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Geosynthetics have been widely used in construction for decades due to their ability to improve soil stabilization, drainage, erosion control and other foundational functions. Traditionally, these materials have been manufactured from petroleum-based products, such as polypropylene, polyethylene and polyester, which contribute significantly to carbon emissions, environmental pollution and resource depletion. The manufacturing of geosynthetics from petroleum-based materials has a high energy demand, which contributes significantly to the carbon footprint of these products.

The increasing demand for sustainable practices in the construction industry has led to the development and adoption of eco-friendly geosynthetics, materials designed to minimize environmental impact while maintaining performance standards. One of the most promising developments is the creation of biodegradable geosynthetics. These materials are designed to break down over time, reducing long-term environmental impact, especially in applications like erosion control or temporary soil stabilization. Some biodegradable geosynthetics are made from natural fibers like jute, coir, or hemp, while others use biodegradable polymers derived from plants, animals, or microbes.

Natural fibers as geosynthetics

Natural fibers like jute, coir, sisal, hemp, kenaf, bamboo and palm are used in geosynthetics for soil reinforcement, enhancing soil stability, shear strength, and load-bearing capacity while offering environmental benefits such as renewability and biodegradability. These natural geotextiles are eco-friendly, biodegradable, and cost-effective alternatives to synthetic materials, though challenges with durability and consistent performance exist due to natural variations and aging effects.

Jute fiber from the jute plant is widely used to create geotextiles and nets. It has a lower lignin content, which makes it faster to biodegrade than coir, and is especially useful for erosion control where rapid vegetation establishment is needed. Coir fiber, extracted from coconut husks, has a high lignin content, making it highly resistant to biodegradation and more durable than jute. It is commonly made into nets, mattresses, and geotextiles for soil reinforcement and erosion control.

Sisal, derived from the leaves of the Agave sisalana plant, is known for its high strength. It is used for soil reinforcement, particularly in problematic or low-bearing capacity subgrades. Hemp fiber from the hemp plant is used for soil reinforcement and in composites. Research has shown that it can increase the shear strength and overall resilience of soil. Kenaf fiber with high mechanical properties is used as a natural geotextile, often in composites to improve soil strength. Known for its high tensile strength and ductility, bamboo fibers can be used to improve the California Bearing Ratio (CBR) of soil and enhance subgrade strength. Fibers from palm trees have been shown to increase the strength and bearing capacity of subgrade soil, particularly when mixed into the soil.

Functions and Applications

Soil Reinforcement

Natural fibers can be mixed directly with soil or laid in layers to increase its strength and stability. The fibers act similarly to rebar in concrete, reinforcing the soil matrix by forming a composite material. This enhances the soil's tensile strength, bearing capacity, and shear resistance. Common applications include stabilizing slopes, reinforcing subgrades for roads and railways, and improving the stability of foundations.

Drainage and Consolidation

Natural fibers, woven into prefabricated vertical drains (PVDs), can enhance the rate of consolidation in soft, compressible soils. The porous fiber drains provide a path for excess pore water to escape from the soil, accelerating the consolidation process. They have been shown to have sufficient discharge capacity and perform well even under high confining pressure. They are used in infrastructure projects on soft ground, such as embankments and reclamation areas, to reduce settlement.

Erosion control and Filtration

Geotextiles, nets, and mats made from natural fibers are used to protect soil surfaces from erosion and act as filters. The fibrous material slows down water flow, traps soil particles, and prevents the formation of erosive channels. They also promote vegetation growth by creating a favourable microenvironment for seeds and roots. Applications include protecting riverbanks, stabilizing slopes, and controlling surface erosion in landscaping projects.

Limitations of natural fiber geosynthetics

Susceptibility to biodegradation limits the lifespan of natural fiber geosynthetics, making them unsuitable for permanent structures. Fibers can degrade due to exposure to elements like sunlight (UV resistance) and moisture, leading to strength loss over time. Natural fibers can be prone to attack by fungi and bacteria, further reducing their mechanical properties and service life. They have poor compatibility with hydrophobic polymer matrices, leading to weak interfacial adhesion and inefficient load transfer. Further, High moisture absorption causes swelling and degradation, affecting their mechanical performance and durability.

Biopolymers as geosynthetics

Biopolymers are gaining interest as sustainable alternatives to traditional petroleum-based geosynthetics, offering improved soil properties such as increased strength, reduced permeability, and enhanced erosion control. They are natural polymers such as guar gum, xanthan gum, lignin, alginate, chitosan, and starch, produced by living organisms: plants, animals, or microbes. Biopolymers function primarily by forming hydrogels and creating a strong bond between soil particles.

Micro-organism based biopolymers like Xanthan gum and Gellan gum are produced through bacterial fermentation and are among the most common biopolymers used for soil stabilization. Xanthan gum is an anionic polysaccharide that forms viscous, pseudo-plastic solutions, significantly enhancing soil shear strength and erosion resistance. It has been shown to be effective for stabilizing slopes and mine tailings. Gellan gum is a high-molecular-weight polysaccharide that forms durable gels. It is also used to enhance soil properties and has shown excellent results in both sand and clay.

Plant based biopolymers includes Guar gum, Cellulose, Lignin and Polylactic Acid (PLA) that are sourced from plants and agricultural waste. Guar gum is extracted from the guar plant, this polysaccharide forms cohesive hydrogels that improve the bonding and strength of soil particles. Cellulose, found in plant cell walls, can be processed into bioplastics for geotextile production. Cellulose-based materials have shown competitive mechanical and durable performance. The second most abundant biopolymer after cellulose is lignin, it is a natural adhesive that can link soil particles together and reduce soil porosity. Polylactic Acid (PLA) is a bioplastic made from renewable resources like corn starch or sugarcane, PLA can be formed into biodegradable geogrids for reinforcing soil.

Animal derived biopolymers come from animal sources, such as shells or milk products. Chitosan is a cationic polysaccharide derived from crustacean shells that can bind to negatively charged clay particles. Its antibacterial properties also make it useful for environmental applications.

Limitations of biopolymer geosynthetics

While promising, the use of biopolymers as geosynthetics still faces several hurdles that limit their widespread adoption. Biopolymer production can be more expensive than synthetic polymers, and raw material prices can fluctuate. The biodegradability of biopolymers can be a disadvantage when long-term strength is required. Their performance can also degrade under exposure to UV radiation and repeated wetting-drying cycles. The effectiveness of biopolymers varies greatly depending on the soil type, environmental conditions, and the specific biopolymer used. Some biopolymers exhibit poor performance when in contact with water, with their hydrogel bonding properties diminishing over time.