Evaluation of asphalt mixture behavior incorporating warm mix additives and reclaimed asphalt pavement

Accepted Manuscript Evaluation of asphalt mixture behavior incorporating warm mix additives and reclaimed asphalt pavement Seyed Reza Omranian, Meor Othman Hamzah, Lillian Gungat, Sek Yee Teh PII:

S2095-7564(16)30225-2

DOI:

10.1016/j.jtte.2017.08.003

Reference:

JTTE 173

To appear in:

Journal of Traffic and Transportation Engineering (English Edition)

Received Date: 26 October 2016 Revised Date:

21 August 2017

Accepted Date: 25 August 2017

Please cite this article as: Omranian, S.R., Hamzah, M.O., Gungat, L., Teh, S.Y., Evaluation of asphalt mixture behavior incorporating warm mix additives and reclaimed asphalt pavement, Journal of Traffic and Transportation Engineering (English Edition) (2018), doi: 10.1016/j.jtte.2017.08.003. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

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Graphical abstract Testing

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Materials

Conclusion

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Original research paper

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Evaluation of asphalt mixture behavior

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incorporating warm mix additives and

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reclaimed asphalt pavement

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Seyed Reza Omraniana, Meor Othman Hamzaha,*, Lillian Gungatb, Sek Yee Teha

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School of Civil Engineering, Universiti Sains Malaysia, Engineering Campus, 14300 Nibong Tebal, Seberang

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Perai Selatan, Malaysia

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Malaysia

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Civil Engineering Programme, Faculty of Engineering, Universiti Malaysia Sabah, 88400 Kota Kinabalu,

Highlights

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Compaction energy index was highly dependent on compaction temperature.

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Warm mix additive enhanced mixture workability, while RAP showed the opposite effect.

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Incorporation of warm mix additives reduced mixtures tensile strength and resilient modulus.

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Mixtures with RH-WMA and RAP exhibited comparable performance as HMA.

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Compacted samples, rather than individual component, significantly impact mixture performance.

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Abstract

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Incorporation of warm mix asphalt (WMA) and reclaimed asphalt pavement (RAP) has

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benefited the asphalt industry in many ways such as reducing the demand for virgin

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materials, lowering energy requirement during the asphalt production and construction, in

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addition to reducing greenhouse-gas emissions. This study evaluated the effects of

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Evotherm and RH-WMA and RAP on mixtures’ behavior in terms of the compaction

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energy index (CEI), indirect tensile strength (ITS) and resilient modulus. The results

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showed that warm mix additives reduced the CEI, ITS and resilient modulus; while RAP

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increased the corresponding values. Statistical analysis showed that mixtures

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incorporating Evotherm and RAP had significant effects on CEI, while the effects of

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RH-WMA on the corresponding value were found to be statistically insignificant. General

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Linear Model showed that Evotherm , RAP and RH-WMA exhibited no significant effects

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on the ITS and resilient modulus. The one-way analysis of variance showed that

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Evotherm influenced mixture behavior significantly, while RAP and RH-WMA effects were

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found to be statistically insignificant. Regression equations with high accuracy levels were

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proposed to predict CEI, ITS and resilient modulus with respect to modification of mixture

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variables such as mix constituents (Evotherm , RH-WMA, and RAP) and compaction

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temperature.

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Warm mix asphalt; Reclaimed asphalt pavement; Workability; Compaction energy index; Indirect tensile

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strength; Resilient modulus.

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* Corresponding author. Tel.: +60 4 599 6210.

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E-mail address: [email protected] (M.O. Hamzah).

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1 Introduction

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Reclaimed asphalt pavement (RAP) and warm mix asphalt (WMA) are being increasingly utilized in

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asphalt technology to reduce pavement construction cost and enhance their performance. The use of

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RAP in road construction reduces the demand for virgin aggregate as a non-renewable material, while

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WMA is now the ideal solution to the conventional hot mix asphalt (HMA) due to several advantages

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associated with its use such as lower fuel consumptions and greenhouse-gas (GHG) emissions. For

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instance, the third generation of Evotherm , which is used in this study, exhibited the potential of

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reducing the mixing and compaction temperatures of HMA by approximately 30 ℃ (EAPA, 2010; Silva

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et al., 2010). Kheradmand et al. (2014) reported that this additive was capable of reducing 46%, 63%,

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30%, 34%, 58% and 81% of CO2, CO, VOC, PM, NOx and SOx emissions, respectively. Comparable rut

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resistance of WMA containing Evotherm with control mixture was also reported by Xiao et al. (2010).

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Zhu et al. (2013) found that the WMA containing Evotherm exhibited slightly higher air voids compared

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to HMA. It was also reported that Evotherm increased the bending failure strain of asphalt mixtures. Xie

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et al. (2013) compared the impacts of aggregate and binder type on the effectiveness of Sasobit ,

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Rediset , and Evotherm as WMA additive. WMA incorporated Evotherm had the lowest mechanical

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strength. Evotherm

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However, the Evotherm impact was more dominant on mixtures produced using limestone aggregate

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compared to those produced using basalt aggregate. Yang et al. (2017) studied the effects of

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Evotherm on crumb rubber modified HMA in terms of environmental and mechanical performance. The

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results indicated that crumb rubber can reduce conventional asphalt binder consumption and

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Evotherm can cause fuel saving and reduction of hazardous emissions. It was also found that the

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crumb rubber WMA had higher tensile strength, better moisture damage resistance, and fatigue

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performance compared to the HMA incorporating crumb rubber, while both exhibited equivalent rutting

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performance.

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was also found to be less effective to improve mix indirect tensile strength.

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It is believed that the aged binder from RAP affects the grade of virgin binder. The binder grade

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change is negligible at low RAP percentages, while such effect becomes significant when a higher

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proportion of RAP is incorporated (Lee et al., 2009). Hence, to compensate this issue, WMA additives

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can be a complementary choice due to their capability of reducing binder viscosity. WMA not only

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permits asphalt binder to coat aggregates with ease at lower temperatures, but it also enhances mix

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workability making it easier to compact. Workability is the term that describes the ease of mixture compaction. According to Bennert et al.

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(2010), WMA increases workability at conventional and lower compaction temperatures. The influence

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of constituents such as RAP and WMA additives on mixture workability or compatibility has been widely

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evaluated. Kristjánsdóttir et al. (2007) compared RAP-WMA and RAP-HMA and discovered the

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RAP-WMA compaction superiority over RAP-HMA. Tao and Mallick (2009) determined the feasibility of

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using RAP and WMA at a lower temperature. It was found that Sasobit H8 or Advera zeolite improved

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mixture workability at temperatures as low as 110 ℃. Tao and Mallick (2009) also reported that the

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addition of these additives stiffened the mixture which was reflected in the tensile strength increment.

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Zhao and Guo (2012) found that samples containing Sasobit (mixed at 145 ℃), exhibited the same

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workability as HMA mixed at 175 ℃. Mogawer et al. (2009) studied the performance of WMA (Advera

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and Sasobit used as WMA additives) containing RAP and found that WMA improved workability but

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increased moisture susceptibility. In order to produce porous asphalt, Goh and You (2012) employed

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RAP-WMA and determined the mixtures’ workability or compactibility using the compaction energy

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index (CEI) concept. The results showed that incorporation of Advera reduced the CEI, which affirmed

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the higher workability attribute of such mixtures. Goh and You (2012) also found that WMA containing

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RAP exhibited the highest tensile strength compared to the other tested mixtures. Significant

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improvement in workability of RAP-WMA mixtures containing asphalt rubber gap graded aggregate

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measured by torque was reported by Mogawer et al. (2013). According to El Sharkawy et al. (2017),

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incorporating RAP with warm-mix asphalt wax (WMAW) improved mixture compactibility and rutting

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resistance. The study reported an increase in binder softening point but reduction in penetration. Zhao

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et al. (2012) reported that WMA (Sasobit used as a WMA additive) mixtures with higher RAP content

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exhibited higher resistance to rutting as well as better resistance to moisture damage and fatigue

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performance. Moghadas Nejad et al. (2014) used the dynamic creep test to assess the rutting behavior

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of WMA (Sasobit used as a WMA additive) containing different percentages of RAP. It was found that

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50% RAP was the optimal content in mixtures. They also found that although RAP enhanced the rutting

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properties, increasing RAP amount resulted in mixtures with higher moisture susceptibility. Lu and

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Saleh (2016) studied the performance of WMA with different proportions of RAP content. The findings

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indicated that Evotherm

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moisture resistance improvement. It was also found that RAP-WMA exhibited better rutting resistance

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compared to HMA, while the addition of RAP reduced mixtures fatigue resistance. The optimum 25%

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RAP content for WMA incorporating Evotherm

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Dinis-Almeida et al. (2016) reported superior performance of warm mix recycled asphalt (WMRA)

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produced with 100% RAP and different emulsion content in terms of water sensitivity compared to HMA.

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Comparable WMRA performance with HMA in terms of fatigue resistance was also reported. Fakhri and

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Hosseini (2017) found that glass fiber modified WMA incorporating RAP (Sasobit used as a warm mix

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additive) exhibited better rutting resistance and moisture susceptibility, while glass fiber modified WMA

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only improved rutting resistance.

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enhanced adhesion between aggregate and binder, which resulted in

was recommended by Lu and Saleh (2016).

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Even though researchers have been exploring RAP and WMA technologies for several years,

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the performance and capability of new materials have yet to be further investigated. This study

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evaluates and compares the effects of two WMA additives (RH-WMA and Evotherm ) and a different

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proportion of RAP content on mixture behavior in terms of the compaction energy index (CEI), indirect

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tensile strength (ITS) and resilient modulus. RH-WMA is a relatively new warm mix additive developed

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in China.

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2.1

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The binders used were unmodified PG-64 (from two sources) and styrene-butadiene-styrene (SBS)

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modified PG-76. Table 1 shows the properties of these binders.

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Materials

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Table 1 Binder properties. Binder type

Aging stage

Test parameters

Value

PG-64 (A)

Un-aged

Penetration (dmm)

80

Softening point (℃) Ductility (cm)

46

G*/sin(δ) at 64 °C (Pa)

1342

PG-64 (B)

Short term aged

G*/sin(δ) at 64 ℃ (Pa)

Un-aged

Viscosity at 135 ℃ (cP) Penetration (dmm) Softening point (℃) Ductility (cm)

PG-76

Un-aged

Short term aged

300

3099 475 86 45

>100 1317

Viscosity at 135 ℃ (cP)

330

G*/sin(δ) at 64 ℃ (Pa)

2989

Viscosity at 135 ℃ (cP) Penetration (dmm)

400

Softening point (℃) Ductility (cm)

72

G*/sin(δ) at 76 ℃ (Pa)

1274

Viscosity at 135 ℃ (cP)

1700

G*/sin(δ) at 76 ℃ (Pa)

2598

Viscosity at 135 ℃(cP)

2700

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G*/sin(δ) at 64 ℃ (Pa)

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Viscosity at 135 ℃ (cP)

>100

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Granite aggregates supplied by Kuad Quarry Sdn. Bhd were used to produce all mixtures. The

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median aggregate gradation for asphalt mixture type AC14 was adopted in accordance with the

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Malaysian Public Works Department (PWD) specifications (PWD, 2008). The RAP was collected from

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Malaysia’s North-South Expressway road by the milling process. The RAP was processed in the

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laboratory through heating, crushing and fractionating. The processed RAP was blended with the virgin

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aggregates at 30% and 50% of RAP content by following the JKR gradation specification. Fig. 1 and

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Table 2 show the aggregate gradation and properties, respectively.

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Fig. 1 Aggregate gradation used in this study.

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Table 2 Granite aggregate properties. Property

Test result 2.62

Absorption (%)

0.40

Fine aggregates bulk specific gravity

2.57

Absorption (%)

0.54

Fine aggregate angularity (%)

47.3

Coarse aggregate angularity (%)

49.5

Flat and elongated (%)

23.3

Los Angeles abrasion (%)

23.86

Aggregate crushing value (%)

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Coarse aggregates bulk specific gravity

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The warm mix additives used throughout were RH-WMA and Evotherm . RH-WMA is a

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polyethylene wax based additive produced from cross-linked polyethylene developed by the Research

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Institute of China Highway Ministry of Transport. The RH-WMA is designed to reduce the viscosity of

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asphalt binder at high temperatures, while strengthening the asphalt crystalline structure at low

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temperatures (Wang et al., 2012). Likewise, Evotherm is a new generation of warm mix asphalt

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chemical additive, introduced and patented by MeadWestvaco (MWV) in 2003 (Buss et al., 2011). The

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third generation of Evotherm used in this study can be added to the binder prior to delivery to the

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asphalt mixing plants (Bonaquist, 2011). Evotherm not only permits asphalt binder to coat aggregates

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with ease at lower temperatures, but it also lubricates the mixtures that further enhance workability and

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compaction. Moreover, Evotherm enhances the adhesion at the binder-aggregate interface, hence,

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overcoming the water sensitivity problems (EAPA, 2010; Logaraj and Almeida, 2014; Silva et al., 2010).

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Table 3 presents the basic physical and chemical properties of the utilized additives.

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Table 3 Physical and chemical properties of warm mix additives. Additive type

Physical state

Color

Odor

Flash point

Solubility in water

pH

Boiling/ condensation point

Evotherm® 3G (M1)

Liquid

Amber (dark)

Amine-like

Closed cup: 204.4 ℃

Insoluble

10-12

> 200 ℃

RH-WMA

Granules or Powder

Yellowish-white

N/A

N/A

Insoluble

N/A

N/A

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2.2

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To incorporate WMA additives to the binders, the binders were first heated to the blending temperature

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prior to be added with liquid Evotherm . According to Mo et al. (2012), the incorporation of WMA was

Sample preparation

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found to reduce the production temperatures of the base and SBS modified binders between 20 to 40 ℃

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. Accordingly, temperatures of 140 ℃ and 160 ℃ were selected as the blending temperatures for PG-64

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and PG-76 binders, respectively. Binders were heated to the mixing temperatures prior to blending the

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binder with WMA additive. The liquid Evotherm was added to the binder manually and then stirred to

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promote a homogeneous and uniform distribution within the modified binders. According to Hurley and

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Prowell (2006), the optimum amount of Evotherm 3G to be added was 0.5% by mass of total binder.

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Hence, the same amount of Evotherm was used for this study. The Evotherm and binder were

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blended using a mechanical mixer for 5 min. Likewise, the RH-WMA supplied by the local distributor

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was blended with a virgin binder at 145 ℃ for 15 min using a laboratory mechanical mixer. The blending

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temperature was 160°C for binders containing 30% and 50% extracted RAP binder. The RAP was

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collected from the milled local, which had been trafficked for five years. The penetration and softening

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point of the extracted RAP were 20 dmm and 70 ℃, respectively. The 3% of RH-WMA by mass of the

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asphalt binder was chosen based on the optimum rheological performance as reported by Gungat et al.

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(2015). Table 4 presents the modified binder properties.

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Table 4 Modified binder properties.

Short term aged PG-76+Evotherm®

Un-aged Short term aged

PG-64+30%RAP

Un-aged Short term aged

PG-64+50%RAP

Un-aged

PG-64+RH

Un-aged

Short term aged PG-64+RH+30%RAP

Un-aged

Short term aged Un-aged

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G*/sin(δ) at 58 ℃ (Pa) Viscosity at 135 ℃ (cP) G*/sin(δ) at 58 ℃ (Pa) Viscosity at 135 ℃ (cP) G*/sin(δ) at 76 °C (Pa) Viscosity at 135 ℃ (cP) G*/sin(δ) at 76 ℃ (Pa) Viscosity at 135 ℃ (cP) G*/sin(δ) at 70 °C (Pa) Viscosity at 135 ℃ (cP) G*/sin(δ) at 70 ℃ (Pa) Viscosity at 135 ℃ (cP) G*/sin(δ) at 76 ℃ (Pa) Viscosity at 135 ℃ (cP) G*/sin(δ) at 76 ℃ (Pa) Viscosity at 135 ℃ (cP) G*/sin(δ) at 58 ℃ (Pa) Viscosity at 135 ℃ (cP) G*/sin(δ) at 58 ℃ (Pa) Viscosity at 135 ℃ (cP) G*/sin(δ) at 64 ℃ (Pa) Viscosity at 135 ℃ (cP) G*/sin(δ) at 64 ℃ (Pa) Viscosity at 135 ℃ (cP) G*/sin(δ) at 70 ℃ (Pa) Viscosity at 135 ℃ (cP) G*/sin(δ) at 70 ℃ (Pa) Viscosity at 135 ℃ (cP)

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Test parameters

Short term aged

Value 1317 250 2989 400 1336 1300 2156 1900 1202 666 3037 N/A 1187 745 2522 N/A 1508 300 4153 N/A 1691 480 4372 N/A 1601 536 3371 N/A

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To produce mixtures in the laboratory, the modified binder and batched aggregates were first mixed

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together. Mixing took about two minutes to ensure that aggregates were sufficiently coated with binder.

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For the preparation of mixtures containing RAP, the RH-WMA was added in dry and wet conditions. The

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wet addition was applied to the virgin binder, and followed the procedure described earlier. Since RAP

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also contained an aged binder, the RH-WMA was added in dry condition to the batched aggregates at

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room temperature. The mixing temperature was determined based on the viscosity obtained from the

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Rotational Viscometer. The dry mixing for the addition of WMA additive into RAP was adopted based on

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a study conducted by Howard et al. (2013). Table 5 shows the mixtures’ optimum binder content (OBC),

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mixing and compaction temperatures and aging duration. The loose mixtures were then placed inside a

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conventional oven for 2 h to simulate short-term aging conditions. Some mixtures were extra aged for 4

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and 8 h to evaluate the effects of extended aging on mixture performance. The oven was set at the

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compaction temperature. The loose mixture, placed on a tray, was blended thoroughly after every one

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hour to ensure they were aged homogeneously. For specimen compaction, the gyratory compactor was

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used to simulate the action of the field roller compactor. Mixtures incorporating RAP should be

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compacted at higher temperatures compared to HMA to reduce the viscosity of the aged binder in the

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RAP and ease the compaction process. However, for better evaluation of the inherent effects of

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RH-WMA on mixture performance, mixtures incorporating RAP were only compacted at the same

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temperatures as the mixtures incorporating RH-WMA. For ease of reference, mixtures were designated

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according to their contents and types as shown in Table 6, which also presents the air voids of each

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compacted mixture.

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Table 5 OBC and production temperatures. Optimum binder content (%)

Mixing temperature (℃)

Compaction temperature (℃)

PG-64 (A)

4.8

150

140

PG-64 (B)

5.2

160

150

PG-76

5.3

180

170

PG-64+Evotherm®

5.2

140, 130 and 120

130, 120 and 110

PG-76+Evotherm®

5.6

160, 150 and 140

150, 140 and 130

PG-64+RH

4.9

130

125

5.6

140

130

5.7

140

130

PG-64+30%RAP+RH

5.4

140

130

PG-64+50%RAP+RH

5.5

140

130

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Table 6 Mixture designation. Air voids (%)

Aging duration (h)

Compaction temperature (℃)

PG-64 (A)

P64A2

4.78

2

140

PG-64 (A)

P64A4

4.82

4

140

PG-64 (A)

P64A8

4.89

8

140

PG-64 (B)

P64B2

6.9

2

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P64E130

7.00

2

PG-64+Evotherm®

P64E120

7.00

2

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P64E110

7.11

2

P76

6.7

2

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P76E150

7.25

2

PG-76+Evotherm®

P76E140

7.3

2

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P76E130

7.05

2

P64R

4.50

2

P64N30

4.50

2

4.50

2

130

4.30

2

130

4.45

2

130

PG-64+Evotherm PG-76 PG-76+Evotherm

PG-76+Evotherm PG-64+RH PG-64+30%RAP PG-64+50%RAP

P64N50

PG-64+RH+30%RAP

P64N30R

PG-64+RH+50%RAP

P64N50R

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140 130 125 130

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2.3

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The compaction energy index (CEI) is an indicator of energy consumption by the roller compactor during

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construction to reach the specified density. It indicates mixture workability or compactibility. The CEI

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was determined based on the maximum specific gravity (Gmm) values from the 8 gyration to 92% of

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Gmm, similar to procedures utilized by Mahmoud and Bahia (2004). The Gmm value of the 8 gyration was

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used to simulate the compaction effort made by the paver during the pavement construction process.

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The selection of 92% Gmm was based on the current state of practice whereby the HMA mat was initially

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roller-compacted to 92% Gmm, and then continued to be compacted under traffic loading. The CEI is

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equivalent to the area under the curve from the 8 gyration to the gyration number corresponding to

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92% Gmm. Fig. 2 clearly illustrates the CEI and the parameters required for its computation. Mixtures with

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lower CEI are more preferred; however, too low of a CEI might indicate that the mixture is tender and

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should be avoided (Mahmoud and Bahia, 2004).

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Fig. 2 Compaction energy index illustration.

The indirect tensile strength (ITS) test was carried out in accordance with ASTM D6931-07 (ASTM,

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2007) procedures. The ITS test is commonly used to evaluate mixtures’ resistance to cracking when

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subjected to force. The test was performed using the Marshall stability apparatus but the two jaws where

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load was applied, were replaced by two steel loading strips. Prior to testing, the specimen was placed in

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the controlled temperature chamber at 15 ℃ and 25 ℃ for at least 4 h. During the test, the conditioned

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specimen was placed on the bottom strip, and the top loading strip was mounted on the sample. Axial

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load was then applied until the specimen failed.

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The resilient modulus test was conducted according to ASTM D4123 (ASTM, 2003) procedures

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using the universal testing machine-25 (UTM-25). To conduct the resilient modulus test, a cylindrical

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specimen was placed in the controlled temperature chamber at 15 ℃ and 25 ℃ for at least 4 h prior to

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testing. The resilient modulus was calculated based on the recoverable strain under repeated loading.

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The Poisson’s ratio was assumed as 0.35 and horizontal deformation was measured using a linear

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variable differential transducers. The flow chart of this research is illustrated in Fig. 3 for ease of

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understanding.

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Fig. 3 Research flow chart.

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3.1

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The CEIs of all mixtures are presented in Fig. 4. It is known that insufficient compaction results in higher

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aging rate, extensive rutting, and more susceptibility to moisture damage. From Fig. 4, mix P64A8 and

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mix P76E150 respectively exhibit the highest and lowest CEI. The difference between the CEI of mixes

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P64A2 and P64B2 which were prepared with the same binder grade, shows that when the compaction

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temperature decreases by 10 ℃, the CEI increases by almost 50%. It signifies the significant effect of

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production temperature upon mixture compactibility. It can also be seen that extra aging slightly

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increases the CEI, which is not substantial compared to the relative effects of temperature. Fig. 4 shows

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that warm mix additives reduce the CEI significantly. For instance, the CEI of mix P76 is about 40, while

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the corresponding value for mix P76E150 is about 10 (even though the compaction temperature has

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decreased by 20 ℃). It shows that despite the small amount of Evotherm (0.5 % by mass of the binder)

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used, the improvement in workability can be significant and this leads to lower CEI. The CEI of mixes

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P76E140 and P76E130 are approximately 20 and 40, respectively. It shows that compaction

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temperature decrement increases the CEI exponentially. A similar explanation can be used to interpret

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the CEI of mixes P64B2, P64E130, P64E120, and P64E110, where the incorporation of warm mix

Results and discussion

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additive reduces the CEI and temperature reduction escalates the corresponding value. As shown out in

260

Fig. 4, the CEIs of Mixes P76E130 and P64E110 are slightly higher compared to the corresponding

261

values for Mixes P76 and P64B2 (as HMA), respectively. The interaction of the CEI trend lines of

262

mixtures incorporating Evotherm with those of HMA shows that Evotherm improves the workability of

263

mixtures produced using PG-76 and PG-64 binders at temperatures as low as 132 ℃ and 112 ℃,

264

respectively. From the presented results, mix P64N50 exhibits higher CEI compared to P64N30. It

265

shows that additional RAP increases the CEI and lowers the workability, while the RH-WMA decreases

266

the CEI. For instance, the CEI of mix P64B2 is about 60, while the corresponding value of mix P64R is

267

about 30 (even though the compaction temperature decreased by 25 ℃). It can also be seen that mixes

268

P64N50 and P64N30 exhibit higher CEI compared to mixes P64N50R and P64N30R at the same

269

compaction temperature, respectively. It reaffirms the ability of RH-WMA to reduce viscosity for a given

270

temperature, which in turns improves mix workability as reflected by the lower CEI.

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Fig. 4 Mixtures workability results.

273

3.2

274

The ITS test results of all mixtures tested are shown in Figs. 5 and 6. The data can be used to infer

275

mixture resistance to cracking. Fig. 5 shows that mixes P64A8 and P64N50 sustain the highest load

276

before cracking, while mix P64E110 exhibits the lowest load bearing capacity. It can be observed that

277

extended aging increases the ITS when tested at both 15 ℃ and 25 ℃. Mixes P64A2 and P64B2 exhibit

Indirect tensile strength

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comparable ITS, which indicates the consistency of mixtures performance when using similar binder

279

grade. The slight difference between the ITS of mixes P64A2 and P64B2 can be attributed to either the

280

PG-64 (B) binder’s higher penetration grade and lower softening point compared to the corresponding

281

values of PG-64 (A) binder (Table 1) or the higher air voids of mix P64B2 compared to mix P64A2 (Table

282

6). The results also showed that warm mix additives decrease the ITS. Li et al. (2015) also reported

283

similar findings. Evotherm decreases ITS more significantly compared to RH-WMA. The ITS of mix

284

P64B2 equals 2.1MPa, while the corresponding values for mixes P64E130 and P64R are approximately

285

1.7 and 2.0MPa, respectively. Since both mixes P64E130 and P64R are compacted at 130℃, it can be

286

seen that the Evotherm reduces the mixtures’ tensile strength more significantly compared to the

287

RH-WMA. The results showed that diminution of compaction temperature results in mixtures’ load

288

bearing capacity reduction, which is not desirable. Figs. 5 and 6 showed that the compaction

289

temperature and Evotherm

290

variation. This can be deduced by comparing between the influence of compaction temperature and

291

Evotherm on mixtures prepared using PG-64 (B) and PG-76 binders. From Fig. 5, compaction

292

temperature reduction and Evotherm decrease the ITS of mixes P64E130, P64E120 and P64E110

293

more significantly compared to the ITS of mixes P76E150, P76E140, and P76E130 but the trend is

294

opposite in Fig. 6. In addition, the ITS of mixtures containing Evotherm are significantly lower than

295

HMA, especially for those mixtures produced using a softer binder. It shows that although Evotherm

296

decreases the CEI considerably, the performance of produced mixtures may not be satisfactory in

297

service. Mahmoud and Bahia (2004) also reported similar findings as highlighted in Section 2.3.

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effects on ITS vary according to mixture type and test temperature

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Comparison between mixtures containing RAP (Fig. 5) shows that higher RAP content in the mixture

299

increases the ITS. For instance, the ITS of mixes P64N50 and P64N30 equal 2.7 and 2.4 MPa,

300

respectively. Meanwhile, RH-WMA causes ITS decrement of mixtures containing RAP. From Fig. 5, the

301

ITS of mixes P64N50R and P64N30R are approximately 2.3 MPa, which is comparable with the ITS of

302

mix P64A2. It indicates that the ITS of mixes P64N50R and P64N30R exhibit similar trends with HMA

303

(mix P64A2). This finding can be attributed to the RH-WMA capability to compensate the effects of aged

304

binder already present in the RAP. Hence, these mixtures can be an ideal alternative to HMA due to a

305

reduction in the demand for raw materials, compaction temperature (lower CEI), fuel consumption, GHG

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306

emissions and mixture production cost. As expected, test temperature increment reduces mixture tensile strength, which is directly

308

associated with the ITS results. For instance, the ITS of mixes P64A2, P64A4, and P64A8 tested at

309

15℃ are approximately 50% higher compared to the corresponding mixes tested at 25 ℃. Similar trend

310

can be observed for other mixtures. Fig. 6 shows that the ITS of mix P76E150 is comparable with the

311

corresponding ITS of mix P64A2. Even though their results are approximately similar, adopting mix

312

P76E150 is not recommended due to the utilization of higher binder grade, which can be more

313

expensive, and higher compaction temperature, which consumes higher energy during mixture

314

preparation. However, it should be noted that these conclusions are drawn based on mixtures with

315

variable air voids (Table 6). Mixtures with higher air voids are more exposed to oxidation. Higher air

316

voids can reduce mixture rutting resistance due to a higher rate of densification (Hamzah et al., 2015).

317

Likewise, higher air voids can adversely affect fatigue life and stiffness of asphalt mixtures (Harvey and

318

Tsai, 1996). Although mixes P64A2 and P64B2 with 4.78% and 6.9% air voids, respectively, exhibit

319

approximately comparable results, the authors would suggest that further studies be undertaken on

320

mixtures with similar air voids for more precise evaluation and comparison of their performance.

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Fig. 5 Mixtures ITS results tested at 15 ℃.

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Fig. 6 Mixtures ITS results tested at 25 ℃.

325

3.3

326

Figs. 7 and 8 show the resilient modulus test results which measure mixture responses in terms of

327

dynamic stresses and corresponding strains. The results showed that mix P64A8 and mix P64E110

328

respectively exhibit the highest and lowest resilient modulus.

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Extended aging duration increases mixture resilient modulus which is consistent with the findings

330

reported by Hamzah and Teoh (2008). Comparison between mixes P64A2 and P64B2 shows that

331

higher binder content and air voids result in lower resilient modulus. Although mix P76 accommodates

332

higher air voids, it exhibits superiority over mixes P64A2 and P64B2 in terms of resilient modulus. It

333

indicates that mixtures containing stiffer binder have better resilience potential compared to mixtures

334

prepared using softer binders. The resilient modulus of mixes P64A4 and P64A8 are higher compared

335

to the corresponding value for mix P76. It can be attributed to the higher rate of aging effects on the

336

binder stiffening, which results in higher resilient modulus. The results also show that the warm mix

337

additives decrease the resilient modulus. This phenomenon can be correlated to the either lower

338

viscosity of binders containing warm mix additives (Tables 1 and 4) or higher mixture compaction

339

temperature, which results in higher binder stiffening due to higher binder aging rate (Table 5). The

340

results for mixes P64E130, P64E120 and P64E110 show that the reduction in compaction temperature

341

significantly reduces mixture resilient modulus. For instance, the resilient modulus of mix P64E130 is

342

16% higher compared to the corresponding value for mix P64E110 when tested at 15 ℃. The difference

343

between the two test results increases to 50% when the test temperature escalates to 25 ℃. A similar

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trend can be seen for mixes P76E150, P76E140, and P76E130 where the resilient modulus decreases

345

with compaction temperature decrement and test temperature increment. For instance, the resilient

346

modulus of mix P76E150 is 21% higher compared to the corresponding value for mix P76E130 tested at

347

15 ℃ and this difference reaches 31% when the test was conducted at 25 ℃. Comparison between the

348

resilient modulus results at 15 ℃ and 25 ℃ shows that Evotherm maintains the resilient modulus more

349

significantly at lower temperatures compared to higher temperature. Since higher and lower stiffness is

350

desirable for hot and cold regions, respectively, it can be concluded that Evotherm is more suited for

351

pavements in cold regions, particularly for mixtures prepared using softer binders. Although Evotherm

352

decreases the CEI, the performance of mixtures containing such additive exhibits lower resilience

353

compared to HMA. It can be attributed to their lower stiffness compared to HMA. Even though lower

354

resilient modulus may be beneficial to improve fatigue resistance, mixtures that incorporate Evotherm

355

may not be able to perform satisfactorily in service in terms of resilient modulus.

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Comparison between mixtures containing RAP (Fig. 8) shows that increasing RAP content

357

increases the resilient modulus. For instance, the corresponding values for mixes P64N50 and P64N30

358

equal 4285 and 3739MPa, respectively. The results also show that RH-WMA influences the resilient

359

modulus of samples containing RAP. For instance, the resilient modulus of mixes P64N30 and P64N50

360

are approximately 9% and 4% higher compared to the resilient modulus of mixes P64N30R and

361

P64N50R, respectively. This finding can be associated with the RH-WMA capability to soften the aged

362

binder. From Table 4, the addition of RH-WMA to the binders containing 30% and 50% RAP reduces the

363

performance grade of the binder by one grade. In contrast with the ITS results, those mixtures that

364

incorporate RH-WMA and RAP exhibit no significant relationship with HMA behavior, which can be

365

related to the variation of mixtures binder content. For instance, mix P64B2 contains 5.2% binder, while

366

mixes P64N50 and P64N50R contain 5.7% and 5.5% binder, respectively. It indicates that the

367

excessive binder content reduces the resilient modulus, which is in line with the findings explained

368

earlier.

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Fig. 7 Mixtures resilient modulus results tested at 15 ℃.

371 372

Fig. 8 Mixtures resilient modulus results tested at 25 ℃.

373

3.4

374

Analysis of variance was conducted using general linear model (GLM) to statistically evaluate the

375

significant effects of variables on the mixtures’ performance. The analysis was performed using Minitab

376

software at 95% confidence level (α = 0.05). Tables 7 and 8 present the results for mixtures

377

incorporating Evotherm and RH-WMA, respectively. In Table 7, the respondents are CEI, ITS and

378

resilient modulus, while the variables are compaction temperature, binder type, Evotherm and binder

379

type * Evotherm which represents the interaction between binder type and Evotherm . A p-value less

380

than 0.05 indicates the factors significantly affect the mixtures’ performance. Table 7 shows that all

381

individual factors, including compaction temperature, binder type and Evotherm influence the CEI

382

significantly, while only compaction temperature exhibits significant effects on the ITS and resilient

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Statistical analysis

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383

modulus. Table 7 also shows that the binder type and Evotherm interaction exhibits no significant

384

impact on the results. Based on the results presented in the Sections 3.2 and 3.3, although binder type

385

and Evotherm affect ITS and resilient modulus, such variables impacts are found to be statistically

386

insignificant. This finding is consistent with the interaction effects of binder type and Evotherm on the

387

CEI, which indicates that when these variables are combined together, their effects are statistically

388

insignificant. In contrast, compaction temperature exhibits significant impacts on all test results. This

389

phenomenon can be attributed to the higher aging rate at higher compaction temperature. Mixtures

390

produced at higher compaction temperatures experience higher aging rate, which makes the binder and

391

mixture become stiffer as a whole, and consequently results in higher ITS and resilient modulus. A

392

one-way analysis of variance (ANOVA) was also conducted to evaluate the significant effects of

393

variables on mixture performance. The analysis was performed using Minitab software at 95%

394

confidence level (α = 0.05). The results indicate that the compaction temperature and binder type exhibit

395

no significant effect on ITS and resilient modulus (due to p-value > 0.05), while Evotherm (by p-value <

396

0.05) affects the corresponding values significantly. The significance level of effects of independent

397

variables on the dependent variables differs by variation of the statistical analysis method. This

398

dissimilarity may be attributed to the difference in the degree of freedom of GLM and ANOVA.

399

Technically, the total sum of squares in GLM is the same for all factors, while the corresponding value is

400

distributed between groups when the analysis is conducted using ANOVA. In GLM, the effects of all

401

independent variables on the dependent variable are taken into account concurrently. However,

402

ANOVA can only detect the effect of a single independent variable on the dependent variable (disregard

403

the effects of other independent variables). This study is more interested in the GLM results due to the

404

application of all conditions (such as using warm mix additives and binder types) to the samples

405

simultaneously. It should be notified that the significance level of independent variables obtained from

406

ANOVA can be interpreted as their dominant effect on the dependent variable. For instance, the effects

407

of Evotherm on the ITS is more dominant compared to binder type.

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The effects of binder type and Evotherm on mixture performance are explored through the surface

409

and interaction plots as shown in Fig. 9. Surface plots indicate that the Evotherm and binder grade

410

increment results in the reduction of CEI. The higher compaction temperature of the mixtures containing

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411

stiffer binder (which significantly decreases binder viscosity) results in their lower CEI compared to the

412

mixtures made with a softer binder. Meanwhile, the interaction plot for CEI shows that the effect of

413

Evotherm on the softer binder is slightly higher compared to the stiffer binder due to the steeper slope

414

of the softer binder line. The surface plots of ITS and resilient modulus are consistent where the addition

415

of Evotherm and using softer binders result in lower ITS and resilient modulus. The higher ITS and

416

resilient modulus of the mixtures containing PG-76 binder are undoubtedly related to their stiffer binder

417

and higher compaction temperature, which escalates the aging rate and increases the binder stiffness.

418

The interaction plot for the ITS results reveals that the Evotherm effects on both binders are consistent,

419

based on their approximate parallel lines, while in resilient modulus case, the effects of Evotherm on

420

the stiffer binder is slightly higher due to its steeper slope of the line. Lastly, the general regression was

421

used to formulate the relationship between mixture variables and test results. Fig. 10 displays the

422

predicted regressions as well as normal probability plots of the residual, where BT, CT, E and BC refer

423

to binder type, compaction temperature, Evotherm and binder content, respectively. The regressions

424

can be used to predict the CEI, ITS and resilient modulus since the R-squares are greater than 90%.

425

The normal probability plots of residual indicate that the residuals evenly or better to say normally

426

distributed along the fitting lines (obtained from the regressions). This finding affirms the regressions

427

ability to quite accurately estimate the CEI, ITS and resilient modulus test outcomes with respect to the

428

mixture variables.

431 432 433 434

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439 440

Table 7 GLM analysis on mixtures incorporating Evotherm DF

Seq SS

Adj SS

Adj MS

F

p

Significant

CEI

Compaction temperature

1

131.58

1497.14

1497.14

42.84

0.007

Yes

Binder type

1

195.50

378.18

378.18

10.82

0.046

Yes

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1

1861.42

1861.42

1861.42

53.26

0.005

Yes

1

4.37

4.37

4.37

0.13

0.747

No

3

104.85

104.85

34.95

7

2297.72

Compaction temperature

1

1.60505

0.37804

0.37804

10.39

0.048

Yes

Binder type

1

0.08694

0.05437

0.05437

1.49

0.309

No

®

1

0.00151

0.00151

0.00151

0.04

0.852

No

1

0.00139

0.00139

0.00139

0.04

0.858

No

3

0.10911

0.10911

0.03637

7

1.80400

®

Total

Evotherm

R-Sq(adj)=89.35%

Binder Type * Evotherm Error

®

Total R-Sq=93.95% Resilient modulus

R-Sq(adj)=85.89%

Compaction temperature

1

Binder type

1

®

1

Evotherm

Binder type * Evotherm Error

®

Total

3

10603755

2241114

2241114

16.93

0.026

Yes

298951

74387

74387

0.56

0.508

No

4810

4810

4810

0.04

0.861

No

184823

184823

184823

1.40

0.323

No

397156

397156

132385

11489496

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R-Sq(adj)=91.93%

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1 7

R-Sq=96.54%

444 445 446

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R-Sq=95.44%

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Binder type * Evotherm Error

(a)

.

Test

Evotherm

441 442 443

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Fig. 9 Effects of binder type and Evotherm through surface and interaction plots. (a) CEI. (b) ITS. (c) Resilient modulus. (a)

(b)

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Fig. 10 Normal probability plot of residual for CEI, ITS, and resilient modulus, respectively, for mixtures ®

incorporating Evotherm . (a) CEI. (b) ITS. (c) Resilient modulus.

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Table 8 presents the GLM results of the mixtures incorporating RH-WMA and RAP. From Table 8,

466

CEI, ITS and resilient modulus represent respondents, while binder content, RH-WMA, and RAP

467

represent variables. The effects of interaction between variables on mixture performance are not

468

applicable due to the rank deficiency to estimate the model. A p-value less than 0.05 indicates the

469

factors that significantly affect the mixtures’ performance. Table 8 shows that only RAP significantly

470

affects the CEI, while binder content and RH-WMA exhibit no significant impact on CEI. The significant

471

effects of RAP content on CEI can be attributed to the excessively aged binder which results in higher

472

compaction effort to densify the loose mixtures. This finding is in agreement with the results of statistical

473

analysis on mixtures that incorporate Evotherm where higher aging rates significantly influence the

474

CEI. Based on the results presented in Sections 3.1 to 3.3, although binder content, RH-WMA, and RAP

475

affect the ITS and resilient modulus test results, such impacts are found to be statistically insignificant. It

476

indicates after compaction, mixtures incorporating RH-WMA and RAP behave as a whole which is

477

similar to HMA. These findings show the mixtures ability to satisfy the need to reduce demand for virgin

478

materials as well as fuel consumptions and GHG emissions. These findings also explain the RH-WMA

479

capability to reduce the excessive stiffness of the aged binder in RAP, which in turn optimizes the

480

mixture performance. The ANOVA was also conducted to evaluate the significant effects of variables on

481

mixture performance. The results indicate that although the level of significance of the RH-WMA and

482

RAP is different from the GLM outcomes, they still exhibit no significant impact on mixture performance

483

(based on a p-value greater than 0.05). The p-values greater than 0.05 from ANOVA also indicate that

484

none of these parameters has a substantial effect on mixture ITS and resilient modulus.

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465

485

The effects of RH-WMA and RAP on mixture performance are studied through the surface and

486

interaction plots as shown in Fig. 11. The surface plots indicate that the addition of RH-WMA results in

487

reduction of CEI, ITS and resilient modulus, while the addition of RAP increases the corresponding

488

values. From the interaction plot for CEI, RH-WMA exhibits similar effects on mixtures with different

489

RAP content. This can be inferred from the approximately parallel lines of variables’ effects of different

490

mixtures. The CEI of HMA, that is, a mixture without RH-WMA and RAP is slightly higher than the

491

mixture incorporating 30% RAP without RH-WMA. This discrepancy can be attributed to the higher

492

aging rate at higher compaction temperature of HMA, which results in the higher binder stiffening and

24

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consequently, higher energy requirement for compaction. The interaction plot for ITS shows that the

494

effects of RH-WMA on mixtures without RAP and with 30% RAP are consistent, while the RH-WMA

495

effects on mixtures incorporating 50% RAP are higher based on their steeper slope of variables effect

496

line. From the interaction plot for resilient modulus, the effects of RH-WMA on mixtures incorporating

497

RAP are consistent, while its effects on mixtures without RAP are higher based on their steeper slope of

498

variables effect line. The general regression is then used to formulate the relationship between binder

499

content, compaction temperature, RH-WMA and RAP (as independent variables) and test outcomes (as

500

dependent variables). Fig. 12 shows the prediction regressions as well as normal probability plots of

501

residual, where BC, CT, RH and R represent the binder content, compaction temperature, RH-WMA

502

and RAP content, respectively. The regressions can accurately predict the CEI, ITS and resilient

503

modulus since the R-squares are greater than 90%. The normal probability plots of residual indicate

504

similar trends for the CEI, ITS and resilient modulus. The residuals normally distributed along the fitting

505

lines. This finding confirms that the high accuracy of the regression equations to estimate the CEI, ITS

506

and resilient modulus test outcomes with respect to the mixture variables.

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Table 8 GLM analysis on mixtures incorporating RH-WMA and RAP. Test

Variable

DF

Seq SS

Adj SS

Adj MS

F

p

Significant

CEI

Binder content

1

1353.57

10.35

10.35

10.35

0.192

No

RH-WMA

1

84.20

2.77

2.77

2.77

0.345

No

RAP

2

1126.24

1126.24

563.12

563.12

0.030

Yes

1

1.00

1.00

1.00

5

2565.01

Binder content

1

0.23246

0.00789

0.00789

0.36

0.658

No

RH-WMA

1

0.00080

0.01791

0.01791

0.81

0.534

No

RAP

2

0.03795

0.03795

0.01897

0.85

0.608

No

Error

1

0.02220

0.02220

0.02220

Total

5

0.29341

Binder content

1

233773

179953

179953

27.09

0.121

No

RH-WMA

1

197014

86980

86980

13.09

0.172

No

RAP

2

524543

524543

262271

39.49

0.112

No

Error

1

6642

6642

6642

Total

5

961972

EP

Error Total

R-Sq=99.96%

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ITS

R-Sq(adj)=99.81%

R-Sq=92.43%

Resilient modulus

R-Sq=99.31%

R-Sq(adj)=62.17%

R-Sq(adj)=96.55%

508 509

25

(a)

511 512 513

(b)

514 515 516

(c)

521

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Fig. 11 Effects of RAP and RH-WMA through surface and interaction plots. (a) CEI. (b) ITS. (c) Resilient modulus.

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(a)

526 527 528 529

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Fig. 12 Normal probability plots of residual for CEI, ITS, and resilient modulus, respectively, for mixtures, incorporating RH-WMA and RAP. (a) CEI. (b) ITS. (c) Resilient modulus.

EP

534 535

4

536

The effects of Evotherm , RH-WMA and RAP on mixture behavior in terms of compaction energy index

537

(CEI), indirect tensile strength (ITS) and resilient modulus were presented. Based on the experimental

538

test results, the following conclusions can be drawn

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Conclusions and recommendations ®

•

Reduction in compaction temperature reduced mixture workability as evident from the

540

increased CEI. The higher CEI due to extended aging was not substantial compared to the

541

effects of variation in compaction temperature. Evotherm and RH-WMA decreased the binder

542

viscosity which resulted in lower CEI (higher workability), while incorporating RAP exhibited the

543

reverse effect.

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544

•

Decreasing the compaction temperature also contributed to the mixtures’ load bearing capacity

545

reduction. Test temperature increment reduced mixtures’ tensile strength. Extended aging

546

caused a considerable increase in ITS. Although both warm mix additives reduced the ITS, the

547

reduction in ITS using Evotherm was more significant compared to RH-WMA. The addition of

548

RAP in the mixture increased the ITS. Mixtures that incorporated RAP and RH-WMA showed

549

comparable ITS as HMA. These findings implied that such mixtures can be ideal alternatives to

550

HMA due to the reduction in the demand for virgin materials and lower energy requirement for

551

mixture compaction. •

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Reduction in compaction temperature reduced the resilient modulus, while test temperature decrement increased the corresponding value. Extended aging, increased the resilient

554

modulus, while higher binder content and air voids resulted in lower resilient modulus. Mixtures

555

produced using stiffer binder exhibited better resilient modulus compared to mixtures prepared

556

using a softer binder. Both warm mix additives reduced the resilient modulus, while the addition

557

of RAP exhibited the opposite results.

559

From the statistical analysis on the experimental data, the following conclusions can be drawn •

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The GLM results showed that the compaction temperature, binder type, and Evotherm

®

560

significantly influenced the CEI, while only compaction temperature exhibited significant effects

561

on the ITS and resilient modulus. According to the interaction plots, the effects of Evotherm on

562

mixtures made with binders PG-64(B) and PG-76 were approximately consistent, and the

563

discrepancy of the results was associated with the variation of compaction temperatures. The

EP

regressions with an excellent accuracy were then proposed to estimate the CEI, ITS and

565

567

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566

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resilient modulus with respect to the mixture variables.

•

The GLM also revealed that RAP significantly influenced the CEI, while binder content and

RH-WMA exhibited no significant effects on the outcomes. The interaction plot showed that the

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effects of RH-WMA on the mixtures incorporating different amounts of RAP content varied. The

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regressions with an excellent accuracy were then proposed to correlate the variables of the

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mixtures containing RH-WMA and RAP with the CEI, ITS and resilient modulus.

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•

The dissimilarity between outcomes of ANOVA and GLM took place, maybe due to differences ®

in their degree of freedom. The ANOVA analysis showed that Evotherm significantly affected

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mixture performance in terms of ITS and resilient modulus, while RAP and RH-WMA exhibited

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no significant impact on the corresponding values. From the GLM results, the effects of all

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independent variables on the compacted mixtures behavior were found to be statistically

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insignificant.

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According to these research findings, the following suggestions were recommended for further studies. •

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In this study, mixtures were produced with different air voids. Thus, the compaction process continued until the desirable air void content was achieved. The CEI was calculated based on

581

Gmm values of 8th gyration to 92% of Gmm. For further studies, CEI can be calculated until the

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end of the compaction process which can be better used to evaluate the correlation between

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the CEI results and mixture performance.

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•

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More research should be conducted to evaluate the fatigue and rutting behavior as well as moisture sensitivity and aging characteristics of mixtures incorporating different proportions of

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Evotherm , RH-WMA, and RAP individually or together. For better understanding of such

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additives effects, the response surface method (RSM), as a reliable and fast technique which

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can reduce the labor work and materials demand and ease the evaluation procedure, can be

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employed to determine the mixture performance at various conditions simultaneously, similar to

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study conducted by Hamzah and Omranian (2016).

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GLM can be employed to determine the effects of independent variables and their interactions

on the dependent variables concurrently. The authors would like to suggest the implication of such analysis for other studies that built upon different independent variables. ANOVA analysis also gives an insight toward an understanding of the significance level of independent variable

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effects on the dependent variable. Since ANOVA can only detect the effect of a single

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independent variable on a dependent variable, such analysis (which is simpler compared to

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GLM) is recommended for those studies built upon fewer independent variables. Surface and

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interaction plots provide a clear illustration of the independent variable effects on the dependent

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variables. These analyses which can ease the understanding and compare the effects of

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independent variables on dependent variables are also recommended to be carried out in future

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research.

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Acknowledgments

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The authors would like to acknowledge the Malaysian Ministry of Higher Education for funding this

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research

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203/PAWAM/6730111).

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Seyed Reza Omranian received his B.E. and M.Sc. degrees from Islamic Azad University and Universiti

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Sains Malaysia (USM) in the field of civil-surveying and pavement engineering, respectively. Before

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starting M.Sc. study, he worked as an engineer and surveyor at the Armi Road Construction and

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Development Company for three years. Currently, he is pursuing his doctoral degree in the field of

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pavement engineering at USM. His research focuses on asphalt pavement durability and early stage

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distresses that affect pavement performance. He has also been engaged in research on pavement

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sustainability and modeling. He is a member of the Sustainable Asphalt Research Group of the USM.

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Dr. Meor Othman Hamzah is currently a professor in highway engineering at the School of Civil

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Engineering, Universiti Sains Malaysia (USM). He spent almost 11 years pursuing his tertiary education

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in England from A Levels until Ph.D. He began his career as an academic staff at the USM in 1984. He

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has published widely in reputed international journals, conference proceedings and had written and

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translated 11 academic books. He has carried out numerous consultancy projects for the public and

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private sectors and produced numerous technical and consultancy reports. He helms the Sustainable

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Asphalt Research Group at his university. The group focuses on research activities that promote

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sustainable asphalt research and practices to ensure the well-being of the asphalt industries.

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Lillian Gungat obtained her degree in civil engineering from Universiti Teknologi Malaysia, M.Sc. in

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highway and transportation from Universiti Putra Malaysia and recently awarded for Ph.D. from

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Universiti Sains Malaysia in asphalt technology. She is currently working as a senior lecturer at

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Universiti Malaysia Sabah. Her research interests are highway materials, transportation, reclaimed

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asphalt pavement, warm mix asphalt and green asphalt. Dr. Lillian is a member of Institution of

734

Engineers Malaysia. She is now appointed as the head of Carbon Footprint and Transportation for

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Eco-Campus at Universiti Malaysia, head of laboratory at Faculty of Engineering and serves the Civil

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Engineering Program as an industrial training coordinator.

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Sek Yee Teh is currently pursuing his doctoral degree in warm mix asphalt at the School of Civil

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Engineering, Universiti Sains Malaysia. He received his bachelor's degree in civil engineering from the

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University of New South Wales, Australia. He is a member of the Sustainable Asphalt Research Group.

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His current research focuses on sustainable road materials and asphalt technology.

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