2009;evaltn of ruring potntl of crmb in ashpt mix;ejer.pdf

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Emirates Journal for Engineering Research, 14 (2), 91-95 (2009)

(Regular Paper)

EVALUATION OF RUTTING POTENTIAL FOR CRUMB RUBBER

MODIFIED BITUMEN IN ASPHALTIC MIXES

S. Shankar and C.S.R.K. Prasad

National Institute of Technology, Transportation Division, Department of Civil Engineering,

A.P, WarangalIndia-506004.

Email: [email protected]

(Received January 2009 and accepted September 2009)

.

. .

(CRMB 55)

.

.))60/70).)5.67

"",.

Flexible pavements with bituminous surfacing are widely used in India. The high traffic intensityin terms of commercial vehicles, over loading of trucks and significant variations in daily and

seasonal temperature of the pavement have been responsible for earlier development of distresssymptoms. Investigations in India and abroad have revealed that the properties of bitumen and

bituminous mixes can be improved to meet the basic requirements. In the present study, anattempt has been made to use crumb rubber modified bitumen (CRMB 55) which is blended at

specified temperatures. Marshalls mix design was carried out by changing the modified bitumencontent at constant optimum rubber content and subsequent tests have been performed todetermine the different mix design characteristics and for conventional bitumen (60/70) also. This

has resulted in much improved characteristics when compared with straight run bitumen and thattoo at reduced optimum modified binder content (5.67%). Specimens for the conduct of wheeltracking test have been prepared using simulated roller compaction equipment and analysis has

been carried out to determine the expected number of standard wheel repetitions for bothconventional and modified bituminous concrete mixes.

Keywords: Pavement, Bitumen, Bituminous surfacing, Crumb rubber, Traffic intensity.

1.

INTRODUCTION

Poor performance of bituminous mixtures underincreased traffic volume and heavier axle load has ledto the increased use and development of modifiedbinders. In India, it is estimated that over 33 lakhkilometers of road exists and out of which of whicharound 50% is surfaced [1-2]. Road transport has

acquired dominant position amongst the variousmodes of transportation system due to its flexibility,

door-to-door service, reliability and speed. In India,road transport carries close to 90% of passenger trafficand 70% of freight transport

[3]. In India, majority of

the pavements are bituminous since they consumelesser initial cost when compared with rigid pavementsi.e. cement concrete pavements. Investigations in India

and countries abroad have revealed that properties ofbitumen and bituminous mixes can be improved to

meet requirements of pavement with the incorporationof certain additives or blend of additives [4]. These

additives are called Bitumen Modifiers and thebitumen premixed with these modifiers is known asmodified bitumen. Modified bitumen is expected togive higher life of surfacing (up to 100%) dependingupon degree of modification and type of additives andmodification process used. Different types ofmodifiers used are Polymers, Natural Rubber and

Crumb Rubber

2. SCOPE OF RESEARCH

There have been numerous research studies on

bitumen as paving material. The bitumen undergoes

the different changes (Low temperature cracking,fatigue cracking ageing and water receptivity) due tohigh traffic intensity, high axle loads, variation in

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traffic and seasonal temperature variation.Considerable research has been carried out by usingcrumb rubber as bitumen modifier since it hasimproved the characteristics of binder as well as mix.

With this back ground the present study was taken upto investigate the effect of the crumb rubber modified

bitumen (CRMB 55), obtained through wet process, onthe performance of modified bituminous concrete mix.To estimate the optimum binder content of crumbrubber modified bituminous concrete mix and

Conventional bituminous concrete mix through theconduct of Marshalls mix design and compare the

results. To carry out the wheel tracking experimentwith simulated wheel arrangement (5.6kg/cm

2contact

pressure) for a specified number of repetitions (20000)on both conventional and crumb rubber modifiedbituminous concrete mixes with a view to study therutting potentiality of both. To carry out analyticalstudy with a view to study the failure propagation

patterns of both the conventional and crumb rubbermodified bituminous concrete.

3. BACKGROUND

Highway engineers around the world have tried to

incorporate scrap tire rubber in asphalt pavements

since 1950s. It was not until 1960s that a formulation

was discovered that was successful. Charles H. Mac

Donald worked with city of phoenix and he has

introduced his thought on asphalt-rubber for the US

Bureau of public roads [5]. He used this material for

pothole repair. By 1968, the Arizona Department of

Transportation began numerous and diverse researchand development projects involving asphalt rubber

under the direction of Gene Morris, the director of

Arizona Transportation Research centre. However, the

progress of crumb rubber modification of bitumen was

not successful till 1975 and during 1988 the worldwide

acceptance of crumb rubber modified bitumen was

observed with the official definition published by

American Society for Testing of Materials (ASTM)[6-7]

.Major leap was taken in this area through

Construction Productivity Advancement Research

Program taken up during 1995 by US Army Corps of

Engineers and other private agencies. Further, severalstates started using the crumb rubber modified bitumen

in actual practice by the year 1995. Combining all the

research activities carried out before, California and

Florida Transportation Research Institutes have issued

detailed guidelines for use of CRMB. Indian based

Research Organizations too had their share of

experience in this emerging field with experiments

carried out by premiere organizations like IRC, CRRI

etc since 1960s and have recommended the use of

crumb rubber modified bitumen in the ongoing

National Highway Development Programs of North-

South, East-West corridor and Golden Quadrilateral

and several other state highway projects. With a view

to aid in choosing a particular type of modifier for a

given situation, a detailed review has been made with

regard to different modifiers [8-11]

.Commonly used

polymers are Ethyl Vinyl Acetate Copolymer (EVC)

Styrene Butadiene-Styrene (SBS) Aromatic Resin.

4. RESEARCH METHODOLOGY

Detailed laboratory experiments were conducted on all

the aggregate, conventional bitumen (60/70) and

Crumb rubber modified bitumen (CRMB-55), to find

out the individual properties of the materials i.e.

Abrasion, attrition, crushing, impact, and shape test,

and Penetration, Softening point, Ductility and

Viscosity respectively. Using the Marshal Mix design

characterization of conventional bituminous mix

(60/70) for dense bituminous mix (DBM), Semi dense

bituminous mix (SDBC) and bituminous concrete

(BC) were carried out and comparison was made for

conventional bitumen mix properties with crumb

rubber modified bitumen and Wheel Tracking test

sample for conventional bituminous concrete mix

(60/70) and for (CRMB -55). Finally detailed analysis

was carried out for development of Prediction models

for permanent deformation characteristics and

Comparative assessment was made between

conventional bituminous mix and Crumb rubber

modified bituminous mix.

5. SAMPLE PREPARATION

To control the gradation of the test specimens, all

aggregates were separated into the various sizedfactions and stored in metal buckets. The quantity of

aggregate is taken so as to produce a batch, which will

result in compacted specimen of 63.5 mm height. The

compaction was done by the standard hammer of 4.5

kg weight falling from 45.7 cm height by giving 75

blows on each of the face .The sample was cured for

24 hours at room temperature before being extracted

using standard extraction procedure. Three specimens

were prepared for DBM, SDBC and BC for grade II

aggregate gradations recommended by MORTH

(2001) at all the Bitumen Content at an increment of

0.5%. Optimum Binder Content (OBC) has been

obtained by taking average of the bitumen contents at

which the mix has maximum Bulk Density, maximum

Stability and 4% design Air Voids. Trials on Grade-II

Conventional Bitumen mix have resulted in Optimum

Bitumen Content of DBM is 5.9%, OBC of SDBC is

5.6% and Bituminous Concrete is 5.7%. In addition to

the OBC, other requisite parameters have been

computed and are summarized in tables 1to 4.

6. ANALYSIS AND DISCUSSION

It becomes imperative to test individual material

properties before they are being used for preparing theBituminous Concrete mix. All the individual materials

viz: Aggregate, Conventional Bitumen and Crumb

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Evaluation of Rutting Potential Crumb Rubber Modified Bitumen in Asphaltic Mixes

Emirates Journal for Engineering Research, Vol. 14, No.2, 2009 93

Rubber Modified Bitumen are being subjected to

number of specified tests as per the relevant IS code of

practice. Aggregate is the granular material used in

bitumen concrete mixtures, which make up 90-95% of

mixture weight and provide most of the load bearing

characteristics of the mix. Therefore aggregate

properties like aggregate crushing

value (21%) abrasion (30%) Attrition (20%) and

Impact value (24%) and combined flakiness and

elongination (16%), and properties like Penetration

(66,58), Ductility (80,47), Softening point (42,52oC),

Specific gravity (1.05, 1.13) and flash & fire point

(320oC, 360

oC, 280

oC, 320

oC) for Conventional

Bitumen (60/70) and Crumb Rubber ModifiedBitumen (CRMB 55) respectively.

Table 1. Conventional (60/70) Dense Bituminous Macadam Mix Properties

Bitumen(%)

Weight of thesample (gm)

Bulk Density(Gb)(g/cc)

% Air Voids(Va)

VMA VFBMarshalStability (kg)

Flowvalue(mm)Air Water

4.5 1186 682 2.35 5.87 13.52 63.89 1361 2.35.0 1187 686 2.37 4.53 14.23 71.95 1423 2.4

5.5 1190 690 2.38 3.39 14.42 73.08 1497 2.6

6.0 1188 686 2.37 3.25 14.64 74.09 1482 2.7

Table 2. Conventional (60/70) Semi Dense Bituminous Concrete Mix Properties

Bitumen (%)

Weight of thesample (Gm)


% Air Voids(Va)

VMA VFBMarshal Stability

(kg)


5.0 1180 675 2.34 5.83 13.24 66.28 1075 2.35.5 1177 676 2.35 4.63 13.48 73.25 1106 2.5

6.0 1184 683 2.36 3.36 14.18 74.52 1149 2.8

6.5 1184 680 2.35 3.25 14.45 72.17 1168 2.9

7.0 1186 678 2.33 3.16 14.80 73.52 1150 3.2

Table 3. Conventional (60/70) Bituminous Concrete Mix Properties

Bitumen(%)

Weight of thesample (Gm)


% Air Voids(Va)

VMA VFBMarshal Stability

(kg)


5.00 1181 675 2.33 5.06 12.84 69.33 1161.60 2.85.50 1188 680 2.34 4.19 13.45 75.05 1260.28 3.3

6.00 1186 678 2.33 3.67 13.86 74.90 1324.00 3.6

6.50 1176 670 2.32 3.43 14.28 73.20 1286.00 3.8

7.00 1190 675 2.31 3.31 14.60 72.73 1260.00 3.9

Table 4. Over view properties of 60/70 DBm,60/70 SDBC and 60/70 BC

Bitumen (%) Wt (Gm) d (g/cc)% Air Voids

(Va)VMA VFB

MarshalStability (kg)

Flowvalue(mm)

Type

5.93 1185 686 2.37 3.3 14.5 70.2 1496 2.6 60/70 DBM6 1184 683 2.36 3.36 14.2 72.5 1149 2.8 60/70SDBC

5.76 1187 689 2.34 3.92 14.11 73.1 1362 2.9 60/70BC

6.1 Marshalls mix design for CRMB

Crumb Rubber Modified bitumen was taken atdifferent bitumen Samples were prepared as per the

MORTH (2001) specifications as 3 samples for eachbitumen content at an increments of 0.5 % for DBM

SDBC and BC. Each of the above samples has beentested after extracting and keeping the samples in thewater bath at a constant temperature of 600C for 30minutes. The comparison of conventional bitumen

(60/70) and crumb rubber modified bitumen aresummarized and are presented in tables 5- 8.


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Table 5. CRMB 55 Dense Bituminous Macadam Mix Properties

Bitumen(%)

Weight of thesample (Gm) Bulk Density

(Gb)(g/cc)% Air Voids

(Va)VMA VFB

MarshalStability

(kg)


4.5 1187 687 2.37 5.94 13.41 63.83 1408 2.2

5.0 1197 690 2.38 5.11 13.77 69.54 1475 2.35.5 1182 688 2.39 3.99 14.89 73.38 1385 2.5

6.0 1188 690 2.38 3.68 14.71 74.24 1347 3.7

Table 6. CRMB 55 Semi Dense Bituminous Concrete Mix Properties

Bitumen(%)

Weight of the sample (Gm) Bulk Density(Gb)(g/cc)

% Air Voids(Va)

VMA VFBMarshalStability

(kg)

Flowvalue(mm)

Air Water

5.0 1180 680 2.36 5.88 13.45 66.30 1111 2.35.5 1174 683 2.39 4.04 13.93 70.14 1198 2.6

6.0 1175 681 2.38 3.94 13.93 72.01 1186 3.1

6.5 1176 680 2.37 3.65 14.76 72.53 1149 3.47.0 1175 678 2.36 3.33 14.56 73.96 1139 3.6

Table 7. CRMB 55 Bituminous Concrete Mix Properties

Bitumen(%)

Weight of the sample (Gm) Bulk Density(Gb)(g/cc)

% Air Voids(Va)

VMA VFBMarshalStability

(kg)


5.0 1180 675 2.34 5.89 13.35 66.07 1309 2.45.5 1190 686 2.36 4.38 13.11 74.40 1416 2.7

6.0 1185 682 2.36 3.99 13.85 74.65 1401 2.8

6.5 1190 684 2.35 3.57 14.55 75.77 1361 3.3

7.0 1187 680 2.34 3.42 14.48 75.47 1298 3.6

Table 8. Comparison of Conventional Bitumen (60/70) and Crumb Rubber Modified Bitumen (CRMB 55)

Type of Bitumen Type of Mix Bulk Density (g/cc) % Air Voids VMA VFBMarshalStability

(Kg)

Flow in(mm)

ConventionalBitumen (60/70)

DBM 2.37 3.3 14.5 70.2 1496 2.6SDBC 2.36 3.36 14.2 72.5 1149 2.8

BC 2.34 3.92 14.11 73.1 1362 2.9

CRMB 55 DBM 2.39 4.18 14.82 72.3 1452 2.11

SDBC 2.38 3.98 14.32 73.2 1192 2.9

BC 2.37 3.88 14.05 74.2 1437 3.2

6.2 Rut Depth Analysis

Permanent deformation observations for both crumbrubber modified bituminous concrete and conventional

bituminous concrete have been plotted and presentedin Figures 1 and 2. Two different equations have beendeveloped, for standard wheel repetitions 0 to 20000.These equations have been utilized to extrapolate thegrowth trends of rut development with increasingwheel load repetitions till failure criteria of 1 inch rut

formation. It is observed that the number of load

repetitions for failure criteria is 319000 and number ofwheel repetitions for failure in case of crumb rubbermodified bituminous concrete is 408000. This clearlyunderlines the improved rut resisting characteristics ofthe crumb rubber modified bituminous concrete and

that too at the reduced bitumen content by almost.Hence it can be concluded that with the use of crumbrubber modified bitumen in bituminous concrete, theoptimum binder content can be reduced and in thisprocess there is no danger of loss of strengthcharacteristics from the point of view of stability and

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