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Airfield and Highway Pavements 2019
136
Potential of RAP as Aggregate Base and Subbase in the Context of Bangladesh
Mohammed Russedul Islam1 ; Mohammad Imran Hossain, A.M.ASCE2; Sakib Hossain3;
Fahim Al Faisal4 ; Mahadi Hasan5 ; and Sheikh Mohibur Rahman6
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1
Assistant Professor, Dept. of Civil Engineering, Military Institute of Science and Technology,
Dhaka 1206, Bangladesh (corresponding author). E-mail: [email protected]
2
Assistant Professor, Dept. of Civil Engineering and Construction, Bradley Univ., Peoria, IL,
USA. E-mail: [email protected]
3
Undergraduate Student, Dept. of Civil Engineering, Military Institute of Science and
Technology, Dhaka 1206, Bangladesh. E-mail: [email protected]
4
Undergraduate Student, Dept. of Civil Engineering, Military Institute of Science and
Technology, Dhaka 1206, Bangladesh. E-mail: [email protected]
5
Undergraduate Student, Dept. of Civil Engineering, Military Institute of Science and
Technology, Dhaka 1206, Bangladesh. E-mail: [email protected]
6
Graduate Student, Dept. of Civil Engineering, Military Institute of Science and Technology,
Dhaka 1206, Bangladesh. E-mail: [email protected]
ABSTRACT
Road agencies of Bangladesh rely mostly on imported bitumen and stone aggregates for
construction, maintenance, and rehabilitation of flexible pavements. Expenses for importing
materials are one of the reasons for the higher construction cost in Bangladesh. The study
attempts to investigate the recycling prospects of RAP in base and subbase layers in accordance
with existing construction practices. RAP is collected from the roadside stockpile of TongiAshulia-Zerabo-EPZ Road a national highway in Bangladesh (N302). Series of laboratory tests
are performed on RAP to determine the bitumen content and physical properties of milled RAP
aggregates. The study reports the laboratory test results of soaked CBR tests for the specimens
prepared with 100%, 70%, 60%, and 50% RAP and remaining virgin aggregates. Since gradation
affects the strength properties of aggregate, it is kept fixed for all the cases. The study finds that
with 100% of RAP aggregates CBR value is 15 and observed a slight increase in CBR values
when RAP is replaced with virgin aggregates. However, when RAP, and virgin aggregate
combinations are treated with a binder, it shows a significant improvement in CBR values.
Maximum CBR value 47 is found for 50% replacement of RAP and treated with 5% cement.
However, CBR value rises to 52 if only RAP is treated with 1% bitumen.
KEYWORDS: Base, California Bearing Ratio, Subbase, RAP
INTRODUCTION
Almost all the developed countries around the world use Reclaimed Asphalt Pavement
(RAP) for recycling or reuse purposes. In Europe, the use of Reclaimed Asphalt Pavement
(RAP) is a widespread practice which started its use for more than 30 years ago (Xavier 2016).
Europe now produces almost 25% of the world's asphalt total, and it is estimated that well over
50 million tons of RAP are produced each year with, 70% being reused for road surfaces
(Business Europe 2011). Over 99% of material removed during maintenance or repair activities
ends up being put back to use in new pavements in USA (World Highways 2015). There are
about 1,150 asphalt plants in Japan, producing approximately 55 million tons of hot-mix asphalt
annually of those about 41.9 million tons contain recycled HMA (West 2015).
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Airfield and Highway Pavements 2019
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Airfield and Highway Pavements 2019
137
Figure 1. Historical structural overlays construction for at RHD road networks.
Figure 2. RHD maintenance and rehabilitation needs for 2018-19.
However, in Bangladesh, there are no standards set by Roads and Highways Department
(RHD) for the use of RAP. RHD controls over 21,000 km of roads in Bangladesh. For the past 5
years, 5,915 km of National Highways and Regional Roads underwent structural overlays to
increase the pavement strength at a total cost of BDT 79,760 million (949.5 million USD; 1 USD
= 84 BDT). More BDT 22,280 million (265.2 million USD) has been demanded future
maintenance and rehabilitation (Razzaque et al. 2018). The most popular maintenance technique
in Bangladesh is providing overlay over the existing road. Fig. 1 describes the overlay
construction history for the last five years in RHD. However, RHD road networks demand
reconstruction in the coming year as shown in Fig. 2. It is likely that these upcoming
reconstruction works will generate a considerable amount of RAP that should be recycled in
pavements. RAP is a better alternative to conventional methods of maintenance and
rehabilitation of deteriorated pavements in case of conservation of the resources and preservation
of the environment. There will be a reduction in cost for about 25 to 30% by reusing the RAP
generated at the same site (Mishra 2015).
The study attempts to recycle RAP in accordance with the existing construction practices in
Bangladesh. Currently, in this country recycling machinery is not available but Dhaka South City
Corporation (DSCC) has purchased Hot Recycling Asphalt Plant and Cold Milling Machine in
2016. The study evaluates the possibility of recycling the RAP as sub-base/base materials with
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and without using any binder materials. The outcome of the study will guide road agencies to
start recycling without further waiting for modern machinery to come.
Photo 1. A stockpile of the RAP.
Photo 2. RAP materials before and after the bitumen extraction test.
METHODOLOGY
Sample collection
The RAP materials were collected from a national highway N-302 named as Tongi - Ashulia
–Zerabo - EPZ road. The bituminous overlay was constructed on January of 2013 and when the
surface became heavily cracked RHD has decided to remove the surface layer in the May of
2016. After removing the surface layer, these were stockpiled after crushing it by a crusher
machine as shown in Photo 1. Materials were collected for this study on 20 April 2018. To carry
out the laboratory tests, 200 kg of RAP materials were gathered. Additionally, commonly used
virgin aggregate (VA), ordinary Portland cement and Virgin bitumen of 80/100 penetration grade
were collected from a road project.
Experiments were designed to assess the collected RAP to be recycled as granular layer of
100% RAP, 70% RAP and 50% RAP with and without cement treatments. The study also
evaluated the possibility of recycling the collected RAP compacted at 155 0C with or without
adding 1% of bitumen. The pervious study showed that 100% RAP sample compacted at 150 0C
gives maximum Marshall stability value and 100% RAP compacted in between 150-160 0C
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givens maximum Marshall flow value (Islam et al. 2018).
Laboratory investigation
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For the investigation, the series of laboratory tests were performed to assess their physical
properties. Moisture content test according to ASTM D7870 was conducted to the collected RAP
materials. The objective of the test was to determine the moisture content of the sample after 2
years of its exposure to the open air.
Photo 3. Aggregate crushing value test on RAP.
Photo 4. Preparation of specimen for CBR test.
Asphalt content of RAP was determined by ignition method according to ASTM D6307.
Photo 2 shows the RAP before and after binder extraction test. Sieve analysis of the RAP
materials was conducted according to ASTM C136. To determine the nominal maximum
aggregate size and the gradation of the sample. Aggregate Crushing Value (ACV) test was
performed according to BS 812-110 to get a measure of the resistance of aggregates sample to
crush under gradually applied compressive load as shown in Photo 3. Los Angeles Abrasion test
was conducted according to ASTM C131 to determine the resistance of aggregates sample
against the impact force. Modified Proctor tests according to ASTM D1557 were undertaken to
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identify the optimum moisture content (OMC) and maximum dry density (MDD) for different
combinations. Finally, soaked CBR tests with 96 hours of the soaking period were conducted
according to ASTM D1883 for different combinations. Photo 4 and Photo 5 show the preparation
and testing of CBR specimens.
Photo 5. Heating the RAP to compact at 155 0C.
RESULTS AND DISCUSSION
The moisture content value of RAP was found to be 0.22% after being exposed to open air
for almost 2 years. Results of sieve analysis are shown in Fig. 3. It is observed that the gradation
curve of the collected RAP falls slightly below lower range for the bituminous wearing course of
Roads and Highways Department (RHD), Bangladesh. There was no pavement reclaimer on that
project site, and the materials were grinded with an unconventional crusher that affects the
aggregate gradation. This gradation was kept fixed for carrying out compaction and CBR tests
for all combinations.
Figure 3. Gradation of RAP materials collected from a wearing course.
The bitumen content of RAP was found from the test was 2.19%, which is remarkably less
than the usual range for virgin mixes. Not following proper quality control while doing the
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construction might be the reason for very low binder content in the RAP sample. The ACV and
LAA value of RAP was found 19% and 27% respectively which are quite satisfactory for
highway materials according to RHD (2011). Table 1 summarizes the ACV and LAA values for
RAP and VA for the study.
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Table 1. Summary of the test results for VA and RAP.
Name of the Test
RAP
VA
Aggregate Crushing Value (ACV)
19%
21%
Los Angeles Abrasion (LAA)
27%
28%
The optimum moisture content for the different combinations of RAP and VA obtained from
Modified Proctor test is shown in Table 2.
Table 2. OMC and MDD for different combinations.
Combination
OMC (%) MDD (g/cm3)
100 % RAP
5.52
0.678
70 % RAP + 30 %
VA
7.33
0.692
60 % RAP+ 40 % VA
6.23
0.692
50 % RAP+ 50 % VA
4.86
0.681
Figure 4. Soaked CBR values for various combinations of RAP and VA.
The CBR Test value that was found for the different combination of RAP and VA is shown
in Fig. 4. According to the specifications of RHD (2011), CBR value for subbase layer is 25% or
more. The study finds that no combinations of RAP and VA satisfy the minimum CBR criteria.
If it is treated with 5% cement for all combinations, CBR value raises above 25% as shown in
Fig. 5 but remain less than 50%, the lower limit for base type II according to RHD specifications.
If the amount of cement is increased may be CBR values for the combinations will increase
further. The study has assessed the collected RAP to be recycled after compacting at 155 0C. Fig.
6 shows that if 100% RAP is heated and compacted CBR value rises to 37%. However, if 1 % of
virgin bitumen is added with the RAP and then heated and compacted at the same temperature
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CBR value rises to 52%, higher than the lower limit for base type II. Due to resource limitation,
only one test was done for each test category.
Figure 5. Soaked CBR values of various cement treated RAP and VA mixture.
Figure 6. CBR values for RAP materials compacted at 155 0C.
CONCLUSIONS
This paper presents experimental results for recycling RAP as sub-base/base materials and to
create an alternative option to fresh aggregates for reconstruction, repair or rehabilitation of
pavement. The study finds that with 100% of RAP aggregates CBR value is 15 and observed
slight increase in CBR values when RAP is replaced with VA. Maximum CBR value 20 was
found when 50% of the RAP is replaced. However, when RAP and VA combinations are treated
with cement, it shows mentionable increase in CBR values and found maximum 47 for 50%
replacement of RAP treated with 5% cement. The study reveals that when the collected RAP is
compacted at 155 0C its CBR value is 37. However, if 1% virgin bitumen is added and mixed at
the same temperature CBR value rises to 52. The study finds that collected RAP alone cannot be
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used as sub-base/base unless it is treated with a binder and raise the strength.
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REFERENCES
Aravind K, Das A (2006). Bituminous pavement recycling, Dep Civ Eng IIT Kanpur 1–
3,http://web.iitd.ac.in/~akswamy/Published%20Articles/ Bituminous %20pavement%20
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Business Europe, Aggregates (2011). Increased use of recycled asphalt pavement
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Brajesh Mishra (2015). “A Study on Use of Reclaimed Asphalt Pavement (RAP) Materials in
Flexible Pavements.”, International Journal of Innovative Research in Science, Engineering
and Technology, 4(12).
Islam, M. R., Hossain, M. I. and Tasfiqur, M. R. (2018) “Investigating the Prospect of Reclaimed
Asphalt Pavement (RAP) as Stabilized Base in the Context of Bangladesh.” International
Conference on Transportation and Development 2018, Pittsburgh, PA, USA, pp. 322-331
Razzaque, Abdur, Rahman, Reazur Rajon, Rumi, Md Shahriar (2018). Maintenance and
Rehabilitation Needs Report of 2018 - 2019 for RHD Paved Roads, RHD, Dhaka,
Bangladesh.
RHD (2011). General Specifications (Technical Specifications), Dhaka, Bangladesh.
West, R. C., and Copeland, A. (2015). High RAP Asphalt Pavements: Japan Practice - Lesson
Learned. Information Series 139, Washington, DC., U.S.
World Highways (2015). Increased use of RAP in asphalt production,
http://www.worldhighways.com/categories/materials-production-supply/features/increaseduse-of-rap-in-asphalt-production > (Nov. 01, 2018).
Xavier, Planas Willis (2016). “Analysis of the use of reclaimed asphalt pavement (RAP) in
Europe”, MSc Thesis, Politecnico Di Milano, Milan, Italy
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