loads. The aim of this study is to evaluate the improvements achieved on the subgrade layers of fiber-treated lime-blended expansive soil. Two types of fibers exhibiting different surface properties were considered and their length(s) and dosage(s) (by dry weight of soil) were varied as 6 mm and 12 mm; and 0.2% and 0.6%, respectively. To ensure bonding between fiber and soil particles, dehydrated lime has been added to the soil-fiber mixture. The compacted specimens were cured up to 28 days. Dynamic resilient modulus MR tests were carried out in the laboratory for soil–lime-fiber mixtures using dynamic triaxial device. The obtained MR values were correlated with California Bearing Ratio (CBR) and Unconfined Compression Strength (UCS) values and appropriate models have been proposed to estimate MR. The results show significant increments in MR due to fiber reinforcement and are affected by fiber type, length and dosage. The proposed models considering CBR and UCS to predict MR have shown excellent correlations.

Soil amelioration is a challenging task in bulk civil engineering applications such as embankment slopes, landfill liner, pavement subgrade, retaining wall back fill. The conventional chemical stabilization techniques (i.e., cement, calcium hydroxide, sodium chloride, calcium chloride, etc.) inherently suffer from associated carbon emissions during their production stages. With the advent of biopolymers derived from natural sources having low embodied energy levels, they can replace conventional stabilizers. The current review article highlights the significant properties of two such biopolymers, i.e., xanthan gum (XG) and guar gum (GG), and their innate potential in stabilizing different soil types including mine tailings. The issues arising with wet and dry mixing of these biopolymers and suggested measures have been critically addressed. The degradation characteristics of biopolymers, which limit their use for bulk civil engineering applications, have been critically discussed, and the potential solutions to overcome durability issues are suggested. Future applications of these biopolymers in geoenvironmental engineering relying on the metal encapsulation properties are discussed in detail. It is believed that the selected biopolymers in this review are renewable, sustainable and remarkable materials with low embodied energy levels and low carbon footprint values compared to existing conventional stabilizers.

In this article, the effect of randomly oriented polypropylene fiber inclusion in enhancing the various geotechnical properties (unconfined compression strength, compressibility index, swell index, hydraulic conductivity, linear shrinkage, California bearing ratio) of a typical expansive semiarid soil is studied. Since the practicing engineer typically has difficulty in selecting the right mix of fiber type, dosage, and lime content to meet the optimum requirements of this targeted group of geotechnical properties, PROMETHEE is here adopted in order to assist in the decision-making process. The primary objective of this study was to evaluate different geotechnical properties for possible alternatives, the first being untreated soil itself and the second treating the soil with 6% lime. The remaining alternatives vary with fiber type, fiber size, and fiber dosage with or without lime. A further objective was to study the combined influence of factors, viz. lime addition, fiber type, fiber dosage, and fiber length at their respective levels of interactions for the targeted soil properties. The results of the study led to the identification of groups of criteria expressing similar preferences. Sensitivity analysis was carried out in order to better understand the conflicts to be solved in order to make this decision.

Global rise in greenhouse gas emissions (GHG) is triggered mainly due to the consumption of fossil fuels for power generation and domestic usage. Among the fossil fuels, coal is a primary contributor to global GHG with substantial emissions generated during its mining and combustion process. Coal gangue, a residue produced during the coal mining process, has found sparse utilization in civil engineering applications. To gauge the feasibility of using coal gangue for geotechnical and geoenvironmental applications, comprehensive characterization study was performed which include understanding the geotechnical, mineralogical, chemical and leaching behavior. Further, to evaluate the environmental impacts associated with coal gangue utilization, carbon footprint assessment (CFA) was performed. The geotechnical properties of coal gangue revealed its potential as fill material in the construction of embankments and retaining walls. Mineralogical and chemical characteristics of coal gangue are comparable to coal combustion residues like coal ash and fly ash which are widely used in bulk civil engineering applications. The leaching studies revealed the presence of trace elements in coal gangue; however, their concentration levels were found to be well below permissible limits. The CFA has shown that utilization of coal gangue in mechanically stabilized earth wall construction resulted in a net savings of 1709 CO2 (kg) emissions. Based on the characterization studies, it can be inferred that coal gangue is a potential alternative to the existing conventional geomaterials like soils and other recycled materials.

The relative performance of two soils as a sustainable material to attenuate the transport of heavy metal ions, cadmium (Cd2+) and nickel (Ni2+), from aqueous solutions has been evaluated. Red earth soil (RS) and black cotton soil (BCS) originating from India, were selected, and batch equilibrium tests including sorption kinetics and leaching studies were conducted. Langmuir isotherm was found to be more suitable than Freundlich isotherm for both the soils. Kinetic data were fitted on four models namely pseudo first order, pseudo second order, Elovich and intraparticle diffusion. Correlation coefficients obtained by all models fitted well in the following ranking: Elovich > Intraparticle diffusion > pseudo second order > pseudo first order. Based on extensive experimental data, it is concluded that the ranking on sorption was of the order Cd > Ni for both the soils, and BCS exhibited relatively higher retention levels compared to RS. It is further concluded that BCS can be used as a substitute to filter material, RS a substitute to main liner material in attenuating Cd2+ and Ni2+ from an industrial landfill leachate.

Most of the chemicals containing non-biodegradable metal pollutants from anthropogenic sources are highly mobile in nature. The only way to contain or limit their movement is through sorption and entrapment in the soil matrices. In this study, the sorptive response of the three most commonly found divalent metal contaminants, copper (Cu+2), lead (Pb+2), and zinc (Zn+2), are studied using two locally available semi-arid soils from Saudi Arabia. To enhance their retention capacity, these soils are amended with lime. The response to sorption at varying initial contaminant concentrations, pH conditions, temperature levels, and dilution ratios are investigated. Relying on empirical models (Langmuir and Freundlich), the nature of sorption (monolayer or heterogeneous) is ascertained. Further, kinetic models are employed to validate the type and nature of sorption that occurs (whether pseudo first-order or second-order). It is found that the experimental results correlate well with these empirical models for both the Al-Ghat and Al-Qatif soils when amended with lime and attenuate Cu, Pb, and Zn to satisfactory levels. The R 2 values are close to 1 for all the tested models. The order of sorption was Pb > Cu > Zn for these heavy metals, and also for soils and soil mixtures that were considered: Al-Qatif soil amended with 6 % lime > Al-Ghat soil with 6 % lime > Al-Qatif > Al-Ghat. Lime-treated soils sorbed 73, 65, and 60 % more than the untreated soils for Pb, Cu, and Zn, respectively.

Soils are known to retain heavy metals through a number of processes. In this study, four different leaching methods viz. ASTM D3987, toxicity characteristics leaching procedure (TCLP), extended TCLP, and caged TCLP have been used to study the leaching behavior of Cd2+, Ni2+ and Pb2+ on red and black cotton soils. Further, these soils were amended with nano calcium silicate (NCS). Also, sequential extraction was performed on these soil mixtures to know the extent of sorption taking place in different phases of soils such as exchangeable, oxidizing, reducing, organic content and residual phases. It was found that as per ASTM D3987, all three heavy metals with red soil and black cotton soil were retained well in the short term, and over a long-term period, the metal ion was released back. When amended with NCS, both red soil and black cotton soil exhibited satisfactory retention levels over long periods which proved that NCS was responsible for encapsulation of metal ions in its matrix. To investigate the retention efficiency, extensive leaching tests were performed, and it was found that as per TCLP, extended TCLP and caged TCLP tests, the retention with NCS-amended red earth soil was 88, 90 and 94 % compared to untreated case. Sequential extraction proved that encapsulation was durable in NCS-amended soils compared to untreated ones. Hence, it is concluded that NCS-amended soil is a prospective material to attenuate heavy metals taking into consideration their long-term encapsulation effect in considered soils. This soil NCS mixture is expected to be a potent agent for in situ treatment of brown fields and an excellent substitute for existing conventional landfill liner materials.

Inclusion of synthetic fibers is becoming a routine task in soil reinforcement. The ability of synthetic fibers in controlling the shrinkage cracks in concrete is the main drive to consider its benefits in clay and other soil materials. The polypropylene fibers are nonbiodegradable and can perform well even in aggressive chemical exposure conditions. The direct shear testing is a popular geotechnical approach to assess the shearing strength for a range of soils. This study is aimed at investigating the effect of fiber inclusion on the direct shear response of semi-arid clay soils. This research is conducted using two different types of polypropylene fibers, viz., Fibercast and Fibermesh, having different surface properties on the shear strength envelope and parameters (angle of internal friction and cohesion). The aspect lengths were varied as 6 and 12 mm, and the dosages were varied as 0.2, 0.4, and 0.6 % by weight of the soil. The results were viewed in relation to the fiber type, size, and dose. The soil response and shear resistance measured in consolidated undrained direct shear test is presented for the targeted doses, and the results revealed useful insight compared to unreinforced. The Fibermesh material proved to be the more appropriate fiber additive to typical semi-arid clay soils. The data provides helpful guide for the design geotechnical engineers.

This paper presents the effects of addition of lime and lime along with gypsum on the compressibility behavior of two class F fly ashes. Since the fly ashes develop strength and exhibit lower compression, consolidation testing with conventional duration of load increment may not be appropriate. Hence, an attempt has been made to assess the minimum duration of load increment necessary to study the compressibility characteristics of such materials. Thus compressibility behavior of fly ashes with additives has been studied using conventional consolidation test with different durations of load increments varying from 30 min to 48 h. The results obtained indicated that 30 min of duration of load increment can be used to assess the compressibility behavior of such materials. The effect of lime which reduces the compression is seen to be maximum from the results obtained with the duration of load increment of 30 min but gradually reduces with higher durations of load increment. It has also been observed that the rate of decrease in the compressibility is maximum up to 2.5% lime and gradual thereafter. The compressibility of lime treated fly ashes further reduces when gypsum is incorporated, the optimum gypsum percentage being 2.5. This reduction in the compressibility of fly ashes enhanced by incorporating lime and gypsum makes them versatile in the construction of embankments and for structural fills, particularly reducing the time required in between laying of each lift.

Fly ash is a waste by-product obtained from the burning of coal by thermal power plants for generating electricity. When bulk quantities are involved, in order to arrest the fugitive dust, it is stored wet rather than dry. Fly ash contains trace concentrations of heavy metals and other substances in sufficient quantities to be able to leach out over a period of time. In this study an attempt was made to study the leachabilities of a few selected trace metals: Cd, Cu, Cr, Mn, Pb and Zn from two different types of class F fly ashes. Emphasis is also laid on developing an alternative in order to arrest the relative leachabilities of heavy metals after amending them with suitable additives. A standard laboratory leaching test for combustion residues has been employed to study the leachabilities of these trace elements as a function of liquid to solid ratio and pH. The leachability tests were conducted on powdered fly ash samples before and after amending them suitably with the matrices lime and gypsum; they were compacted to their respective proctor densities and cured for periods of 28 and 180 days. A marked reduction in the relative leachabilities of the trace elements was observed to be present at the end of 28 days. These relative leachability values further reduced marginally when tests were performed at the end of 180 days.

The purpose of this study was to use the concept of metastable equilibrium solubility (MES) to describe the anomalous solubility behavior of carbonated apatite (CAP) in the presence of solution strontium. A CAP sample (4.8 wt% CO(3), synthesized at 70 degrees C) was prepared by precipitation. Baseline MES distributions were determined in a series of 0.1 M acetate buffers containing only calcium and phosphate (no strontium) over a broad range of solution conditions. In order to assess the influence of strontium, MES profiles were then determined in a similar fashion with 20, 30, 40, 50, 60, 70, and 80% of the solution calcium being replaced on an equal molar basis by solution strontium. From the compositions of the equilibrating buffer solutions, ion activity products (IAPs) of the form Ca(10-n)Sr(n)(PO(4))(6)(OH)(2) (n = 0-10) were calculated in an attempt to determine the correct function governing the dissolution of the CAP preparation. The results demonstrate the following important findings: (a) at high solution strontium/calcium ratios (i.e., when 60% or more of the solution calcium was replaced by strontium), the MES profiles in all the experiments were found to be essentially superimposable when the solution IAPs were calculated using the stoichiometry of Ca(6)Sr(4)(PO(4))(6)(OH)(2), and (b), at low solution strontium/calcium ratios (i.e., when 40% or less of the solution calcium was replaced by strontium), the stoichiometry yielding MES data superpositioning was found to be that of hydroxyapatite. When other stoichiometries were assumed, good superpositioning of the data was not possible.

It has been shown that biominerals such as dental enamel and bone demonstrate a non-thermodynamic equilibrium state following initial dissolution where no further mineral dissolution or precipitation occurs; this state is termed metastable equilibrium solubility (MES). Furthermore, these minerals are composed of a distribution of domains each with their own MES. Recent studies have also demonstrated a linear relationship between crystallinity and the mean MES of these minerals, with solubility decreasing with increasing crystallinity. This study investigates the effect of age on the MES and crystallinity of rat bone mineral. The bone mineral samples were prepared by protein extraction with a series of hydrazine and alcohol solutions. The MES distributions of the bone mineral were measured by exposure to 0.1 M acetate buffers containing a range of calculated amounts of calcium (Ca) and phosphate for 48 h. The amount of mineral dissolved in each solution was determined from Ca and phosphate analyses of the undissolved residue. The full width of the half maximum (FWHM) of the 002 reflection of the X-ray powder diffraction was used as an indicator of crystallinity. The MES of mineral from bone of rats of different ages (1-25 months) were compared. Results of this study indicate that (l) there is a difference in the mean MES of bone mineral from rats of different ages, with older bone mineral being less soluble and more crystalline than bone mineral from younger rats; (2) the nature of the solubility distribution changes from a narrow to a broader distribution with age; and (3) all of the bone samples demonstrated an inverse-linear correlation between crystallinity and mean MES value consistent with previous results obtained with synthetic apatites and dental enamel.

SnF2 is an important toothpaste ingredient, added for the provision of clinical efficacy for hard and soft tissue diseases and in breath protection. Synthetic calcium hydroxyapatite powders were exposed to liquid supernates (25 w/w% toothpaste water slurries, centrifuged) of Crest Gum Care® (SnF2) dentifrice. One-minute treatments were followed by 3x water washing, centrifugation and lyophilization. Post treatment, powders were analyzed by Mossbauer spectroscopy with 0.5–1 gram of treated apatite powder. Results show that tooth mineral stannous fluoride interactions include: (1) formation of surface reaction products with both Sn(II) and Sn(IV) oxidation states; (2) Sn-F binding on mineral surfaces with no evidence of SnO. The surface binding is, however, not pure Sn-F but contains contributions of other ligands, probably oxygens from surface phosphates or hydroxyl groups. Results also suggest that surface reacted stannous tin is oxidized with time, even when bound as a layer on the tooth surface. This study demonstrates for the first time the presence of Sn-F on tooth enamel post treatment and the contribution of passivation to long term stannous chemistry on tooth surfaces. The study also illustrates the practical applications of the Mossbauer technique.

Previous studies have shown that the metastable equilibrium solubility (MES) behavior of carbonated apatites (CAPs) may be described by a surface complex with the hydroxyapatite (HAP) stoichiometry in the absence of solution fluoride and by that with the fluorapatite (FAP) stoichiometry when appreciable solution fluoride is present. Studies have also shown that the magnitude of the MES is directly related to the crystallinity of the CAP. The aim of the present investigation was to examine the relationship between the CAP MES determined in the presence of solution fluoride and CAP crystallinity and to examine the effect of the change in the stoichiometry of the surface complex (from that of HAP to that of FAP) upon the relationship of the CAP MES to crystallinity. CAP samples were prepared by methods based on the precipitation of CAP from calcium phosphate solutions and the hydrolysis of dicalcium phosphate dihydrate in bicarbonate solutions. From X-ray diffraction experiments, the crystallite microstrain, and the full width at half maximum (FWHM) of the 002 reflection were determined for the CAPs. From CAP MES experiments conducted in the presence of solu tion fluoride, linear plots of the mean MES (i.e., mean pK(FAP)) values vs the crystallinity parameter (i.e., microstrain and FWHM) were obtained that yielded slopes that were essentially the same as those obtained in the absence of solution fluoride (i.e., mean pK(HAP) values vs crystallinity). This parallel finding suggests that the CAP crystallite disorder affects the energetics of the two surface complexes essentially to the same extent and provides new insight into the nature of CAP surface complexes.

Previous studies have shown that carbonated apatites with a range of carbonate contents and crystallinities exhibit the phenomenon of metastable equilibrium solubility (MES) distributions. The purpose of the present study was to investigate the solubility behavior of bone mineral using the concepts of MES and MES distributions and, together with crystallinity and chemical composition data, examine the similarity of bone mineral to carbonated apatite (CAP). Bone samples were harvested from 1-, 5-, and 8-month-old rats. The organic components of the bone samples were removed by hydrazine deproteination. Carbonated apatite was synthesized by the hydrolysis of dicalcium phosphate dihydrate (DCPD) in a NaHCO3-containing media at 50 degrees C. The MES distributions of bone mineral and CAP were determined by equilibrating predetermined amounts of CAP or bone mineral in a series of 0.1 M acetate buffers containing calculated levels of calcium and phosphate and maintained at essentially constant pHs of 5.0, 5.3, 5.7, and 6.5. From the compositions of the equilibrating buffer solutions, ion activity products based upon the stoichiometries of octacalcium phosphate, hydroxyapatite, and carbonated apatite were calculated in an attempt to determine the function governing the dissolution of CAP and bone mineral. The results of this study demonstrated that the MES distribution phenomenon appeared to hold for bone mineral and that the changes in crystallinity of bone mineral with age correlated well with changes in the MES values. A CAP sample was prepared that was found to be an excellent synthetic prototype closely mimicking the physicochemical behavior of bone mineral from an 8-month-old rat. Another finding of this study was that the ion activity product function based upon the hydroxyapatite stoichiometry well described the MES results obtained with both CAP and bone mineral. The interpretation that a surface complex with hydroxyapatite stoichiometry governs the solubility behavior of bone mineral is, therefore, consistent with the experimental data. Other calcium phosphate stoichiometries for the surface complex showed systematic variations in the MES profiles when the pH of the equilibrating solution was varied.