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, Warangal–India-506004. Email: shreebunty@gmail.com

(Received January 2009 and accepted September 2009)

من حيث الحرآة ةالمروري ارتفاع الكثافة. المرنة مع سطح من القار تستخدم على نطاق واسع في الهند األرصفةالتجارية والشاحنات والحمولة الزائدة للمرآبات مع وجود تباينات آبيرة في درجات الحرارة اليومية والموسمية

ات في الهند والخارج ،آشفت أن التحقيق. عراض الضغطأ آانت مسؤولة في وقت سابق عن تطوير ةرصفلألفي هذه الدراسة ، جرت محاولة الستخدام . خصائص القار و مزيج القار يمكن تحسينها لتلبية االحتياجات األساسية

تصميم مزيج مارشال تم تنفذته . الذي يتم مزجه في درجات حرارة معينة (CRMB 55) قار فتات المطاط المعدلخصائص قصى درجة ثبات لمحتوى المطاط والتجارب الالحقة آانت لتحديدأمن خالل تعديل محتوى القار تحت

ع أدى ذلك إلى تحسن آبير في الخصائص بالمقارنة م. يضاأ) 60/70( آل مزيج مختلف و لخصائص القار التقليديتم اخذ عينات إلجراء اختبار تتبع ). ٪ 5.67( الربط المنخفض للقار ذو درجة يضًاأصلي وخصائص القار األ

و تم تحليل النتائج لتحديد العدد المتوقع " ةالتسوي" هاز محاآاة أسطوانة الدكعداد االختبار باستخدام جإتم , العجلة . سفلت الممزوج بالقار المعدلو اإل ير التقليدلقاسفلت الممزوج بالمرور العجالت القياسية على اإل

Flexible pavements with bituminous surfacing are widely used in India. The high traffic intensity in 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 distress symptoms. 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, an attempt has been made to use crumb rubber modified bitumen (CRMB 55) which is blended at specified temperatures. Marshall’s mix design was carried out by changing the modified bitumen content at constant optimum rubber content and subsequent tests have been performed to determine 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 that too at reduced optimum modified binder content (5.67%). Specimens for the conduct of wheel tracking 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 both conventional and modified bituminous concrete mixes. Keywords: Pavement, Bitumen, Bituminous surfacing, Crumb rubber, Traffic intensity.

1. INTRODUCTION Poor performance of bituminous mixtures under increased traffic volume and heavier axle load has led to the increased use and development of modified binders. In India, it is estimated that over 33 lakh kilometers of road exists and out of which of which around 50% is surfaced [1-2]. Road transport has acquired dominant position amongst the various modes of transportation system due to its flexibility, door-to-door service, reliability and speed. In India, road transport carries close to 90% of passenger traffic and 70% of freight transport [3]. In India, majority of the pavements are bituminous since they consume lesser initial cost when compared with rigid pavements i.e. cement concrete pavements. Investigations in India and countries abroad have revealed that properties of bitumen and bituminous mixes can be improved to

meet requirements of pavement with the incorporation of certain additives or blend of additives [4]. These additives are called “Bitumen Modifiers” and the bitumen premixed with these modifiers is known as modified bitumen. Modified bitumen is expected to give higher life of surfacing (up to 100%) depending upon degree of modification and type of additives and modification process used. Different types of modifiers 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 to high traffic intensity, high axle loads, variation in

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

traffic and seasonal temperature variation. Considerable research has been carried out by using crumb rubber as bitumen modifier since it has improved the characteristics of binder as well as mix. With this back ground the present study was taken up to investigate the effect of the crumb rubber modified bitumen (CRMB 55), obtained through wet process, on the performance of modified bituminous concrete mix. To estimate the optimum binder content of crumb rubber modified bituminous concrete mix and Conventional bituminous concrete mix through the conduct of Marshall’s mix design and compare the results. To carry out the wheel tracking experiment with simulated wheel arrangement (5.6kg/cm2 contact pressure) for a specified number of repetitions (20000) on both conventional and crumb rubber modified bituminous concrete mixes with a view to study the rutting potentiality of both. To carry out analytical study with a view to study the failure propagation patterns of both the conventional and crumb rubber modified 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 research and 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, several states 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 1960’s 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 sized factions 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 the Bituminous 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

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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, 360oC, 280oC, 320oC) for Conventional Bitumen (60/70) and Crumb Rubber Modified Bitumen (CRMB 55) respectively.

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

Bitumen (%)

Weight of the sample (gm) Bulk Density

(Gb)(g/cc) % Air Voids (Va) VMA VFB Marshal

Stability (kg) Flow value (mm) Air Water

4.5 1186 682 2.35 5.87 13.52 63.89 1361 2.3 5.0 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 the sample (Gm) Bulk Density

(Gb)(g/cc) % Air Voids

(Va) VMA VFB Marshal Stability (kg)

Flow value (mm) Air Water

5.0 1180 675 2.34 5.83 13.24 66.28 1075 2.3 5.5 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 the sample (Gm) Bulk Density

(Gb)(g/cc) % Air Voids

(Va) VMA VFB Marshal Stability (kg)

Flow value (mm) Air Water

5.00 1181 675 2.33 5.06 12.84 69.33 1161.60 2.8 5.50 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) γd (g/cc) % Air Voids (Va) VMA VFB Marshal

Stability (kg) Flow value (mm)

Type

5.93 1185 686 2.37 3.3 14.5 70.2 1496 2.6 60/70 DBM 6 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 Marshall’s mix design for CRMB

Crumb Rubber Modified bitumen was taken at different bitumen Samples were prepared as per the MORTH (2001) specifications as 3 samples for each bitumen content at an increments of 0.5 % for DBM

SDBC and BC. Each of the above samples has been tested after extracting and keeping the samples in the water bath at a constant temperature of 600C for 30 minutes. The comparison of conventional bitumen (60/70) and crumb rubber modified bitumen are summarized and are presented in tables 5- 8.

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

Table 5. CRMB 55 Dense Bituminous Macadam Mix Properties

Bitumen (%)

Weight of the sample (Gm) Bulk Density

(Gb)(g/cc) % Air Voids

(Va) VMA VFB Marshal Stability

(kg)

Flow value (mm) Air Water

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 2.3 5.5 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 VFB

Marshal Stability

(kg)

Flow value (mm) Air Water

5.0 1180 680 2.36 5.88 13.45 66.30 1111 2.3 5.5 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 3.4 7.0 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 VFB

Marshal Stability

(kg)

Flow value (mm) Air Water

5.0 1180 675 2.34 5.89 13.35 66.07 1309 2.4 5.5 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 VFB Marshal Stability

(Kg) Flow in (mm)

Conventional Bitumen (60/70)

DBM 2.37 3.3 14.5 70.2 1496 2.6 SDBC 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 crumb rubber modified bituminous concrete and conventional bituminous concrete have been plotted and presented in Figures 1 and 2. Two different equations have been developed, for standard wheel repetitions 0 to 20000. These equations have been utilized to extrapolate the growth trends of rut development with increasing wheel 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 of wheel repetitions for failure in case of crumb rubber modified bituminous concrete is 408000. This clearly underlines the improved rut resisting characteristics of the 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 crumb rubber modified bitumen in bituminous concrete, the optimum binder content can be reduced and in this process there is no danger of loss of strength characteristics from the point of view of stability and

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rut resistance. The developed prediction models are as follows for conventionnel bituminons mix

909.09.2800071.0

2 =

+=

RXY

(6.1)

and for Crumb Rubber Modified Bituminous Mix

820.067.2590056.0

2 =

+=

RXY

(6.2)

where Y = Number of repetitions, X = Vertical deformation. n = Number of data points, k = Number of variables

0 5000 10000 15000 20000

200220240260280300320340360380400420

Defo

rmati

on in

0.01

mm

No of revolution

Bitumen6070 CRMB55

Fig1: Rutdepth variations (Observed)

.

0 100000 200000 300000 4000000

500

1000

1500

2000

2500

3000

3500

Defo

rmat

ion in

0.01

mm

No of revolution

Bitumen6070 CRMB55

Fig2: Rutdepth variations (Predicted)

7. CONCLUSION

Based on this study the following can be concluded:

1. By using the crumb rubber modified bitumen, penetration value had come down from 66 to 58 while softening point has improved from 420oC to 520oC.

2. There is a considerable reduction in the Ductility from 80cm to 47cm, indicating improvement in individual characteristics of bitumen.

3. Marshall’s mix design conducted on crumb rubber modified bituminous concrete has resulted in 5.6% optimum binder content with Marshall’s stability value (600C–30 min. of 1437kgs), flow value of 3.2 mm (within 2 to 4 mm range), VMA of 14.05 (Range 13-15), VFB of 74.2 (Range 65-75) and volume of voids of 3.88% (within design air voids range of 3-5%) indicating the acceptability of the crumb rubber modified bituminous concrete mix as per MORTH recommendations.

4. With the straight run bitumen (5.76%) the modified bitumen has resulted in the bituminous concrete mix having better Marshall’s stability value (1437kgs as against 1362kgs) and improved rut resistance to tune of 27.89% as against straight run bituminous concrete mix.

REFERENCES

1. Indian road congress, IRC–SP 53 (2002). Guidelines on use of polymer and rubber modified bitumen in road construction (first revision), IRC New Delhi.

2. Kumar, M. and Kumar, M.S. (2001). A study on rubberised bitumen mixes, “Indian Highways, 17-34.

3. R.S. Shukla, Col. Vijay K.P. Singh & Lt. Col. R.S. Bhanwala, (April 2003) “Polymer modified bitumen for construction of heavy traffic density Corridors “Indian Highways, 31(4), 55- 66.

4. Kumar, M. and Kumar, M.S. (2001). Studies on rubberised bituminous mixes, Regional seminar on Technological Developments for the third Millennium, 719-731

5. Palit, S.K., Reddy, K.S. and Pandey, B.B. (2004). Evaluation of rutting potential of modified bituminous mixes, Indian Highways, 32(2), 13-27.

6. Billiter, T.C., Davison, R.R., Glover, C.J. and Bullin, J.A. (1996 ). Production of asphalt-rubber binders by high-cure conditions, Transportation Research Record, 1586, 50-56.

7. Hanson, D.I. and Duncan, G.M. (1996). Characterization of crumb rubber-modified binder using strategic highway research program technology, Transportation Research Record 1488, 21-31.

8. Liang, R.Y. and Lee, S. (1996). Short-term aging behavior of rubber modified asphalt paving mixture, Transportation Research Record, 1530, 11-17.

9. Sibal, M.A., Das, B.A. and Pandey, B.B. (1998). Fatigue of bituminous concrete with crumb rubber, Highway Research Board, 45-61.

10. Gowda, G.V., Hall, K.D. and Elliott, R.P. (1996). Arkansas experience with crumb rubber using marshall and strategic highway research program level I design methods, Transportation Research Record 1530, 25-33.

11. Dharmaraj, S.J.P. (2002). Rubberised Bitumen for Roads, Indian highways 30(10), 55-59.

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