Application of Technical Textiles in Everyday Life

Geo Textiles

Geotextiles were one of the first textile products in human history. Excavations of ancient Egyptian sites show the use of mats made of grass and linen. Geotextiles were used in roadway construction in the days of the Pharaohs to stabilise roadways and their edges. These early geotextiles were made of natural fibres, fabrics or vegetation mixed with soil to improve road quality, particularly when roads were made on unstable soil. Only recently have geotextiles been used and evaluated for modern road construction. Geotextiles today are highly developed products that must comply with numerous standards. To produce tailor-made industrial fabrics, appropriate machinery is needed.

Geotextiles have been used very successfully in road construction for over 30 years. Their primary function is to separate the sub-base from the subgrade resulting in stronger road construction. The geotextile performs this function by providing a dense mass of fibres at the interface of the two layers.

Geotextiles have proven to be among the most versatile and cost-effective ground modification materials. Their use has expanded rapidly into nearly all areas of civil, geotechnical, environmental, coastal, and hydraulic engineering. They form the major component of the field of geosynthetics, the others being geogrids, geomembranes and geocomposites. The ASTM (1994) defines geotextiles as permeable textile materials used in contact with soil, rock, earth or any other geotechnical related material as an integral part of civil engineering project, structure, or system.

Geotextiles should fulfil certain requirements like it must permit material exchange between air and soil without which plant growth is impossible, it must be penetrable by roots etc. and it must allow rainwater to penetrate the soil from outside and also excess water to drain out of the earth without erosion of the soil. To obtain all these properties in geotextiles, the proper choice of textile fibre is of paramount importance. The different synthetic fibres used in geotextiles are nylon, polyester, polypropylene while some natural fibres like ramie, jute etc. can also be used.

Important Characteristics of Geotextiles

1. Physical properties
   1. specific gravity
   2. weight
   3. thickness
   4. stiffness
2. Mechanical properties:
   1. tenacity
   2. tensile strength
   3. bursting strength
   4. drapability
   5. compatibility
   6. flexibility
   7. tearing strength
   8. frictional resistance
3. Hydraulic properties:
   1. porosity
   2. permeability
   3. permittivity
   4. transitivity
   5. turbidity /soil retention
   6. filtration length
4.  Degradation properties:
   1. biodegradation
   2. hydrolytic degradation
   3. photo degradation
   4. chemical degradation
   5. mechanical degradation
   6. other degradation occurring due to attack of rodent, termite
5. Endurance properties:
   1. elongation
   2. abrasion resistance
   3. clogging length and flow

Selection of Fibre for Geotextiles

Different fibres from both natural as well as a synthetic category can be used as geotextiles for various applications.

Natural fibres

Natural fibres in the form of paper strips, jute nets, wood shavings or wool mulch are being used as geotextiles. In certain soil reinforcement applications, geotextiles have to serve for more than 100 years. But bio-degradable natural geotextiles are deliberately manufactured to have a relatively short period of life. They are generally used for the prevention of soil erosion until vegetation can become properly established on the ground surface.

The commonly used natural fibres are

Ramie: These are subtropical bast fibres, which are obtained from their plants 5 to 6 times a year. The fibres have a silky lustre and have a white appearance even in unbleached conditions. They constitute pure cellulose and possess the highest tenacity among all plant fibres.

Jute: This is a versatile vegetable fibre that is biodegradable and has the ability to mix with the soil and serve as a nutrient for vegetation. Their quick biodegradability becomes a weakness for their use as a geotextile. However, their life span can be extended even up to 20 years through different treatments and blendings. Thus, it is possible to manufacture designed biodegradable jute geotextile, having specific tenacity, porosity, permeability, transmissibility according to need and location specificity.

Soil, soil composition, water, water quality, water flow, landscape etc. physical situation determines the application and choice of what kind of jute geotextiles should be used. In contrast to synthetic geotextiles, though jute geotextiles are less durable they also have some advantages in certain areas to be used particularly in agro-mulching and similar areas to where quick consolidation is to take place. For erosion control and rural road considerations, soil protection from natural and seasonal degradation caused by rain, water, monsoon, wind and cold weather are very important parameters. Jute geotextiles, as a separator, reinforcing and drainage activities, along with topsoil erosion in shoulder and cracking are used quite satisfactorily.

Furthermore, after degradation of jute geotextiles, lignomass is formed, which increases the soil organic content, fertility, texture and also enhance vegetative growth with further consolidation and stability of the soil.

Synthetic Fibres

The four main synthetic polymers most widely used as the raw material for geotextiles are – polyester, polyamide, polyethylene and polypropylene. which was discovered in 1935. The next oldest of the four main polymer families relevant to geotextile manufacture is polyester, which was announced in 1941. The most recent polymer family relevant to geotextiles to be developed was polypropylene, which was discovered in 1954.

Polyamides (PA): There are two most important types of polyamides, namely Nylon 6 and Nylon 6,6 but they are used very little in geotextiles. The first one is an aliphatic polyamide obtained by the polymerization of petroleum derivative ε- caprolactam. The second type is also an aliphatic polyamide obtained by the polymerization of salt of adipic acid and hexamethylene diamine. These are manufactured in the form of threads which are cut into granules. They have more strength but fewer moduli than polypropylene and polyester They are also readily prone to hydrolysis.

Polyesters (PET): Polyester is synthesised by polymerizing ethylene glycol with dimethyle terephthalate or with terephthalic acid. The fibre has high strength modulus, creep resistance and general chemical inertness due to which it is more suitable for geotextiles. It is attacked by polar solvents like benzyl alcohol, phenol, and meta-cresol. At pH range of 7 to 10, its life span is about 50 years. It possesses high resistance to ultraviolet radiations. However, the installation should be undertaken with care to avoid unnecessary exposure to light.

Polyethylene (PE): Polyethylene can be produced in a highly crystalline form, which is an extremely important characteristic in fibre-forming polymer. Three main groups of polyethylene are – Low density polyethylene (LDPE, density 9.2- 9.3 g/cc), Linear low-density polyethylene (LLDPE, density 9.20-9.45 g/cc) and High density polyethylene (HDPE, density 9.40-9.6 g/cc).

Polypropylene (PP): Polypropylene is a crystalline thermoplastic produced by polymerizing propylene monomers in the presence of stereo-specific Zeigler- Natta catalytic system. Homo polymers and copolymers are two types of polypropylene. Homo polymers are used for fibre and yarn applications whereas co-polymers are used for varied industrial applications. Propylene is mainly available in granular form. Both polyethylene and polypropylene fibres are crept prone due to their low glass transition temperature. These polymers are purely hydrocarbons and are chemically inert. They swell by organic solvent and have excellent resistance to diesel and lubricating oils. Soil burial studies have shown that except for the low molecular weight component present, neither HDPE nor polyethylene is attacked by micro-organisms.

Polyvinyl chloride (PVC): Polyvinyl chloride is mainly used in geomembranes and as a thermoplastic coating material. The basic raw material utilized for the production of PVC is vinyl chloride. PVC is available in free-flowing powder form.

Types Of Geotextiles

Geotextiles are permeable synthetic materials made of textile materials. They are usually made from polymers such as polyester or polypropylene. The geotextiles are further prepared in three different categories – woven fabrics, non-woven fabrics and knitted fabrics.

Woven fabrics: Large numbers of geosynthetics are of woven type, which can be sub-divided into several categories based upon their method of manufacture. These were the first to be developed from synthetic fibres. As their name implies, they are manufactured by adopting techniques that are similar to weaving usual clothing textiles. This type has the characteristic appearance of two sets of parallel threads or yarns –.the yarn running along the length is called the warp and the one perpendicular is called the weft. The majority of low to medium strength weaved geosynthetics are manufactured from polypropylene which can be in the form of extruded tape, silt film, monofilament or multifilament. Often a combination of yarn types is used in the warp and weft directions to optimize the performance/cost. Higher permeability is obtained with monofilament and multifilament than with flat construction only.

Non-woven: Non-woven geosynthetics can be manufactured from either short-staple fibre or continuous filament yarn. The fibres can be bonded together by adopting thermal, chemical or mechanical techniques or a combination of techniques. The type of fibre (staple or continuous) used has very little effect on the properties of the non–woven geosynthetics. Non-woven geotextiles are manufactured through a process of mechanical interlocking or chemical or thermal bonding of fibres/filaments. Thermally bonded non-wovens contain a wide range of opening sizes and a typical thickness of about 0.5-1 mm while chemically bonded non-wovens are comparatively thick usually in the order of 3 mm. On the other hand, mechanically bonded non-wovens have a typical thickness in the range of 2-5 mm and also tend to be comparatively heavy because a large quantity of polymer filament is required to provide a sufficient number of entangled filament cross wires for adequate bonding.

Knitted fabrics: Knitted geosynthetics are manufactured using another process that is adopted from the clothing textiles industry, namely that of knitting. In this process of interlocking, a series of loops of yarn together is made. An example of a knitted fabric is illustrated in the figure. Only a very few knitted types are produced. All of the knitted geosynthetics are formed by using the knitting technique in conjunction with some other method of geosynthetics manufacture, such as weaving. Apart from these three main types of geotextiles, other geosynthetics used are geonets, geogrids, geo-cells, geomembranes, geocomposites, etc. each having its own distinct features and used for special applications.

Functions Of Geotextiles

Every textile product applied under the soil is a geotextile. The products are used for the reinforcement of streets, embankments, ponds, pipelines, and similar applications (Figure 3.5). Depending on the required function, they are used in open-mesh versions, such as a woven or, rarely, warp-knitted structure, or with a closed fabric surface, such as a non-woven. The mode of operation of a geotextile in any application is defined by six discrete functions: separation, filtration, drainage, reinforcement, sealing and protection. Depending on the application the geotextile performs one or more of these functions simultaneously.

 

The principal functions performed by geotextiles are given below.

1. Confinement/ Separation: Confinement provides a media between the aggregate and the subsoil which absorbs the load in the form of tension and prevents change in the alignment of the Geotextile economically helps the separation concept of keeping two dissimilar apart to maximize the physical attributes of each of those materials. ( Fig 3.6)

2. Reinforcement: The purpose of geo-textiles in the reinforcement function is to reinforce the weak subgrade or subsoil. It helps to strengthen the soil surface and to increase the soils ability to stay put especially on the slopes. This function is important in wall embankments, foundations and slops. There is no problem of corrosion and there is minimum excavation behind the face of the wall when geo-textiles fabrics are laid.
3. Filtration: The purpose of geo-textiles with reference to drainage and filtration is simply to retain soil while allowing the passage of water. When geotextiles are used as drains, the water flow is within the plane of the geotextile itself i.e., they have lateral permeability. Adequate dimensional stability becomes an important factor to retain their
4. Drainage: Use of Geo-textiles in drainage has outstanding advantages. They eliminate the filter sand with the dual media backfill. In some cases, they eliminate the need for perforated They are used as a chimney drain or a drainage gallery in an earth dam as a drain behind a wall or beneath railroad ballast, athletic fields and for salt migration in arid areas.
5. Protection: Geotextiles are used with geo-membranes to provide long term protection of geo-membranes used for applications such as landfill and waste containment from puncture or training by sharp stone or stress. Typical application areas are highway tunnels, landfills, water and sewage tunnels, railroads and subway tunnels and reservoirs