Page 1 of 5

European Journal of Business &

Social Sciences

Available at https://ejbss.org/

ISSN: 2235-767X

Volume 07 Issue 05

May 2019

Available online:https://ejbss.org/ P a g e | 866

Experimental Study Of Bituminous Mixes Using Natural Fibre

R. SELVAGANESH

DEPARTMENT OF CIVIL ENGINEERING

PRIST(Deemed to be University), THANJAVUR

ABSTRACT

Stone Matrix Asphalt (SMA) is a gap graded mix, characterized by high coarse aggregates, high

asphalt contents and polymer or fiber additives as stabilizers. Highconcentration of coarse

aggregate maximizes stone-to-contact and interlocking in the mix whichprovides strength, and

the rich mortar binder provides durability. The stabilizing additives composed of cellulose fibers,

mineral fibers or polymers are added to SMA mixtures to preventdraindown from the mix. In

comparison to dense graded mixtures SMA has a higher proportion ofcoarse aggregate, lower

proportion of middle size aggregate and higher proportion of mineral filler. It resists permanent

deformation and has the potential for long term performance and durability.

INTRODUCTION

Aggregates bound with bitumen are

conventionally used all over the world in

construction and maintenance of flexible

pavements. The close, well, uniform, or

dense gradedaggregates bound with normal

bitumen normally perform well in heavily

trafficked roads ifdesigned and executed

properly and hence very common in paving

industry. However, it is notalways possible

to arrange dense graded aggregates available

at the site. In such situations abituminous

mix called stone matrix asphalt (SMA)

which basically consists of gap graded

aggregates, can be attempted. SMA was

developed in Germany in the 1960s by

Zichner of the Straubag-Bau AG central

laboratory, to resist the damage caused by

studded tires. As SMA showed

excellentresistance to deformation by heavy

traffic at high temperatures, its use

continued even after the ban of studded tires.

SMA is a gap graded mixture containing 70-

80% coarse aggregate of totalaggregate

mass, 6-7% of binder, 8-12% of filler, and

about 0.3-0.5% of fiber or modifier. Thehigh

amount of coarse aggregate in the mixture

forms a skeleton-type structure providing a

Page 2 of 5

European Journal of Business &

Social Sciences

Available at https://ejbss.org/

ISSN: 2235-767X

Volume 07 Issue 05

May 2019

Available online:https://ejbss.org/ P a g e | 867

betterstone-on-stone contact between the

coarse aggregate particles, which offers high

resistance torutting. Aggregate to

aggregatecontact is also there in dense

graded mixtures but it occurs within the fine

aggregate particles as the coarse aggregate

floats in the fine aggregate matrix, which

don’t give the same shear resistance as the

coarse aggregate skeleton. Brown and

Manglorkar(1993) reported that the traffic

loads for SMA are carried by the coarse

aggregate particles instead of the fine

aggregate asphalt-mortar. The higher binder

content makes the mix durable.

The fibers or modifier hold the binder in the

mixture at high temperature; prevent

drainage during production, transportation

and laying. SMA has been proved to be

more cost effective than dense graded mixes

for high volume roads. Brown (1992)

observed that a number of factors influence

the performance of SMAmixtures, such as

changes in binder source and grade, types of

aggregate, environmentalconditions,

production and construction methods etc.

Evaluation of these factors would help to

determine the long term performance of

SMA and provide information to make

changes as needed to suit different

environmental conditions. The SMA

Technical Working Group ofFHWA defined

SMA as “A gap graded aggregate hot mix

asphalt that maximizes the bindercontent

and coarse aggregate fraction and provides a

stable stone-on-stone skeleton that is held

together by a rich mixture of binder, filler

and stabilizing additives”.

Advantages over Conventional

Bituminous Mixes

Conventional bituminous pavements lack

the strength, durability and longevity of

SMA. There are several factors for which

SMA is better than the conventional mixes.

As mentioned byBose et al. (2006) SMA

provides better resistance to rutting due to

slow, heavy and high volumetraffic,

resistance to deformation at high pavement

temperatures, improved skid resistance,

noisereduction over conventional alternative

pavement surfaces, improved resistance to

fatigue effectsand cracking at low

temperatures, increased durability, reduced

permeability and sensitivity tomoisture.

According to Brown and Manglorkar (1993)

SMA has also shown good resistance

toplastic deformation under heavy traffic

Page 3 of 5

European Journal of Business &

Social Sciences

Available at https://ejbss.org/

ISSN: 2235-767X

Volume 07 Issue 05

May 2019

Available online:https://ejbss.org/ P a g e | 868

loads with high tyre pressures as well as

good lowtemperature properties. Further,

SMA has a rough texture which provides

good frictionproperties after surface film of

the binder is removed by the traffic.

Kamaraj et al. (2004) havereported that

SMA has an extended life as compared to

conventional dense graded mixes. Theyhave

also reported that the cost of SMA has been

estimated to be about 20-25 percent more

than conventional dense graded mixtures,

but this can be justified by the increased life

of pavement. In view of these advantages

SMA has been proved to be superior over

HMA mixes.

ANALYSIS OF TEST RESULTS AND

DISCUSSION

Marshall stability value with binder content

for the three binder types at fiber

concentrations of 0%, 0.3%, 0.5% and 0.7%

respectively. The binder content in the mix

was varied from 3% to 7% by weight. It can

beobserved from the above figures that, with

increase in binder content the stability value

increasesup-to a certain binder content then

decreases as per the normal trend for a

bituminous mix. It isobserved that the

stability value in general increases with the

hardness (in terms of penetrationvalue) of

the binder. For example at a particular fiber

content, the samples prepared with

80/100bitumen result the least stability

values and that with CRMB 60 has the

highest stability value.

This is because with higher viscous binders

the interlocking between aggregates with

thickervoid packing is better retained. It can

also be observed that, when a stiffer binder

is used morebinder content is required to

attain the maximum stability value. This

may be due to the fact thatthe higher

viscosity of the binder requires more amount

in its voids as its draindown effect isless.

It is observed that with increase in fiber

content the stability value increases up to

0.5% fiber, thereafter decreases. This is due

to the fact that at higher percentage of fiber

homogeneousmixing of the fiber materials is

not possible and this results conglomeration

of fibers. Such aheterogeneous mixture

affects the aggregate-binder bonding and

interlocking between the

aggregates resulting in low stability value. It

can be observed from these plots that the

maximumstability value without fibers in

the mix is even more than the stability value