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7/27/2019 1use of Discrete
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USE OF DISCRETE FIBER
IN R OAD CONSTRUCTION
PREPARED BY,
V.KOTESWARA REDDY,
III-BTECH (CIVIL),
G.PULLA REDDY ENGINEERING COLLEGE,
PH.NO:9440452865,
MAIL:ESWAR [email protected]
AND
N.SARATH KUMAR
III-BTECH (CIVIL),
G.PULLA REDDY ENGINEERING COLLEGE,
PH.NO:9032290630
MAIL:[email protected]
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ABSTRACT:
New materials and construction
techniques are required to provide Civil
Engineering with alternatives to
traditional road construction practices.
Traditional techniques have not been
able to bear the mixed traffic load for a
long time. Therefore the pavement
requires overlaying. To overcome this
problem fiber inclusion in pavements is
adopted nowadays. This paper highlights
on the use of discrete fiber in road
construction. Recently Geosynthetics
have been used to reinforce and separate
base course material for aggregate-
surfaced roads and flexible pavements.
Inclusion of discrete fibers increases
shear strength and ductility.
INTRODUCTION:
Traditional road construction
practices require alternative materials
and techniques. Quality construction
materials are not readily available in
many locations or are costly. New
techniques available are expensive
and require skilled labour and special
equipments. Recently Geosynthetics
have been used to reinforce and
separate base course material for
aggregate-surfaced roads and flexible
pavements.
Sand-fiber stabilization uses
common construction equipments and
requires no special construction
skills. Sand-fiber stabilization is
applicable for a wide variety of sands
and silty sands found around the
world. This method is used for
expedient road construction over
loose sands.
The new sand-fiber
stabilization technology uses small
amounts of hair-like polypropylene
fibers to stabilize the sand. The two-
inch-long fibers are simply mixed
into the top eight inches of moist sand
using a self-propelled rotary mixer. A
wearing surface is added by spraying
a resin modified emulsion (undiluted
road oyl) or emulsified asphalt onto
the road surface. The emulsion
penetrates and bonds the top inch of
sand-fiber mixture. The new sand-
fiber technology allows quick
construction of roads over sands at
remote sites using reduced
equipment, manpower and materials.
The sand-fiber mixture is a very
erosion resistant material that could
be useful in many erosion control
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applications. This technique requires
very little or no maintenance for
years.
LITERATURE R EVIEW:
A review of the literature
revealed that various laboratory
investigations have been conducted on
fiber-reinforced materials. Gray and
Ohashi indicated increased shear
strength, increased absorbed strain
energy, and reduced postpeak strength
loss due to the inclusion of discrete
fibers.
The inclusion of discrete fibers
increases both the cohesion and the
angle of internal friction of the
mixtures. Arteaga suggested the termapparent cohesion for the increase in
cohesion of cohesion less materials.
Properties improves due to the
inclusion of discrete fibers was
determined to be a function of various
parameters including fiber type, fiber
length, aspect ratios, fiber content,
orientation and soil properties. The
peak strength increases with the
increase in fiber content and fiber
length (Gray and Ohashi 1983;
Arteaga 1989).
0.8% fibers by dry weight of
material were the optimum dosage
rates for a 51 mm monofilament
polypropylene fiber. The unconfined
compressive strength can be used as an
index of field performance based on
the tests conducted. For sand-fiber
stabilization over sandy subgrade, the
stabilized thickness requirement should
be 305 mm. A 203 mm thick sand-fiber
layer is sufficient (Webster and Santoni
1997).
The resin modified emulsion
(Undiluted Road Oyl) improves the
properties of the mixture. It works as
the binder for expedient road and serve
the purpose for dust control (Webster
and Santoni 1997).
PREPARATION OF THE MIXTURE:
The literature review gives us
the lesson that there are three critical
components for preparing fiber-
stabilized material:
1. Moisture control
2. Mixing
procedure
3. Compaction.
MOISTURE CONTROL:
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Moisture is required to
adequately mix and mold the mixture.
It is required to prevent separation of
the sand and fibers during the mixing
process and to prevent mixture
disturbance.
MIXING PROCEDURE:
An appropriate amount of sand
was placed in the mixing container.
Then the required water is mixed into
the sand in small increments to ensure
uniform coverage. The fibers are
mixed in small increments using a
two-bladed mortar mixing bit
powdered by an electric drill. Take
care during the mixing procedure to
ensure a uniform sand-fiber mixture.
COMPACTION:
Compaction is required for the
mixture densification, which is done,in different layers to get more stable
layers. The idea of compaction
procedure can be obtained by study of
compaction test in which sand-fiber
mixture is placed in a high cast iron
split mold and then densification in
different layers is performed by
hammering. Generally, up to 20 or
more blows.
EFFECTS OF USING DISCRETE
FIBER :
The inclusion of discrete
fibers increases the cohesion
of the mixture. The increase in
cohesion of typically cohesion
less materials due to the
inclusion of discrete fibers
was termed the “apparent
cohesion” of the material.
The inclusion of discrete
fibers increases the angle of
internal friction of the
mixture.
EFFECT OF FIBER LENGTH:
Fiber length improves the
unconfined compressive strength of
the mixture. As the fiber length is
increases the strength of the mixture
also increases.
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EFFECT OF FIBER CONTENT:
The performance of the mixture
increases with the increase in fiber
content. Mixture prepared at dosage
rates of 0.6-1.0% exhibits the strain
hardening characteristics. Strain
hardening is characterized by increase
in unconfined compressive strength
with a corresponding increase in
strain. The density of the mixture
decreases with the increase in fiber
content. Hence it performs best up to
a dosage rate of 1.0% only.EFFECT OF FIBER DENIER :
The unconfined compressive
strength of the mixture decreases
slightly with the increase in fiber
denier. The decrease in the strength is
not significant. The increase in performance with decreasing fiber
denier may be attributed to the slight
increase in the number of fibers due
to using smaller diameter fibers when
dosage rates are calculated.
EFFECT OF SILT CONTENT:
The inclusion silt decreases the
unconfined compressive strength of
sand. The inclusion of up to 8% silt
does not affect much in terms of
increased unconfined compressive
D e n s i t
k
/ m 3
Fiber, %
U n c o n f i n e d c o m
r e s s i v e s t r e n
t h
Deflection
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strength when compared to the fiber-
stabilized clean sands. The results
show that silt content up to 12%
performs similar to the fiber-
stabilized clean sand.
EFFECT OF MOISTURE CONTENT:
The performance of the mixture
enhance by the inclusion of discrete
synthetic fiber at any moisture
content. The results show that the
performance increases with the
increase in moisture content. The
mixture’s unconfined compressive
strength increases significantly from
base moisture content of 2.6% to
14%. Beyond 9.0% moisture, the
mixture’s unconfined compressive
strength is less beneficial and less
effective as the saturation point of
14% moisture content is achieved. At
the saturation point its performance is
less with the composite mixture.
EFFECT OF COMPACTION:
EFFECT OF EMULSION:
Road Oyl is sprayed over sand-
fiber surface such that it penetrates in
the top one inch of the surface.
S t r e n
t h
k P a
Deflection, %
Moisture content %
D e n s i t
k / m
3
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Thickness of the sand subgrade is
eight inches and the thickness of
fiber-stabilized sand is four inches.
This process controls dust and binds
the mixture. It provides higher
bonding strength than hot applied
asphalt emulsion.
ADVANTAGES OF USING SAND-FIBER
STABILIZATION:
Increases life Strain hardening
characteristics are obtained.
Apparent cohesion of the
mixture increases.
Angle of internal friction of the
mixture increases.
Shear strength and absorbed strainenergy are increased.
It uses common construction
equipments and requires nospecial construction skills.
It is erosion resistant materialhence of roads.
It requires little maintenance
hence economical.
It is also environmental friendly
as prevent the use of asphalt as
binder.
CONCLUSIONS:
Sand- fiber technology is
economical and far more durable than
normal methods of road construction.
With respect to mixed traffic
conditions like the one existing in
India this type of roads will prove far
more successful than the roads built
with traditional methods. Materials
used can be easily transported even to
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remote areas. As specified above this
technique does not require much
skilled labour. This technology
allows quick construction of roads .
References:
Arteaga, C.B. (1989). “The
shear strength of Ottawa sand mixedwith discrete short length plastic
fibers.” Thesis, Mississippi State
University, Mississippi State, Miss.
Gray, D.H., and Ohashi, H.
(1983). “Mechanics of fiber reinfor cement in sand.” J. Geotech.
Engrg ., ASCE, 109(3), 335-353.
Webster, S.L., and Santoni,
R.L. (1997). “Contingency airfield
and road construction usinggeosynthetic fiber stabilization of
sands.” Tech. Rep. GL-97-4, U.S.
Army Engr. Waterways Experimentstation, Vicksburg, Miss.