RAW MATERIALS FOR GEOTECH

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• RAW MATERIALS FOR GEOTECH

by
Dr. S.R. VENGSARKER
Zenith Fibres Limited,
Vadodara.
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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
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Geotextiles
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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
Fibre Type Consumption (000 te)
Polyester 126.9 49.7
Polypropylene 120.8 47.4
Poly-Acrylonitrile NIL -
Viscose NIL -
Natural 7.4 2.9
TOTAL 255.1 100.0
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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 gt9.5
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)
lt 2
PP (Polypropylene)
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PP Staple Fibre grades for Geotextiles
Typical Specifications
Sr. No. Test Property 3 Denier x 60mm or 80mm Raw white 5 Denier x 80mm or 100mm Raw white
1. Specific Gravity 0.91 0.91
2. Denier 3.0 5.0
3. Breaking Tenacity (gm/den) 6.0 5.8
4. Breaking Elongation () 40 45 (60-70 Desireable)
5. Crimps per cm 5.6 3.5
6. Oil Pick-up 0.50 0.50
7. UV Stabilizer Addition - Depends specific on customers requirement
8. MFI of Fibre 16
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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
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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
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Weight of Non-Woven

225 gsm

89.6
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Porosity of fabric
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Pore size

180 Microns
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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.
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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.
Geonets are 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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