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RAW MATERIALS FOR GEOTECH

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RAW MATERIALS FOR GEOTECH. by. Dr. S.R. VENGSARKER. Zenith Fibres Limited,. Vadodara. ABOUT ZENITH FIBRES LID.,. Located Near Vadodara , Gujarat State. Fibre Type. :. Polypropylene Staple Fibre. Capacity. :. 350 tonnes /month. Fibre Denier Range. :. 1.5 to 110 Denier.

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RAW MATERIALS FOR GEOTECH

by

Dr. S.R. VENGSARKER

Zenith Fibres Limited,

Vadodara.

slide2

ABOUT ZENITH FIBRES LID.,

Located Near Vadodara, Gujarat State

Fibre Type

:

Polypropylene Staple Fibre

Capacity

:

350 tonnes/month

Fibre Denier Range

:

1.5 to 110 Denier

Fibre Denier Range

:

6mm to 150mm

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RAW MATERIALS FOR GEOTECH

1.

Definition

According to ASTM, A “Geotextile” is any permeable textile material used with foundation, soil, rock, earth or any other geotechnical engineering related material, as an integral part of a man-made project, structure or system.

Bureau of Indian Standards (BIS) has approved the standards for Geosynthetics made from Polyolefin or Polyester material for Highways.

The term “Geosynthetics” Covers :

-

Geotextiles

-

Geogrids

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-

Geomembranes and

-

Geocomposites

A “Geogrid” is characterized by high dimensional stability and high tensile modulus at very low elongation.

When geogrids / geotextiles / geo-membranes are combined with woven or non-woven geotextiles or geogrids for specific applications like drainage, erosion control, bank protection etc. they are designated as “Geo-composites”.

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2.

Worldwide Geotech Consumption Polymer/ Fibre Type

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The major contribution to Geotech consumption is from Polyester (PET) and Polypropylene (PP). The major area in which PET and PP compete hard is in ground stabilization in Geotech.

CAGR between 2000-2010 worldwide shows 3.7% growth rate of PET as against 4.1% for PP in Technical Textiles consumption taken together.

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Indian Scenerio

Woven Geotextiles

:

35%

Total : 63%

Non-woven Geotextiles

:

28%

Geogrid

:

15%

Geomembrane

:

22%

Total

:

100%

Nearly 40% domestic demand of Geotech is met by imports.

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3.

Selection of Raw Materials :

The fibres and yarns selected for civil engineering applications are synthetic polymers which offer long term stability against mechanical, chemical and bio-degradable degradation.

Polyester and Polypropylene are the most common polymers meeting these requirements.

Polypropylene Polymer has following distinct advantages :

1.

Resistant to chemical attack.

2.

Stable to pH between 3 and 13.

3.

Non-biodegradable.

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4.

Resistant to commonly encountered soil-bound chemicals, landfil leaches, mildew and insects.

5.

Lightest fibre which means volume to weight ratio is one of the highest.

Polyethylene Terephthalate (PET) Polymer on the other hand has :

1.

Superior Breaking Tenacity (Strength)

2.

Superior creep characteristics required in some critical reinforcement materials.

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PET must not be used in contact with soils with pH >9.5

For Geotextile application in case of PE and PP Oxidative resistance is required to be observed.

For PET made Geotextiles hydrolytic resistance is required to be observed.

It is worth mentioning the use of Aramid Fibre which has low short-term extension and good creep strength. Principal end-uses for Aramid Geotextiles include slip resistant embankments and steep slopes for refuse dumps.

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Jute Geotextiles

Jute is also used as a raw material since it is a cheap fibre in the North-East region. Loss of strength after a year is not a deterent as by that time, the Jute Geotextile is seen to have helped in providing a self-sustaining sub-grade for most type of soils. With the passage of time soil becomes increasingly less dependent on Jute Geotextile for its stability. It has significant share of the erosion control segment.

Synthetics contribute 95 percent of the market share while Natural fibres like Jute, coir etc. account for only about 5% of the market.

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4.

Geotech : Geotextile Products

Geotextiles are used in a wide range of applications including construction of buildings, bridges, dams, roads, railways and paths as well as embankments, cuttings, dykes and sub-sea coastal engineering projects.

Polyester has superior Tenacity and Creep characteristics and is preferred in critical reinforcement applications.

84% of PP consumption is found in ground stabilization products where it accounts for nearly half of the total market (i.e. ground stabilization, soil reinforcement, Erosion Control and Pit linings).

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Stress-strain Properties of Geotextiles

Normally the breaking strength or tenacity is used to compare the strengths of different polymers. However, from reinforcing point of view, Initial Modulus which indicates the initial resistance to extension of a polymer is of greater significance. When a polymer has resistance to stretching, it will have high Modulus indicating fibre inextensibility and brittleness.

Amongst the Polymers used for Geotextiles, PET has one of the highest Initial Modulus.

When a constant stress value is applied to a Geotextile, extension with time is measured and this phenomenon is called “creep”.

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Polypropylene yarns extend less on initial loading but more strongly when the load is removed.

Polyester and Aramid have very low tendency to creep (i.e. high long term strength and minimum creep strain) and this is desireable for ideal reinforcement.

Creep behavior of different Polymers :

Polymer Type

Creep %

PET (Polyester)

< 2

PP (Polypropylene)

5

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On testing of 5 Denier imported fibre sample it was noticed that 5 MFI Resin was used. Therefore available RIL grade H050MN (MFI 5) was used to achieve high Tenacity (5.8 gm/den). But % Breaking Elongation of 45 max. only was achievable. Even varying of Process parameters and blending of Polymers of different MFI values could not give elongation values more than 45%. Higher Breaking Tenacity and higher Breaking Elongation are the pre-requisites for a Good Quality Geotextile.

*

Local manufacturers of PP Resin donot generally supply less than 15 MFI Multifilament resin grades.

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Both Polyester and Polypropylene are readily processable into Non-wovens, especially by increasingly important technology of “Spun-bonding”.

In the case of Non-wovens the process is relatively simple. It involves preparation of card web and then mechanically needle punching the web to get the desired weight of the Non-woven fabric.

Typical Fabric Grammage :

140-200 gsm

New Asphalted Roads & Repairs of old Roads.

:

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350-450 gsm

:

For Building Foundations.

500, 600, 700 gsm

:

For Sea Erosion Control.

Manufacturing of Non-woven by mechanical needle punching appears a simpler process. However, there are Non-woven manufacturers abroad who guarantee no weight variation when one square inch fabric pieces are cut and weighed. This point requires careful consideration by local manufacturers.

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In Ground Stabilization application, the split is between broad-woven fabric (using Monofilaments and split tape) and Non-woven fabrics. These products help to distribute loads and prevent erosion and cracking in embankments, railway track beds, roads and other surfaces. Broad-woven fabrics are woven products made from pre-stressed Polypropylene Tapes.

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Non-woven Geotextiles are preferred over wovens due to :

1.

High void Percentage in Non-wovens.

2.

Higher Uni-directional Elongation and Higher Puncture Resistance.

3.

Excellent Hydraulic Properties.

4.

Finer Pore size makes the fabric as efficient filter media.

5.

Good interlocking of fabric in Non-woven.

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Geotextiles Consumption in India

India is currently consuming :

-

6000 tonnes of Geotextiles.

-

85% of this is being used in Road Sector.

-

About 2% is being used in Landfills

-

13% consumption is in other sectors including Airports, Ports, Railways , Dams, canals, etc.

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Case study on Geotextiles on Ichalkaranji, Maharashtra Road.

In 1993 a Non-woven Geotextile produced by needle punching 3 Denier x 75mm Natural White PPSF Grade was laid for the purpose of reinforcement and soil stabilization of the road.

Geotextile had following basic specs :

-

Weight of Non-Woven

:

225 gsm

:

89.6%

-

Porosity of fabric

-

Pore size

:

180 Microns

-

Resistance to puncture in terms of hole diameter.

:

18.25mm

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The road had to be initially levelled using mixtures of granules, slits and fine soil and moving a heavy roller on top of it. Then the Non-woven fabric was placed on the road and overlaying was done by moving a heavy roller.

The condition of the road even after 8 years of service life was found to be good with hardly any rut whereas, other road without a Geotextile in the nearby region exhibited heavy rut depth ranging between 10 cm and 30 cm and also waviness in the road.

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The Non-woven fabric when removed after 8 years from the road was tested for tensile properties and no adverse effects were observed.

5.

Geogrids for Reinforcement

Geogrids are matrix-like materials with large open spaces called apertures (10mm-100mm size).

Uniaxially and Biaxially oriented Geogrids are made from High Density Polyethylene (HDPE) or Polypropylene Sheet having a uniform pattern of pre-punched holes. Geogrids are also available from Aramid and Glass. Glass Geo-grids have been used as reinforcement of Airport Runways, Pavements and Roads.

slide25

Woven or knitted Geogrids are made mainly from high tenacity Polyester Yarns to give transverse and longitudinal rib structure. The entire fabric is coated with PVC, latex or bitumen for dimensional stability. Such Geogrids have high Strength, high Modulus and low creep sensitive polymers.

Geonetsare made from a single un-oriented process from PE or PP.Geonets have square or rectangular net shape apertures when used for protective works. It is not used as soil reinforcement due to its high creep characteristics.

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6.

Landfill Application with Geomembrane

The purpose of Landfill is to bury the trash in such a way that it will be isolated from ground water, will be kept dry and will not be in contact with air. Under these conditions, trash will not decompose much.

After excavating the ground sufficiently deep, the water is extracted out and then Geomembrane (HDPE with 2.5% carbon black to protect from UV exposure) is laid covering the entire excavation and the slope. Geomembrane is then welded to make it water tight. Protection of Geomembrane

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is done by a non-woven Geotextile (Polypropylene of 400 gsm weight). The system is then ready to dump the solid waste.

Promotion of Geomembrane as lining for Canals, Ponds and Reservoirs is likely to boost the consumption of Geomembranes.

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7.

Bi-component Fibres for Geotextiles

Terram Industries is putting up a Plant near Moondra to produce Spun Bond Fabric. It involves following stages :

1.

Production of concentric Heterofil FDY having 30% Polyethylene and 70% Polypropylene (sheath-core combi-nation).

PE-LDPE has MFI of 13-17 and Polypropylene has MFI of 23-28.

2.

After lay-down of Bi-component fibres the material is bonded by passing through an Oven to make a fabric.

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The bonded product has high tensile strength (isotropic) and the weight range is between 60 gsm and 400 gsm.

Typical applications in Geotextiles include Filter separator/Reinforcement, Roads, Railways, Airports.

Where prolonged exposure to sunlight is inevitable, UV light resistance is enhanced by addition of UV Stabilizers in the polymers so that they retain 50% of their original strength after exposure to 70,000 Langley\'s of solar radiation.

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In Conclusion :

The major Raw Materials for use in Geotech are undoubtedly PET and PP Polymers.

The market for Geotech is big in our country. However, co-ordinated approach is necessary between Raw Material suppliers, Fibre producers and Geotech manufacturers to provide the right grade of Geotech material for the end-use application for which it will ultimately serve the purpose. This appears to be the right way to boost the domestic consumption and to prevent Geotech imports into our country.

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THANK YOU

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