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Engineering Properties of Foam Bitumen Mixtures in Thailand

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Engineering Properties of Foam Bitumen Mixtures in Thailand Powered By Docstoc
					             ENGINEERING PROPERTIES OF FOAM BITUMEN
                      MIXTURES IN THAILAND

Teeracharti Ruenkrairergsa1, Chayatan Phromsorn1, Pornchai Silarom1 and
Worapat Ketnoot2
1
 Bureau of Road Research and Development, Department of Highways, Thailand.
2
 Department of Civil Engineering, Faculty of Engineering, Chulalongkorn University, Thailand.


ABSTRACT

This research investigates the feasibility and suitability of foamed bitumen to treat reclaimed
asphalt pavement (RAP) or reclaimed crushed stone in Thailand. RAP was mixed with new
crushed stone at proportion of 80:20, 50:50 and 0:100. The optimum foamed asphalt binder of
mixtures was found to be 2.1%, 2.6% and 3.4% for 80%, 50% and 0% RAP mixtures
respectively. Although mixtures with higher percentages of RAP produce the lower indirect
tensile strengths, their retained strength, under influence of water, is higher. Resilient modulus
tests show that the 50% RAP mixture produces higher resilient moduli than the other mixtures.
In the case of fatigue and permanent deformation tests, which are useful indicators of practical
applications, the mixture containing 80% RAP is shown to produce poorer properties than either
50% RAP or 0% RAP mixtures.

Keywords: Foamed Asphalt, Cold Recycling, Indirect Tensile Strength, Retained Strength,
Resilient Modulus, Fatigue Resistance, Permanent Deformation

1. INTRODUCTION

In Thailand, road recycling technologies have been used since 1994. Cold in-place recycling
using cement as a stabilising agent has been widely used by Department of Highways (DOH).
Due to the worldwide popularity of foamed bitumen, as well as some perceived advantages over
cement recycling, preliminary testing of the engineering properties of foamed asphalt mixtures
was carried out by DOH’s laboratory.

Three blends of reclaimed asphalt pavement (RAP) and new crushed stone, comprising 80%,
50% and 0% of RAP, were made up to produce well-graded mixes. AC 60/70, the standard
bitumen grade used in Thailand, was utilised to produce foamed bitumen using a Wirtgen
WLB-10 foamed bitumen laboratory unit. Furthermore 1% cement was added to improve the
water resistance of the mixtures.

Engineering properties of each of the mixes, including (1) Indirect Tensile Resilient Modulus
Test, (2) Indirect Tensile Fatigue Test and (3) Uniaxial Repeated Load Test, were investigated.

2. OBJECTIVES

1. To introduce foam bitumen as a technique for stabilising RAP in Thailand.
2. To carry out preliminary investigations into the engineering properties of mixes with various
   proportions of RAP and new crushed stone, stabilised with foamed bitumen.




Proceedings of the 8th Conference on Asphalt Pavements for Southern Africa (CAPSA'04)   12 – 16 September 2004
ISBN Number: 1-920-01718-6                                                               Sun City, South Africa
Proceedings produced by: Document Transformation Technologies cc
            8th CONFERENCE ON ASPHALT PAVEMENTS FOR SOUTHERN AFRICA


3. TESTING PROGRAM

3.1 Materials

AC 60/70, which is the conventional grade of binder used in Thailand, was used to produce
foam bitumen using the WLB-10 foamed bitumen laboratory unit, shown in Figure 1. Samples of
RAP were taken from an in-plant recycling construction site. New aggregate, consisting of
crushed limestone, as well as cement, were sampled from local commercial sources.




                                               Figure 1. Set of WLB-10 and mixer.

Foamed bitumen characteristics, tested at 170oC and 180oC, are presented in Figure 2. Based
on these results, a temperature at 170oC and water content of 2.5 % by mass of bitumen were
selected as optimum requirements to produce foamed bitumen for further testing. (Expansion
Ratio = 14, Half–life = 11.7 second).

Three blends of RAP and new aggregate were made up to conform with the grading envelope
proposed in the Wirtgen Cold Recycling Manual (Wirtgen Group, 2001):

•   Mix 1 > RAP : New Aggregate = 80%:20% > “80% RAP”

•   Mix 2 > RAP : New Aggregate = 50%:50% > “50% RAP”

•   Mix 3 > RAP : New Aggregate = 0%:100% > “0% RAP”

Gradation curves of these mixes are shown in Figure 3. One percent of cement by mass of
aggregate was added to each of the mixes to improve water resistance.

                                 24                                                                       20.00

                                 22
                                                                                                          18.00
                                 20
                                                                                                          16.00
               Expansion Ratio




                                 18
                                                                                                                  Halt life(s)




                                 16                                                                       14.00

                                 14                                                                       12.00
                                 12
                                                                                                          10.00
                                 10
                                                                                                          8.00
                                  8

                                  6                                                                       6.00
                                       1.5        2.0           2.5      3.0        4.0       5.0
                                                                Water Content (%)

                                      Expansion Ratio @ 170 Degree C           Expansion Ratio @ 180 Degree C
                                      Half Life @170 Degree C                  Half Life @ 180 Degree C


                                             Figure 2. Expansion ratio and half-life.


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                              100

                               90           low er spec

                               80
                                            upper spec
                               70
                                            80% RAP
                               60



                  % Passing
                                            50% RAP
                               50
                                            0% RAP
                               40

                               30

                               20

                               10

                                0
                                               0.075 0.15 0.30 0.60 1.18 2.36 4.75 9.50 19.0 37.5

                                                             Sieve Size (mm)


                                       Figure 3. Gradation of researched blends.

3.2 Mix Design

In the mix design the foamed bitumen was produced using the optimized temperature, water
content and gradations discussed in 3.1 above, the aim being to establish the optimum bitumen
content of each of the three mixes. The mix design procedure conformed to part A2.3 of the
Wirtgen Cold Recycling Manual (Wirtgen Group, 2001).

3.3 Laboratory Test

The three mixtures, manufactured using the optimum foamed bitumen content found in the mix
design stage, were tested in the laboratory for the following four engineering properties:

•   Indirect Tensile Strength Test, ITS, conforming to AASHTO T283.

•   Indirect Tensile Resilient Modulus Test, MR, conforming to ASTM D 4123 and AASHTO TP
    31-94 but tested at 15, 25, 35 and 45oC by load equal to 25, 20, 15 and 10 % of ITS
    respectively.

•   Indirect Tensile Fatigue Test, tested by Indirect Tensile mean of 0.25 MPa at 25oC until
    failure, Nf (MR = 50% of initial MR).

•   Permanent Deformation Test, tested by uniaxial repeated load of 200 kPa, 0.5 Hz (Load:
    Unload = 0.5 : 1.5 sec) at 50oC.




      UTM – 5P machine                            Indirect tensile figure                 Uniaxial load figure

                                    Figure 4. Laboratory testing machine and figures.

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4. RESULTS

Based on the results of the mix designs, the optimum bitumen contents of the blends of 80%
RAP, 50% RAP and 0% RAP were found to be 2.1%, 2.6% and 3.4% respectively, showing that
the optimum bitumen of the mix decreases with higher proportions of RAP due to the lower
absorption of the partially coated RAP.

Table 1 summarises the optimum bitumen contents and related results of the mix design.

                                                       Table 1. Mix design results.

                                                      Mix 1: 80%RAP             Mix 2: 50%RAP             Mix 3: 0%RAP
    Optimum Content (%)                                        2.1                       2.6                  3.4
     Unsoaked ITS (kPa)                                       453                       465                   540
       Soaked ITS (kPa)                                       366                       348                   390
       Retained ITS (%)                                        80                        75                   72
                                       3
      Dry Density (g/cm )                                    2.188                      2.190                2.210

It can be seen that both dry and soaked indirect tensile strengths decrease as the proportion of
RAP is increased. However resistance of the mix to water, as indicated by retained ITS,
improves as the proportion of RAP is increased.

The results of the resilient modulus tests (MR) are shown in Figure 5. Surprisingly the resilient
modulus of the mix that contains 50% RAP is higher than the other two mixes. This testing was
repeated three times with similar results. The modulus of Mix 1, containing 80% RAP, shows the
largest drop in modulus with increased temperature, indicating slightly more temperature
susceptibility compared to the mixes containing less RAP.


                                      00
                                     1 ,0 0

                                     ,0 0
                                     80
                    Resilient Modu




                                     ,0 0
                                     60

                                     ,0 0
                                     40                     0 RAP
                                                           8%
                                                            0 RAP
                                                           5%
                                     ,0 0
                                     20
                                                            %
                                                           0 RAP
                                           0
                                               10     15      20     25     30     35    40     45   50
                                                                                o
                                                                      Te p ra re(C)
                                                                        me tu

                                                    Figure 5. Resilient modulus result.


Figure 6 and 7 show respectively the results of the fatigue and permanent deformation tests.
The mix containing 80% RAP showed the poorest resistance to deformation under repeated
loads, as well as slightly inferior fatigue properties compared to the other mixes. The fatigue
properties and rut resistance of the mixes containing 50% and 0% RAP are shown to be similar.
This is an indication that 50% of new aggregate could be replaced with RAP, thus reducing
haulage costs.




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                                                           6

                                                           5

                                                           4




                                               Log (N f)
                                                           3

                                                           2

                                                           1

                                                           0                                                 Mix
                                                               80%RAP      50%RAP            0%RAP

                                                                  Figure 6. Fatigue result.



                                            0.350


                                            0.300
                   Accumlated strain (% )




                                            0.250


                                            0.200


                                            0.150


                                            0.100                                     80% RAP mixture

                                            0.050
                                                                                      50% RAP Mixture

                                                                                      100% Chushed Stone mixture
                                            0.000
                                                    10             100            1,000             10,000         100,000
                                                                         Number of Pulses (cycle)


                                                           Figure 7. Permanent deformation result.


5. SUMMARY

This limited research shows that there are some opportunities for the use of foamed bitumen
treated materials using local materials in Thailand.

Laboratory tests that were included in this research, which include indirect tensile strength,
fatigue and permanent deformation test, indicate that high RAP content (80%) mixes give
poorer test results than mixes containing 50% or less of RAP. A mix containing 50% RAP
produced similar results compared to a mix manufactured using all new aggregate.

Reduced usage of new material is shown to be an advantage - cold recycled mixes could be
produced using as much as 50% of RAP, but have the same performance as all-new aggregate
mixes.




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6. RECOMMENDATIONS

This pilot laboratory project shows potential for applying foamed bitumen technology as a
means of improving Thailand’s local materials in recycled layers, but the proportion of RAP to
new crushed stone should be considered case-by- case to prevent the possibility of low quality
mixes. The next stage should be a trial section where a comparison of performance using
cement and foamed bitumen treatments can be properly evaluated.

7. ACKNOWLEDGEMENTS

General support throughout the research project came from Mr. Buncha Fu-Trakul, Director of
Bureau of Road Research and Development, Department of Highways. Testing materials were
provided by Mr. Hem Ngowsiri from Bureau of Materials Analysis and Inspection, Department of
Highways. Technical assistance and machinery were provided by Mr. Tony Lewis, Wirtgen Hong
Kong Limited, Mr. Banya Roongchao and Somboon Rattananiti, Wirtgen Machinery (Thailand)
Co.,Ltd.

8. REFERENCES

Chiu, C.T., Huang, M.Y. and Lu, L.C., 2002, A Study on The Application of Foamed Asphalt
in Taiwan, Department of Civil Engineering Chung Hua University Taiwan.
Koender, B.G., Stoker, D.A., Robertus, C., Larsen, O., and Johansen, J., 2002, WAM-Foam,
Asphalt Production at Low Operating Temperatures, Ninth International Conference on
Asphalt Pavement.
Robert, F.L., Engelbrecht, J.C. and Kennedy, T.W., 1984, Evaluation of Recycled Mixtures
Using Foamed Asphalt, Transportation Research Record, Vol.968: 78-85.
Ruckel, P.J., Acott, S.M., and Bowering, R.H., 1983, Foamed-Asphalt Paving Mixture:
Preparation of Design Mixture and Treatment Test Specimens, Transportation Research
Record, Vol.911: 88-95.
Wijk, A.V. and Wood, L.e., 1983, Use of Foamed Asphalt in Recycling of an Asphalt
Pavement, Transportation Research Record, Vol.911: 96-103.
Wirtgen Group, 2001, Future-Orientated Technologies, Germany.
Wirtgen Group, 2001, Wirtgen Cold Recycling Manual, Germany.




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