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]



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



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:



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.



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



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



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



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.

1use of discrete

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