Fly Ash Bentonite Research Articles

Exploring the viability of Bentonite-amended blends incorporating marble dust, sand, and fly ash for the creation of an environmentally sustainable landfill liner system

The development of effective and cost-efficient landfill liners is crucial to prevent groundwater contamination from leachate, safeguarding soil quality and the environment. Composite liners, particularly those combining bentonite with supplementary materials such as fly ash or marble dust, present a promising solution. This study delves into a comprehensive investigation of the physical properties of landfill liners composed of bentonite-fly ash and bentonite-marble dust mixtures through an extensive series of laboratory tests. The research systematically analyzes various proportions of bentonite with fly ash and marble dust, evaluating their impact on liner performance in comparison to Bentonite-sand mixtures. Physicochemical analyses are employed to understand the interactions and behaviors of these distinct substances within the amended bentonite. A wide array of physical properties, including Atterberg’s limits, compaction characteristics, free swell index, modified free swell index, California bearing ratio, cohesion, and angle of internal friction, are meticulously examined. Collectively, these properties offer a comprehensive overview of the suitability and performance potential of bentonite-fly ash and bentonite-marble dust mixtures as landfill liners, presenting a viable alternative to traditional bentonite-sand mixtures. The study reveals synergistic effects between bentonite and both fly ash and marble dust, highlighting their significant contributions to enhancing the physical traits of landfill liners. This advancement in landfill liner design holds the promise of effectively mitigating detrimental environmental impacts associated with waste disposal. While this study provides a robust foundation, it is essential for future investigations to prioritize long-term performance assessments and real-world implementation. Validation and fine-tuning of these findings are crucial to ensuring practical applicability and efficacy within authentic landfill construction scenarios. This holistic approach will contribute to the continued evolution and optimization of landfill liner design, addressing the pressing challenges of sustainable waste management and environmental protection.

Contaminant retention affected by controlled and uncontrolled pH for fly ash-bentonite composites used as landfill liner material

Contaminant retention characteristics of clay-based composites as affected by pH needs to be quantified for its design, functionality, and performance as a landfill liner material. The efficacy of four fly ash (FA) in bentonite-fly ash (B-FA) mixes was investigated for its lead (Pb2+) retention characteristics under controlled pH (pH = 5) and realistic uncontrolled pH conditions anticipated in the landfill liners. B-FA mixes with 30%, 50%, and 70% FA amendment, bentonite-sand (B–S) mixes, and parent materials were tested by batch sorption tests. Under uncontrolled pH conditions, the retention capacity of all parent materials and mixes was higher than the controlled pH condition due to significant precipitation reaction and complexation associated with pH. Beyond 1000 mg.L-1 initial concentration, B-FA mixes constituting FA with inherent pH > 10.5 were the most efficacious adsorbents. Under both pH conditions, the metal retention capacity of B-FA mixes was higher than that of conventional B-sand mixes. All results were analytically substantiated by detailed FESEM micrographs, XRD, and EDX spectra of samples before and after sorption. The Freundlich and Langmuir nonlinear retention model parameters indicate that the uncontrolled pH condition results in nonlinear sorption, the higher energy of sorption, and stronger interactive bonds between Pb2+ ions and sorbent.

Thermophysical Properties of Bentonite–Sand/Fly Ash-Based Backfill Materials for Underground Power Cable

The surrounding (backfill) materials around the underground power cable systems are essential for dissipating the heat away from it, during the exertion phases. The heat dissipation restrains the thermal instability and risk of progressive drying of the backfill materials, thus reducing the thermal stress on the power cable. Thermal instability indicates the reduction in thermal properties (conductivity or diffusivity) due to the migration of moisture because of heat accumulation. Thus, the backfill materials should have adequate thermal properties and water retention capacity to transfer the heat from the heat source to the surrounding area with minimal moisture migration. The bentonite has high water retention capacity, but low thermal conductivity, whereas sand/fly ash exhibits low water retention and has higher thermal conductivity than bentonite. The addition of bentonite promotes the water holding capacity and thermophysical properties of sand and fly ash. Therefore, this study presents the thermal properties of backfill materials, bentonite–fly ash (B–F) and bentonite–sand (B–S), at varying weight-percent of sand and fly ash with bentonite. Various compositions of the mixtures were compacted to varying dry densities, and water contents and thermal properties variation of backfill materials were measured using a dual thermal needle probe ‘KD2 Pro’ at room temperature. The study deals with the systematic evaluation of the volumetric specific heat capacity, thermal conductivity, and diffusivity of backfill materials against varying dry density and water content. The threshold water content (TWC) has been determined from the thermal diffusivity–water content variation curve, and it has correlated with plastic limit (PL) and optimum moisture content (OMC). Thereafter, the efficacies of two thermal conductivity prediction models have also been evaluated statistically with respect to experimental results.

Compressibility of Fly Ash and Fly Ash-Bentonite Mixtures

Environmental protection, one of the most important issues nowadays, forces civil engineers to look for alternative solutions to the known ones. The use of substitute materials as an embankment fill or a ground material under the embankment instead of natural soil follows these trends. A great amount of fly ash is disposed of in landfills. It is a cost-effective material that can be used in construction instead of natural soil. The geotechnical properties of fly ash as a construction material in place of soil need to be examined. It includes laboratory tests to determine the chemical composition and geotechnical characteristics. In the present work, one-dimensional consolidation tests have been conducted to examine the compressibility behaviour of compacted fly ash and fly ash-bentonite mixtures used in the earth structures like road embankments. The analysis of the consolidation phenomenon is useful for predicting the magnitude and rate of settlement of the structure. Materials compacted at OMC to their MDD, according to Standard Proctor, were tested in Rowe-Barden type consolidometer on saturated and non-saturated samples. Coefficients of consolidation have been compared between values derived from log-time and square-root-of-time methods and direct hydraulic conductivity tests. Bentonite amount in fly ash-bentonite mixtures influences the vertical deformation of the sample.

Geotechnical Behaviour of Fly Ash–Bentonite Used in Layers

Increasing infrastructure growth has forced the construction industry to look for wasteful, cheap, and suitable materials for construction. An investigation into the geotechnical utilization of fly ash was carried out in the present study. Practical applications normally involve the use of large quantities of fly ash, so proper mixing of the fly ash with other materials may not be significantly achieved. Therefore, the present paper investigates the behaviour of a fly ash–bentonite layered system with different ratios. The physical properties and chemical composition of fly ash and bentonite were determined. SEM and energy dispersive X-ray experiments were also used to investigate the morphology and phase compositions of fly ash and bentonite. A series of consolidated undrained (CU) triaxial tests on fly ash–bentonite were carried out to investigate shear strength characteristics. Fly ash (F) and bentonite (B) were used in the following ratios: 1:1 (50% F:50% B), 2:1 (67% F:33% B), 3:1 (75% F:25% B), and 4:1 (80% F:20% B), with different numbers of interfaces (N), i.e., 1, 2, and 3 for each ratio. The deviator stress and cohesion value were found to increase with the number of interfaces for each ratio. The angle of shear resistance changed marginally with the increase in the fly ash–bentonite ratios and varying interfaces.

Crack formation behavior of composite fly ash – bentonite (FAB) in landfill liner system

This study aims to investigate the influence of different mixtures on the phenomenon of desiccation cracking in bentonite-fly ash mixtures as a landfill liner system. Fly ash is quite potential to be used as a landfill liner mixture because it has a low hydraulic permeability or conductivity value. This study uses class F fly ash from the Paiton power plant production process, Indonesia, which has been distributed commercially. Desiccation test was conducted in this study. The composition of fly ash and bentonite which is used are pure fly ash (FAB0), fly ash and bentonite 15% (FAB15), fly ash and bentonite 20% (FAB20) and fly ash and bentonite 25% (FAB25). The smallest CIF value is found in the pure fly ash layer. However, the pure fly ash cannot be used as landfill liner because the high permeability value. Therefore, the addition of bentonite will increase the possibility of crack formation. This study reveals that the addition bentonite in the fly ash composite will increase the crack. However, determining appropriate mixture composition is critical when working on the landfill liner system.

Geotechnical characterization of bentonite-fly ash mixtures for their application as landfill liner in Pakistan

Geotechnical characterization of bentonite-fly ash mixtures for their application as landfill liner in Pakistan

Analysis of WRCC of Fly Ash-Bentonite Mixes Based on Combined Shrinkage and Suction Measurement

Sand-Bentonite mixtures are used in landfill liner application in appropriate proportions. However, effort has been made to replace the sand by some waste materials like fly ash without compromising the required properties for liner construction. In recent years, many studies were carried out to determine the suitability of different fly ashes for using with bentonite based on different geotechnical parameters. On the other hand, limited studies were found in determining the unsaturated characteristics i.e. Water Retention Characteristics Curve (WRCC) of fly ash-bentonite mixes. The determination of WRCC in case of bentonite is very complexed compared to other types of clay soil due to its high shrinkage and swelling characteristics upon drying and wetting. In this study, a combined shrinkage and suction measurement was carried out in fly ash-bentonite mixes to accurately represent the WRCC under drying condition only. The shrinkage measurement was carried out using balloon method and suction measurement was carried out with the help of WP4 dew point potentiameter device. Both the shrinkage and suction results were finally used to obtain the WRCC for the different mixes. Further, the study on the variability of WRCCs for the different mixes indicates that WRCC can be represented by a generalized plot with 20% variation.

Mechanical performance and micro-structure of bentonite-fly ash and bentonite-sand mixes for landfill liner application

Abstract Low permeability (10−9 m/s) and adequate unconfined compressive strength (UCS = 200 kPa) forms the basis of using compacted bentonite (B) clay in landfill liner. However, B induces cracks or swells upon excessive drying and wetting events, respectively. To overcome failure of liner layer, B is amended with cohesionless sand (S), despite S being costly and ecologically unsustainable. In the recent past, fly ash (FA) a by-product from thermal power plants, has been explored as a suitable additive material in landfill liner, in line with the adoption of cleaner usage of waste material in construction. The objective of this study was to investigate the mechanical performance of both B-FA and B–S mixes along with the related changes in microstructure and physio-chemistry. 180 sets of UCS tests were conducted on 4 B-FA mixes (including class C and F) and B–S mixes at different compaction state and additive rate. Unlike B–S mixes, all B-FA mixes showed an increase in UCS with respect to B regardless of compaction state and additive rate. Detailed microstructure and physio-chemical characterization for B–FAs revealed the relative abundance in the formation of calcium aluminosilicate hydrate, and ettringite minerals after curing as compared to B–S mixes. In fact, Class C FA exhibited the largest UCS even at high moisture content, which can be attributed to higher formation of minerals upon curing. All B-FA mixes showed UCS greater than the minimum limit for liner application regardless of the compaction state. All B–S mixes did not adhere to the minimum UCS criterion at higher moisture content. FA additive at 50% showcased the highest increase in strength improvement factor (10 out of 12 cases), while for B–S mixes, this factor decreased with an increase in additive rate. Based on the measured data, two new linear relationships of UCS with pH and electrical conductivity (both indicative of reaction) of the mixes were observed. The relationship with respect to pH was more pronounced at higher moisture content as pH indicates the existence of CaO minerals.

Modelling contaminant transport in fly ash\u2013bentonite composite landfill liner: mechanism of different types of ions

Generated hazardous or toxic waste posses a serious threat if dumped into ponds or low lying areas which leads to contamination, this necessitates the effective landfill liner system. Mainly compacted clayey soils are used as an engineered barrier. Recently, composite materials have gained popularity as landfill liner materials, including the use of waste materials amended with low permeable soils. Though, studies on the composite optimum mix and its corresponding thickness are very scarce. Here, we evaluated the unconfined compressive strength and hydraulic conductivity of fly ash–bentonite composites. Efforts were also made to determine the thickness of landfill liner composite using a finite difference method (i.e. MATLAB). The results reveal that composite consists of 30% bentonite and 70% fly ash is suitable for landfill liner, which meets strength and permeability criteria. Numerical simulation for five major contaminants shows that the composite plays a crucial role in reducing the leaching of heavy metals and suggests an optimum thickness in the range of 126–154 cm. Overall, the findings of the study indicate that fly ash–bentonite composite can be used to solve real-life challenges in a sustainable way.

A feasibility study of Indian fly ash-bentonite as an alternative adsorbent composite to sand-bentonite mixes in landfill liner

Multi-layered engineered landfill consists of the bottom liner layer (mainly bentonite clay (B)) upon which the hazardous wastes are dumped. In current practice, sand (S) is mixed with bentonite to mitigate the adverse effects of using bentonite alone in the liner layer. Incorporation of waste and unutilized fly ash (FA) as an amendment material to B has been explored in terms of its hydro-mechanical properties, but not gauged its adsorption potential. Indian subcontinent primarily relies on the thermal power source, and FA dumps have already reached its full capacity. The objective of this study is to explore the adsorption characteristics of four B-FA composite mixes sourced within India, considering Pb2+ as a model contaminant. The effect of fly ash type, fly ash amendment rate and adsorbate concentration was explored in the current study and juxtaposed with B-S mixes, based on 960 batch adsorption tests. Both B-FA and B-S mixes reached equilibrium adsorption capacity within 65 min. At higher adsorbate concentrations (commonly observed in the liner), B-FA mixes exhibited superior adsorption capacity, mainly one mixed with Neyvelli fly ash (NFA). The effect of higher amendment rate had little impact on the adsorption capacity at different concentration, but gradually decreased the percentage removal of Pb2+. The B-S mix showed a drastic decrease in percentage removal at higher adsorbate concentration among all tested mixes. Systematic characterization including geotechnical properties, microstructure and chemical analysis was also done to interpret the obtained results. Both Freundlich and Langmuir models fitted the isotherm data well for all B-FA mixes. The maximum adsorption capacity from the isotherm was correlated to easily measurable Atterberg limits by two empirical relationships.

Water Retention Characteristics of Fly Ash–Bentonite Mix

The use of sand–bentonite mixes as hydraulic barrier in municipal and hazardous landfills are established in the literature. Environmental awareness and stringent rules on river conservation has restricted the free availability of construction sand making it non-viable for massive geo-environmental projects such as waste containment. Following the same philosophy for which sand was used in bentonite, this study propose to replace the former with fly ash. Apart from being an alternate material to sand, this proposition would ensure mass utility of waste fly ash for environmentally advantageous waste containment project. For this purpose, it is important to study the unsaturated characteristics of fly ash–bentonite mix, which is not reported in the literature. This study explores the influence of fly ash properties and its classification on the water retention characteristics curve (WRCC) of fly ash–bentonite mixes. The extent of variability in WRCC attributed to different sources of fly ash were quantified to investigate whether there is a possibility of generalizing the unsaturated behavior of fly ash–bentonite mixes. In addition, the influence of bentonite water content on the WRCC of mixes were studied and compared with the previously published results in the literature. It was found that at high suction (> 105 kPa), all the WRCC of FA–B mixes merges together and is mainly dominated by the water retention of bentonite only. It was also established from this study that any types of fly ashes irrespective of its source can be used in this application if compacted at optimum moisture content.

Reuse of Excavated Clayey Silt in Cement–Fly Ash–Bentonite Hybrid Back-fill Grouting during Shield Tunneling

Excavated soils from tunnel construction need high treatment cost and pollute the environment. To investigate the feasibility of excavated clayey silt reused in back-fill grout, the flowability, stability and strength were taken as measurement indexes of grouting performance. The clayey silt was tested to be reused as substitutes for fly ash, bentonite and sand, respectively. The experimental results indicated that the clayey silt reused as a substitute for fly ash decreased the flowability and strength of grout mixes, and the clayey silt reused as a substitute for bentonite decreased the stability of grout mixes, and neither of them was feasible. The clayey silt reused as a substitute for sand decreased the flowability, but the grouting performance could be improved by adjusting the mix proportion to meet all grouting requirements. After adding the proportion of water to improve the flowability and increasing the cement:fly ash ratio to improve the strength, a scheme of clayey silt reutilization was suggested, which was cement:fly ash:bentonite:clayey silt:water = 280:230:100:680:660. At the end of this paper, the pore structure feature tests, X-ray diffraction (XRD) tests and scanning electron microscope (SEM) tests were performed to analyze the different morphology, microstructure and mineralogy characteristics before and after the clayey silt was reused as a total substitute for sand in grout mixes.

Exploring Potential of Fly Ash–Bentonite Mix as a Liner Material in Waste Containment Systems Under Concept of Sponge City

Abstract Many studies have been conducted to evaluate fly ash as an additive for the modification of hydraulic properties of soil. However, rarely are studies carried out that quantify physiochemical, strength, and hydraulic properties of fly ash–bentonite mix. Fly ash–bentonite mix may have the potential to be used as a landfill liner material instead of conventional sand in sand-bentonite landfills. Also, with the introduction of the new concept of sponge city, one of the aims of which is to minimize contamination and maximize the use of waste material, the exploration of fly ash–bentonite mix as a cover material in retention systems is highly crucial. The main objective of this study is to explore physicochemical, strength, and hydraulic properties as well as sorption characteristics of fly ash–bentonite mix. The sorption characteristics of the fly ash–bentonite mix for two heavy metals, lead ions (Pb+2) and nickel ions (Ni+2), were investigated. A criterion based on cation exchange capacity (CEC) and specific surface area (SSA) has been proposed. The study also developed correlations for estimating the CEC of soils with SSA and other soil parameters. Hydraulic conductivity decreases approximately four orders of magnitude with an increase in 30 % of bentonite. Unconfined compressive strength (UCS) is found to increase first (up to 40 % fly ash) and then reduces with further increase in fly ash. Furthermore, the curing time is also found to affect UCS significantly. The findings stated that the mix of 70 % or lower fly ash content (in fly ash–bentonite mix) is able to meet standard requirements for hydraulic conductivity and UCS. The Langmuir isotherm is found to better represent sorption behavior of fly ash–expansive soil, with nickel and lead as model contaminants. All the mixes considered in this study exhibited maximum uptake of Pb+2. Sorption decreases very mildly for mixes that have some expansive soil content, whereas it reduces drastically for only fly ash content.

Novel approach to control adsorbent aggregation: iron fixed bentonite-fly ash for Lead (Pb) and Cadmium (Cd) removal from aqueous media

In the present study, a novel approach was used to control zero valent iron aggregation and separation problems by fixing zero valent iron (ZVI) on bentonite-fly ash pellets. For this purpose, porous low cost bentonite-fly ash (BFA) pellets with size of 2.00 cm in length and 0.35 cm in diameter were prepared and fixed with ZVI to manufacture zero valent iron bentonite-fly ash (ZVI-BFA) pellets. Importantly, unlike powdered adsorbents, ZVI-BFA can easily be separated from final effluents when exhausted without any disintegration. The performance of the developed novel adsorbent was investigated for the removal of Pb2+ and Cd2+ from aqueous media. At 100 mg·L–1 and 1 g adsorbent, a maximum of 89.5% of Cd2+ and 95.6% of Pb2+ was removed by ZVI-BFA as compared to 56% and 95% removal by BFA. At 200 mg·L–1, Cd2+ and Pb2+ removal by ZVI-BFA was 56% and 99.8% respectively as compared to only 28% and 96% by BFA. Further, the removal kinetics was best fitted for pseudo-second order model. The study provides the basis for improving the removal capacity of porous materials by iron fixation while taking separation ability into consideration.

Evaluation of Bentonite-Fly Ash Mix for Its Application in Landfill Liners

Abstract Compacted landfill liners are required to minimize the migration of harmful contaminants to the surrounding geoenvironment and groundwater. This is mainly achieved by restricting hydraulic conductivity of the compacted liners within a permissible limit of 10−7 cm/s. For geomaterials used in liners, it is important to determine the appropriate range of compaction parameters (water content and dry unit weight) that would ensure hydraulic conductivity and strength characteristics within safe limits. There are not many studies in the literature for specifying such a range for bentonite-fly ash mixes. The addition of cohesionless fly ash would improve the strength and reduce the shrinkage behavior of bentonite but at the same time would increase the hydraulic conductivity. Therefore, it is of utmost importance to determine the ranges of water content and dry unit weight for different bentonite-fly ash mixes that would satisfy the desired ranges of hydraulic conductivity and strength. The objective is to identify the bentonite-fly ash mix that enables maximum use of fly ash, which is advantageous from an environmental perspective. The performance evaluation of different compacted mixes has been done using hydraulic conductivity and unconfined compressive strength as the two reference parameters. The study clearly demonstrates the utility of a bentonite-fly ash mix as a compacted landfill liner. On the basis of the results, it can be noted that up to 70 % by weight of fly ash can be mixed with bentonite for satisfying the requirements of compacted landfill liners.

Properties of Fly Ash as Hydraulic Barrier

This study examines the suitability of pozzolanic fly ash as a hydraulic barrier and the use of bentonite to enhance geotechnical properties of fly ash. The behavior of fly ash is studied not only with water but also with different pore fluids, such as acid, alkali, salts, and neutral organic fluid to assess its chemical compatibility. While some geotechnical properties of fly ash meet the requirements of liner material, the disadvantage of using of fly ash alone is that it has a low cation exchange capacity and high hydraulic conductivity. The compressibility of fly ash reduces with alkaline solution but increases with acidic solutions. While alkaline or neutral inorganic solutions do not affect the hydraulic conductivity of fly ash, the addition of dilute acid increases the hydraulic conductivity. Addition of bentonite improves the geotechnical properties of fly ash such as cation exchange capacity, shrinkage and volume change behavior, etc. Fly ash-bentonite mixtures possess low shrinkage and hence do not crack. Compacted fly ash-bentonite mixtures undergo very little volume changes under various stress conditions. The hydraulic conductivity of fly ash is reduced after amendment with bentonite. Though the unconfined compressive strength of the mixture is lower than that of fly ash alone, the fly ash-bentonite mixture still possesses good strength. The compressibility of fly ash bentonite mixtures are lower with different pore fluids studied than with water. The hydraulic conductivity of fly ash-bentonite mixtures are slightly higher in different pore fluids studied than with water.