ijciet_06_09_001

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International Journal of Civil Engineering and Technology (IJCIET)

Volume 6, Issue 9, Sep 2015, pp. 01-07, Article ID: IJCIET_06_09_001

Available online at

http://www.iaeme.com/IJCIET/issues.asp?JTypeIJCIET&VType=6&IType=9

ISSN Print: 0976-6308 and ISSN Online: 0976-6316

© IAEME Publication

___________________________________________________________________________

INVESTIGATING THE MARSHALL

STABILITY REQUIREMENTS OF ASPHALT

CONCRETE MIX WITH GROUND SCRAP

TYRES AS AGGREGATE

D.B. Eme and T.C. Nwofor

Department of Civil Engineering, University of Port Harcourt,

P.M.B 5323 Port Harcourt, Rivers State,

Nigeria.

ABSTRACT

Ground scrap tyres can be used in asphalt mixtures either as a binder

modifier (wet process) or as a fine and/or coarse aggregate replacement (dry

process). To evaluate the effect of rubber-bitumen interaction on the dry

processed mixtures, a laboratory investigation was conducted on a range of

dense graded dry process with 4.75mm, 2.36mm and 0.600mm particle size

rubber modified asphalt mixtures containing 0 (control), 2, 4 6, 8 and 10%

ground rubber by aggregate mass. The mixtures were subjected to Marshall

Stability test. The stability, flow, percentage air void, unit weight, voids in

mineral aggregate, and specific gravity were determined. The results

indicated that, in general, as the rubber percentage increase, the stability, unit

weight and specific gravity value decrease. In addition, as the rubber content

increase, the flow of specimen also increases. The result also showed that as

the rubber content increases the percent air voids and VMA increase for

4.75mm RPS and 2.36mm RPS, while for 0.600mm RPS the reverse was the

case. Generally as regards the Marshall Stability tests, the rubber modified

specimens remained intact after failure. Such behavior will be beneficial for a

pavement that requires good impact resistance properties. The use of 10%

4.75mm, 4% 2.36mm or 4% 0.600mm RPS by weight of aggregate mass in

asphaltic concrete is recommended for medium traffic volume pavements.

Cite this Article: D.B. Eme and T.C. Nwofor. Investigating The Marshall

Stability Requirements of Asphalt Concrete Mix with Ground Scrap Tyres as

Aggregate. International Journal of Civil Engineering and Technology, 6(9),

2015, pp. 01-07.

http://www.iaeme.com/IJCIET/issues.asp?JTypeIJCIET&VType=6&IType=9



1. INTRODUCTION

As population grow, so do the volume of waste and by-product materials generated.

Attempts are still been made by various organizations and researchers to find methods

for effectives utilization of waste materials which also includes efforts to the

application of some of the waste products in highway construction. The construction

of highway pavements requires large volume of materials hence highway agencies

have become participants in these recycling efforts. Experience and knowledge

regarding the use of these materials differ from material to material hence to recover

these materials for potential use, engineers and researchers need to be aware of the

properties of the materials, how they can be used and what limitations may be

associated with their use. Every year, an estimated eight hundred and fifty thousand

(850,000) scrap tyres are generated and carelessly discarded in Nigeria, resulting in

serious waste disposal problems, [1].

The introduction of scrap tyre rubber into asphalt concrete production has the

potential to solve this waste problem as has been effectively carried out in the

production of most construction materials, [2-7]. The use of scrap tyre-rubber as an

additive for asphalt concrete has been developing for over thirty years, where it was

generally observed that the benefits outweighs the higher cost of the conventionally

produced asphaltic concrete material, especially on some highways with peculiar

problems, [8-9].

The basic contribution made in this study is to find out the optimum effect of the

substitution of the aggregates for asphalt concrete production with locally available

scrap tyre on the standard strength parameters.

2. MATERIALS AND METHOD

The aggregates were collected from crush rock Nigerian Limited in Rivers State,

Nigeria. This source was chosen because of its proximity. The aggregates supplied

consisted of 9.5mm granite chippings and 0.5mm quarry sand.

The scrap tyres used in this research were collected from a scrap tyre dump along

Anozie street, Diobu, in Port Harcourt, Nigeria. These tyres were cleaned through

washing with water and then dried. The clean tyres were shredded into sections freed

from steel breeds and later the sections were cut into small pieces with aid of knives

and hacksaw. The shredded tyres were also grinded using electric grinding machine

which reduced them into rubber particles and synthetic fibre mixture. The mixture

was then sieved and rubber particles retained on 4.75mm, 2.36mm and 0.600mm

sieves were collected.

Bitumen is a viscous liquid consisting essentially of hydrocarbons and their

derivates. The bitumen used in this research was collected from the building material

market Mile III, Diobu, Port Harcourt.

2.1. Sample Preparation

The following tests were used in the classification and preparation of the samples.

2.1.1 Sieve Analysis

The sieve analysis was carried out in accordance with BS1377:1975 – methods of

tests for soils for Civil Engineering purposes. The gradation requirement used in this

Investigating The Marshall Stability Requirements of Asphalt Concrete Mix with Ground

Scrap Tyres as Aggregate


research was for Asphalt Institute Mix No. IV(a), in order to meet the specification

requirement of 49% granite chippings and 51% of quarry sand.

2.1.2 Specific Gravity

The specific gravity test was carried out in accordance with BS1377:1975 methods of

test for soils for Civil Engineering purposes. Close values 2.66 and 2.57 were

obtained for granite chippings and Quarry sand respectively, while the ground scrap

tyre specimens gave specific gravity values of 1.11, 1.16 and 0.96 for rubber particle

sizes of 4.75, 2.36 and 0.6mm respectively which also indicates their light weight.

2.1.3 LOS Angles Abrasion and Aggregate Crushing Test

This test is used for measuring the abrasion resistance of aggregates. The top layer of

a pavement gets abraded due to the movement of tyres. A material which has high

abrasion resistance has a long life. The LOS Angles Abrasion test was carried out in

accordance with AASHTO-T96. Also one of the modes in which a pavement material

can fail is by crushing under severe stresses. A test devised to express the crushing

strength is the aggregate crushing test. The test consists of subjecting the aggregate

specimen in a standard mould to a compression test under standard loading

conditions. The aggregate crushing test was carried out in accordance with BS1377

:(1975). The granite chippings gave a Los Angeles abrasion value of 31.19% and

aggregate crushing value of 36.80%. From the specification recommended in

Emesiobi [10], the granite chipping is adequate for use in asphalt concrete mix.

2.1.4. Penetration Test

The penetration of bitumen is defined as the distance in tenths of a millimeter that

a standard needle will penetrate into the bitumen under a load of 100g applied in five

seconds at 250C. The higher the penetration, the softer is the bitumen. It is used for

classifying bitumen into standard grade. The bitumen test was carried out in

accordance with AASHTO-T49. The bitumen gave a penetration of 63pen. The result

indicates that the bitumen used is a 60/70 grade bitumen which is adequate for use in

hot mix asphaltic concrete in tropical climate.

2.2. Mix Design

The mix was designed as dense graded with 100% passing the 12.5mm sieve using

the Asphalt institute IV (a) specification. The aggregates were blended using the

Rothfuch’s method. The control mix with no chunk or crumb rubber was designed

and the amount of rubber used in the mixes varied from 2% to 10% by weight of the

granite chippings for scrap tyre rubber particles retained on sieves 4.75mm and

2.36mm and quarry sand for rubber particles retained on 0.600mm sieve.

2.3. Specimen Preparation and Testing Method

The method adopted in preparing the test specimens was the same as that

recommended for Marshall test specimens by Emesiobi [10] in accordance with

ASTMD 1559. The basic test carried out in the laboratory was the Marshall Stability

test. Marshall Stability values which are maximum load at failure and their

corresponding flows were recorded. Also values of stability flow air void, unit weight

and aggregate voids filled with binder (VMA) against bitumen content were also

obtained. During the test procedure an optimum bitumen content of 6.22%

(corresponding to the average of the maximum stability, average air voids of 3-5%



and average maximum unit weight) was obtained. Thereafter the bitumen content

(optimum bitumen content) was fixed while the effect of other parameters was

investigated. The parameters such as scrap tyre rubber particle sizes and rubber

content of the hot-mix asphaltic concrete were varied. The mix parameter chosen

were rubber particle sizes retained on 4.75mm, 2.36mm and 0.600mm sieves and

rubber content of mix from 2 to 10 percent by weight of granite chippings.

3. RESULTS AND DISCUSSION

A total of 103 laboratory prepared Marshall specimens were made and tested. All of

the testing was conducted at the Civil Engineering laboratory of the Rivers State

University of Science and Technology and in accordance with AASHTO and/or

ASTM procedure. Table 1 contains Marshall Test results from this study as a function

of rubber content and rubber particle size.

Table 1: Values of Marshall Stability test properties of asphaltic concrete.

Rubber

Content

(%)

Rubber

Particle

Size (mm)

Marshal

Stability

(kN)

Flow

(mm)

Air voids by

Total

Mixtures (%)

Unit

Weight

(kg/m3)

Voids filled

with Bitumen

(VMA) (%)

Specific

Gravity

0 7.24 4.04 3.23 2.354 81.19 2.385

2

4.75 4.63 3.68 3.09 2.275 81.11 2.355

2.36 5.47 3.71 3.05 2.288 81.92 2.360

0.600 6.20 3.74 3.02 2.300 81.79 2.316

4

4.75 3.61 3.25 3.40 2.230 80.16 2.332

2.36 4.95 4.05 3.53 2.276 79.45 2.335

0.600 4.97 4.22 2.28 2.246 85.52 2.316

6

4.75 3.49 3.61 4.30 2.206 75.19 2.306

2.36 4.90 4.52 4.46 2.268 74.56 2.311

0.600 4.33 4.48 2.13 2.231 86.70 2.283

8

4.75 3.14 4.21 4.34 2.191 75.43 2.267

2.36 4.85 4.97 4.76 2.177 73.63 2.289

0.600 3.84 4.69 2.04 2.205 86.72 2.251

10

4.75 2.69 4.52 4.37 2.158 75.51 2.255

2.36 4.28 5.54 4.89 2.164 72.89 2.265

0.600 3.61 5.43 1.35 2.190 90.74 2.220

3.1. The Effect of Rubber Content on Marshall Stability

A study of Table 1 shows that at 0% rubber content, the stability was 7.24kN for

4.75mm rubber particle size. At 2% rubber content, the stability reduced to 4.63kN

while at 4% rubber content, the stability is 3.61 KN. When the rubber content was

increased from 6 to 10%, the stability reduced from 3.49kN to 2.69kN. With these

results it can be seen that Marshall stability decreases with increasing rubber content

of 4.75mm rubber particle size (RPS). This follows the normal trend when using the

dry process in mixing aggregates and ground scrap tyre rubber where similar trend

has also been reported that the Marshall stability of an asphalt aggregate-chunk rubber

mix would be lower than that of the control mix, [11-12]. Since rubber is not as hard

as the crushed stone aggregates, the rubber chunks tend to absorb some of the energy




imparted, resulting in a weaker aggregate structure. The Marshall stability result

shows the same trend with the other two rubber particle size, see Table 1. It can also

be seen that as the rubber content increases from 2 to 10%, the Marshall stability

decreases from 6.20kN to 3.5lkN which is higher than 2.0KN which the minimum

stability for medium volume traffic roads, Emesiobi [10].

3.2. The Effect of Rubber Content on Flow

Observing Table 1 for the flow characteristic of the rubber modified asphaltic

concrete, it can be seen that as the rubber content is increased, the flow also increased.

The flow value for the control mix (0% rubber content) which was 4.04mm, reduced

to 3.68mm flow for 2% 4.75mm, rubber particle size (RPS) content. It starts to

increase to 3.71mm for 4% rubber content and as the rubber content increased from 6-

10 percent, the flow also increased to 4.52mm from 3.61mm. The results show trend

that would be expected for flow property and it is reported by Hossain et al (1996)

and Amirkhanian et al (1996). The same trend is noticed for 2.36mm RPS modified

asphaltic concrete because the flow value increased from 3.71mm to 5.54mm when

the rubber content was increased from 2 to 10 percent. Also the flow value increased

from 3.74mm to 5.43mm when 0.600mm RPS rubber content was increased from 2 to

10 percent. From the results gotten, it can be deduced that the addition of ground

scrap tyre rubber into asphaltic concrete using the dry process method generally

increase the flow value no matter the size of rubber used. Specimen produced with the

three different rubber particle sizes, within the range of rubber content tested have

their resulting flows falling within 5mm maximum specification for wearing courses

Emesiobi (2000) except 10% rubber content of 2.36mm and 0.600mm RPS.

3.3. The Effect of Rubber Content on Percentage Air Void

Table 1 gives the results of the effect of rubber on air voids of the mix. The control

mix (0% rubber content) gave an air void of 3.23% which meets the requirement for

medium volume traffic pavement as given by Asphalt institute. At 2%, 4.75mm RPS

content, the air void was 3.09%, at 4% rubber content the air void increased to 3.40%.

On further increase of rubber content from 6 to 10%, the air void increased also from

4.30 to 4.37 percent. The same trend was noticed for 2 36mm RPS , where 2% rubber

content gave an air void of 3.05% and it increased to 3.40% at 4% rubber content.

When the rubber content increased from 4-10 percent, the air void increased from

3.40-4.89%. The reverse was the case for 0.600mm RPS where at 2% rubber content,

the air void was 3.02% and when the rubber content increased to 10%, the air void

reduced to 1.35%. This follows the normal trend when using the wet process method

in asphalt concrete mix as was also reported by Roque etal., [13]. Referencing the

recommendation that percentage air voids for medium volume roads should range

between 3-5% Emesiobi [10], only specimens produced with 4 75mm, 2.36mm and

2% of 0.600mm RPS meet these specification.

3.4. The Effect of Rubber Content on Unit Weight

From Table 1, it can be seen that at 0% rubber content, the unit weight was

2.354kg/rn3. When the rubber content increases from 2 to 10%, the unit weight

reduced from 2.275 to 2.158kg/m3 for 4.75mm RPS mix. The same trend was noticed

for 2.36mm RPS whose unit weight reduced from 2.288kg/rn3 to 2.164kg/rn

3 when

the rubber content increased from 2 to 10% and also 0.600mm RPS mix whose unit

weight decreased from 2.300kg/rn3 to 2.190kg/m

3 for the same increased rate in



rubber content. The results show the trend that would be expected for the three

different rubber particle sizes and is also in agreement with Roque etal., [13].

3.5. The Effect of Rubber Content on Voids in Mineral Aggregate

The control mix gave a VMA value of 81.19% which meets the specification given by

Asphalt Institute. As ground rubber was added, the VMA generally decreased. At 2%

rubber content, the VMA was 81.11% for 4.75mm RPS which decreased to 75.43% at

8% rubber content. The same trend is noticed for 2.36mm RPS. While for the

0.600mm RPS the reverse was the case in which at 2% rubber content, VMA was

81.79% which increased to 90.74% as the rubber content increased to 10%. The result

of VMA for 4.75mm RPS and 2.36mm RPS follows the normal trend and is in

agreement with Hossain etal., [11].

3.6. The Effect of Rubber Content on Specific Gravity

It is generally expected that the specific gravity of the specimen will decreases as the

rubber content increases. From Table 1, at 0% rubber content, the specific gravity was

2.385 and decreased to 2.255, 2.265 and 2.220 for 4.75, 2.36 and 0.600mm RPS

respectively as the rubber content increased to 10%. This trend is as result of the

lightweight and low specific gravity of ground scrap tyre rubber as compared to the

conventional aggregates used.

4. CONCLUSION AND RECOMMEDATIONS

4.1. CONCLUSON

The following conclusion was drawn in this study:

1. The control specimen (i.e. 0% rubber content) produced higher stability value

compared to specimens containing various percentages of rubber. The stability

generally decreases as the rubber content increases and the lower the RPS, the

higher the stability.

2. The flow increases as the rubber content increases for the various RPS and there

is no set pattern between RPS and flow.

3. The percent air voids increases as rubber content increases for 4.75mm RPS and

2.36mm RPS. However, the same trend is not true for 0.600mm RPS.

4. As the rubber percentage increases, the unit weight decreases and there is no set

pattern for RPS.

5. The VMA decreases as the rubber content increases for 4.75mm RPS and

2.36mm RPS but for 0.600mm RPS where the VMA increases as the rubber

content increases. In general, the VMA increases as the RPS increases from

2.36mm to 4.75mm.

6. As the rubber percentage increases, the specific gravity decreases and there is no

set pattern for RPS.

4.2. RECOMMENDATIONS

1. The upper limit of 10% of 4.75mm RPS and 4% of 2.36mm and 0.600mm RPS

meets the design criteria for medium volume pavement surface. .

2. Other alternatives uses of scrap tyre rubber, not related to asphaltic concrete

should be studied, for example, use of rubber in producing lightweight concrete.




3. 0.600mm RPS modified asphaltic concrete is highly recommended for

intersections (high volume, slow moving traffic)

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