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Bitumen and Mixture Characteristics of Lawele Buton Rock Asphalt Madi Hermadi , Kemas Ahmad Zamhari

Universiti Tun Husein Onn Malaysia

86400 Parit Raja, Batu Pahat, Johor, Malaysia

email: madihermadi@yahoo.com

Abstract

The biggest deposit of Buton Rock Asphalt (natural asphalt from Buton Island) located in Lawele Region.

It is called Lawele Buton Rock Asphalt, locally known as Lawele-BRA. Lawele-BRA deposit is about 100,000,000

tons. In dry condition, the row material consists of about 30% bitumen, 7% light (volatile) oil, and 63% mineral.

The bitumen penetration value is around 180 dmm. It is too soft especially for asphaltic pavement in tropical

country. In this study, the row material of Lawele-BRA was heated to dry and reduce the light oil content. It

decreases bitumen penetration value. Next, four samples of four times production were tested to examine the

physical characteristics. One of the products was chosen as a binder in the mixture characteristics. Then, the

characteristics were compared with the characteristics of petroleum bitumen mixture. Based on the test results,

the Lawele-BRA product should has volatile oil (that loss on heating) 1-2% or 2-3% to produce Lawele-BRA with

bitumen penetration value of 60-80 dmm or 80-100 dmm. Based on dynamic shear test, Lawele-BRA bitumen with

penetration 60-80 dmm and 80-100 dmm are sufficient as asphaltic mixture binder for road with field maximum

temperature 58 oC and 64

oC. Comparing to petroleum bitumen mixture, the Lawele-BRA mixture has Marshall

Stability 11% higher, retained stability 5% higher, dynamic stability 2.4 times higher, and resilient modulus about

2 times higher.

Keyword: Rock Asphalt, Bitumen, Hot mix asphalt, Lawele-BRA

1. Introduction

In 2008, the price of crude oil reached 150 USD per barrel, the most expensive it has ever had. As a

consequence the price of petroleum bitumen was also increased tremendously. Although at the present

time the price of crude oil is reduced due to the worldwide economic down turn. To anticipate the same

cases in the future, it is necessary to look for other alternative of petroleum bitumen. One of the

alternatives is to utilize the natural asphalt.

Buton rock asphalt is natural asphalt from Buton Island in Southeast Sulawesi Province in

Indonesia. Buton Island has been known as natural asphalt sources. A Dutch geologist, Hetzel, found

the natural asphalt deposit in Buton Island in 1920. He completed the natural asphalt deposit map of

Buton in 1936. The Directorate of Inventory and Mineral Resources in Bandung - Indonesia shows that

natural asphalt in Buton Island located in many places, such as Kabungka, Lawele, Winto, Wariti,

Waisiu, Rongi and Ereke areas. The exact deposit of the natural asphalt resources has not been known

clearly. PT. Sarana Karya, a state own asphalt mining company, estimates that sources of the Buton

rock asphalt is about 300,000,000 tons, spreaded in Kabungka about 60,000,000 tons, in Lawele about

100,000,000 tons, in Winto about 3,200,000 tons, in Wariti about 600,000 tons, in Waisiu about

100.000 tons. However, only two locations have been exploited. Those are Kabungka (since 1980) and

Lawele (since 2003). Nevertheless, the exploitation is still very limited [5].

Previous studies indicates that, in general, Lawele-BRA has bitumen content about 35%, water

content about 12%, loss on heating about 6%, and penetration value of bitumen about 180 dmm. An

International Conference on Building Science and Engineering 2009

December 14th

-15th

, 200, Johor Bahru, Malaysia

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investigation has been done to assess its characteristics as a binder in hot mix asphalt mixture. The

investigation includes the effect of preprocessing on the physical characteristiecs of Lawele-BRA, and

comparing the mixture characteristics between Lawele-BRA and ordinary petroleum bitumen as the

control.

2. Materials and Methods

The characteristics of raw material of Lawele-BRA that used in this study are shown in Table 1.

The characteristics, especially penetration, water content and loss on heating, are not comply with those

of petroleum bitumen pen grade 60-80 or 80-100 that normally used as a binder in asphaltic pavement

in tropical country. In order to reduced the water content and decrease the penetration, the material was

preprocessed by heating. The effect of heating on characteristics of Lawele-BRA bitumen was

evaluated especially in penetration and dynamic shear value.

Table 1 Characteristics of the raw materials of Lawele-BRA

The characteristics of petroleum bitumen that used in this study are shown in Table 2. In addition,

the bitumen has dynamic shear G*/sin () minimum 1kPa at 580 C for fresh bitumen and dynamic shear

G*/sin () minimum 2kPa for TFOT aged bitumen.

Table 2 Characteristics of the petroleum bitumen

No. Petroleum Bitumen Characteristics Values

1. Solubility in C2HCl3; % 99.7

2. Water content; % 0.0

3. Penetration at 25 C, 100 g, 5 sec; dmm 65

4. Loss on heating (RTFOT); % 0.032

5. Penetration after RTFOT, % Original 76.9

Marshall Mix Design method was used to find out the optimum of Lawele-BRA and petroleum

bitumen mixture than the mixtures were tested in dynamic stability and stiffness.

3. Results and discussion

Bitumen Characteristics of Lawele-BRA

The raw materials of Lawele-BRA was preheated and stirred at 130oC at an increasing duration to

get four processed Lawele-BRA product called Product-1, Product-2, Product-3 and Product-4. Each

product has different values of loss on heating. The loss on heating indicates percentage of volatile oil

that loss in weight after heating at 1630 C during 5 hours in Thin Film Oven Test (TFOT). These loss on

heating have been corrected for water content that also lossed during the heating. The value of loss on

heating is used as an indicator during the processing of Lawele-BRA to achieve the product with the

required characteristics.

Based on the data in Table 3 and Figure 1, the bitumen of Lawele-BRA with penetration values of

60 to 80 dmm can be produced by heating until the loss on heating of 1.2% to 2.0%. While bitumen

No. Lawele-BRA Characteristics Raw Material

1. Bitumen Content; % 35.3

2. Water Content; % 11.8

3. Penetration of bitumen at 25oC, 100g, 5 sec; dmm 183

4. Loss on Heating minus water content; % 6.1

5. Penetration of bitumen after TFOT; %Original 28.8

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with penetration value of 80 to 100 dmm can be produced by heating until loss on heating value of

2.0% to 2.8%.

Table 3 Penetration Value of Lawele-BRA Bitumen

No. Lawele-BRA Characteristics Raw Material Product-1 Product-2 Product-3 Product-4

1. Loss on Heating of Lawele-BRA; % 6.1 3.52 2.673 2.127 1.083

2.

Penetration of Lawele-BRA bitumen

at 25oC, 100g, 5sec; dmm

183

112

93

83

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Figure 1. The Effect of Loss on Heating on Bitumen Penetration of Lawele-BRA

Superpave PG-grade specification required that the rutting resistance parameters, G*/sin() of fresh

bitumen shall be minimum of 1.00 kPa at the maximum design temperature. Based on the data in Table

4 and Figure 2, Lawele-BRA with loss on heating value of 1.2 to 2.0% is suitable for pavement with

maximum design temperature of 64 oC and those with loss on heating value of 2.0 to 2.8% is suitable

for pavement with maximum design temperature of 58 oC.

Table 4 Dynamic Shear Value of Original Lawele-BRA Bitumen

No. Lawele-BRA Characteristics Product-1 Product-2 Product-3 Product-4

1. Loss on Heating of Lawele-BRA; % 3.52 2.673 2.127 1.083

2.

Dynamic shear of Lawele-BRA

bitumen, G*/Sin () at:

52 oC; kPa 2.233 2.820 3.501 7.544

58 oC; kPa 1.315 1.536 1.909 3.791

64 oC; kPa 0.676 0.796 0.932 1.866

70 oC; kPa - - - 0.935

1.00 kPa; oC 60.7 61.8 63.4 69.1

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Figure 2. The Effect of Loss on Heating on Bitumen Dynamic Shear of Lawele-BRA

Superpave PG-grade specification also required that for rutting resistance parameters, G*/sin() of

TFOT residue bitumen shall be minimum of 2.00 kPa at the maximum design temperature. Based on

the data in Table 5, raw material of as well as all of Lawele-BRA products are suitable for pavement

with maximum design temperature of 64 oC.

Table 5 Characteristics of Lawele-BRA Bitumen after TFOT N

o. Lawele-BRA Characteristics Raw Material Product-1 Product-2 Product-3 Product-4

1. Loss on Heating of Lawele-BRA; % 6.10 3.52 2.67 2.13 1.08

2. Penetration after RTFOT; %Original (dmm) 28.8 (53) 39.4(44) 45.7(43) 50.8 (42) 65.2 (40)

3.

Dynamic shear of bitumen after RTFOT,

G*/Sin (), kPa

58 oC; kPa 4.313 4.356 4.633 4.931 5.453

64 oC; kPa 2.037 2.420 2.461 2.475 2.534

70 oC; kPa 0.991 1.182 1.210 1.218 1.234

To anticipate cracking at the intermediate temperature, Superpave PG-grade specification required

G*sin() of PAV aged residue bitumen should be not more than 5,000 kPa. The experiment is still going

on for a more comprehensive rheological data on PAV aged residue bitumen. The result will be

presented during the paper presentation.

Table 6 shows that flash point of the raw Lawele-BRA is 178 oC whilst the four products in average

are 2170 C. These temperatures are close to the normal mixing temperature of hot mix asphalt.

Therefore, for safety reason, it is recommended that the Lawele-BRA should not be directly heated in

the dryer of the asphalt mixing plant during its application. In addition, heating may cause Lawele-BRA

with bitumen content more than 30% to clot and difficult to mix with aggregates. In this case, water

content of the Lawele-BRA must be controlled. As indicates in Table 6, all of the Lawele-BRA

products have water content less than 2%.

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Table 6 The other characteristics of Lawele-BRA No. Lawele-BRA Characteristics Raw Material Product-1 Product-2 Product-3 Product-4 1. Bitumen Content, % 35.3 32.6 32.6 32.4 31.3 2. Water Content, % 11.8 1.1 1.4 1.1 1.2

3. Flash Point, oC 178 220 198 222 226

4. Maximum Size; inch - 3/8 3/8 3/8 3/8

Mixture Characteristics of Lawele-BRA

Characteristics of Hot Mix Asphalt with Lawele-BRA Product-3 and petroleum bitumen are shown

in Table 7. Both mixtures have the similar gradation as shown in Figure 3. Design of the mixtures was

done by Marshall Method. The optimum Lawele-BRA mixture consists of 10% Lawele-BRA, 3.5%

petroleum bitumen (ie. total bitumen of 6.7%) and 86.5% aggregates. The optimum petroleum bitumen

mixture consists of 5.9% petroleum bitumen and 94.1% aggregates.

Figure 3 Gradation of Lawele-BRA and Petroleum Bitumen Mixture

Table 7 Marshall Characteristics of Lawele-BRA and Petroleum Bitumen Mixtures

No. Mixture Characteristics Petroleum Bitumen Lawele-BRA Unit

1. Bitumen content optimum 5,9 6,7* %

2. Density 2,325 2,285 gr/cc

3. Void in Mix Aggregates 17,0 19,2 %

4. Voids Fill Bitumen 72,0 74,0 %

5. Voids in Mix 4,4 5,0 %

6. Voids in Mix at refusal density 3,5 2,9 %

7. Stability 930 1030 Kg

8. Flow 3,2 4,1 Mm

9. Marshall Quotient 300,0 260,0 kg/mm

11. Retained Stability 87,8 92,6 %

* Percent of Lawele-BRA bitumen + petroleum bitumen

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Table 8 Performance Base Characteristics of Lawele-BRA and Petroleum Bitumen Mixtures

No. Mixture Characteristics Petroleum Bitumen Lawele-BRA Unit

1. Dynamic Stability:

- Deformation 2,21 1,97 mm

- Deformation rate 0,0293 0,0120 mm/min

- Dynamic Stability 1432 3500 track/mm

2. Resilient Modulus: 25 oC 2950.7 4235.5 MPa

35 oC 1066.0 1835.5 MPa

45 oC 371.3 733.5 MPa

55 oC 230.5 289.2 MPa

In general, hot mix asphalt with Lawele-BRA is outperform the mixture with ordinary petroleum

bitumen in term of Marshall Stability (11% higher), retained stability (5% higher), dynamic stability

(2.4 times higher), and resilient modulus (about 2 times higher). This is in accordance with rheological

bitumen. As was mention previously, the fresh bitumen of Lawele-BRA Product-3 is comply with

Performance Grade of 580 C and after TFOT aged it is comply with Performance Grade of 64

0 C.

Whereas the petroleum bitumen, fresh and after TFOT, suitable for pavement with maximum design

temperature of 580 C.

4. Conclusion

Based on the this study it may conclude that:

(i) The raw material of Lawele-BRA has high volatile oil content so it is not sufficient as a

bitumen binder especially for pavement in tropical country. It is should be processed.

(ii) Preprocessing of the row material by heating will decrease the volatile oil and improve the

consistency of its bitumen.

(iii) Based on dynamic shear value, the preprocessed Lawele-BRA to comply the pen grade

60 – 80 is suitable for pavement with maximum design temperature of 64 oC. The fresh

preprocessed Lawele-BRA to comply the pen grade of 80 - 100 is suitable for pavement

with maximum design temperature of 580 C. Nevertheless, rheology of TFOT aged

bitumen of this Lawele-BRA also complies for pavement with maximum temperature of

640 C.

(iv) The mixture of Lawele-BRA Product-3 in term of Marshall stability, dynamic stability,

and resilient modulus at 450 C is better than the mixture of petroleum bitumen.

5. References

[1] Chipperfield, E.H., J.L. Duthie, R.B. Girdler (1970). Asphalt Characteristics in Relation to Road Performance. Proceeding

of Asphalt Paving Technologist, Vol 39, p 575.

[2] Hermadi, M., Syahdanulirwan, M. (2009), Suggestion Specification of Asbuton-Lawele Hot Mix Asphalt Pavement for

Road, Institute Of Road Engineering Journal, Public Work Department, Bandung,

[3] Research and Development State of Public Work Departemen (2000), Development of Production and Utilization

Asbuton, Public Work Departmen, Jakarta.

[4] Roberts, F.L., P.S. Kandhal, F.R. Brown, D.Y. Linn, T.W. Kennedy (1996). Hot Mix Asphalt Materials, Mixture Design

and Construction. Edition, NAPA Education Foundation, Lanham, Maryland.

[5] Utilization and Improvement Team of Asbuton (1999). ” Increasing and Utilization Recommendations of Buton Natural

Asphalt, Menko Ekuin. Jakarta