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PAPER TITLE

TRACK

Recycled Hot Mix Asphalt using Natural/Plant-Based Binder towards
Decarbonated Society
4. Innovative Materials and Technology- Reducing the carbon footprint of road pavements

AUTHOR(Capitalize Family Name)POSITIONORGANIZATIONCOUNTRY

Hiroshi FUJII

Senior Researcher

Technical Research Institute
The Nippon Road Co., Ltd.

Japan

CO-AUTHOR(S)(Capitalize Family NamePOSITIONORGANIZATIONCOUNTRY

Katsura ENDO

Chief Researcher

Technical Research Institute
The Nippon Road Co., Ltd.

Japan

Yuuya HAMANO

Researcher

Technical Research Institute
The Nippon Road Co., Ltd.

Japan

E-MAIL(for correspondence)

hiroshi.fujii@nipponroad.co.jp

KEYWORDS:
Natural/plant-based binder, Asphalt alternative, Recycled hot mix asphalt, Reduction of CO2 emissions,
Decarbonized society.

ABSTRACT:
Efforts to reduce carbon dioxide in the pavement field are also very important issue to realize decarbonate society. Morethan 40 million metric tons of hot mix asphalt (HMA) is annually produced in Japan. And about 75% of them arerecycled HMA (RHMA).
It should be one of the measures to reduce its carbon footprint of HMA if using natural/plant-based binder (NPB), i.e.,asphalt alternative. Some NPBs are commercially available. The authors produced RHMA using one of them. And that
produced RHMA was evaluated through some laboratory tests, test pavement and so on.
Used NPB can be adjust penetration by changing two components from the laboratory tests. And this has similarrheological property as petroleum asphalt. When using this NPB with penetration of 90, produced RHMA shows as
similar performance as a general RHMA and shows about twice as rutting resistant performance. This RHMA can beproduced at a general asphalt plant and paved with general sets of paving machines. Paved surface is good condition.
On estimating the carbon footprint, reduction rate of materials is 38%, that of production is 2% and total reduction rate
including hauling is 8% comparing to a general RHMA.
One of the biggest challenges is cost, which is estimated about 1.7 times of a general RHMA. This paper shows thatsuch a NPB can be an alternative binder. The authors hope that asphalt alternative can be widely used resulting in lower
costs and further this RHMA contributes decarbonated society.

Recycled Hot Mix Asphalt using Natural/Plant-Based Binder
Towards Decarbonated Society
Hiroshi Fujii 1, Yuuya Hamano 1, Katsura Endo 1
1 Technical Research Institute, The Nippon Road Co., Ltd., Tokyo, JAPAN

Email for correspondence, hiroshi.fujii@nipponroad.co.jp

1 INTRODUCTION
It is one of the important issues to address reducing greenhouse gas including carbon dioxide (CO2).
Therefore, the carbon neutral policy is a great task to be achieved for all industries all over the world. The
pavement industry is no exception, and lots of studies are continuously conducted for building a sustainable
society with harmonizing infrastructure development and environmental protection. These are low-carbon
technologies and effective usage of CO2 for materials of pavement, asphalt plant facilities, paving technologies
and so on for more details.
Reducing CO2 equivalent emission of hot mix asphalt (HMA) is one of the important issues as wellas in Japan. Because HMA is the most major paving material in Japan. Figure 1 shows the asphalt pavement
related CO2 equivalent emissions cited from data by Japan Road Association (Japan Road Association 2023a)
and a paper (Sakamoto 2023). This figure indicates that 89% of all CO2 emissions are related to the productionof HMA including raw materials like aggregates and binders. The remaining 11% occurs during deliveries of
HMA to construction sites and constructions. About the production of HMA, productions and deliveries of raw
materials are 34% and the production of HMA itself is 66%. Among these, CO2 emissions from a petroleum
bitumen is high because it is made by petroleum and it is required to be heated at every process of mining,refining, transporting, and using it. Then replacing a petroleum binder with alternate binder is one of theeffective ways to realizing decarbonized society.

Figure 1 A estimated example of CO2 equivalent emissions of asphalt concrete pavements(Japan Road Association 2023a, Sakamoto 2023)
The authors are interested in the natural and/or plant base binders and studies the applicability inJapan of one of the commercially available natural and/or plant base binders as an alternate binder. This paper
describes some laboratory tests results including binder properties and mixture properties. Test mix results at
an asphalt plant and test pavement results using general paving machines are also described in this paper.
Finally, an example of reduction of CO2 equivalent emission is estimated.

2 OBJECTIVES OF THIS STUDY
Objectives of this study are to evaluate the applicability and effectiveness as an alternate binder ofthe selected natural and/or plant base binder in this study (hereinafter NPB) from the viewpoints of binderproperties, mixture properties, manufacturability, workability, surface characteristics and so on from the resultsof laboratory tests and field tests and estimated reduction of CO2 equivalent emissions.

3 MATERIALS INFORMATION
3.1 The selected NPB
Composition of a petroleum binder generally contains asphaltene and maltene (Iijima 1978). The
NPB has similar composition to a petroleum binder and former is made from cashew nut shells and later ismade from natural originated materials. Then some CO2 emissions are offset because it is based on plants andnatural materials. Asphaltene component of the NPB is liquid state and maltene component is powder at aambient temperature as shown in Photo 1 and Photo 2, respectively. This means that this NPB is not required
to be heated during delivery to and storing at an asphalt plant. This is another important factor of reducing CO2
equivalent emissions. This NPB is thrown into a mixer and melted by the heated aggregates and then acts as abinder.

Photo 1 Asphaltene component of the NPB

Photo 2 Maltene component of the NPB

3.2 Recycled Hot Mix Asphalt
About 40 million metric tons of HMA is annually produced in Japan. And about 75% of them isrecycled hot mix asphalt (RHMA) with an extent of reclaimed asphalt pavement (RAP) as an aggregate (Japan
Asphalt Mixture Association 2022). RHMA is used in this study because RHMA is the major paving material
in Japan. A general dense graded mixture is used, and this has 50% of RAP and 50% of virgin aggregates.
Table 1 shows the mixture proportions and Figure 2 shows the gradation curve of this mixture. Virgin binder,
which is the NPB in this study, content is 3.1%. RHMA with a petroleum binder is also produced as a control
mixture. Rejuvenator is not used in this study. Instead, straight-run binder of penetration of 80/100 (hereinafter
PB80/100) is used in this case. Target temperature of mixing of PB80/100 is 155-160oC and target temperatureof compaction is 143-148oC.
For the reference, an amount of RAP for the use of RHMA depends on the amount of milled and/or
removed asphalt pavement through processes of rehabilitation works and length of road networks and so on in
Japan. Then cities or prefectures sometimes specify the allowable maximum amount of RAP and asphalt plants
follow the area-by-area limitations. The asphalt plant, which is used in this study, is located at the area where
RAP contents are limited to 50%, this is why mixture with 50% of RAP is used.

Table 1 Mixture proportions
Coarse aggregates
Fine aggregates
MineralHard sandstone Hard sandstone Screenings Natural sand filler
Sieve (mm)12.5 - 4.75
4.75 – 2.36
2.36 - 02.36 - 0
0.3 - 0
Proportion (%)
19.0
15.0
10.0
4.0
2.0
Aggregates

RAP

Total

12.5 - 0
50.0
100.0

Figure 2 Gradation curve of the RHMA in this study
4 TEST METHODS
4.1 Binder properties
4.1.1 Consistency
Penetration and softening point are mainly used to identify the binder properties in Japan.
Penetration and softening point of the NPB and PB80/100 are evaluated using ASTM D5 and ASTM D36,
respectively.
4.1.2 Viscoelasticity / Rheological property
Viscoelasticity is one of the important parameters on not only evaluating binder properties but also
understanding and evaluating mixture properties. Viscoelasticity of the NPB is measured using the dynamic
shear rheometer (DSR) as AASHTO T315 under the test conditions shown in Table 2, while this test method
is for asphalt binders.

Table 2 Test conditions of DSR
Test temperatures range
Angular frequency
Strain level
Diameter of specimen
Thickness of specimen

5 to 60oC
10rad/s
0.05%
25mm
1mm

4.2 Mixture properties
Mixture properties of RHAM with the NPB is evaluated as follows.
4.2.1 Mix design
Marshall mix design method is generally used for HMA and RHMA in Japan. Mix design isconducted as ASTM D1559.
4.2.2 Water sensitivity
Water sensitivity of RHMA with the NPB is evaluated using the Hamburg Wheel Tracking (HWT)
test as shown in AASHTO T324 under the water temperature is 60oC. This test temperature is also used atother tests considering the high-temperature and humidity during summer in Japan. Maximum passes of wheelload are 20,000, while loading is stopped and data is retrieved when it is impossible to continue the test.
Stripping inflection point (SIP) is obtained when an intersection of the first steady-state of the deformation
curve and the second steady-state of the curve appears.

4.2.3 Rutting resistanceRutting resistance of HMA and/or RHMA is generally evaluated using a wheel tracking test (WTT)
result specified as B003 in the handbook in Japan (Japan Road Association 2019b). For the reference, specimen
size is 300mm square and thickness is 50mm. This specimen is compacted using a roller compactor to meet a
degree of compaction, which is percent of a compacted density by a design density of the mixture, is 100%±1%.
This compacted specimen is cured in a constant temperature chamber at 60oC for 5 through 24 hours. A solidtire, which is 200mm in diameter and 50mm in width, with 686N±10N of load is moved on the cured specimen
at a loading speed of 42 passes/minute. Deformations are measured at the center of the specimen with theaccuracy of 1/100mm during this loading process. Loading is stopped after more than 60 minutes. And dynamic
stability (DS) is calculated using the deformations at 45 minutes and 60 minutes as shown in equation 1. DS
indicates the number of passes until the 1mm of deformation occurs after the deformation shows a steady state.
Figure 3 shows an example of a deformation curve of the WTT.
t t
630
(1)
DS  42 2 1  c 
d 2 d1
d 2 d1
where DS : dynamic stability (pass/mm)
t1 : elapsed time at 45 minutes
t2 : elapsed time at 60 minutes
d1 : deformation (mm) at t1
d2 : deformation (mm) at t2
c : correction factor (=1 in this study)

Figure 3 An example of a deformation curve of the WTT
4.2.4 Fatigue resistance
Fatigue resistance of RHMA is evaluated by the four-point bending (4PB) test as shown in AASHTO
T321 under the conditions of strain level is 500µ, frequency is 5Hz and test temperature is 5oC. However, sizeof specimen is 40mm*40mm*400mm and cycle to failure is obtained at the intersection point of the first steadystate of the curve and the second steady-state of the curve according to the Japanese test condition.
4.3 Test mix, test construction and field tests
Test mix is produced at our own asphalt plant in Ibaraki, Japan. Aggregates temperature are set at
174oC and temperature of PB80/100 is set at 148 oC, then mixing temperature should be around 155-160oC.
The NPB is no need to heat itself, so temperature of RHMA with the NPB will a little lower than that with
PB80/100. Produced RHMA with the NPB and with PB80/100 are paved using general paving machines, which
are an asphalt paver, a three-wheel steel roller for a breakdown compaction, a pneumatic tire roller for anintermediate compaction and a two-axle tandem roller for a finish compaction. Some specimens are prepared
for the laboratory tests using actual produced RHMA. All paving processes are carefully observed by theauthors. Some field tests are conducted on the surface including ASTM E965 for texture and ASTM E1911 forsurface friction. And International Friction Index (IFI) is calculated (Abe et.al. 1999).
4.4 Recommended compaction temperature of the NPB
Recommended mixing and compaction temperatures of a petroleum binder as well as PB80/100 isbased on the viscosity in Japan. Same temperatures as PB80/100 are adopted for the NPB in this study. The

authors notice the possibility of reducing mixing and compaction temperatures from the test construction.
Therefor relationship between the mixture temperature and compacted densities is evaluated using a gyratorycompactor.

5 TEST RESULTS AND CONSIDERATIONS
5.1 Binder properties
Evaluated binder properties are as follows.
5.1.1 Consistency
Penetration values of the NPB when varying the blending ratio of the two components, which areasphaltene and maltene, are shown in Figure 4. From this result, it is possible to adjust penetration of the NPB.
PB80/100 is the control binder in this study, then the amount of asphaltene is decided to 51.5% from theregression equation.
Table 3 shows the penetration test result and softening point test result of the NPB when 51.5% ofasphaltene and 48.5% of maltene are blended. This blended NPB meets specifications of penetration andsoftening point of PB80/100 in Japan. Both values of PB80/100 are shown in this table for the reference.

Figure 4 Penetration values according to amount of asphaltene
Table 3 Penetration and softening point test results
BinderNPB
PB80/100
Specification of PB80/100 in Japan

Penetration (1/10mm)
9681
80 -100

Softening point (oC)
49.9
44.8
42.0 – 50.0

5.1.2 Viscoelasticity
DSR test is conducted on three binders, which are PB80/100, the NPB and a polymer modified
binder type II (hereinafter PMBII), which is commercially available in Japan, to evaluate their viscoelasticity
properties. PMBII is one of the modified binders widely used in Japan. PMBII is made by adding several
percent of the SBS (styrene-butadiene-styrene) as a modifier to a petroleum binder and this binder is widelyused not only for roads but also for parking lots and so on where rutting resistance are required. Figure 5 shows
the test results.

Complex modulus (G*) of the NPB is like that of PB80/100 at lower temperature and is like that of
PMBII at higher temperature. It is expected that this NPB has a higher rutting resistance property than
PB80/100.

Figure 5 Complex modulus of the NPB, PB80/100 and PMBII
5.2 Mixture properties
Mixture properties of RHMA with the NPB and RHMA with PB80/100 are shown below.
5.2.1 Mix design
Marshall test results are shown in Table 4. All results meet the specifications for dense-gradedmixtures in Japan. Marshall mix design method can be adapted to the NPB and this NPB can be an alternate
binder.

Table 4 Marshall tests results
BinderBulk density(g/cm3)NPB
2.362
PB80/100
2.379
Specification* in Japan
N/A* Specification for dense-graded mixtures

Air voids
(%)
3.8
3.1
3-6

Void filled withbinder (%)
76.7
80.1
70 - 85

Stability
(kN)
8.7
11.3
4.9 and higher

Flow(1/10mm)
29
24
20 - 40

5.2.2 Water sensitivity
Table 5 shows the HWT test results. SIP is found in the RHMA with the NPB and PB80/100 and
SIP and rut depths after 6,000 passes for both mixtures are compared. Note that this test is performed under
severer test condition in water of 60oC as noted previously. RHMA with the NPB shows equal or better water
sensitivity than RHMA with PB80/100.

Table 5 HWT test results
Indicator
SIP (pass)
Rut depth after 6,000 passes(mm)

NPB
1,890
27.6

PB80/100
1,690
26.8

5.2.3 Rutting resistance
WTT results are shown in Table 6 and the specimens after WTT are shown in Photo 3. A greater DSshows a higher rutting resistance. RHMA with the NPB has about twice DS of mixture with PB80/100. And
rut depth after 60 minutes of RHMA with the NPB is less than that of RHMA with PB80/100. From these,
RHMA with the NPB has greater rutting resistance than PB80/100. DS is specified in the technical standards

for pavement in Japan and DS shall be more than 3,000 (pass/mm) for the use of heavy-duty roads with a daily
heavy traffic volume of more than 3,000 (heavy vehicle/day/direction) and more. Note that this traffic volume
is equivalent to 6,700 ESAL/day and more, because Japan uses a single axle load of 98kN. This NPB meets
this requirement.

Table 6 WTT results
Indicator
DS (pass/mm)
Rut depth after test completed (mm)

NPB
3,940
2.12

PB80/100
1,970
2.92

Photo 3 Top view of the specimen after WTT
5.2.4 Fatigue resistance
4PB test results are shown in Table 7. These test results indicate RHMA with the NPB has morethan twice fatigue resistance of RHMA with PB80/100.

Table 7 4PB test results
Used binder
NPB
PB80/100

Cycles to failure
3,940 ± 330
1,435 ± 154

5.3 Field test
5.3.1 Mixture properties
Table 8 shows test results using RHMA produced at the actual asphalt plant. Marshall stability of
RHMA with the NPB is about 35% higher than RHMA with PB80/100. For water sensitivity by HWT test,
SIP is found at both mixtures. SIP of the specimen with PB80/100 is greater than the laboratory test results and
SIP of the specimen with the NPB is almost equal to the laboratory result as previously shown in Table 5. For
rutting resistance by DS values, DS of the specimen with PB80/100 is smaller than the laboratory test result
and DS of the specimen with the NPB is greater than the laboratory result. The later is 6,300 (pass/mm) andthis level of RHMA is fully applicable to heavy-duty roads. For fatigue resistance by 4PB test, cycles to failureof the specimen using the NPB is greater than that using PB80/100 and these are almost similar to the laboratory
test results.
The NPB can be an alternate binder of PB80/100 for RHMA produced at the asphalt plant fromabove test results.

Table 8 Mixture properties using RHMA produced at the asphalt plantMixture property
Marshall stability
Water sensitivity
Rutting resistance
Fatigue resistance

Indicator
stability (kN)
SIP (pass)
DS (pass/mm)
cycles to failure

NPB
16.6
1,730
6,300
2,540±295

PB80/100
12.3
2,140
1,050
1,350±434

5.3.2 Test pavement result
1) Workability / constructability
Test pavements are constructed in early March 2023. RHMA with the NPB is produced at a batch
mixing plant and general RHMA is supplied from a storage silo, which is a general way in Japan. As the result,production temperature of RHMA with PB80/100 and the NPB are 162 oC and 152oC, respectively. These
mixtures are paved on a milled asphalt concrete surface with 3.5m in width and 50mm in thick. This is intended
to the major repair method of asphalt pavement, which is a mill and overlay, in Japan. A general wheeledasphalt paver to lay RHMA, 10 metric tons of steel roller for a breakdown compaction, 12.5 metric tons ofpneumatic tire roller for an intermediate compaction and 3.5 metric tons of tandem steel roller for a final
compaction are used in this study. Two examples of construction conditions are shown in Photo 4. RHMA with
the NPB is laid at temperature of 141oC and RHMA with PB80/100 is laid at temperature of 151oC andtemperatures during construction are measured as shown in Figure 6. Temperature drop trends are similar forboth with the initial temperature difference remaining. RHMA with the NPB is fully workable. No differences
are observed during constructions including mixtures, placement, compactions and so on even though allmeasured temperatures for RHMA with the NPB during construction are lower than PB80/100 cases.

Photo 4 Examples of construction conditions

Figure 6 Temperature measurement results during constructions2) Surface texture
Top views of constructed RHMA are shown in Photo 5 with measured surface texture of the Mean
Profile Depth (MPD). No differences are found there. Both surfaces show similar MPD values. RHMA with
the NPB can be finished by a general paving machines like general RHMA.

Photo 5 Top views of constructed RHMA and measured MPD
3) Skid resistanceInternational Friction Index (IFI) parameters are calculated using MPD and skid resistance bydynamic friction tester and these are shown in Table 9. Two parameters, which are the speed constant, Sp, andthe friction number, F60, show almost same values. RHMA with the NPB is expected to have similar skid
resistance to PB80/100 cases.

Table 9 Calculated Sp and F60
IFI parameters
Speed constant, Sp
Friction number, F60

NPB
35.17
0.19

PB80/100
38.91
0.20

5.4 Recommended temperatures of the NPB
From above, RHMA with the NPB has as same properties as RHMA with PB80/100 when produced
and constructed at the similar temperatures as PB80/100. On the other hand, it is reported that some natural
and/or plant base binders have possibilities to be used at lower temperature than general petroleum binders
from literature review results (TRB 2012, WSP New Zealand Limited 2021). And this is expected from thetest construction. Then relationship between mixture temperature and compaction property is evaluated. Figure
7 shows the relationship between the number of gyrations between the degree of compaction at several test
temperatures, which are decreased by 10oC from 144oC. This figure includes the test result of PB80/100 as acontrol specimen at 144oC.

Figure 7 Relationship between the number of gyrations and the degree of compaction
It is found that RHMA with the NPB has equal or better compactability when compaction
temperature is 124oC or higher comparing to RHMA with PB80/100 at 144 oC. RHMA with the NPB at 114oC
has a little worse compactability than RHMA with PB80/100 at 144 oC but this is within the acceptable range.
Sampling temperatures are at 10oC intervals and so the recommended temperature for compaction of the NPB

is about 114oC, which is about 30oC lower than a petroleum binder used in this study. From this, mixing
temperature is expected to decrease about 20-30oC comparing to PB80/100. This means that heating
temperatures of aggregates are also expected to be lowed. This leads to decreasing the amount of heavy oil toheat aggregates, resulting in lower CO2 equivalent emissions.
5.5 Applicability of the NPB as a paving material
RHMA with the NPB shows similar mixture properties to RHMA with PB80/100. RHMA with the
NPB can be produced properly and it is capable to pave using general construction machines and construction
management. The NPB and RHMA with the NPB are applicable to a paving material. Furthermore, the NPB
is expected to be used at lower temperature than PB80/100 and this is also expected to reduce CO 2 equivalentemissions comparing to general petroleum binders. Of course, medium to long term pavement performance
should be observed and confirmed and whether it will be approved as a material for the public roads is unknow
at this time.
5.6 Estimation of CO2 equivalent emissions
Reducing CO2 equivalent emissions are estimated when the NPB is used to RHMA comparing to
PB80/100. Some published documents and public data are used for these estimations. Estimated CO2
equivalent emissions include on producing and transporting raw materials and producing RHMA at an asphalt
plant. CO2 equivalent emissions are calculated as following.
Total CO2 equivalent emissions =  Vm  EF 
where

(2)

Vm : Volume of material used (unit depends on material like metric tons, liters or kWh)
EF : emission factor of each material

This calculation method is referred to two documents (Japan Road Association 2023a, Kawakami etal. 2009, Nishizaki et al. 2014) published in Japan and emission factors are cited from data published by the
Ministry of the Environment (the ministry of the environment, Japan. 2023). The calculation result is shown in
Figure 8. For materials, reducing rate of CO2 equivalent emissions is 38% using the NPB comparing to
PB80/100 due to the carbon-neutral feature of the NPB. For mixture productions, reducing rate of CO 2
equivalent emissions is 2% using the NPB comparing to PB80/100 because the NPB does not require heating
at storage. And totally 16% of CO2 reducing rate is estimated when lower producing temperature is considered
as noted above. For delivering materials, all are estimated as equal values in this case, because origin ofmaterials and location of asphalt plants may vary and then it is assumed that the locations are the same. Thenestimated total reducing CO2 equivalent emissions is 9% and it is 19% when considering lower temperature on
using the NPB instead of PB80/100 to produce RHMA. Note that 30 oC of temperature drop is assumed in thiscase. An alternate binder like the NPB contributes well to a decarbonated society when considering that 89%
of CO2 emissions of asphalt pavement construction is due to producing HMA as already shown in Figure 1.

Figure 8 Estimation results of CO2 equivalent emissions

6 SUMMARYS AND CONCLUSIONS









This paper is summarized as follows.
The selected NPB can be adjust its penetration value with changing the two components of asphaltene
and maltene.
The NPB can be mix designed replacing it to a petroleum binder of RHMA.
Mix properties of RHMA with the NPB is same or greater than that with PB80/100 and it has better
rutting resistance, especially.
RHMA with the NPB can be produced at a general asphalt plant and this can be paved using general
construction machines.
Surface characteristics of paved RHMA with the NPB is similar to that with PB80/100.
RHMA with the NPB can reduce the construction temperatures comparing to using PB80/100 and it
is 20-30oC lower than PB80/100.
CO2 equivalent emissions can be reduced 38% for materials, 2% for mix productions and 9% for all
stages including hauling when using the NPB.
CO2 equivalent emissions can be reduced 19% in total when using the NPB considering a possibilityof production temperature drop.

From these, it is possible to replace a petroleum binder with the selected NPB. There are somecommercially available natural and/or plant base binders in the world, so the authors expect that such natural
and/or plant base binders will be widely used. Cost or price will be one of the keys and this will be resolved tosome extent as the market scale of natural and/or plant base binders increases. But raw materials for suchnatural and/or plant base binders are finite. There will be a price equilibrium point somewhere. While taking
these points into consideration, the authors hope that social infrastructure including pavement is properly
maintained to a sustainable and environmental-friendly society.

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