LOW SWELLING HYDRAULIC LANDFILL BARRIER COMPOSITION AND METHOD OF PREPARING THE SAME

Abstract

According to the present disclosure, an environment friendly and sustainable low swelling hydraulic barrier composition for landfills and other geotechnical applications, and a method of preparing the same are disclosed. The method comprises the step of preparing a blend of polymer bentonite mixture with coal ash in dry state and mixing the water with the dry mixture uniformly. The polymer bentonite is mixed in the range of 10% to 25% (considering the feasibility of blending polymer bentonite mixture with coal ash and water) by total weight. The coal ash is mixed in the range of 90% to 75% (with an intention of promoting bulk utilization) by total weight and the water is mixed in the range of 17% to 27% of the total weight of the dry mixture uniformly. The polymer bentonite blended coal ash mixture acts as an effective impermeable barrier material and shows low swell behaviour. Reference Fig.: Figure 2

Specification

Description:LOW SWELLING HYDRAULIC LANDFILL BARRIER COMPOSITION AND METHOD OF PREPARING THE SAME

TECHNICAL FIELD
[0001] The present disclosure relates to hydraulic barriers, and more particularly relates to a low swelling hydraulic barrier composition comprising polymer bentonite blended coal ash mixture for landfills and other geotechnical applications and a method of preparing the low swelling hydraulic barrier composition.

BACKGROUND OF THE INVENTION
[0002] Over 50% of India's electricity generation relies on coal-based thermal power plants. These power generation plants produce huge amounts of inorganic coal waste. A critical aspect of these plants is the combustion of coal, which produces coal combustion residues (CCR), commonly referred to as ash. The ash produced is broadly categorized as Pond ash and Bottom ash. Pond ash is a mixture of fly ash and bottom ash, commonly used in construction applications such as embankments, road sub-base, and as a raw material in the production of bricks and concrete blocks. Whereas bottom ash is the heavier, coarse component of coal ash that settles at the bottom of the boiler in a coal-fired power plant and also deposited in ash dykes along with water. A significant amount of coal ash by-products, amounting to 226.13 million tons annually (CEA, New Delhi, 2020) is generated and a large portion of these by-products is dumped in open areas without proper management. These dumped by-products cause huge environmental problems including pollution of air by particulate matters, pollution of water bodies by heavy metal leaching, etc. The significant generation of coal ash, particularly from thermal power plants has created an urgent need for its utilization, thereby leading to research in many possible avenues to find sustainable and beneficial uses of coal ash across various industries.
[0003] Utilization of coal ash by-products, particularly fly ash, has seen substantial growth, increasing from 9.63% in 1997 to 83.02% in 2020. These by-products are utilized in various other sectors, including cement production to enhance the strength and durability of concrete while reducing the demands for raw materials. Coal ash by-products are also used in manufacturing bricks and tiles, providing a sustainable alternative to traditional clay products. Bulk utilization of coal ash by-products is also found in mine filling, road construction, embankment building, land reclamation, ash dyke raising, and even in agriculture, where the coal ash can improve soil properties. This increased utilization not only helps in reducing the environmental impact of coal ash disposal but also contributes to resource conservation and economic efficiency. With an increase in demand for power generation, there is also a need for meeting the ever demand for finding other avenues for ash utilization. This implies that the volume of unused material continues to grow each year due to increasing power demand, urbanization, industrialization, and other factors. Consequently, managing these by-products has become increasingly challenging, with pollution associated with their disposal posing a significant concern.
[0004] In recent years, studies have been carried out by blending bentonite with coal ash by-products for barrier application. The use of bentonite blended with coal ash by-products in specific proportions has been studied for its permeability characteristics to achieve values lower than 10-9 m/s, which is one of the main key requirements for a barrier material. Bentonite is a type of clay known for its high swelling capacity and low permeability. It is often used to promote containment within various types of retention facilities such as ponds, reservoirs, landfills, etc. It is also used in various engineering applications, including as a liner material in landfills and containment systems in the form geosynthetic clay liner, due to its ability to form impermeable barriers when hydrated.
[0005] Some studies have been conducted to blend bentonite with coal ash by-products, primarily aiming to leverage the advantage of properties of both materials to create a composite material suitable for barrier applications. Compacted clay barriers are traditionally used to promote containment within various types of retention facilities such as ponds, reservoirs, landfills, etc. Landfill sealing layers safeguard groundwater and the soil from contamination caused by the leachate generates from the waste. Coal ash, which is a by-product of coal combustion, can be used as a substitute material for scarcely available suitable natural soils to build sealing layers. These layers act as a barrier, preventing hazardous substances from infiltrating and compromising the surrounding environment. One of the approaches for constructing these sealing layers involves utilizing coal ash, by-product generated from coal combustion, as an alternative to natural soils/sand blended with polymer bentonite. By substituting coal ash, we can effectively create robust and efficient landfill sealing layers, thereby promoting environmental sustainability and resource conservation.
[0006] In one prior art, an improved bentonite was disclosed by adding polyanionic cellulose polymer to be sandwiched in geosynthetic clay liner instead of a standard bentonite to achieve reduced permeability for containment applications. In another prior art, a method to improve the natural bentonite by adding acrylamide copolymer, two types of cross-linking agents, thiourea in certain parts or proportions was disclosed. The method uses fly ash and silica fume as raw material to be added with bentonite and then modified or improved bentonite using polymer mentioned.
[0007] In another prior art, a polyethyleneimine modified fly ash and a polymer modified bentonite having a sulfonic acid anion to add to bentonite has been disclosed. The modified bentonite involves with the complex processes and steps, comprising of initially modifying fly ash and then the bentonite, further both are combined to arrive at the desired barrier. In another prior art, an impermeable material for barrier is formed by mixing 40% to 65% of clay, 5% to 10% of granulated blast furnace slag powder, 5% to 10% of fly ash, 1% to 5% of magnesium oxide and 5% to 10% of sodium bentonite. In yet another prior art, 80% to 85% of in situ soil are mixed with 5% to 10% polymer, modified bentonite (natural bentonite modified using a polymer) and up to 10% additive, which is a combination of cement and fly ash, for vertical barrier applications to restrict movement of heavy metal ions and achieve impermeable barrier behaviour.
[0008] In accordance with another prior art, lightweight synthetic aggregates (SLA's) comprised of various combinations of low or negative value materials, namely fly ash and multipolymer component mixtures have been described. The lightweight aggregates consist of various ratios (by weight) of fly ash and recycled plastics compounded under heat and pressure. Aggregates with fly ash-to-plastic ratios ranging from 0%:100% to 80%:20% were compounded and tested for specific gravity and particle-size distribution.
[0009] However, the composite materials, including clay barriers and geosynthetic clay liners mentioned in the aforementioned state-of-the-art documents are effective, they are particularly effective in retaining substances within the designated areas, yet they have limitations, particularly when exposed to ionic substances. These substances can alter the swelling properties compromising the barrier's effectiveness. Moreover, leachates often contain varying concentrations of metal ions and electrolytes, which can interact unpredictably with barrier materials posing a significant containment challenge.
[0010] Moreover, in the case of ponds, reservoirs, and other non-hazardous bodies of water, the water leakage increases over time if the containment structure is not adequately sealed. Hence, there is a need for an economical, environment friendly lightweight and a low swelling hydraulic barrier composition for landfills (as the overburden is limited in landfill cap covers, ponds and canal lining applications) and for other geotechnical applications, where low swelling and hydraulic sealing efficiency is required. The present invention discloses a low swelling hydraulic barrier composition using a polymer bentonite blended coal ash mixtures moist-compacted at their respective maximum dry unit weight and optimum moisture content (according to standard Proctor compaction) that can enhance the seal of a pond or reservoir or landfill, thereby preventing contamination due to ingress of water and egress of methane gas into the atmosphere and the loss of water.

OBJECT OF THE INVENTION
[0011] It is the primary object of the present disclosure to provide a low swelling hydraulic barrier composition for landfills and other geotechnical applications.
[0012] It is another object of the present disclosure to provide a method involving steps for preparing low swelling hydraulic barrier composition for landfills and other geotechnical applications.
[0013] It is another object of the present disclosure to provide an effective and environment-friendly hydraulic landfill barrier material comprising a polymer bentonite blended coal ash mixture.
[0014] It is another object of the present disclosure to provide a sustainable barrier material with enhanced lower permeability for other geotechnical applications.

SUMMARY OF THE INVENTION
[0015] In an aspect of the present disclosure, a method of preparing a low swelling hydraulic barrier composition for landfills and geotechnical applications is disclosed. The method comprises the step of preparing a blend of polymer bentonite mixture with coal ash in dry state and mixing the water with the dry mixture uniformly. The polymer bentonite is mixed in the range of 10% to 25% (considering the feasibility of blending polymer bentonite mixture with coal ash and water) by total weight. The coal ash is mixed in the range of 90% to 75% (with an intention of promoting bulk utilization) by total weight and the water is mixed in the range of 17% to 27% of the total weight of the dry mixture uniformly. The coal ash comprises one of bottom ash and pond ash.
[0016] In another aspect of the present disclosure, a low swelling hydraulic barrier composition for landfills and other geotechnical applications is disclosed. The composition comprises a dry mixture comprising a blend of polymer bentonite mixture in the range of 10% to 25% by total weight and coal ash in the range of 90% to 75% by total weight in dry state and mixing the water in the range of 17% to 27% by total weight of the dry mixture uniformly.

BRIEF DESCRIPTION OF THE DRAWINGS
[0017] The exemplary embodiments of the present invention have been described with reference to the accompanying figures.
[0018] Figure 1 illustrates a cross-sectional view of a conventional top barrier of landfills in accordance with the present disclosure
[0019] Figure 2 illustrates a cross-sectional view of a top barrier system made using the low swelling hydraulic barrier composition in accordance with the present disclosure.
[0020] Figure 3 illustrates the variation of swell/compression and swell potential with time for a mixture 1 in accordance with an example of the present disclosure.
[0021] Figure 4 illustrates the variation of swell/compression and swell potential with time for a mixture similar to the combination as mixture 1 but without the polymer content in accordance with the example of the present disclosure.
[0022] Figure 5 illustrates the variation of swell/compression and swell potential with time for a mixture 2 in accordance with the example of the present disclosure.
[0023] Figure 6 illustrates the variation of swell/compression and swell potential with time for a mixture similar combination as mixture 2, but without the polymer content in accordance with the example of the present disclosure.
[0024] Figure 7 illustrates the determination of swell pressures obtained from swell-consolidation tests for the mixture 1 and the mixture 2 plotted from the variation of swell/compression with time observed in Figure 3 and Figure 5 in accordance with the example of the present disclosure.
[0025] Figure 8 illustrates the determination of swell pressures from swell-consolidation tests for mixtures made with similar combination without the polymer, plotted from the variation of swell with time observed in Figure 4 and Figure 6 in accordance with the example of the present disclosure.
[0026] Figure 9 illustrates the variation swell/compression and swell potential with time for a mixture made similar to mixtures 1 and 2, but without coal ash in accordance with another example of the present disclosure. Figure 9 shows the high swell behaviour of the mixture.
[0027] Figure 10 illustrates the determination of swell pressure from swell-consolidation test for the mixture made similar to mixtures 1 and 2, but without coal ash in accordance with another example of the present disclosure. Figure 10 is plotted from the variation of swell/compression with time (Figure 9).
[0028] Figure 11 illustrates the comparison of coefficient of permeability with time for mixture 1 and mixture 2 against similar combination of mixtures without the polymer, in accordance with the example of the present disclosure.
[0029] Figure 12 illustrates the variation of crack intensity factor (CIF) with time for mixture 1 and mixture 2 in accordance with the example of the present disclosure.
[0030] Figure 13 illustrates the coefficient of permeability of cracked samples immediately after inundation with time for mixture 1 and mixture 2 in accordance with the example of the present disclosure. Figure 13 shows the variation of coefficient of permeability measured on tests conducted on samples collected with maximum CIF with time for mixture 1 and mixture 2.
[0031] Figure 14 illustrates a cross-sectional view of a canal lining system composed of the low swelling barrier composition in accordance with the present disclosure.
[0032] Figure 15 illustrates a cross-sectional view of a core of an earthen dam composed of the low swelling barrier composition in accordance with the present disclosure.

DETAILED DESCRIPTION OF THE INVENTION
[0033] A low swelling hydraulic barrier composition for landfills and other geotechnical applications and a method of preparing the same are disclosed. The present invention uses industrial waste materials such as coal ash by-products blended with polymer bentonite as a barrier material for landfills and other geotechnical applications, where low swelling and hydraulic sealing efficiency is required. A low swelling hydraulic barrier was prepared by mixing polymer bentonite with two types of coal ash including bottom ash and pond ash. The polymer bentonite coal ash mixture acts as an effective impermeable barrier material and shows low swell behaviour.
[0034] Referring to Figure 1, illustrated is a cross-sectional view of a conventional top barrier of landfills in accordance with the present disclosure. The conventional barrier landfill consists of a vegetation cover layer, a top soil consisting of an erosion control layer and a protection soil layer, a water drainage layer, a clay liner, a gas drainage layer, a soil barrier layer and a waste. The vegetation cover layer includes grass, shrubs, or other plants, followed by an erosion protection layer and protection layer that controls erosion and manage rainwater runoffs. The drainage layer consists of gravel to collect and channel the leachates that seeps through the waste material. The clay liner is a layer of compacted clay that serves as a primary barrier to prevent leachates from escaping into the surrounding soil and groundwater.
[0035] The conventional barrier material is placed above a gas drainage layer. As waste decomposes, gases such as methane gets generated, and the gas drainage layer collects the methane generated by decomposition of the waste using pipes to further utilize it for generating energy. The conventional top barrier system further comprises a soil layer followed by a waste serves as a foundation where waste is initially deposited. The primary purpose of this layer is to contain the waste materials and to provide structural support for the entire landfill. However, the conventional barrier landfills face several challenges and limitations, including high permeability which can lead to develop cracks over time and allow leachate to escape. Further, conventional barriers can degrade due to weathering, erosion thereby reducing their long-term effectiveness. Some materials may swell or shrink with moisture changes, leading to potential cracks.
[0036] In an embodiment of the present disclosure, a method of preparing a low swelling hydraulic barrier composition for landfills and other geotechnical applications is disclosed.
[0037] The method comprises the step of preparing a blend of polymer bentonite mixture and coal ash in dry state and mixing the water with the dry mixture uniformly. The polymer bentonite is mixed in the range of 10% to 25% (considering the feasibility of blending polymer bentonite mixture with coal ash and water) by total weight. The coal ash is mixed in the range of 90% to 75% (with an intention of promoting bulk utilization) by total weight and the water is mixed in the range of 17% to 27% of the total weight of the dry mixture uniformly. After completion of mixing process, the polymer bentonite blended with coal ash is kept for hydration for a minimum time period of 24 hours and moist compacted at standard Proctor compaction at a maximum dry unit weight and at an optimum moisture content of bottom ash mixture and pond ash mixture respectively. The coal ash comprises one of bottom ash and pond ash.
[0038] In an embodiment of the present disclosure, the maximum dry unit weight of polymer bentonite blended bottom ash mixture is in the range of 12.0 kN/m3 to 13.5 kN/m3 and the optimum moisture content of polymer bentonite blended bottom ash mixture is in the range of 24% to 27%.
[0039] In an embodiment of the present disclosure, the maximum dry unit weight of polymer bentonite blended pond ash mixture is in the range of 14.0 kN/m3 to 15.5 kN/m3 and the optimum moisture content of polymer bentonite blended pond ash mixture is in the range of 17% to 19%.
[0040] In an embodiment of the present disclosure, the polymer bentonite in dry state comprises bentonite mixture in the range of 96% to 98% by total weight and a polymer in the range of 2% to 4% by total weight.
[0041] In an embodiment of the present disclosure, the polymer is a hydrophilic polymer selected from the group comprising Polyvinyl Alcohol (PVA), Polysaccharides, Polyacrylic acid, Polyacrylamide (PAM), Sodium Polyacrylate, Hydroxyethyl Cellulose, Polyethylene Glycol (PEG) and Carboxymethyl Cellulose and a combination of thereof.
[0042] In an embodiment of the present disclosure, the bentonite mixture comprises a sodium bentonite.
[0043] In an embodiment of the present disclosure, wherein bottom ash has an average particle size (d50) in a range of 0.10 mm to 0.80 mm and a small particle size or an effective particle size (d10) in a range of 0.010 mm to 0.090 mm.
[0044] In an embodiment of the present disclosure, the pond ash has an average particle size (d50) in a range of 0.050 mm to 0.080 mm and a small particle size or an effective particle size (d10) in a range of 0.005 to 0.020 mm.
[0045] Figure 2 illustrates a cross-sectional view of a top barrier system made using the low swelling hydraulic barrier composition in accordance with the present disclosure. The barrier system uses the low swelling hydraulic barrier composition instead of conventional barrier materials including compacted clay barriers, sand bentonite mixtures, Geosynthetic clay liners and Geomembranes.
[0046] The composition comprises a dry mixture comprising a blend of polymer bentonite mixture in the range of 10% to 25% by total weight and coal ash in the range of 90% to 75% by total weight in dry state and mixing the water in the range of 17% to 27% by total weight of the dry mixture uniformly.
[0047] In an embodiment of the present disclosure, water mixed with dry mixture in the range of 24% to 27% by total weight of the dry mixture prepared by blending polymer bentonite and bottom ash.
[0048] In an embodiment of the present disclosure, water mixed with dry mixture in the range of 17% to 19% of the total weight of the dry mixture prepared by blending polymer bentonite and pond ash.
[0049] The present invention is now further described by the following non-limiting examples. The low swelling hydraulic barrier material was prepared by blending polymer bentonite with both two types of coal ash by products that is bottom ash and pond ash at different percentages of the total weight of the mixture and properties were evaluated. The bottom ash used in the experimentation has an average particle size (d50) of 0.72 mm and an effective particle size (d10) of 0.085 mm and the Pond ash used in the experimentation has an average particle size (d50) of 0.071 mm and an effective particle size (d10) of 0.017 mm. The pH value of bottom ash and pond ash are 9.19 and 8.73 respectively. Electrical conductivity of bottom ash and pond ash are 123.1 μS/cm and 114.3 μS/cm. For the experimentation, a commercially available polymer bentonite, TRISOPLAST® polymer bentonite was used, which has a very high Free Swell Index of 81 ml/2g and specific gravity of 2.79. For comparison, two mixtures were prepared. One mixture was prepared by blending bentonite (without polymer) with coal ash and another mixture was prepared by blending polymer bentonite with coal ash. Bentonite utilized in experimenting had a Free Swell Index of 26 ml/2g and specific gravity of 2.84. Mixtures were prepared in the laboratory with varying percentages of polymer bentonite as 10%, 15% and 25%. Once the mixtures were prepared, their geotechnical properties were evaluated and further experimental investigations were carried out to determine their swell behaviour and permeability, tensile stress-strain characteristics, and desiccation behaviour. All the mixtures were compacted at optimum moisture content (OMC) and maximum dry unit weight (MDU) according to standard Proctor compaction.
Swell Behavior
[0050] To determine the swell behavior of mixtures and swell pressure, the percentage swell and the swell pressure for both mixtures with varied bentonite percentages were evaluated by performing swell-consolidation tests in the laboratory. The test apparatus and methodology confer to ASTM D2435 and ASTM D4546 standards, respectively. Swell is defined by the net increase in thickness of the sample. Percentage swell is defined as the ratio of change in height of the sample to the initial height of the sample. The swell pressure is defined as the pressure required to bring back the sample to its initial height after the sample is swollen.
[0051] From the results, it was noticed that at 10% blend of polymer bentonite/bentonite, no swelling was observed. When the blend percentage of polymer bentonite/bentonite was increased to 15%, a very limited swelling was observed. At the 15% polymer bentonite/bentonite, the percentage swell values of 0.5% for bentonite-bottom ash, 1.65% for bentonite-pond ash, and 1.27% for polymer bentonite-bottom ash, and 4.3% for polymer bentonite pond ash and their respective swell pressure values being 9 kPa, 11 kPa, 16 kPa and 52 kPa were determined. Further, the blend percentage was increased to 25%, and an increase in both the percentage swell values and the corresponding swell was observed. Figure 3 illustrates the variation of swell/compression and swell potential with time for a mixture 1 in accordance with an example of the present disclosure. In mixture 1, the polymer bentonite mixture of 15% is blended with bottom ash of 85%. Figure 4 illustrates the variation of swell/compression and swell potential with time for a mixture of similar combination as mixture 1, but without the polymer content in accordance with the example of the present disclosure.
[0052] Figure 5 illustrates the variation of swell/compression and swell potential with time for a mixture 2 in accordance with the example of the present disclosure. In the mixture 2, the polymer bentonite of 15% is blended with pond ash of 85%. Figure 6 illustrates the variation of swell/compression and swell potential with time for a mixture of similar combination as mixture 2, but without the polymer content in accordance with the example of the present disclosure. Further, Figure 7 illustrates the determination of swell pressure obtained from swell-consolidation tests for the mixture 1 and mixture 2 plotted from the variation of swell/compression with time observed in Figure 3 and Figure 5 in accordance with the example of the present disclosure. Figure 8 illustrates the determination of swell pressure obtained from swell consolidation tests for the mixtures made with similar combination without the polymer, plotted from the variation of swell/compression with time observed in Figure 4 and Figure 6 in accordance with the example of the present disclosure. Emphasising on the limited swell behaviour of polymer bentonite blended coal ash mixtures, a comparison is made with mixture prepared by blending 15% polymer bentonite with 85% sand (without coal ash). These mixtures show very high swell behaviour and swell pressure as illustrated in Figure 9 and Figure 10 respectively. The comparison is made by maintaining the similar combination as that of polymer bentonite coal ash mixtures and also, placed at OMC and MDU.
[0053] When mixed with coal ash, the bentonite or polymer bentonite mixtures show limited swelling ability due to the presence of calcium (Ca) in the coal ash, though the bentonite or polymer bentonite individually has a very high swelling capacity. The swelling ability of the bentonite or the polymer bentonite is very high due to the excessive sodium Na+ cations present on the clay surface. The excessive sodium cation results to the high-water holding capacity between clay particles and creates a larger double diffuse layer. Such high-water holding capacity was noted when bentonite or polymer bentonite was blended with sand. For the 15% blend of bentonite or polymer bentonite, percentage swell of more than 25% and swell pressure values more than 200 kPa were observed. The presence of Calcium (Ca++) in coal ash, with its higher valence and larger atomic radius, replaces Sodium (Na+) in the clay structure, resulting in a reduction of exchangeable cations that promote water holding capacity and swelling. Consequently, coal ash-based mixtures show limited swelling. However, marginal increase in water holding capacity of the mixtures was observed due to the presence of the polymer. Relatively higher percentage swell and swell pressure values of the mixtures with polymer content indicated the increase in water holding capacity in comparison with the mixtures without polymer content.
Permeability
[0054] The permeability was evaluated for the prepared mixtures, and it was observed that for any given blend percentage, polymer bentonite-based coal ash mixtures showed lower permeability values than those with bentonite alone. When the polymer comes into contact with water, it forms gel-like structures and dispersed completely, such as chain, sheet, or globule patterns, which occupy the void spaces within the mixture due to the polymer action. This polymer action restricts or reduces the available flow paths, making the mixtures less permeable.
[0055] For the mixtures with 15% blend of polymer bentonite, the permeability values were lower than 10-9 m/s for both types of coal ash used, specifically 7.2 x 10-10 m/s for polymer bentonite-bottom ash and 5.2 x 10-10 m/s for polymer bentonite-pond ash, which is the key requirement for a barrier material (Fig. 11). Similarly, at 15% blend of bentonite, the permeability values were 2.6 x 10-7 m/s for bentonite-bottom ash and 6.7 x10-9 m/s for bentonite-pond ash. Therefore, for the bentonite-based coal ash mixtures with the same 15% blend, the permeability values did not meet the required criterion for the barrier material. For the mixtures with 25% blend of both polymer bentonite and bentonite, permeability values were lower than 10-9 m/s for the types of coal ash used except for 25% bentonite blend with bottom ash. Permeability values were as follows: 2.4 x 10-10 m/s for polymer bentonite bottom ash, 4.5 x 10-11 m/s for polymer bentonite pond ash, 7.3 x 10-10 m/s for (bentonite pond ash) and 3.2 x 10-8 m/s (bentonite bottom ash).
[0056] The reported permeability values were obtained after the sample mixtures were inundated for 8 days, followed by continuous monitoring of permeability for approximately 40 days. The swell behaviour and permeability of the mixtures were assessed at their respective maximum dry unit weight and optimum moisture content according to standard Proctor compaction, with a seating load of 6.25 kPa. From the reported values, it was observed that by blending 15% polymer bentonite with bottom ash and pond ash, it was possible to achieve the required permeability value of less than 10-9 m/s, making the composition an effective hydraulic barrier with low swell properties. Figure 11 illustrates comparison of coefficient of permeability with time for mixture 1 and mixture 2 against similar combination of mixtures without the polymer in accordance with the example of the present disclosure. In the mixture 1 and mixture 2, polymer bentonite (15%) is blended with bottom ash (85%) and pond ash (85%) respectively. These mixtures were compacted at optimum moisture content (OMC) and maximum dry unit weight (MDU) according to standard Proctor compaction. It should be noted that coefficient of permeability (k) for Bentonite (15%) and Bottom ash (85%) mixture (similar to Mixture 1 but without polymer content) is higher, in the order of 2.6 x 10-7 m/s, hence variation with time was not presented in Figure 11 along with other mixtures.
Tensile stress strain characteristics
[0057] The tensile stress and strain characteristics of the polymer-bentonite blended mixtures exhibit ductile behaviour and register higher strain values and a delayed onset of crack formation at peak strength values when compared with bentonite mixtures without polymer. In the polymer bentonite coal ash mixtures, the polymer action imparts enhanced flexibility to the mixture, making the mixture more ductile and inhibiting crack formation. The tensile stress strain study was carried out on mixtures with varying percentage of the polymer-bentonite blend/ bentonite blend and the moulding water content at respective unit weights for assessing tensile stress and strain at cracking.
Desiccation behaviour
[0058] Desiccation behavior refers to the patterns and characteristics exhibited by a material as it loses moisture. Understanding desiccation behavior is important for predicting how a material behaves under drying conditions, which is crucial in fields like geotechnical engineering, construction, and materials science. The behavior includes factors like the rate of moisture loss, the formation of cracks, changes in volume, and the impact on the material's strength and stability. The desiccation behaviour of the mixtures was also evaluated using the test set up assembled indigenously in the laboratory. For studying the desiccation behavior, only mixtures with 15% blend of polymer-bentonite and bentonite were considered, and mixtures were evaluated by varying the placement water content (OMC to OMC + 20% with 5% increment) at their respective unit weights. Further, the mixtures were exposed to 50º C ± 2º C for a period of 72 hours and continuous imaging was done along with monitoring of moisture variation.
[0059] Further, a crack intensity factor was determined using Image J software available in open domain. The Crack intensity factor (CIF) is the ratio of total area of cracks to the total area which includes cracked and uncracked area and expressed in percentage. An increased susceptibility to crack formation was observed with higher placement water content, finer particle size gradation, and greater plasticity. Finer coal ash, particularly the pond ash-based mixtures showed a higher susceptibility to desiccation cracking, reflected by its higher CIF values compared to bottom ash-based mixtures. However, both types of coal ash, when blended with polymer-bentonite, showed better resistance to crack formation with negligible surface cracks and lower CIF values. CIF values for polymer bentonite blended bottom ash at OMC were 1.068% and CIF values for polymer bentonite blended pond ash at OMC were 2.955% and at OMC + 20% for polymer bentonite blended bottom ash was 5.199% and polymer bentonite blended pond ash was 7.721%. Figure 12 illustrates the variation of crack intensity factor (CIF) with time for mixture 1 and mixture 2 in accordance with the example of the present disclosure.
Self-healing behaviour
[0060] The self-healing behavior of mixtures subjected to desiccation cracking was evaluated by measuring their permeability over time under inundation without any surcharge. The test set up for the same was fabricated indigenously with the provision to measure discharge, water level drop, and maintain the necessary supply head for the study. Both polymer-bentonite and bentonite-blended mixtures showed self-healing behavior. However, in terms of permeability measurements over time, the polymer-bentonite blended mixtures performed better, moving more effectively toward achieving the required permeability below 10-9 m/s. Permeability values were measured for 8 days after the constant head and/or discharge was achieved during initial few minutes. For polymer bentonite bottom ash, permeability at the start was 8.0 x 10-7 m/s and on the 8th day it improved to 4.8 x 10-9 m/s and similarly for polymer bentonite pond ash, the permeability values at the start were 8.0 x 10-8 m/s and on the 8th day it improved to 9.5 x 10-10 m/s. These permeability values of the mixtures correspond to samples studied at optimum moisture content for desiccation behavior and then for subsequent permeability. Figure 13 presents the coefficient of permeability of cracked samples immediately after inundation with time for mixture 1 and mixture 2 in accordance with the example of the present disclosure.
[0061] The above study of the mixtures shows importance of blending polymer-bentonite to improve the performance of mixtures intended for use as barrier materials. Additionally, utilizing coal ash by-products as barrier by blending polymer-bentonite/ bentonite shows the added advantage as the coal ash by-products are a waste produced and is managed and utilized for a better purpose as barrier. Hence, scarcely available suitable natural materials like sand can be preserved and consumed selectively for the other geotechnical applications.
[0062] The polymer blended coal ash mixture of the present invention can effectively be considered for landfill barrier applications as shown in Figure 2. Also, from the above study, polymer blended coal ash mixture can be used for other geotechnical applications. For example, the low swelling barrier composition is also used in canal lining. Canal lining is very important to avoid seepage losses leading to effective irrigation, erosion of material from the bed and side slopes and weed growth, reducing the operational and maintenance costs. Conventionally materials used for canal lining include compacted earth, bricks, boulders, cement and concrete. Instead of these materials, the barrier composition of the polymer bentonite blended coal ash mixtures can be used as the barrier composition leads to utilisation and management of waste produced. Figure 14 illustrates a cross-sectional view of a canal system composed of the low swelling barrier composition in accordance with the present disclosure.
[0063] The canal lining system comprises of compacted subgrade layer of soil that is compressed to increase its density and stability, forming the foundation for the subsequent layers. It is further covered with a non-woven geotextile material. Above to the non-woven geotextile material, the low swelling barrier composition of polymer bentonite coal ash mixture forms a barrier that prevents water from percolating downward. The polymer bentonite coal ash mixture is covered with a geomembrane to prevent migration of contaminants, such as leachate and gases, from the landfill into the surrounding environment. The barrier composition does not have swelling problems and shows impermeable nature which is evident from the above study and experimentations. Hence, the low swelling barrier composition is advantageous in places requiring canal constructions due to swelling soils, as the composition restricts the interaction of existing soil and canal water.
[0064] Further, the utility of the low swelling barrier composition is extended to pond or an artificial lake lining. In such linings, there is a need of a separation from the material below, the low swelling barrier composition act as a barrier. Also, the polymer bentonite coal ash mixtures can be used in place of swelling soils by partial replacement under pavements or any other structures. The barrier composition can also be used to make the core impervious in an earthen dam due to the impermeable behaviour of the mixtures and limited swell behaviour replacing natural clay or silty soils that are used conventionally. Figure 15 illustrates a cross-sectional view of a core of an earth dam composed of the low swelling barrier composition in accordance with the present disclosure.
[0065] The low swelling hydraulic barrier composition serves as an effective impermeable barrier with low swelling characteristics. The polymer bentonite blended coal ash barrier mixture demonstrates strong resistance to desiccation cracking, exhibiting minimal surface cracks and notable self-healing when exposed to moisture. The polymer bentonite blended coal ash hydraulic barrier mixture is suitable for use in landfill barriers or containment systems. Additionally, the mixtures are useful for other geotechnical applications such as canal lining, pond or artificial lake lining, and as a replacement for swelling soils in pavement or structural applications. The mixture can also be used in composite systems alongside geomembranes or other membrane materials. Further, the polymer bentonite coal ash mixture addresses the problems related to natural materials scarcity, waste utilisation, management and environmental sustainability.
, Claims:We Claim:

1. A method of preparing a low swelling hydraulic barrier composition for landfills and other geotechnical applications, the method comprises the step of:
preparing a blend of polymer bentonite mixture with coal ash in dry state, wherein the polymer bentonite mixture is mixed in the range of 10% to 25% by total weight, the coal ash is mixed in the range of 90% to 75% by total weight; and
mixing the water with the dry mixture in the range of 17% to 27% of the total weight of the dry mixture;
wherein the coal ash comprises one of bottom ash and pond ash.

2. The composition as claimed in claim 1, wherein the polymer bentonite blended with coal ash is kept for hydration for a minimum time period of 24 hours and moist compacted at standard Proctor compaction at a maximum dry unit weight and at an optimum moisture content of bottom ash mixture and pond ash mixture respectively.

3. The composition as claimed in claim 2, wherein the maximum dry unit weight of polymer bentonite blended bottom ash mixture is in the range of 12.0 kN/m3 to 13.5 kN/m3 and the optimum moisture content of polymer bentonite blended bottom ash mixture is in the range of 24% to 27%.

4. The composition as claimed in claim 2, wherein the maximum dry unit weight of polymer bentonite blended pond ash mixture is in the range of 14.0 kN/m3 to 15.5 kN/m3 and the optimum moisture content of polymer bentonite blended pond ash mixture is in the range of 17% to 19%.

5. The method as claimed in claim 1, wherein the polymer bentonite mixture comprises bentonite mixture in the range of 96% to 98% by total weight and a polymer in the range of 2% to 4% by total weight.

6. The method as claimed in claim 2, wherein the polymer is a hydrophilic polymer selected from the group comprising Polyvinyl Alcohol (PVA), Polysaccharides, Polyacrylic acid, Polyacrylamide (PAM), Sodium Polyacrylate, Hydroxyethyl Cellulose, Polyethylene Glycol (PEG) and Carboxymethyl Cellulose and a combination of thereof.

7. The method as claimed in claim 2, wherein the bentonite mixture comprises a sodium bentonite.

8. The method as claimed in claim 1, wherein the bottom ash has an average particle size (d50) in a range of 0.10 mm to 0.80 mm and a small particle size or effective particle size (d10) in a range of 0.010 mm to 0.090 mm.

9. The method as claimed in claim 1, wherein the pond ash has an average particle size (d50) in a range of 0.050 mm to 0.080 mm and a small particle size or effective particle size (d10) in a range of 0.005 mm to 0.020 mm.

10. A low swelling hydraulic barrier composition for landfills and other geotechnical applications, comprising:
a dry mixture comprising a polymer bentonite mixture in the range of 10% to 25% by total weight and coal ash in the range of 90% to 75% by total weight; and water mixed with dry mixture in the range of 17% to 27% by total weight of the dry mixture uniformly, wherein the coal ash comprises one of bottom ash and pond ash.

11. The composition as claimed in claim 10, wherein water mixed with dry mixture in the range of 24% to 27% by total weight of the dry mixture, prepared by blending polymer bentonite and bottom ash.

12. The composition as claimed in claim 10, wherein water mixed with dry mixture in the range of 17% to 19% of the total weight of the dry mixture, prepared by blending polymer bentonite and pond ash.

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