A review on the application of biopolymers (xanthan, agar and guar) for sustainable improvement of soil – Springer

In the area of soil engineering, the quest for sustainable solutions for improvement has become more pressing. With escalating concerns over degradation, erosion, and the depletion of essential nutrients, there is a growing imperative to explore alternative approaches that prioritise environmental stewardship without compromising the impact on the environment. One such promising avenue lies in the application of biopolymers-organic compounds derived from natural sources-as agents for improvement. Previously, as suggested by Ingles and Metcalf [47], improvement techniques for base soil were classified into two major categories: chemical and mechanical methods of stabilisation; the first involved cementitious binders that could be mixed or injected; and the latter involved compaction, vibration, anchors, and geo-synthetic stabilisation. In the chemical stabilisation of the ground, cementitious binders are used to make it stronger by increasing the bonds between particles and blocking holes in the soil’s pores or with minerals in the soil [62]. Lime and cement are the most commonly used cementitious binding materials. Although there are a number of other materials that have been implied by Leong et al. [59], Saberian et al. [78], Gomes Correia et al. [41], Cola et al. [30], Toghroli et al. [86], Jahandari et al. [49] for base soil to improve stability, bitumen, fly ash, and sodium sulphate are examples of additives that are frequently used.

However, it’s important to remember that there are serious concerns about the chemical effects of commonly used soil binders on the environment. The commonly used soil binders as identified by Celauro et al. [13] are lime, cement, fly ash, bitumen and polymer emulsions. Although chemical soil treatment is more preferable, but including their toxicity, leaching, and potential health effects on living things is not considered good for environment. Chemicals like lime, cement, fly ash, bitumen, and polymer emulsions can introduce toxic elements. Lime itself is not said to be typically toxic, its use can increase soil pH, which affects the mobility of heavy metals, such as arsenic (As), lead (Pb), and mercury (Hg), further leading to their leaching into the soil. Cement contains compounds like calcium oxide, which releases pollutants during production. These pollutants includes heavy metals such as arsenic, lead, cadmium, chromium, and mercury. Fly ash contains radioactive elements like thorium and uranium, depending upon the source of coal, and polycyclic aromatic hydrocarbons (PAH). Bitumen has trace of polycyclic aromatic hydrocarbons (PAHs) and heavy metals. Polymers are generally safe, but their additives are harmful. Environmental assessments and monitoring are essential for containment and management to reduce contamination risks. On another note, we must not lose sight of the fact that current climate change and global warming are two of the most alarming occurrences.

According to Chang et al. [14], Etim et al. [38], Rahgozar et al. [76], Afshar et al. [3], both synthetic products and conventional, calcium-based materials used in geotechnical applications (such as cement and lime) have produced greenhouse gas (GHG) emissions that are directly associated with global warming. Referring to the article by Uwasu et al. [88], the cement producing industry generates approx. 3 billion tonnes of carbon dioxide, which is equal to 8% of the total (text {CO}_{2}) amount, and half of this amount is produced during the calcination process for making clinkers. Therefore, it becomes important to promote the use of alternative and less harmful materials. Dejong et al. [34] has identified that the development of several ecologically friendly soil enhancement strategies, some of which rely on microbial processes and biomaterials, has occurred recently. Microbial-Induced Calcite Precipitation (MICP) is an interdisciplinary approach that combines microbiology with other disciplines, such as biology and geotechnical engineering. By precipitating calcite ((text {CaCO}_{3})) in the soil matrix using bacteria, this process would strengthen the soil through the calcite network that has formed connections to soil grains. MICP can reduce liquefaction by improving soil permeability, either through a bio-clogging process or the dissipation of excess pore water pressure. Achal and Mukherjee [1], Sharma et al. [80], Dhami et al. [37], Tang et al. [84], Choi et al. [27], Mujah et al. [69], Bahmani et al. [8], Omoregie et al. [73, 74] mentions a few issues regarding MICP, including the fact that it only works on mostly coarse-grained soil, produces ammonia, and is challenging to get the calcite to spread out evenly.

To make soil more stable, stop it from washing away, and make it less permeable, another biological method suggested by Chu et al. [28], Kwon and Ajo-Franklin [54], Noh et al. [71] is to get microorganisms to make biopolymers (accumulation microbial biopolymer) inside the soil matrix. In recent times, it has been strongly recommended that biopolymers be utilised in the field of geotechnical engineering. Biopolymers are natural polymers created by plants and living organisms in their natural environment. Most often, biopolymers were used as adhesives or water-retaining agents. Some biopolymers, such as lignin and its derivatives, work well as additives in concrete and oil well drilling. Cellulose, as well as derivatives of starch, worked well in a variety of applications, including tile adhesives and oil well building. In particular, we need to study biopolymers, which are biodegradable polymers, as construction materials for improving soil.

The biopolymer soil treatment is faster and more precise than other biological soil treatments. Endo-cultivating (A process that involves cultivation or enhancement occurring internally, inside, or within a specific host or system.) MICP requires a lot of time and money to ensure enough (text {CaCO}_{3}) precipitation for soil fortification, which varies by case. Biopolymer soil remediation uses exo-cultivated (A process or practice that involves cultivation or enhancement occurring externally or outside of a particular system.) biopolymers. Biopolymer mixing directly with soil creates a homogeneous, electrostatic biopolymer-soil matrix that strengthens immediately. It has been observed through Chang et al. [18], Chang and Cho [15, 17], Chang et al. [20], Al Qabany et al. [4], DeJong et al. [36] that only a few theoretical and experimental biopolymer studies have led to real-world applications.

This review tries to bring up-to-date and rate the research on biopolymer-treated soil from different points of view, such as testing the soil’s shear strength, unconfined compressive strength, compaction characteristics, Atterberg limits, and ability to stabilise pavement.

Under ideal conditions for a typical biopolymer, the factors affecting the enhanced soil geotechnical performance were analysed (i.e., xanthan gum, guar gum, and agar gum). Furthermore, the mechanisms through which biopolymers interact with various soil types have been explored. Moreover, the potential of biopolymer application in the remediation of mine tailings has also been identified. This area is opulent with environmental challenges because these mine tailings are characterised by their high toxicity and low fertility, which in turn pose serious risks to surrounding ecosystems and health. By investigating the efficacy of biopolymers in mitigating the environmental impact of mine tailings and promoting their rehabilitation, this review also aims to highlight yet another promising field for the sustainable utilisation of biopolymers.

There are several distinct categories for biopolymers, including biodegradability (biodegradable and non-biodegradable) and raw material origin.

Biopolymers based on their biological parentage were derived by Niaounakis [70], and this can be further summarised as either plant-based, animal-based, or microbial-derived.

Biopolymers derived from plants and the byproducts of agricultural processes are referred to as plant-based. In the field of geotechnics, biopolymers most commonly refer to plant-based compounds, the majority of which are polysaccharides. This class includes carrageenan, guar, lignin, agar, and beta-glucan, in addition to alginate and lignin. The guar plant yields guar gum, also known as guaran, a polysaccharide. The two sugars galactose and mannose combine to form it. Earlier, Gupta et al. [42] identified that the water-soluble polysaccharide guar gum has the largest molecular weight of any of the water-soluble polysaccharides. Microorganism-based biopolymers include xanthan gum, gellan gum, and dextran, all of which are byproducts of bacterial fermentation processes. The bacteria Xanthomonas campestris ferments glucose and sucrose to create xanthan gum, an anionic polymer. Pseudo-plasticity and strong shear stability, even at low concentrations, are the most well-known properties of xanthan gum. It is also compatible with ionic salts and has a long shelf life without changing pH. Xanthan is used as a gelling, thickening, suspending, flocculent, and viscosity control agent in a broad variety of industries, including the cosmetics, oil, paper, paint, pharmaceutical, food, and textile sectors [23, 39, 65]. Animal-derived biopolymers are those that start with a source from the animal kingdom. Milk and other dairy products are processed into protein-based biopolymers, while crustacean shell waste is processed into chitin and chitosan [57]. Out of all these classified biopolymers based on their source of origin, this paper discusses and summarises the studies about the three most commonly used biopolymers, i.e., Xanthan gum, Guar gum, and Agar gum.

2.1 Xanthan gum

In the Xanthomonas campestris bacterium, an anionic polysaccharide called xanthan gum is produced by the aerobic fermentation of sugar. Figure 1 shows the chemical structure of this microorganism based biopolymer It forms a very viscous hydrogel when mixed with water at any temperature, making the solution quite thick when agitated. Xanthan gum frequently serves as a thickener due to its capacity to absorb water through hydrogen bonding. By enhancing water retention, it decreases the permeability of sandy soil and improves erosion resistance in geotechnical engineering. Chang et al. [21] showed that a low dose of Xanthan gum significantly enhanced the erosion resistance and plant development of Korean red–yellow soil. Further Chang et al. [18, 20], Garcia-Ochoa et al. [39], Brune et al. [10], Chang et al. [22], Yeong-Man et al. [92], Smitha and Sachan [82], Gioia and Ciriello [40], Im et al. [46] concluded that Xanthan gum-treated soil has strong water adsorption during the rainy season and high soil moisture retention during the dry season.

Chemical structure of xanthan gum [82]

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The experiment demonstrated by Bagheri et al. [7] shown in Fig. 2 indicated that Xanthan gum treatment can effectively maintain the integrity of soil and enhance its resistance to water. The untreated soil disintegrated quickly when submerged in water, while the Xanthan gum-treated specimens maintained their general shapes and only experienced slight disintegration after a few days. The 2% Xanthan gum-treated sample showed the highest integrity even after five days of submersion, with a significant increase in diameter. This suggests that Xanthan gum can be a valuable additive for improving soil stability and water resistance.

Xanthan gum specimen submerged in water by Bagheri et al. [7] at a 1 h b 4 h c 1 day d 5 day

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2.2 Agar gum

Algae of the genus Agar (Gelidiella, Gracilaria, and Gelidium) are harvested for their red colour, which is used to make agar. The chemical structure of agar gum as indicated by Lahaye [55] in their research is shown in Fig. 3. This plant based biopolymer has found to be used as a stabiliser because of the stiff texture it offers as it gels.

Agar gum’s chemical structure

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The agar’s hydrophobicity makes it highly soluble and gel-forming. As demonstrated by Chang et al. [21], Rhein-Knudsen et al. [77], agar’s gelling point was obtained between 32 and 45 °C, whereas its melting point lied between 85 and 95 °C. At (20,^{circ }text {C}), the gel strength of 1.5 percent agar was between 70 and 1000 g/cc. The viscosity of agar at 1.5% at 60 °C ranged from 10 to 100 cP, ranging in molecular weight from 36 to 144 kDa.

2.3 Guar gum

Polysaccharide guar gum is extracted from the seeds of the plant Cyamopsis tetragonoloba. Galactomannan (75–85%), water (8–14%), protein, fibre, and ash make up the rest of guar gum’s basic components.

Guar gum is a polymer with a high molecular weight that dissolves in water, Fig. 4 shows the chemical structure of this gum as indicated by Mudgil et al. [67] in their literature and it was also observed that the addition (0.25–2% concentration) of guar gum to both silt and sand increases sand cohesive strength and decreases permeability. As observed by Sujatha and Saisree [83], when it comes to how water affects the treated soil, the treated soil’s dry density increases marginally with guar gum content, while its optimal moisture content decreases. This suggests that guar gum-treated soil can compact at low energy levels and is not sensitive to water content changes.

Chemical structure of guar gum

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Furthermore, scanning electron micro-graphs demonstrated by Chudzikowski [29] showed that guar gum’s pore filling action between soil particles is greatly enhanced at 2% concentration after a curing period of 5 weeks.

Since the dawn of civilization, humans have refined techniques for engineered soil treatment in buildings. Natural elements and binders such as mud, straw, lime, and notably cement were employed by ancient civil engineers to improve soil quality.

During the Industrial Revolution, the development of ordinary Portland cement led to significant advancements in cement-based concrete. After devastating wars, people have developed an interest in the potential of chemical compounds and waste products from industry.

Cement is commonly used for soil improvement, and since its production releases a lot of carbon dioxide-the principal culprit in global warming-geotechnical engineers and researchers have a clear social need for sustainability in geotechnical engineering since the Kyoto agreement in 2005. A number of carbon dioxide ((text {CO}_{2})) reduction strategies have been proposed, including the use of ecologically friendly products for soil enhancement. Materials like biopolymers and geopolymers are used. Since the invention of geopolymer in 1979, it has seen widespread use in products including thermal shock refractories, fireproof drywall, thermally insulated walls, and geopolymer-based concrete. Geopolymer applications in cement and concrete have been the subject of much investigation. As a biological process, Martinez et al. [63] along with De Muynck et al. [33] and van Paassen et al. [89] established that MICP uses calcium carbonate precipitation to seal up soil pores and strengthen ties between soil grains. The engineering qualities of soil (such as sand) have been enhanced by MICP, which is superior to non-bio-mediated treatment approaches [35, 43]. Coarse soil particles have better characteristics after being treated with the MICP technique (e.g., sand or silt), but in contradiction, Mahawish et al. [61] and Terzis and Laloui [85] found that, when the proportion of fine particles to the total fraction of fine and coarse soil particles is 25 percent or greater, the MICP approach may not be an effective means of increasing soil strength. Soils treated with biopolymers have better soil strengthening, hydraulic conductivity, soil dynamic characteristics, and resistance to soil erosion, all of which are important in geotechnical engineering [6, 9]. There are many disadvantages to conventional biological soil treatment methods, such as the need for microbial and nutrient injection, the time required for cultivation and the precipitation of excrement, and the applicability of these methods to clayey soils [12, 18, 32, 36, 46, 60, 90]. All these flaws, as discussed, can be avoided when biopolymers are used directly in the soil. Because biopolymers are abundant and non-toxic, they may be used in place of cement, which contributes to global warming.

In particular, Table 1 summarises the features of three widely used biopolymers. The physical and chemical characteristics of commercial biopolymers are shown in Table 2. Moisture content, viscosity, melting point temperature, and gel point temperature are also included in Table 2 as a consequence of the experiment. Even if all biopolymers are biodegradable polymers, we still need engineering expertise to put their similar physiochemical features to good use.

Biopolymer has been implemented in the sectors of geotechnical engineering and construction fields, with biopolymer mainly acting as a binder for soil. Biopolymers such as xanthan, guar, agar, gellan, chitosan, starch, and caesin are commonly used for studying because of their easy availability. The application of biopolymer substances in geotechnical engineering can be justified by a number of literature supporting the engineering response. Biopolymers, such as Xanthan, Guar, Agar, Gellan, Chitosan, Starch, and Caesin, have been widely used in the fields of geotechnical engineering and construction as binders for soil. These biopolymers are commonly studied due to their easy availability. The application of biopolymers in geotechnical engineering is supported by numerous literature that highlight their positive effects on soil consistency, unconfined compressive strength (UCS), and soil erosion control. In terms of consistency, research by Chang et al. [19] shows that the addition of biopolymer-stabilized soil can change the classification of clayey soils, affecting their liquid limit (LL) and electrical sensitivity. Chen et al. [25], Chang and Cho [16], Nugent et al. [72] indicated how biopolymer-stabilized soil shows improved LL by increasing pore fluid viscosity and wetting ability through the presence of biopolymers in soil particles. It also reduces LL in clays because of high specific surfaces and by forming direct ionic bonds between particles, resulting in the aggregation of biopolymers and a decreased liquid limit. An investigation by Latifi et al. [56] showed how biopolymers also enhance the UCS of dry soil through conglomeration of particles and adhesion due to electrostatic. For example, adding 2% xanthan gum BPST to clays can increase the UCS of montmorillonite by 2.9 MPa and kaolinite by 1.3 MPa. Because ionic and hydrogen bonds cause the formation of a biopolymer-clay matrix, xanthan gum treatment has a greater impact on clayey soils like sandy lean clay, kaolinite, and montmorillonite. Bueno et al. [11], Coutinho et al. [31], Hess and Srubar III [44] observed that wetting and saturation weaken the links, but biopolymer-stabilized soil still exhibits higher saturated strength than untreated soils, making it a promising option for waterfront or wetland geotechnical engineering. Soil erosion control cannot be ignored, as it is a noticeable issue in geotechnical engineering. Conventional methods, such as stabilization with binder material, for controlling soil erosion require frequent application and are ineffective, raising environmental and health concerns. In order to limit their use, biological methods, such as microbial precipitation and biopolymer based soil strengthening, have been explored as alternatives. Spraying biopolymer solutions or mixing them directly into the soil are considered effective methods for controlling surface erosion. However, field conditions often result in higher erosion ratios than laboratory tests, so further research is needed to enhance the in-situ condition.

The application of xanthan gum-treated soils in geotechnical engineering are compiled in Table 3. It can be concluded that xanthan gum is used to minimize wind erosion, remediate soil and grout soil, and enhance plant development in dry lands. Sand and other coarse soils are typically treated using xanthan gum. The application of soils treated with agar are outlined in Tables 4. Last, but not least, Table 5 lists all potential uses for geo-materials treated with guar gum (e.g., mine tailings and clay).

The diagram in Fig. 5 shows how biopolymers make soil stronger by covering sand particles with a biopolymer solution. This fills in the gaps between the particles, which increases the shear strength even more, resulting in a peak strength of the sand. However, the process of getting strength is different for clay particles because they have a negative charge on their surface and contain minerals like alumina and silica that ionise and create a negative charge. These biopolymers (Xanthan, Guar, and Agar) bond with clay particles through hydration, swelling, and electrostatic interactions. All biopolymers are hydrophilic and absorb water molecules, leading to hydration and swelling. On the other hand, it is also noticed that all biopolymers are negatively charged in aqueous solution. They can interact electrostatically with clay particles through attractive forces [64].

Diagrammatic representation of the biopolymer-based strengthening mechanism for clay (middle and bottom) and sand (above)

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Figure 6 represents the direct shear test with natural sand and biopolymer-treated soil. It can be clearly seen from Fig. 6 inter-particle adhesion between soil grains and biopolymers that a layer of hydrogels is formed over the particles of sand, which affects the rheology (viscosity and shear strength) of the soil. These hydrogels of biopolymer are condensed into biofilms through drying and dehydration. This biofilm has a flexible and elastic feature, causing it to have a higher peak strength [58].

Visual depiction of the direct shear test of natural sand treated with biopolymer

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Xantham gum: The behaviour of peak strength of xanthan gum-treated sand with a range of xanthan gum in gel phase concentrations at initial, dried, and re-submerged conditions is tabulated in Table 6. The graphical representation can be seen in Fig. 7. In this case, Lee et al. [58] evaluated the sand samples as soon as they were formed in the disk-shaped mould after being treated with xanthan gum (the “initial condition”) (diameter of 60 mm and height of 20 mm). The dry state indicates that testing was performed on sand samples treated with xanthan gum after they had been air dried for 28 number of days at room temperature. Finally, the re-submerged state indicates that half of the dried sand samples were re-hydrated by being submerged in room-temperature distilled water for 24 h prior to testing.

Shear strength behaviour of xanthan gum-treated sand by Lee et al. [58]

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The strength-changing behaviour of xanthan gum-treated sand can be influenced by even a minute quantity of xanthan gum (i.e., 0.5 %). The original xanthan gum gel’s cohesiveness rises with increasing xanthan gum concentration, while the friction angle remains the same. Further, it was identified by Lee et al. [58] and Ivanov and Chu [48] that the bio-film of xanthan gum forms on the sand particles’ surfaces and the viscous hydrogels of this gum block the pores, The cohesion and friction angle increase with increasing xanthan gum concentration in the dried gel phase. The higher swelling pressure generated by half of the pure dried sand specimens reduces interaction (e.g., surface friction and interlocking) between interparticles when the sand is re-submerged, which is why the peak friction angles of xanthan gum-treated sand decrease with increasing xanthan gum content (from 1 percent xanthan gum).

The residual shear strength properties of the sand after xanthan gum treatment depend on the condition of the gel phase of xanthan gum. The amount of xanthan gum added to sand has little effect on its initial cohesiveness or friction angle since the van der Waals interaction may have an effect on constant values. Table 7 displays the values of the residual inter particle cohesion (kPa) and friction angle (°) of xanthan-treated sand in its original, dry, and re-submerged states and graphical representation can be observed in Fig. 8. However, the features of xanthan gum-treated sand, including its residual shear strength, improve as xanthan gum quantity is increased once the sand has dried. Residual cohesiveness increases with increasing xanthan gum concentration in the re-submerged state of sand, while residual friction angle decreases. For instance, the reduced friction angle of xanthan gum-treated sand could be attributed due to the pseudo-plasticity behaviour of xanthan gum hydrogels at high strain levels, which occurs as a result of the hydrogels’ decreased viscosity at higher strain levels Lee et al. [58].

Residual strength behaviour of xanthan gum-treated sand by Lee et al. [58]

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Agar gum: Figures 9 and 10 demonstrate the time-dependent unconfined compressive strength of sandy and clayey soils, respectively, treated with air-dried biopolymers (i.e., up to 28 days). The unconfined compressive strength of biopolymer-treated clayey/sandy soil (i.e., treated with agar and gellan gum) improves with increased air drying time. Compressive strength is increased in both sandy and clayey soils when biopolymer content is increased. Figure 11 is a scanning electron micrograph of a combination of agar and clayey soils, which demonstrates by Chang et al. [21] states that the agar gels completely cover the clayey soil particles through indirect contacts mediated by the lengthy molecular structures of the agar.

Unconfined compressive strength with time for biopolymer-treated clayey soil Chang et al. [21]

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Variation in unconfined compressive strength with time for sandy soil treated with biopolymer at ambient temperature ((20 pm 2,^{circ }text {C})) Chang et al. [21]

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SEM image. a Natural soil, b agar gum-treated clayey soil mixtures [21]

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Guar gum: The interaction between guar gum and soil properties intricately affects soil compaction and dry unit weight. At lower concentrations, guar gum reduces particle-on-particle friction, enhancing compaction and increasing dry unit weight. However, as the concentration increases, the high viscosity of the gum solution can impede compaction, leading to decreased dry unit weight as soil particles separate in the thickened solution. This phenomenon is particularly pronounced at higher percentages of gum added, where compaction efficiency diminishes. Also, the process of guar gum hydration changes the best level of moisture for compacting, so clay-guar gum mixes need less water to reach their highest dry unit weight. Understanding these dynamics is crucial for effectively managing soil stabilization and compaction processes involving guar gum treatment. Table 8 comprises all the data obtained by Sujatha and Saisree [83]. In addition, they also concluded that the hydrogel will continue to build until full polymer linkages have formed, at which point the gel will become viscous. The OMC goes down as the biopolymer concentration goes up because the galactose and mannose in guar gum soak up most of the water used for the compaction process to make hydrogels between particles. This is shown in Fig. 12. The extra galactose and mannose branches in the resulting colloidal dispersion help to make the guar gum matrix in the soil stronger. Hydrogels build up in pores, covering soil particles and connecting light particles. This makes treated soil consistently lower in void ratio compared to untreated soil. The higher guar gum concentration and viscosity give treated soil a more rigid matrix despite a lower dry unit weight.

Max. dry density/OMC vs bi-polymer content of guar gum treated soil [83]

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The unconfined compressive strength of soil is a key indicator of its viability as a building material. It’s useful for learning about how the addition of biopolymers affects shear strength. With its ability to drastically change undrained shear strength, Chang et al. [21] also proposed that guar gum is a promising biopolymer for use in soil stabilisation. Because of its large specific surface area and electro-kinetic charges, gum may grab dirt particles and hold them in place. As it can be seen in Fig. 13 the concentration of guar gum rises, so does the unconfined compressive strength of soil-gum combinations. Soil containing 2% guar gum improved its strength by 52% after 90 days, from 221.7 kPa without curing to 463.6 kPa. This pattern holds true for all guar gum therapies studied as people get older. The chemical structure of guar gum has a role in the development of hydrogen bonds between multiple hydroxyl groups, which contributes to the rise in strength.

UCS vs curing period of guar gum-treated soil

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Chudzikowski [29] showed that minerals hydrates to form hydrogen bonds with inorganic surfaces in clay soil, acting as coagulant. Moreover, Muguda et al. [68] further proposed that drying transforms the hydrogels into rubbery, glassy states, tending to bond with particles. The effect of the soil’s age on this phenomenon is age-dependent. There is a lot of water that can be held in these Dry rubber links. Guar gum accumulates in that voids, coating soil particles, which leads to creation of hydrogels. The soil-guar gum matrix’s strength and density depend on the pore spaces’ guar gum links. As guar gum content increases, the links become thicker and stronger, allowing it to hold up higher loads. Guar gum is superior to other biopolymers at filling void spaces due to its thicker, wider links. In addition, Ayeldeen et al. [6] identified that the behaviour of treated and non-treated soil is similar at lower guar gum content.

However, it was also proposed that, with increasing guar gum content, strength changes significantly with age. Biopolymer formation at 90 days consists of bundles that provide more friction to resisting loads. The gel fills pore spaces, dehydrates, and thickens with age, with cross-links forming after 0, 7, 28, and 90 days. These connections between particles help to fill in gaps and integrate the entire soil-gum matrix Fig. 14 shows the development of fibre for cross linking of soil before and after biopolymer treatment with respect to curing period. Figure 15 shows the illustration of soil treated with guar gum and circle shows the gap filled with biopolymer.

The development and thickening of cross-links during curing occurs a after 0 days, b after 7 days, c after 28 days, and d after 90 days [83]

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An illustration of a untreated soil and b soil treated with guar gum (2%) without curing [83]

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In a nutshell, the following is a rundown of the Limitations and difficulties associated with the application of biopolymers in the field for the purpose of soil enhancement:

1. 1.

   Some restrictions include:

   1. (a)

      The variable nature of the soil’s qualities when exposed to actual environmental conditions.

   2. (b)

      Apprehensions regarding the biodegradability and longevity of the product.

   3. (c)

      Variations in performance based on the time of year and the parameters of the environment.

   4. (d)

      A sensitivity to water, especially in conditions of high humidity or saturation.

2. 2.

   Obstacles that arise during field application include:

   1. (a)

      Variable conditions of the soil in different places and even within the same site.

   2. (b)

      The impact of the prevailing conditions on the performance of the biopolymer.

   3. (c)

      The process of bio-degradation leads to a gradual loss of efficacy over time.

   4. (d)

      Variations in terms of performance qualities depending on the season.

   5. (e)

      Concerns regarding compatibility with several additional soil stabilising agents and additives.

   6. (f)

      It is necessary to implement quality control methods in order to guarantee consistent application.

   7. (g)

      The price of biopolymer products as well as their availability.

   8. (h)

      Evaluation of long-term durability in high-traffic regions or under large loads.

   9. (i)

      Ongoing monitoring and maintenance in order to evaluate its efficacy and make necessary adjustments.

In order to address these constraints and challenges and provide dependable soil stabilisation outcomes, in-depth research, evaluations tailored to the specific site, and continuous monitoring are required.

In conclusion, the field of soil engineering has used a variety of soil treatment techniques to enhance the geotechnical characteristics of marginal soils. Traditional soil stabilization methods rely on chemical and mechanical techniques. However, concerns regarding their environmental impact and contribution to global warming have led to the exploration of alternative, eco-friendly materials. One such approach is the utilisation of biopolymers.

Biopolymers, derived from plants, animals, or microbial sources, have shown promising results in soil stabilization. Xanthan gum, agar gum, and guar gum are among the most commonly studied biopolymers. Xanthan gum improves impermeability and water storage capacity; agar gum enhances shear strength and accelerates the cementation process; and guar gum increases soil imperviousness and strengthens shear characteristics. The behavior of biopolymer-treated soils depends on factors such as biopolymer concentration, drying time, and re-submergence influence the behavior of biopolymer-treated soils. Xanthan gum-treated sand demonstrates improved cohesion and friction angle, whereas clayey soil treated with agar gum exhibits increased unconfined compressive strength over time. Soils that have been treated with guar gum have higher dry unit weight and unconfined compressive strength. This is because the cross-links get thicker, which makes the soil stronger and denser. Biopolymer-treated soils have a variety of application possibilities, ranging from anti-wind erosion and soil remediation to slope stability and mine tailing stabilization. These biopolymers offer potential solutions for soil improvement in geotechnical engineering, providing eco-friendly alternatives to conventional soil stabilisation methods. Further research and exploration are required to optimise the application of biopolymers in soil stabilisation and to better understand their long-term effectiveness, compatibility with different soil types, and economic feasibility. By harnessing the potential of biopolymers, geotechnical engineers can contribute to sustainable development while mitigating the environmental impact of infrastructure projects. Finally, I’d like to point out that this paper provides a detailed overview of the properties and applications of three biopolymers: xanthan gum, guar gum, and agar gum. While the present review does not include a quantitative comparison of these biopolymers with conventional construction materials such as concrete or alternative systems like Microbial-Induced Calcite Precipitation (MICP), future studies could focus on this aspect in order to better understand the potential of biopolymers in a variety of applications. Such comparative analyses might be beneficial for identifying particular fields where biopolymers could be effective alternatives to traditional materials.

In addition to soil improvement, biopolymers can show promise in addressing the geotechnical challenges of mine tailings stabilisation and dust control. Mine tailings, known for their high toxicity and susceptibility to erosion, pose significant environmental risks if left untreated. Biopolymers can be a sustainable and effective solution for stabilising mine tailings, preventing erosion, and reducing dust emissions. Here are some key areas for scope in the future:

1. 1.

   Biopolymer-tailings interaction studies: By conducting extensive research to better understand the interactions between biopolymers and mine tailings. This includes looking into the binding mechanisms, surface modification effects, and long-term stability of biopolymer-treated tailings. By elucidating the underlying processes, researchers can optimise biopolymer formulations for maximum tailings stabilisation efficiency.

2. 2.

   Tailings erosion control: Investigating the use of biopolymers to reduce erosion and runoff at mine tailings facilities. Biopolymer-based erosion control measures, such as surface sealing and vegetation enhancement, can help to prevent soil loss and contamination of nearby water bodies. Studies that assess the efficacy of biopolymers in reducing erosion rates and improving soil stability in tailings environments are critical for developing long-term mine reclamation strategies.

3. 3.

   Dust suppression techniques: Researchers are investigating the potential of biopolymers to suppress dust on mine tailings surfaces. Dust emissions from exposed tailings can endanger the respiratory health of nearby communities and contribute to environmental degradation. Surface sealing and dust agglomeration are two biopolymer-based dust suppression techniques that provide a long-term alternative to conventional chemical treatments. Research into the efficacy, durability, and environmental impact of biopolymer-based dust control measures can help guide best practices for reducing dust emissions from mine tailings.