Performance of Warm Mix Asphalt containing Sasobit®: State-of-the-art

Construction and Building Materials 38 (2013) 530–553

Contents lists available at SciVerse ScienceDirect

Construction and Building Materials

journal homepage: www.elsevier .com/locate /conbui ldmat

Review

Performance of Warm Mix Asphalt containing Sasobit�: State-of-the-art

Ali Jamshidi a, Meor Othman Hamzah a,⇑, Zhanping You b

a School of Civil Engineering, Universiti Sains Malaysia, Engineering Campus, 14300 Nibong Tebal, Seberang Perai Selatan, P. Pinang, Malaysiab Department of Civil and Environmental Engineering, Michigan Technological University, 1400 Townsend Drive, Houghton, MI, USA

h i g h l i g h t s

" More than 230 literatures on binder and WMA mix incorporating Sasobit� are summarized." It is essential to optimize the performance of the warm binders at high and low temperatures." Warm asphalt mixes containing Sasobit� perform as well as or better than traditional hot asphalt mixes." Sasobit� in mixes containing waste materials permitted construction at lower temperatures." Sasobit� WMA exhibit good field performance compared with traditional hot asphalt mixes.

a r t i c l e i n f o

Article history:Received 5 April 2012Received in revised form 20 July 2012Accepted 4 August 2012Available online 12 October 2012

Keywords:Sasobit�

Asphalt binder rheologyAgingViscosityRuttingFatigueMoisture sensitivityGreenhouse gas emissions

0950-0618/$ - see front matter � 2012 Elsevier Ltd. Ahttp://dx.doi.org/10.1016/j.conbuildmat.2012.08.015

⇑ Corresponding author. Tel.: +60 4 599 6210; fax:E-mail address: [email protected] (M.O. Hamzah

a b s t r a c t

Warm Mix Asphalt (WMA) technology has become increasingly popular in pavement constructionbecause of its environmental benefits and its ability to improve the engineering properties of asphaltbinders and mixtures. This state-of-the-art article focuses on various aspects of the WMA technologyincorporating Sasobit� which includes the rheological characteristics of asphalt binders containing Sas-obit�. The findings from laboratory tests and field performance of Sasobit�-modified WMA are also pre-sented. This paper also reviews the life-cycle assessment, energy savings potential and greenhouse gas(GHG) emission reduction potential of WMA containing Sasobit�. The review concludes with a proposalfor incorporating aspects related to environmental and energy-efficient asphalt mixes in Superpave™ mixdesign method.

� 2012 Elsevier Ltd. All rights reserved.

Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5312. Background. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5313. Introduction to Sasobit� . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5334. Mechanism of Sasobit� performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5335. Asphalt binders containing Sasobit� . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 534

5.1. Effects of Sasobit� on asphalt binder rheological characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5345.2. Effects of Sasobit� on rutting performance of asphalt binder . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5345.3. Effects of Sasobit� on fatigue properties of asphalt binder . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5345.4. Effects of Sasobit� on low-temperature cracking potential of asphalt binder. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5345.5. Effects of aging on Sasobit�-modified asphalt binder . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5355.6. Effect of Sasobit� on thermal characteristics of asphalt binder . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5355.7. Interaction of Sasobit� with other binder additives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 536

5.7.1. Crumb rubber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5365.7.2. Aged binder. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 536

ll rights reserved.

+60 4 594 1009.).

http://dx.doi.org/10.1016/j.conbuildmat.2012.08.015

mailto:[email protected]

http://dx.doi.org/10.1016/j.conbuildmat.2012.08.015

http://www.sciencedirect.com/science/journal/09500618

http://www.elsevier.com/locate/conbuildmat

A. Jamshidi et al. / Construction and Building Materials 38 (2013) 530–553 531

5.7.3. Polymer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5366. Performance of WMA mixtures using Sasobit� . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 537

6.1. Laboratory performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 537
6.1.1. Effects of Sasobit� on construction temperatures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5376.1.2. Effects of Sasobit� on mix design and volumetric properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5376.1.3. Effects of Sasobit� on rutting properties of asphalt mixes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5386.1.4. Effects of Sasobit� on fatigue properties of asphalt mixes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5386.1.5. Effects of Sasobit� on low temperature performance of asphalt mixes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5386.1.6. Effects of Sasobit� on moisture sensitivity of asphalt mixes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5386.1.7. Effects of Sasobit� on resilient modulus of WMA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5396.1.8. Sasobit�-WMA mixtures Containing Crumb Rubber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5406.1.9. Sasobit�-WMA mixtures containing RAP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5406.1.10. Sasobit�-WMA mixtures Containing RAS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5416.1.11. Sasobit�-WMA mixtures containing RCA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 541
6.2. Field performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 541
6.2.1. Europe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5426.2.2. United States. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5426.2.3. Canada. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5446.2.4. Australia and New Zealand . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5446.2.5. South Africa . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5446.2.6. Asia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 545
7. LCA analysis, energy savings and GHG emissions reductions of Sasobit�-WMA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 545
7.1. LCA analysis and of Sasobit� WMA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5457.2. Energy savings and GHG emissions reductions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 545
8. Suggested Superpave™ modification based on the results outlined in the literature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5469. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54810. Suggestions for further research . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 549

Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 549References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 550

1. Introduction

Asphalt mix production depends on energy resources in twoways: (1) energy required to produce asphalt binders in oil refiner-ies; and (2) carbon-based energy carriers that are used as industrialfuels in asphalt mixing plants. In addition, asphalt production wasthe second most energy-intensive manufacturing industry in theUnited States [1].

From the commercial viewpoint, oil refineries prefer to producehigher-value-added products rather than asphalt binder, whichwas once regarded as a waste material from ‘‘the bottom of thebarrel’’, Furthermore, the price of crude oil, which is the majorsource of asphalt binder and industrial fuels, has significantly in-creased in recent years. This has led to an increase in the total priceof asphalt mixes, which are among the materials most consumedin transportation infrastructure construction and maintenance.For example, the price of asphalt mix increased from $68 per tonin 2004 to $104 per ton in 2007, an increase of 53% over a 3-yearspan [2]. In addition, to combat global warming and promotingsustainable practices, industries around the world, including as-phalt pavement manufacturers, have made persistent efforts to re-duce greenhouse gas (GHG) emissions and fossil fuel consumption.The asphalt industry meets these challenges by promoting the fol-lowing three strategies: development of inexhaustible and non-polluting new energy sources, use of renewable natural resourcesand synthetic adhesive binders as replacements for asphalt bind-ers, and development of new technologies to produce asphaltmixes suitable for use at lower construction temperatures withoutsacrificing mix properties.

The first and second of these strategies require construction ofnew infrastructure for the production and distribution of new en-ergy sources and synthetic binders, and reduction of asphalt mixproduction costs. In addition, the benefits of developing new,non-polluting energy sources and synthetic asphalt binders on alarge industrial scale will not be realized until a much later date.

The third alternative strategy, development of new technologiesto produce asphalt mixes suitable for use at lower constructiontemperatures, may impact the industry within a short period oftime. One such technology is Warm-Mix Asphalt (WMA), whoseuse permits the reduction of emissions and energy consumptionby decreasing production temperatures by 30–50 �C in comparisonto traditional hot-mix asphalt (HMA) [3,4]. The sustainability ofWMA technology is highlighted by the fact that each 10 �C reduc-tion in asphalt mix production temperature decreases fuel oil con-sumption by 1 l and CO2 emission by 1 kg per ton, according toWorld Bank estimates [5]. Ideally, the performance of WMA shouldbe the same as that of HMA, both structurally and functionally.There are many asphalt binder and mixture additives available toproduce WMA, of which Sasobit� is one.

The purposes of this state-of-the-art are to summarize morethan one hundred of the leading studies, including scientificpapers, technical reports, and theses, that have been conductedon both warm asphalt binders and warm mixes incorporatingSasobit� over the last decade, and to draw general conclusionsregarding the present state of knowledge of warm asphaltbinder rheology and mix performance. The findings of the state-of-the-art are presented in three main sections that begins withthe rheological characteristics of asphalt binders containingSasobit�, followed by the laboratory and field performances, andfinally the LCA, fuel saving, and GHG emission reduction ofSasobit�-WMA mixtures. Fig. 1 illustrates the flow chart ofdiscussion in this state-of-the-art.

2. Background

Wax additives for asphalt have two substantially different func-tions that are based on the physical phase of the asphalt binder.The first function of the wax can be observed when the asphalt bin-der is in the liquid phase at temperatures higher than 100 �C.

Fig. 1. The flow chart of discussion in this state-of-the-art.

Fig. 2. A typical example of Sasobit� granules as additive for Warm Mix Asphalt.

532 A. Jamshidi et al. / Construction and Building Materials 38 (2013) 530–553

Above this temperature, the wax reduces the binder viscosity. Thesecond function of the wax can be observed at intermediate andlow temperature ranges, when the asphalt binder is in the colloidor the solid phase, which asphalt binder viscosity increases.Although lower and higher viscosity values at elevated and inter-mediate temperatures, respectively, are more desirable in termsof lowering construction temperatures and improving plasticdeformation (rutting) resistance, these objectives conflict with tothe objective of minimizing fatigue and low-temperature cracking.The effect of wax depends on the chemical composition and therheological characteristics of the asphalt binder, the compositioncrystallinity of the wax, the application temperature range, andthe amount of wax [6]. In some countries such as Germany, France,and China, the amount of wax in the asphalt binder is restricted,based on the assumption that melting waxes at elevated tempera-tures may decrease the asphalt mix’s resistance to rutting, and thatwax crystallization can lead to mixture cracking at low tempera-tures [7]. Although waxy asphalt may cause damage in asphaltpavements, the potential of some synthetic commercial waxessuch as Sasobit� to improve asphalt mixture properties andachieve better performance at reduced construction temperatures

Table 1Properties of Sasobit� [8,13].

Properties Units Specification Values and range

Quantitive Congealing Temperature �C Min 100 100Penetration at 25 �C 0.1 mm 1 max NRPenetration at 65 �C 0.1 mm 13 max NRFlash point �C 290 NRPH Neutral NRPolydispersity Index 1.33 NRDensity kg/m3 622 (Pastille) NR

590 (Pill)Brookfield Viscosity at 135 �C cP 10–14 12

Qualitive Odor No odorVisual color Greyish-white to yellowishPhysical State Pastilles and pills

NR: No range.


offers a practical option to lessen energy consumption and increasesustainability in asphalt pavement technology.

3. Introduction to Sasobit�

Sasobit� is an organic warm binder additive that is registeredby the Chemical Abstract Service (CAS) as number 8002-74-2 andwhose chemical formula is CnH2n+2 [8]. Sasobit� is a productionof Sasol Wax in South Africa. Fig. 2 shows a typical example of Sas-obit� granules. It is a long chain of aliphatic hydrocarbons pro-duced by the gasification of coal, a process involving the treatingof white-hot hard coal or coke with a blast of steam via theFischer–Tropsch method [9].

The manufacturer’s description of the production process is asfollows [10]:

‘‘During the Fischer–Tropsch process, carbon monoxide is con-verted into a mixture of hydrocarbons having molecular chainlengths of 1–100 carbon atoms and greater. The beginning pointfor the process is a synthetic gas which is a mixture of carbon mon-oxide and hydrogen, produced by gasification of coal. The gas ismanufactured in vast quantities for commercial use’’. In 2003, Sa-sol Wax invested $360 million to pipe natural gas from Mozam-bique to Sasolburg, South Africa, for the production of Sasobit�

[11]. It is essential in the preparation of hydrogen and as a fuelin the making of steel and in other industrial processes. ‘‘The syn-thetic gas is reacted in the presence of an iron or cobalt catalyst;heat is created and products such as methane, synthetic gasoline,waxes, and alcohols are made’’ [10]. The chemical reaction is pre-sented in Eq. (1) [12]. The liquid products are separated and theFischer–Tropsch waxes are collected. Table 1 shows Sasobit�

properties.

ð2nþ 1ÞH2 þ nCO2 ! CnH2nþ2 þ nH2O ð1Þ

Sasobit� is available in 2, 5, 20, and 600 kg bags [13,14]. It can beadded into asphalt binder without using a shear mixing apparatus,while adding Sasobit� into asphalt mixes requires a few modifica-tions to the mixing process [13–17]. In Asia, Europe and, SouthAfrica, Sasobit� has been added directly to the aggregate as solidpills (small pellets) or as a molten liquid (produced from flakes).Sasobit� has also been blended with hot asphalt binder at theterminal (no high-shear mixing required) and as pills blown directlyinto the mixing chamber in asphalt mixing plants in the UnitedStates [13]. Sasobit� can also be blended with hot binder manuallyand or mechanically; this blending method has no effect onthe properties of the resultant Sasobit�-modified asphalt binderproperties [18]. Sasol Wax recommends the use of from 0.8% to4% Sasobit� by mass of binder [13,14,16]. However, the addition

of more than 4% of Sasobit� can lead to negative effects on thelow-temperature properties of the asphalt binder [6].

4. Mechanism of Sasobit� performance

Waxes are often classified into the following three generalgroups: including macro crystalline, microcrystalline and/or amor-phous (noncrystalline) waxes [19,20]. In general, asphalt wax ismicrocrystalline may also be amorphous, and different asphaltsmay contain larger or smaller amounts of wax [6]. In addition, dif-ferent wax types are produced, including artificial, partially artifi-cial and natural waxes [21].

Microcrystalline wax mainly consists of naphthenes and isopar-affins. Sasobit� is a synthetic microcrystalline wax that differs fromnatural asphalt waxes in its longer chain length and its finer crys-talline structure. The predominant chain length of the hydrocar-bons in Sasobit� is in the range of 40–115 carbon atoms, whilethat of natural asphalt paraffin waxes is normally in the range22–45 carbon atoms [22]. The wider range of chain lengths extendsthe plastic limit and increases the range of melting temperatures ofasphalt binders [23,24]. The longer chains also help to keep thewax in solution, thereby reducing the asphalt binder’s viscosityand the construction temperatures at which asphalt mixes con-taining the Sasobit�-modified asphalt binder can be placed. Themanufacturer states that the approximately melting point of Sas-obit� is almost 100 �C and that it is fully miscible in asphalt binderat temperatures higher than 116 �C. Beyond Sasobit�’s meltingpoint, the wax liquefies and significantly reduces asphalt binderviscosity, enabling asphalt mix production temperatures to be de-creased by 20–30 �C [4,25,26]. At temperatures below its meltingpoint, Sasobit� forms a lattice structure in the asphalt binder andprovides better stability according to reports on field trials[13,14]. In other words, Sasobit�-modified warm asphalt binderbehaves as a Newtonian fluid at temperatures higher temperaturesthan Sasobit�’s melting point and as a non-Newtonian fluid at tem-peratures lower than the melting point. Sasobit�’s formation of alattice structure prevents the movement of molecules in the mod-ified binder, consequently increasing the viscosity at low and inter-mediate temperatures [18]. Eq. (2) is valid for Sasobit�’srheological sweep temperature at a frequency of 1 Hz in complexshear modulus (G�) testing [27]:

G� ¼106 Pa 30 � T � 95

�38732T þ 4� 106 95 � T � 120

0:5 Pa 120 � T � 180

8>><>>:

R2 ¼ 86% ð2Þ

where T is temperature (�C).


Eq. (2) clearly shows that G� decreases significantly in the tem-perature range of 95–120 �C around the melting point of 100 �C,while at temperatures below 95 �C and above 120 �C, G� is rela-tively constant. Using the Fischer–Tropsch process to produce Sas-obit� maintains control over the chain length, avoids branching,and produces a wax without the contaminants (such as sulfur) thatare frequently found in other sources of natural hydrocarbon [28].In additional, the absence of double bonds along the molecularchain’s backbone alleviates oxidative chain scission in Sasobit�

and extends the service lives of asphalt mixes containing this addi-tive [28].

Thermal degradation of Sasobit� occurs at temperatures be-tween 350 �C and 520 �C and follows a polynomial trend as indi-cated by Eq. (3). The corresponding temperature at whichthermal degradation of neat asphalt binder begins is 250 �C [8].Thus, Sasobit� is more thermally stable than asphalt binder is.

Weight loss¼100% 50�T�3500:0009T2�1:34Tþ472:36 350�T�550

�R2¼94%

ð3Þ

where T is temperature (�C).

5. Asphalt binders containing Sasobit�

5.1. Effects of Sasobit� on asphalt binder rheological characteristics

Sasobit� increases the complex shear modulus (G�) of asphaltbinder at medium-sweep temperatures as well as the softeningpoint and maximum force of ductility, while it decreases thenon-recoverable compliance (Jnr), penetration number and Fraassbreaking point irrespective of binder source [22,23,27,29–41].

The degree of change in the rheological and chemical propertiesof Sasobit�–modified asphalt binder, including the decrease in vis-cosity at high temperatures and the increase in rutting resistanceor fatigue potential at intermediate and low temperatures, as wellas aging, depend on the Sasobit� content, the asphalt binder typeand source, and the amount of natural wax in the asphalt binder,in other words, the chemical structure of the asphalt binder[12,18,23,33,35–37,41–49]. For example, a Fourier transform infra-red (FTIR) spectroscopy analysis of an unaged asphalt bindershowed that the carbonyl content decreased by 25.58% and26.74% with the addition of 3% and 6% Sasobit�, respectively [36].The results for the same binder type and aging state but from an-other source showed that the carbonyl content increased by 2.99%and 13.96% with the addition of 3% and 6% Sasobit�, respectively.

Hamzah et al. [49] defined a parameter called the non-dimensional viscosity gradient (Dgs) to characterize the reductionin the relative viscosity of asphalt binder per unit Sasobit� content(1%) at a given test temperature. This parameter was used to eval-uate Sasobit� performance at high temperatures. The resultsshowed that although Sasobit� consistently reduces the viscosityof the asphalt binder, the degree of reduction in viscosity at a giventest temperature depends on the binder type and its aging state.

Seller [28] proved using epiflourescence microscopy imaging(EMI) that the average size and shape of crystals formed in the Sas-obit�-modified asphalt binder depends on the Sasobit� content.For instance, crystals that appear in a modified binder containing20% Sasobit� have an angular shape similar to a needle, while crys-tals in a warm binder containing 1% Sasobit� are less needle-likeand rounder in shape.

5.2. Effects of Sasobit� on rutting performance of asphalt binder

Rutting potential in asphalt binder is evaluated by differentmethods. The Superpave™ asphalt mixture design and analysis

system defines and recommends minimum values for the ruttingfactor, G�/sin d (where d is the phase angle) which represents thehigh-temperature viscous component of overall binder stiffness[50]. G�/sin d must be at least 1 kPa and 2.2 kPa for unaged andshort-term-aged binders, respectively, to meet the Superpave™binder test’s criteria [50]. A higher G�/sin d corresponds to betterasphalt binder rutting resistance.

Another test method uses the zero shear viscosity (ZSV) con-cept. ZSV is theoretically the viscosity in shear deformation at ashear rate approaching zero [51]. Asphalt binder being a viscoelas-tic material, its behavior depends on time and temperature. Thetime includes both the time of testing and the time of loading.Time of testing can be simulated in the laboratory via syntheticaging, while the time of loading is simulated using a frequencysweep. Because G�/sin d is determined at a constant frequency(1.59 Hz) in Superpave™ testing, the effects of loading time cannotbe investigated in great detail. Furthermore, G�/sin d does not re-flect binder recovery, because it does not distinguish between totalenergy dissipated and energy dissipated in permanent flow [52].

As expected, Sasobit� increases G�/sin d, increases ZSV, and de-creases the creep compliance of asphalt binder for a given agingstate and binder type and source [23,29,30,33,36,40,41,44,45,49,51,53,54]. Sasobit� also increased G�/sin d and failure tempera-ture and reduced creep compliance and phase angle more thanother warm asphalt binder additives such as Rediset� and Cec-abase� at each aging state (unaged and short-term-aged) and foreach binder source [29,30].

Hamzah et al. [49] defined a parameter called the non-dimen-sional Superpave™ rutting parameter (NSRP), derived from G�/sind, to characterize the effect of Sasobit� on rutting performance atintermediate temperatures, the analysis demonstrated that theNSRP and its trend with sweep temperature changed with Sasobit�

content, aging conditions, and asphalt binder type.Because ZSV is computed using different techniques, ZSV values

can be different. For example, the ZSV of Sasobit�-modified asphaltbinder was 960 Pa s based on Carreau’s model, while it was480 Pa s for the same source of asphalt binder using the Cross/Sybliskis model [51].

It was also observed that the shear thinning for a Sasobit�-mod-ified asphalt binder at 60 �C is a pseudoplastic phenomenon[33,51].

5.3. Effects of Sasobit� on fatigue properties of asphalt binder

Since Sasobit� increases G�, G�sin d is expected to increase withincreasing Sasobit� content. Therefore, to avoid fatigue cracking inasphalt mixes, a value of G�sin d less than 5 MPa is desirable,according to Superpave™ [50]. The degree of Sasobit� effect on G�-

sin d depends on the binder type, the chemical properties of thebinder, and the Sasobit� content [40,41,43,44,46,55]. Although as-phalt binders containing Sasobit� age more slowly because theycan be used at lower construction temperatures, Sasobit� contentand binder type should be selected with care because stiffening ef-fects due to aging associated with a high Sasobit� content can in-crease G�sin d beyond 5 MPa.

5.4. Effects of Sasobit� on low-temperature cracking potential ofasphalt binder

The advantageous effects of Sasobit� at high and intermediatetemperatures can correspond to detrimental effects at low temper-atures. In this regard, the following two phenomena should beevaluated for Sasobit�-modified asphalt binders: creep stiffnessand physical hardening. Creep stiffness is evaluated using a bend-ing beam rheometer (BBR) in Superpave™ testing. Physical harden-ing is a reversible procedure that can lead to changes in rheological

Table 2Percentage change in creep stiffness and PHI [42].

Binder source Sasobit� content (%) Changes (%)

Stiffness at �20 PHI

1 0 – –3 +63 �6.816 +101 �21

2 0 – –3 +81 �37.56 +112 0

3 0 – –3 +75 �6.126 +114 �22.5

Table 3Percentage change in low temperature cracking [62].

Sasobit� content (%) Increase (%)

1 5.312 8.53 12.76

(a)

(b)

0102030405060708090

100110120130140150

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180

Tem

pera

ture

(ºC

)

Time (Minute)

0 102030405060708090

100110120130140150

0 50 100 150 200 250 300 350 400 450 500 550 600 650 700 750 800 850 900 950T

empe

ratu

re (

ºC)

Time (Minute)

(A)

Fig. 3. Different methods of asphalt binder heating.


characteristics without changing the chemical composition of thematerial [56]. The physical hardening of asphalt can be due tomolecular self-assembly and molecular agglomerations of crystal-line phases at intermediate and low temperatures, respectively[57,58]. Another possible cause is spinodal decomposition, a pro-cess by which a homogeneous liquid separates into two liquidphases as the material is cooled [59].

Sasobit� increases binder stiffness, indicating less resistance tolow-temperature cracking for a given binder source [42,44,60,61].The degree of increase in binder stiffness and decrease in physicalhardening index (PHI) depend on the Sasobit� content and the bin-der source as presented in Tables 2 and 3. You et al. [62] suggestedthat guidelines should be provided to select the maximum Sasobit�

content in order to minimize the potential for low-temperaturecracking in the asphalt mix. Hamzah et al. [55] also developedsome design charts for this purpose based on Superpave™ fatiguefactor in the intermediate temperature range.

Liu and Peng [61] evaluated the effects of Sasobit� contents onthe cracking temperatures of unaged and long-term aged PG 58-28asphalt binders using an asphalt binder cracking device. The re-sults indicated that in general, the cracking temperatures of bothunaged and long-term aged binders increased slightly as the Sas-obit� content increased. In other words, binders containing higherSasobit� contents were more susceptible to cracking at lower tem-peratures. However, within the range of Sasobit� contents investi-gated (0–3%), the increment of cracking temperatures for bothunaged and long-term aged binders was not significant(�38.98 �C to �35.67 �C for unaged binders and �33.23 �C to�31.70 �C for long-term aged binders). The effects of asphalt bin-der type and source were not investigated.

5.5. Effects of aging on Sasobit�-modified asphalt binder

Aging and moisture damage are the main factors influencing thedurability of asphalt pavements [63]. Aging affects binder rheolog-ical properties throughout the life of the asphalt pavement. This ef-fect is primarily due to two mechanisms. The first is the loss ofvolatile components and oxidation of the asphalt binder duringmixing at the plant, asphalt mix transportation, and paving, whichis called short-term aging [50]. The second is the progressive oxi-dation of the material in the field, namely long-term aging[50,64]. Resins, which have small molecular sizes (SMS), turns into

asphaltenes, which have large molecular size (LMS), consequentlyincreasing the viscosity and the elastic solid properties of the as-phalt binder during aging [65,66]. In other words, the proportionof LMS increases while the proportion of SMS decreases with aging.Asphalt mix properties are more strongly related to the proportionof LMS than to the proportions of SMS and medium molecular size(MMS) [67–71]. Other factors that may lead to aging includemolecular structuring over time (steric hardening) and actinic light(primarily ultraviolet radiation, particularly in arid conditions)[72]. Aging depends on the asphalt binder content and properties,the type of aggregate and its particle size distribution, the mixtype, the void content in the mix, time, and the ambient tempera-ture [73]. Additives may affect the rate and degree of short andlong-term aging. Gandhi and Amirkhanian [47] conducted a labo-ratory study to evaluate aging in Sasobit�-modified asphalt bind-ers. They found that for each binder source considered, asphaltbinder extracted from short-term-aged and long-term-aged Sas-obit�-modified Warm-Mix Asphalt samples show less aging interms of normalized viscosity, G�/sin d, G�Sin d, and binder stiffness,compared to binder extracted from HMA samples. The reducedaging in the Sasobit�-modified asphalt binder is due to reducedvolatilization and oxidation because of lower construction temper-atures [46]. Meanwhile, Sasobit�-modified asphalt binder exhib-ited lower rate of gain in amount of G� over time as compared tobinder samples without Sasobit�, indicating lesser susceptibilityto aging of asphalt binders blended with Sasobit� [74].

5.6. Effect of Sasobit� on thermal characteristics of asphalt binder

The thermal characteristics of Sasobit�-modified asphalt bind-ers have been investigated by some researchers. The crystallizationtemperature of Sasobit� is 102.5 �C [28], while the crystallizationtemperature of Sasobit�-modified asphalt binder decreases withdecreasing Sasobit� content. For example, the crystallization


temperatures of modified asphalt binder containing 20% and 1%Sasobit� were 95.9 �C and 73.8 �C, respectively.

Sasobit� increases the crystal starting and wax melt out tem-peratures, but has no effect on the glass transition temperature,according to laboratory research conducted by Edwards et al.[42]. In another study, Gnadhi [75] carried out a thermal analysison Sasobit�-modified asphalt binders. The results showed two dif-ferent trends with temperature. At low temperatures, adding Sas-obit� increased the glass transition temperature of the modifiedasphalt binders compared to that of the control binder.

At higher temperatures (higher than 80 �C), Sasobit� decreasedheat flow for the warm binder samples, meaning that the waxmelted at those temperatures. From Eq. (2), a significant reductionin G� is also expected beyond 100 �C because this temperature isapproximately the melting point of Sasobit�.

Different methods of heating the asphalt binder samples cangive different results for the crystallization temperature. Fig. 3aand b illustrate the first and second methods of heating the Sas-obit�-modified binder samples using differential scanning calorim-etry (DSC) [28].

Line segment (A) in Fig. 3b shows 720 min (12 h) of annealing at40 �C. Measurements showed that the enthalpy for modified bin-der containing 1% Sasobit� heated by the second method, whichis illustrated in Fig. 3b, was 3.86 times greater than the enthalpyfor modified binder with the same Sasobit� content heated bythe first method, as shown in Fig. 3a. In addition, the melting tem-perature obtained using the second method was 110.74 �C, whilethat obtained using the first method was 103.3 �C. The explanationfor this is that Sasobit� molecules have enough time to rearrangethemselves in the structure of the Sasobit�-modified asphalt bin-der during annealing. Therefore, co-crystallization happens andmore crystals are formed in the Sasobit�-modified binder struc-ture. As a result, the area under the heat flow-time curve and themelting point are both increased due to annealing.

5.7. Interaction of Sasobit� with other binder additives

5.7.1. Crumb rubberCrumb rubber has been used as an asphalt binder modifier since

the mid-1960s [76]. In 2006, China was the country ranked first inthe world in the production of new tires, generating 280 millionunits [77]. These new tires will eventually be discarded and posea potential threat to the environment and human health. One ofthe solutions to offsetting the detrimental effects of scrapped tireson the environment is to use them in pavement construction worksas crumb rubber modifier in asphalt binder or mix. Although rub-berized asphalt mixtures have several benefits, such as reducedtraffic noise, reduced maintenance and rehabilitation costs, re-duced asphalt binder temperature susceptibility, and possibly in-creased structural capacity of asphalt mixes in terms of bothrutting and cracking [78–80]. However, the use of crumb rubberin pavement construction is accompanied by two main challenges.The first and more important of the two challenges is the high con-struction temperatures of rubberized asphalt mixtures becausesuspended swollen crumb rubber forms a viscous gel that in-creases the viscosity of the hot binder [81–85]. This can lead to in-creased fuel requirements and GHG emissions.

The second challenge pertains to the fact that crumb rubberparticles are not miscible in hot asphalt binder but rather are sus-pended in the hot binder. Therefore, crumb rubber particles canseparate out as sediment in asphalt binder storage tanks.

The use of Sasobit� is a viable alternative for achieving goodmix workability at lower temperatures. Akisetty et al. [78] showedthat Sasobit� decreases the viscosity of rubberized asphalt binderat high temperatures. They also found that the binder source hasa significant effect on the degree of reduction in viscosity and

increase high failure temperatures of Sasobit�-modified rubber-ized asphalt binders. For instance, the average construction tem-peratures of rubberized asphalt mixes from 173 �C and 155 �C(for mixing and compaction temperature, respectively) could bedecreased to 150 �C and 140 �C, respectively, using Sasobit� [86].This can lead to reduced fuel requirements and GHG emissions inasphalt mixing plants producing Sasobit�-modified rubberizedwarm-asphalt mixes.

Sasobit� also reduces permanent deformation potential, pene-tration, and the ductility of Sasobit�-modified rubberized asphaltbinders, while increases the softening point, fatigue resistance (interms of G�sin d), and stiffness of the modified binders. The degreeto which each of these items are changed depends on the amountof crumb rubber, the rubber mesh, the Sasobit� content, and theasphalt binder source [87–90]. For example, the use of crumb rub-ber decreased G�sin d at 25 �C and asphalt stiffness at �12 �C by al-most 42% as compared to control samples (without Sasobit�),while G�sin d and asphalt stiffness at �12 �C decreased by almost30% when Sasobit� was used in a rubberized asphalt binder [86].The 12% (42–30%) difference in reduction of the of Superpave™ fa-tigue factor and binder stiffness may be considered an effect ofcrystal lattice formed in the binder structure because of Sasobit�.

Sasobit� increased the storage stability of rubberized asphaltbinder, but it does not stop crumb rubber sedimentation at hightemperatures [91].

5.7.2. Aged binderWhen aged binder from reclaimed asphalt pavement (RAP) is

combined with fresh (unaged) asphalt binder in an asphalt mix,the aged binder affects the resultant binder blend. Constructiontemperatures of asphalt mixes containing RAP materials are higherthan those of conventional asphalt mixtures. On the one hand, Sas-obit� reduces the viscosity of asphalt binder blended with agedbinder, and the interaction between Sasobit� and aged binder in-creases high failure temperatures, indicating less likelihood of rut-ting, irrespective of the asphalt binder source and aging state [92].On the other hand, synergistic effects of aged binder and Sasobit�

may increase the binder stiffness and asphalt binder performancegrade (PG) [93], making the mix more susceptible to fatigue andlow-temperature cracking. To offset increased binder stiffnessdue to interaction between an aged binder and Sasobit�, the useof a lower-PG (less viscous) virgin asphalt binder is recommended[92,94,95]. For instance, laboratory results obtained by Lee et al.[92] showed that the use of a lower-PG-grade base asphalt binderfor an asphalt binder blend containing aged binder and Sasobit�

decreased G�sin d at 25 �C by almost 42% and decreased the binderstiffness at �12 �C by almost 35%, for the same binder source.

Kim et al. [94] also found that lower-PG asphalt binder contain-ing aged binder and Sasobit� exhibited shear thinning flow at60 �C, a pseudoplastic phenomenon that can also be observed inpolymers. This implies that the combination of Sasobit� and agedbinder could be polymerized.

5.7.3. PolymerPolymer is one of the materials that most commonly used to

modify the engineering properties of asphalt binders. Although as-phalt mixes containing polymer-modified asphalt binders im-proved resistance to rutting and thermal cracking, as well asreduced fatigue and stripping [96], these mixes also have higherconstruction temperatures. Sasobit� has been shown to have thepotential to decrease polymer-modified binder viscosity for a givenbinder source [95,97–102] thereby decreasing the constructiontemperatures of asphalt mixes, and hence the cost of polymer-modified asphalt pavement construction. Polymer-modifiedasphalt binders containing Sasobit� have a higher G� and


consequently higher G�sin d and stiffness than control samples(polymer-modified binders without Sasobit�) [94,95,97,102].

Because traditional polymers are not miscible in the binder,homogenous dispersion of polymer materials and storage stabilityare problems that regularly affect the quality of polymer-modifiedasphalt binders. Not only was no separation observed in the bind-ers containing Sasobit� in the work reported by Susana et al. [98],but Sasobit� also improved the storage stability of modified as-phalt binders [103]. For example, Edwards et al. [103] reportedthat the difference between the softening point of top and bottomof Sasobit�-polymer-modified asphalt binder samples were 6.8%and 4.70% for 3% and 6% Sasobit�, respectively, while the differencebetween the softening point of top and bottom of polymer-modified asphalt binder without Sasobit� was 28%.

As Sasobit� is blended with a compatible polymer, the blendcan become a phase change material (PCM) because Sasobit� hasa high heat of fusion [28]. Therefore, Sasobit�, as a PCM, can storeor liberate energy from its polymeric surroundings over crystalliza-tion or melting processes. Krupa et al. [104] showed that in ablend of Sasobit� and low-density polyethylene (LDPE), Sasobit�

co-crystallizes with the polymer upon cooling. They also observedthat a blend of Sasobit� and LDPE reinforces the LDPE matrix in thesolid phase at up to 50% wax loading and was decreased the effectsof thermal and dynamic stresses.

6. Performance of WMA mixtures using Sasobit�

6.1. Laboratory performance

This section addresses the effects of Sasobit� on the perfor-mance of asphalt mixtures. As mentioned in Section 5, numerousexperiments have been conducted to study the rheological proper-ties of Sasobit�-modified asphalt binder. Although the results indi-cated that adding Sasobit� decreases asphalt binder viscosity andincreases stiffness, as represented by the Superpave™ rutting fac-tor (G�/sin d) and fatigue factor (G�sin d), respectively, the effectsof Sasobit� on the properties of warm asphalt mix needs to beinvestigated in the laboratory prior to field construction. The ef-fects of Sasobit� on construction temperatures, mix design and vol-umetric properties, as well as engineering properties, i.e., rutting,fatigue and moisture sensitivity of warm asphalt mixes, are re-viewed. In addition, the performance Sasobit�-WMA mixturesincorporating waste materials such as reclaimed asphalt pavement(RAP), crumb rubber, recycled asphalt shingles (RASs) and recycledcoal ash (RCA) are studied.

6.1.1. Effects of Sasobit� on construction temperaturesViscosity is one of the asphalt binder rheological properties

typically used to determine appropriate construction temperaturesfor asphalt mixes. For example, the Asphalt Institute recommendsthat the mixing and compaction temperatures of net asphaltbinder correspond to viscosity ranges of 170 ± 20 mPa s and280 ± 30 mPa s, respectively [105].

West et al. [106] recommends determining construction tem-peratures as a function of the viscoelastic properties of asphalt bin-der using Eqs. (4) and (5):

Mixing temperature ¼ 325 x�0:0135 ð4Þ

Compaction temperature ¼ 300 x�0:012 ð5Þ

where the temperatures are in Fahrenheit (�F) and x if the fre-quency in rad/s for a phase angle of 86�, because a phase angle be-tween 85� and 90� corresponds to the transition from purelyviscous to viscoelastic behaviour.

When construction temperature is determined using viscosity,no notable differences can be observed in the construction temper-ature indicated for Sasobit�-WMA mixtures and HMA, even whenthe maximum Sasobit� content (4%) is used [27,38,45,53]. Whenconstruction temperature is determined using asphalt mix volu-metric properties such as asphalt binder film thickness are used,the construction temperature indicated for Sasobit�-WMA mixtureis 21 �C less than that for HMA [14]. This indicates that using binderviscosity range to select construction temperatures may producemisleading results. On the other hand, the method presented byWest et al. [106] for measuring film thickness using a dynamic shearrheometer (DSR) cannot really simulate the film thickness of asphaltbinder, which coats aggregate particles in asphalt mixes in the fieldor in the laboratory [107]. Therefore, Bonaquist [108] recommendedthat trial WMA mixes at the selected construction temperaturesshould be employed to study coating of aggregate particles by as-phalt binder, workability, and compactability. For example, in a lab-oratory study conducted by Zhao and Guo [26], Sasobit�-WMAsamples mixed at 145 �C had the same workability as HMA mixedat 175 �C. Lubricity tests can also be employed to evaluate the work-ability of asphalt binders containing Sasobit� [107].

Appropriate construction temperatures can also be determinedusing the compaction energy index (CEI) and the traffic densifica-tion index (TDI) [109]. CEI is a measure of the energy required tocompact an asphalt mix to the design density in the constructionprocess, while TDI is a measure of the energy required to compacta mix to the compaction level imposed by traffic. A lower CEI andhigher TDI are more favourable because a lower CEI means thatless energy is required to reach the target density and a higherTDI indicates more resistance to compaction under traffic loadingduring the service life of the mix. Consequently, it is essential toestablish a balance between CEI and TDI to determine an appropri-ate construction temperature. Experimental results have shownthat Sasobit� decreases CEI but increases TDI [99,100]. Based onCEI and TDI, Sanchez-Alonso et al. [109], selected 160 �C as anoptimized construction temperature for control HMA and 140 �Cfor Sasobit�-WMA mixtures.

6.1.2. Effects of Sasobit� on mix design and volumetric propertiesThe HMA mix design process usually includes selection of the

aggregate gradation, materials (asphalt binder, aggregate particles,filler, and any additives), and asphalt binder content; evaluation ofmoisture sensitivity; and analysis of asphalt mix performance.Bonaquist [108] indicated that minimal changes in current HMAmix design are required for WMA. The literature reviewed coveredtraditional mix design methods, including Superpave™, Hveem,and Marshall. Mix design for Sasobit�-WMA mixtures apply thesame mix design criteria but at lower temperatures than the onesused for HMA. Vatikus et al. [110] and Kilas et al. [111] showedthat at a given temperature, increasing Sasobit� content increasesMarshall stability and mix density because the crystal latticeformed in the binder structure by the addition of Sasobit� madethe asphalt mix stiffer. Hamzah et al. [112] showed that althoughfor a given mixing temperature the maximum Marshall stabilityoccurs at a lower binder content as the Sasobit� content increases,the corresponding increase in Marshall strength is negligible. How-ever, Marshall stability is not an appropriate parameter for distin-guishing changes in asphalt binder rheological characteristics[113]. Moreover, optimum asphalt content (OAC) was found tobe similar for HMA and Sasobit�-WMA mixtures irrespective ofthe mix design method employed [14,107,114,115]. In otherwords, laboratory data from research studies show no significantdifference between the volumetric properties of Sasobit�-WMAmixtures mixes and HMA [14,26,108,114,116–120].

Achieving final density can be quicker for Sasobit�-WMA mix-tures than for HMA even at lower curing temperatures [32].


Laboratory results showed that the Sasobit�-WMA mixturesreached final density after 100 gyrations at 135 �C, while HMAreached final density after 170 gyrations at 155 �C.

The same traditional mix design methods and criteria have beenemployed to design Sasobit�-WMA mixtures containing RAP andcrumb rubber. Volumetric analysis of rubberized asphalt mixes atdifferent compaction temperatures showedthat Sasobit� decreasesvoids in the mineral aggregate (VMA) and increases voids filledwith asphalt (VFA) in the rubberized Sasobit�-WMA mixtures,compared with rubberized HMA, irrespective of aggregate source[121,122].

6.1.3. Effects of Sasobit� on rutting properties of asphalt mixesWheel path rutting is the most common form of permanent

deformation in asphalt pavements [105]. Various factors contrib-ute to rutting. In WMA, construction temperatures, aggregate andadditive types, and asphalt binder grade, as well as interactionsamong these factors, can affect the rut depth [14]. For instance,HMA and Sasobit�-WMA mixtures containing granite coarseaggregate exhibited less rutting than mixes containing granite fineaggregate. In contrast, HMA and Sasobit�-WMA mixtures contain-ing slag coarse aggregate exhibited more rutting than mixes con-taining slag fine aggregate [123].

Sasobit�-WMA mixtures exhibited smaller strains than HMAmixes in dynamic creep tests [37,124]. The data also indicated thatSasobit�-WMA mixtures had a higher dynamic modulus than an-other commercial wax and that this may be due to the presenceof larger wax crystals in asphalt binder containing Sasobit� thanin other modified-asphalt binders [125].

The use of wet aggregate is one way to reduce energy consump-tion in the asphalt mix production process. Xiao et al. [126] showedthat Sasobit�-WMA mixtures containing 0.5% moisture with 1% or2% hydrated lime proposed exhibited less rutting under dry condi-tions. Furthermore, the Sasobit�-WMA mixtures were within rutdepth limits after 10,000 loading cycles in the Homburg wheeltracking test (HWTT) [102,127–132]. Testing conducted using theAsphalt Pavement Analyzer (APA) have shown that the rutting per-formance of HMA and Sasobit�-WMA mixtures mix containing 1.5%Sasobit� are similar after 8000 loading cycles [118,119,127,130].Solaimanian et al. [133] also conducted a laboratory study on therutting of Sasobit�-WMA mixtures using shear Superpave™ tester(SST) and model mobile load simulator third scale (MMLS3). TheSasobit�-WMA mixtures showed the lowest shear strain after5000 loading cycles, indicating excellent resistance to rutting ascompared to the HMA and the other WMA mixtures.

All other things being equal, asphalt binder increases in perfor-mance grade (PG) with increasing Sasobit� content. Rutting in Sas-obit�-WMA mixtures is correspondingly reduced [44,45].

The rutting potential of asphalt mixtures can also be evaluatedusing the dynamic modulus test, in which a higher complex mod-ulus (E�) typically corresponds to a more rut-resistant mix [134].The dynamic modulus |E�|, which is the absolute value of E�, is de-fined as the ratio of maximum dynamic stress to maximum recov-erable axial strain at a given temperature and frequency.

Although Mohammad et al. [114] found no significant differ-ence in |E�| between Sasobit�-WMA mixtures and HMA, Petitet al. [135], Haggag et al. [136], Yanhai et al. [137], Sampath [12]and Goh and You [118] showed that Sasobit�-WMA mixtures havea higher |E�|. It can be concluded that the rutting resistance of Sas-obit�-WMA mixtures, as indicated by dynamic modulus, is greaterthan or equal to that of HMA in the terms of dynamic modulus[44,127–130,138].

6.1.4. Effects of Sasobit� on fatigue properties of asphalt mixesAlthough inadequate structural design, repeated heavy loads,

poor drainage, and poor construction can all contribute to fatigue

in asphalt pavements, asphalt binder stiffening due to aging atlow and intermediate temperatures can also cause fatiguecracking.

Not only does Sasobit�-WMA mixtures perform as well as HMAin terms of fatigue resistance [119,136], but also the lower con-struction temperatures made possible by the use of Sasobit� canfurther improve resistance to fatigue [38,137].

Selection of appropriate construction temperatures for Sas-obit�-WMA mixtures can result in fatigue performance better thanor equal to that of HMA. For instance, Goh and You [139] foundthat Sasobit�-WMA mixtures compacted at 100 �C and at 115 �Cwere equal to HMA and superior to HMA, respectively, in termsof fatigue life. Conversely, Sasobit�-WMA mixtures compacted at130 �C exhibited a shorter fatigue life. Because the tensile strengthof an asphalt mixture is related to its fatigue resistance [140], mix-tures with higher tensile strength are expected to exhibit less fati-gue cracking. Sasobit�-WMA mixtures have lower tensile strengthsthan HMA [114,118,137], indicating less resistance to fatigue.

Benert et al. [141] also showed WMA mixtures containing 1% Sas-obit� and produced at 110 �C, had superior performance in terms ofoverlay tester fatigue life compared to asphalt mixtures containingno Sasobit� and produced at 110 �C, 130 �C, and 160 �C. Petit et al.[135] studied the shear fatigue behaviour of Sasobit�-WMA andHMA mixtures. It was found that both mixtures exhibit linear rela-tionships between dissipated energy and fatigue life (defined as50% reduction in modulus) with R2 correlation values greater than95%. However, the WMA mixture exhibited better resistance to fati-gue at lower levels of dissipated energy. For high dissipated energylevels, WMA and HMA fatigue laws were very similar. It was con-cluded that adding Sasobit� to produce WMA and the correspondinglower compaction temperatures did not undermine the shear fati-gue response of a traditional hot asphalt mixture.

6.1.5. Effects of Sasobit� on low temperature performance of asphaltmixes

Liu and Peng [61], Medeiros et al. [142] and Edwards et al.[37,124] studied the effects of Sasobit� on asphalt mixtures atlow temperature. They found that low temperature cracking aswell as the fracture temperatures were slightly decreased by add-ing Sasobit� [61,124,142]. Furthermore, Edwards et al. [37]showed that in the general trend, the stiffening effect of Sas-obit�-associated aging reduces the fracture temperatures inWMA mixture. However, the overall results implied that Sasobit�

have a marginal effect on low temperature performance of asphaltmixtures [61,124].

6.1.6. Effects of Sasobit� on moisture sensitivity of asphalt mixesThe strength of an asphalt pavement structure depends on the

following factors: (i) the cohesive bond between the aggregateand the asphalt binder, (ii) the cohesive resistance of the binder,and (iii) the frictional resistance and development of interlock be-tween aggregate particles [143]. Everything affecting these threefactors can influence the strength and integrity of an asphalt pave-ment structure. One of the most important influences is moisture.WMA is prone to moisture damage because lower constructiontemperatures can lead to incomplete drying of entrapped waterin the aggregate. The phenomenon of moisture damage, consistingof a set of physical, chemical and mechanical processes, involvestwo mechanisms, moisture transport and system response[144,145]. The moisture transport mechanism involves moisturein liquid form such as runoff or in the gas form of vapour penetrat-ing into the asphalt’s pavement structure and coming into contactwith the asphalt binder and the binder-aggregate interface. Thesystem response mechanism involves the internal texture of theasphalt pavement being influenced via adhesive failure betweenasphalt and aggregate particles (a phenomenon called ‘‘stripping’’),


cohesive failure within the asphalt binder, cohesive failure withinthe aggregate, spontaneous emulsification, and freezing. By thesemechanisms, moisture influences the durability of asphalt pave-ment structures and can cause premature failures [146]. Becausedifferent asphalt binders and mixture modifiers can perform differ-ently in response to water exposure [147], the role of Sasobit� inthe development of moisture damage in asphalt mixes needs tobe understood. Asphalt binder and Sasobit� are hydrophobic mate-rials and combinations of the two can be even more hydrophobic.Buddhala et al. [148], Wasiuddin et al. [149], and Wei et al. [150]investigated the effects of different levels of Sasobit� content onwettability and adhesion between asphalt binder and aggregateusing surface free energy (SFE) method. Buddhala et al. [148] andWasiuddin et al. [149] found that the wettability of asphalt bindersover aggregate and adhesion in dry condition increases as the Sas-obit� content increases. In addition, the changes in values of SFEand contact angle are functions of binder type, aggregate type, Sas-obit� content, and the presence of aged binder [148–152].Although the wettability and adhesion of asphalt binder is in-creased by the addition of Sasobit� in dry condition, adhesion be-tween aggregate and asphalt binder is reduced in wet conditiondue to an increase in the acidity of the asphalt binder [153,54].For example, 3% Sasobit� showed that decrease in adhesion byan average of 13.2%. This reduced adhesion initiates strippingand moisture-related failure.

Moreover, different measurement methods yielded different re-sults concerning the effect of Sasobit� on the cohesive strength ofasphalt binder. For instance, Sasobit� decreased the dry cohesionstrength of asphalt binder in pull-off tests, while it increased thedry cohesion strength measured using the SFE method, irrespectiveof binder type [24].

Aggregate size is also an important factor in moisture damage inSasobit�-WMA mixtures. For instance, Kanitpong et al. [123] foundthat although granite fine-graded mixture exhibited less perma-nent deformation than coarse-graded mixtures for both HMA andSasobit�-WMA mixtures, the fine-graded mixtures are more resis-tant to moisture damage because they have fewer interconnectedvoids in the mix structure. Kanitpong et al. [123] also found thatslag fine-graded mixtures show lower resistance to permanentdeformation due to their higher porosity and lower abrasion resis-tance but can also be less susceptible to moisture damage due tothe presence of calcium oxide (CaO) or lime. In practice, CaO pres-ent in the chemical structure of the slag aggregate particles acts asan anti-stripping agent. In this regards, asphalt mixtures preparedusing aggregates with higher amount of CaO and lower SiO2 con-tent should exhibit more resistance to moisture damage [154].

Moisture damage can be more severe in porous asphalt than indense-graded asphalt mixes due to largely interconnected air voidsin the mix that form channels throughout the mix structure. A lab-oratory study to evaluate the potential for moisture damage in Sas-obit�-WMA porous mixtures was carried out by Hamzah et al.[155]. A specially designed asphalt dynamic stripping machinewas fabricated to simulate a rainfall event and hasten strippingof the mix samples in the laboratory. Sodium carbonate was dis-solved in water to accelerating stripping. The results indicated thatSasobit� slightly increased indirect tensile strength (ITS) values forthe samples in wet and dry conditions, but had no effect on theresistance to stripping of porous mixes, which is consistent withresults reported by Liu et al. [44] but for dense mixtures. Liuet al. [44] also found that tensile stress ratio (TSR) values for Sas-obit�-WMA mixtures increases as Sasobit� content increases.

The use of anti-stripping agents to minimize moisture damagein asphalt mixes is widespread. In the United States, 56% of asphaltmixes are treated with liquids, 15% with liquid and lime, and 29%with lime only [146]. Liquid anti-stripping agents are the easiestto use [156]. However, Sasobit�-WMA mixtures containing

hydrated lime as the anti-stripping agent exhibited better moistureresistance, in terms of TSR and stripping inflation point, than mixescontaining a liquid anti-stripping agent [157,158]. Meanwhile,Xiao et al. [159] found that the Sasobit�-WMA mixtures containingaggregate with 0.5% moisture with 1% or 2% lime exhibited highermoisture resistance, as indicated by TSR values, than mixes con-taining dry aggregate, for each aggregate source studied. However,synergistic effects of decreased mixing temperature and initialmoisture of aggregate can increase moisture damage potentialsin terms of TSR and HWTT [141].

Aging is another factor that affects moisture sensitivity. Moga-wer et al. [157] studied the effect of aging time on the moisturesensitivity of Sasobit�-WMA mixtures as measured by the strip-ping inflation point. The results showed that the stripping inflec-tion points in the Sasobit�-WMA mixtures with and withoutanti-stripping agents increases as aging time increases. Xiao et al.[160] also showed that hydrated lime employed as an anti-stripping agent improves the moisture resistance after aging ofSasobit�-WMA mixture samples containing RAS and RCA. In thatstudy, TSR values greater than 90% and even 100% were observed.

Because the most damaging effects of moisture on asphaltmixes occur in the first 4 months [156], Xiao et al. [161] conductedlaboratory studies to evaluate the long-term effects (at 1 day,60 days and 90 days) of anti-stripping additives on Sasobit�-WMA mixtures in terms of TSR. The general trend observed wasa reduction in TSR values after 60 days for all Sasobit�-WMA mix-tures, including samples with and without anti-stripping agentsand for each aggregate source. TSR values increased slightly after90 days but never returned to the peak levels observed after1 day of conditioning. The results also revealed that aggregatesource and type of anti-stripping agent seem to influence thelong-term moisture sensitivity of Sasobit�-WMA mixtures.

Sasobit�-WMA mixtures constructed using damp or dry aggre-gates from different sources and incorporating hydrated limeexhibited better performance than HMA without hydrated limein terms of TSR [159]. Hearon and Diefenderfer [119] found hy-drated lime increased TSR values of unaged Sasobit�-WMA mix-tures even at low production temperatures.

Although the effectiveness of hydrated lime is a function of thehydrated lime content and the method of use [162], the size of thehydrated lime particles is important as well [163]. Cheng et al.[164] evaluated the effects of hydrated lime’s size on the moisturesusceptibility of Sasobit�-WMA mixtures. They used hydrated limein two sizes, 1.3 lm (normal size) and 660 nm (nanosize), which isapproximately 50% of the normal size. Most of the Sasobit�-WMAmixtures containing nano-size hydrated lime exhibited higher ITS,toughness and flow number in dry and wet conditions than themixes containing normal-size hydrated lime. The degree of in-crease of each mix property depended on the aggregate type usedin the asphalt mix samples.

Shivaprasad et al. [165] studied moisture susceptibility of poly-merized stone matrix asphalt mixtures containing Sasobit� (SMA–Sasobit�-WMA mixtures) in terms of TSR. The mixtures were con-structed with aggregate extracted from different sources and vari-ous asphalt binder types (PG 64-22 modified by 10%, 15%, 20%, andPG 76-22 modified cellulose fiber). Aggregate moisture and hy-drated lime contents, as anti-stripping agent, were 0.5% and 2%by weight of dry aggregate, respectively. The results indicated thatTSR values of SMA-Sasobit�-WMA mixtures constructed using dryand wet aggregates and asphalt binder modified by 15% crumbrubber and cellulose fiber meet TSR requirement (higher than85%) for each aggregate source.

6.1.7. Effects of Sasobit� on resilient modulus of WMAResilient modulus (Mr) is an important characteristic in struc-

tural design and the response of asphalt pavements under loading.

Table 4Changes in properties of asphalt mixes according to data provided by Akisetty et al. [166].

Aggregate sources Mix type Increase in ITS (%) Increase in rut depth (%) Increase in resilient modulus (%)Test temperature

5 �C 25 �C 40 �C

Source 1 Control sample – –Sasobit�-WMA mixtures �26.26 0 +38 �11.82 �13.97rubberized-Sasobit�-WMA mixtures �28.53 �63.15 +56.61 +31.18 +193.10

Source 2 Control sampleSasobit�-WMA mixtures �15.50 �45 �28.39 �14.93 �13.20rubberized-Sasobit�-WMA mixtures 1.44 �68 �17.00 �5.20 +32.08

Note: Decrease (�) and increase (+) as compared to control sample.


Higher asphalt mix Mr can enhance the pavement structure’s load-bearing capacity. Although Sasobit�-WMA mixtures exhibit higherrutting resistance at a given temperature, no significant effect onMr has been reported [14], indicating that Sasobit� does nothave a significant effect on the load-bearing capacity of warm as-phalt mixes. Moreover, the resilient modulus may be reduced asthe construction temperature is reduced. In other words, it is notadvisable to decrease the asphalt concrete layer thickness whenSasobit� is used in a warm asphalt mix. In the case of aged Sas-obit�-WMA mixtures, Gandhi [75] demonstrated that Mr increasedby 5 �C for each aggregate and binder source studied, which meansthat Sasobit� may increase the potential for low-temperaturecracking while improving rutting resistance at high temperatures.

6.1.8. Sasobit�-WMA mixtures Containing Crumb RubberCrumb rubber increases binder stiffness, thereby making as-

phalt binder more elastic. Sasobit� increases binder stiffness bythe formation of crystalline lattice in the binder, so one might ex-pect that a rubberized warm asphalt mix containing Sasobit�-modified asphalt binder would be more brittle than one containingnon-modified binder. Nonetheless, the interaction between Sas-obit� and crumb rubber may offset the stiffening effects of Sas-obit�. Xiao et al. [86] studied the fatigue characteristics ofrubberized-Sasobit�-WMA mixtures containing aggregates fromdifferent sources. The results showed that the interaction betweencrumb rubber and Sasobit� extended the fatigue life of rubberized-Sasobit�-WMA mixtures compared to that of samples withoutcrumb rubber and Sasobit� (control), for all aggregate sourcesstudied. The control, rubberized and, rubberized-Sasobit�-WMAmixtures followed exponential trends in loading cycles with re-spect to dissipated energy and stiffness. These results imply thatcrumb rubber and the interaction between crumb rubber and Sas-obit� had no effect on the observed trends.

The aggregate source can affect the performance of rubberized-Sasobit� -WMA mixtures. For example, Table 4 indicates the effectsof aggregate source, crumb rubber and test temperature in terms ofITS, rut depth and resilient modulus. For instance, the resilientmodulus of the rubberized-Sasobit�-WMA mixtures containingaggregate from source 2 is 17% lower than for the control conditionat 5 �C, while the resilient modulus of rubberized-Sasobit�-WMAmixtures containing aggregate from source 1 is 56.61% higher atthe same test temperature.

Taking crumb rubber as an example, the resilient modulus ofthe Sasobit� -WMA mixtures containing aggregate from source 1was 13.97% lower than that of the control mix at 40 �C, while theresilient modulus of Sasobit�-WMA mixtures with crumb rubber,using the same aggregate source and test temperature, was 1.93times greater than that of the control sample.

With respect to the effect of test temperature, the resilientmodulus of the rubberized-Sasobit� -WMA mixtures containingaggregate from source 2 was 5.2% lower than that of the control

sample at 25 �C. However, the resilient modulus of the same mixwas 32.08% higher than that of the control sample by at 40 �C.

Lower ITS values in warm mixes than in hot mixes can be attrib-uted to lower asphalt binder stiffness due to lower constructiontemperatures. The aggregate source has significant effects on thefatigue characteristics of rubberized-Sasobit�-WMA mixtures interms of fatigue life, stiffness, and cumulative dissipated energy[86,167]. Cumulative dissipated energy and stiffness in rubber-ized-Sasobit�-WMA mixtures depend on the aggregate sourceand test temperature.

6.1.9. Sasobit�-WMA mixtures containing RAPRAP is another material widely used to produce asphalt mixes.

For example, almost 100 million tons of RAP are produced per an-num, with about 60 million tons reused in new asphalt pavementconstruction and the remaining 40 million tons employed in otherpavement-related applications, such as aggregate road base in theUnited States [168]. In Canada, the Ministry of Transportation ofOntario (MTO) used RAP materials to pave 3,500,000 m2 (approxi-mately 500 lane-km) over 17 years [168]. The use of RAP reducesdemand for virgin aggregate, a non-renewable material, and theuse of RAP materials in pavement base and sub-base layers couldpotentially reduce global warming (20%), energy consumption(16%), water consumption (11%), life-cycle costs (21%) and hazard-ous waste generation (11%) [169]. In addition, water leached froma stockpile of tar asphalt and oil gravel have high amounts of poly-aromatic hydrocarbons (PAHs) [170], which have toxic effects onhuman health [171–174]. Using RAP may also help to ease pressureon landfills [175,176]. Therefore, use of RAP materials is in har-mony with efforts to develop sustainable pavements. The primaryproblem associated with producing asphalt mixtures incorporatingRAP is the high construction temperature required due to the agedbinder in RAP materials. Sasobit� has shown potential for decreas-ing construction temperatures. The amount of heat energy re-quired and GHG emissions depend on the RAP source andcontent and the Sasobit� content [177,178]. It is obvious that theuse of higher percentages of RAP in asphalt mixtures producesgreater savings in paving projects.

The primary concern about the use of RAP in warm asphalt mixis whether RAP can be blended with new asphalt binder at lowerconstruction temperatures. An interfacial mixing investigationusing atomic force microscope imaging (AFM) was conducted toinvestigate this [108]. In this study, an artificially aged asphalt bin-der was used as RAP. The images showed a transition in the struc-ture of the artificially aged binder and the asphalt bindercontaining Sasobit�, meaning that two asphalt binders, includingthe RAP and the warm binders, can be blended together duringthermal conditioning at 130 �C. In another laboratory test, blendingof RAP asphalt binder with Sasobit� warm binder was investigatedusing mixing tests. Sasobit�-WMA mixture samples containingRAP were produced at different temperatures. The Sasobit�-WMAmixtures and HMA were subjected to short-term aging conditions


from 0.5 h to 2 h. The degree of blending of the RAP with the Sas-obit�-modified asphalt binder was quantified in terms of the ratio(M/R) of dynamic moduli obtained from tests on mixtures (M) todynamic moduli estimated from tests on recovered asphalt binderfrom the mixtures (R). If M/R approaches a value of 1, it indicates ahigh degree of blending of RAP with warm asphalt binder. The M/Rof the HMA and the Sasobit�-WMA mixtures scored around a valueof 1 after 2 h thermal conditioning.

Howard et al. [179] showed that Sasobit� significantly reducesair voids in base course mixtures containing 100% RAP.

Tao and Mallick [180] also evaluated the performance of asphaltmixtures containing 100% RAP with different Sasobit� contents(1.5%, 2% and 5%) mixed at 125 �C to be used in base courses. Theyfound that increasing Sasobit� content increases the bulk specificgravity of the mixtures, making them more workable and achiev-ing higher density as a result. The structural response of Sas-obit�-WMA mixtures incorporating RAP were evaluated usingseismic modulus testing [180,181]. The seismic modulus test is anondestructive test based on the generation and detection of stresswaves in the pavement structure [182]. Some researchers prefer touse seismic modulus testing because it permits measurement offundamental material parameters in the linear viscoelastic range,and it is not as time-consuming as the dynamic modulus test[183,184]. Tao and Mallick [180] showed that Sasobit� increasesthe seismic modulus of the mixtures incorporating 100% RAP ateach test temperature studied. No significant difference was shownbetween the seismic modulus of Sasobit�-WMA mixtures incorpo-rating 75% RAP produced at 125 �C using PG 52-28 showed andthose of asphalt mixtures produced at 150 �C and 135 �C [181].

Mallick et al. [185] showed that asphalt mixtures incorporating100% heated RAP, 2% asphalt emulsion, and Sasobit� produced at125 �C were more workable than the mixtures produced usingthe same RAP and emulsion contents and produced at 150 �C with-out Sasobit�.

Laboratory and field studies of asphalt mixtures incorporatingRAP and Sasobit� were conducted by West et al. [186]. The resultsindicated that the performance of Sasobit�-WMA mixtures incor-porating 45% RAP perform better in terms of rut depth and dy-namic modulus. In this study, the potential for top-downcracking of asphalt mixtures was evaluated using dissipated creepstrain energy (DSCE) results. An energy ratio value less than 1 indi-cates a high potential for top-down cracking in asphalt mixtures.The energy ratio of RAP Sasobit�-WMA mixtures was 2.08 timesgreater than the control mixtures containing no RAP neither Sas-obit�, indicating considerable lower potential for top-down crack-ing in the RAP–Sasobit�-WMA mixtures.

6.1.10. Sasobit�-WMA mixtures Containing RASAround 11 million tons of RAS are produced in the United States

per annum [187]. RAS used as a construction material in asphaltmixtures may contain 18% to 40% asphalt binder, depending onthe asphalt shingle source [188]. Al-Qadi et al. [189,190] investi-gated the engineering properties at different times of Sasobit�-WMA mixtures containing RAP and RAS (RAS–RAP-Sasobit� warmasphalt mixtures) subjected to short-term aging. The amount ofSasobit�, RAP, and RAS were 1.5%, 5%, and 5%, respectively. Thehighest dynamic modulus and the lowest rut depth were observedfor RAS–RAP–Sasobit�-WMA mixtures, compared to the control(containing 8% RAP, no RAS and no warm mix additives) and otherwarm mix samples at different curing times. Furthermore, RAS–RAP–Sasobit�-WMA mixtures showed the lowest fracture energyand rut dept at different curing times [189,190]. More detailsregarding engineering properties of RAS–RAP–Sasobit�-WMA mix-tures can be found in a technical document by Al-Qadi et al. [191].

Shivaprasad et al. [187] studied the performance of Sasobit�-WMA mixtures containing different amount of RAS constructed

using wet aggregate, in terms of compaction gyration number(CGN), TSR and rut depth. The CGN required to reach the targetair void content increased with increasing RAS content in most ofthe cases of Sasobit�-WMA mixtures, because RAS is an aged as-phalt binder material. All RAS–Sasobit�-WMA mixtures fulfilledthe requirements of the TSR limit (higher than 80%), indicating thatthe samples containing wet aggregate and RAS exhibited sufficientresistance in moisture conditioning. Moreover, the wet-conditioned RAS–Sasobit�-WMA mixtures samples often exhibitedless deformation, in terms of rut dept, and flow index, than the drysamples [160,187].

6.1.11. Sasobit�-WMA mixtures containing RCAShivaprasad et al. [187] studied the performance of Sasobit�-

WMA mixtures prepared using moist aggregate and RCA. Theyfound that the CGN required to achieve the target air void contentsignificantly increases as the RCA content increased in all RCA–Sas-obit�-warm asphalt mixture samples irrespective of the aggregatetype. This is because RCA is a dust material and Sasobit�-WMAmixtures containing more RCA requires more compaction effortthan Sasobit�-WMA mixtures containing less RCA. Although mostRCA–Sasobit�-WMA mixtures samples satisfied the TSR limit,aggregate source should be considered an important factor. Rutdepth decreased with increasing RCA content for each aggregatesource and conditioning case studied and the samples exhibitedsmaller rut depths in wet conditions.

Xiao et al. [160] and Shivaprasad et al. [187] showed that rutdepth and asphalt mix flow in RCA–Sasobit�-WMA mixtures arereduced in wet conditions, in similar fashion as for RAS–Sas-obit�-WMA mixtures.

RAS or RCA–Sasobit�-WMA mixtures can be used to constructlow-volume roads (LVR) according to the results of laboratory testsby Xiao et al. [160] and Shivaprasad et al. [187].

6.2. Field performance

Sasobit�-WMA mixtures are used in the construction of numer-ous paving projects with various applications, including runwaysand taxiways in airports, container yards, parking lots, driveways,race tracks, and roads in many countries (such as Australia, Austria,Belgium, China, Czech Republic, Denmark, France, Germany, Hun-gary, Italy, Lithuania, Macau, Malaysia, Netherlands, New Zealand,Norway, Russia, Slovenia, South Africa, Sweden, Switzerland, theUnited Kingdom, and the United States) [11,14,111]. Typically,the paving projects were a variety of dense-graded mixes, stonematrix asphalt (SMA) and gussasphalt [192].

Because the paving projects used Sasobit�-WMA mixtures forvarious utilities, a wide variety exists of transportation fleets withdifferent levels of traffic during the design life of the pavement. Forinstance, combinations of different vehicle types (such as lifttrucks, tractors, transtainers and straddle carriers) operate in portsand airports. Therefore, loading modes can be substantially differ-ent based on the pavement utility (e.g., the major loading modes inairport runways, airport taxiways and accessible industrial roads inports move dynamically, while those in apron and stacking con-tainer yards are usually static). Therefore, the structural responseof the Sasobit�-WMA pavements and related failures developedover the pavement’s service life depends on the number of loadingsand those loadings’ sizes and modes. Additionally, the type of fleetmaneuver influences pavement structural responses; for instance,the acceleration, de-acceleration, braking and turning maneuversof the fleet impose severe dynamic stresses on pavements in ports.The effects of the fleet’s maneuvers on Sasobit�-WMA pavements(particularly on those pavements subjected to post-heavy loads)should be investigated. Moreover, the required specifications forasphalt mixes, mix design, aggregate properties (e.g., aggregate


size and gradation), binder type and source, mix design, requiredspecifications for asphalt mixes, methods of pavement construc-tion, equipment and environmental conditions can be significantlydifferent in various countries. Therefore, the experiences gainedfrom field evaluations of different countries’ experiences can actas a database to evaluate the general performance of pavementconstructed using Sasobit�-WMA mixtures under different envi-ronmental conditions and the levels and modes of traffic loading.However, there is an insufficient amount of detailed, publisheddata regarding the performance of Sasobit�-WMA pavements inmany of the countries in which they were constructed. This sectiondiscusses the field performance of Sasobit�-WMA mixtures thathave been tried in different countries over the last decade.

6.2.1. EuropeIn 1997, Sasobit� was introduced in Europe as an asphalt mix

compaction aid [193]. A wide variety of infrastructures were pavedusing Sasobit�-WMA in Europe. In 2007, the National AsphaltPavement Association (NAPA) sponsored a scanning tour duringwhich United States materials experts evaluated various WMAtechnologies and paving projects in Belgium, France, Germany,and Norway [4]. The reports showed that in Germany, trials havebeen constructed using Sasobit�-WMA mixtures that incorporated90–100% recycled asphalt pavement (RAP). The evaluation of theuse of Sasobit�-WMA mixtures in Europe found generally accept-able results. For instance, there was no deformation in the Veddel-er Damm–Hamburg road that was paved using Sasobit�-WMAmixtures, while there was a rut depth of 4–8 mm in other sectionspaved using traditional HMA [194]. Table 5 shows samples of Sas-obit�-WMA pavements with various utilities that were con-structed in different European countries.

Some of the main reasons for using Sasobit�-WMA mixture inairports were the high compaction and void contents, improveddeformation resistance required, earlier time at which the road isopen to the traffic and limited required curing time [8]. For exam-ple, a 60-cm Sasobit�-WMA mixture was placed during a 7.5-hwindow to resurface one of the Frankfurt Airport’s runways. Therunway was opened to aircraft traffic at a temperature of 85 �C[194]. An appropriate performance of Sasobit�-WMA mixturescan spur interest in using this technology in other countries.

6.2.2. United StatesIn the United States, approximately 96% of 2.3 million miles of

paved road (asphalt or concrete) was constructed using asphaltmaterials, and the total amount of asphalt mix production is 500million tons [195,196]. According to the traditional United Stateshighway traffic, the performance of Sasobit�-WMA mixtures hasto be evaluated.

In 2007, a field trial using 330 tons of WMA with 1.5% Sasobit�

was implemented in California on Quarry Road [197]. The con-struction temperature for the HMA was 152 �C, and the corre-sponding temperature for the Sasobit�-WMA mixtures was 121–131 �C. The fumes were significantly reduced during the dumpingof the truck load, which is consistent with a trial study imple-mented by Saboundjian et al. [138], Goh and You [118], and Die-fenderfer et al. [120]. This is very beneficial for the welfare ofasphalt pavement construction workers, including staff workingin asphalt mixing plants, ground construction, and paving crewswho are usually exposed to 0.1–2 mg/m3 of asphalt fume, whichit contains 10–200 mg/m3 of benzopyrene [171]. In this trial study,the Sasobit�-WMA mixtures was compacted at a temperature28 �C lower than that used for the HMA, with a compaction degreeof approximately 98%. In a 2005 trial study by the Maryland StateHighway Administration, a SMA binder course using Sasobit� wasalso constructed at a temperature 28 �C lower than that used forthe HMA [197].

In 2006, two trial sections were installed in Virginia. The firsttrial was an overlay consisting of SMA containing 1.5% Sasobit�,and the second trial was SMA containing 10% RAP and the sameSasobit� content [120]. The results showed that the control andSasobit�-warm trial sections had similar permeability levels. Fur-thermore, the average amount of air void in the Sasobit�-WMAmixtures cores was slightly lower than that in the control cores.The study also found that the Sasobit�-WMA and the HMA hadsimilar performances during the first 2 years of service.

Although a preliminary study using a heavy vehicle simulator(HVS) determined that the selected WMA technologies (includingSasobit�) had no significant effects on rutting performance in Cal-ifornia [198], a field performance study conducted in Texas foundthat the Sasobit�-WMA mixtures performed as well as the HMAin the first year of service and did not show any evidence of ruttingor cracking [132].

In 2006, a trial study was conducted by Hurley et al. [130] onSasobit�-WMA containing 1.5% Sasobit�. The 1000 tons of asphaltmix were used to overlay the surface course. The mixing and con-struction temperatures were 127 �C and 121 �C, respectively, whilethe corresponding temperatures for the control HMA were 163 �Cand 149 �C. Data obtained from the field investigation showed norutting, while the HMA’s rut depths were 1.6 mm (1/16 in.) and3.18 mm (1/8 in.) in the right and left wheel paths, respectively.Furthermore, a minor coarse aggregate pop-out was also reportedfor the Sasobit�-WMA mixtures.

In 2007, a trial field study was conducted in Colorado byAschenbrener et al. [199] to compare the field performance of Sas-obit�-WMA mixtures and HMA in terms of rut depth, cracking, ra-veling and weathering. Approximately 1000 tons of WMAcontaining 1.5% Sasobit� were produced to evaluate the field per-formance. The trial field study was conducted after 3 years. The re-sults showed that Sasobit�-WMA pavement comparably performsto HMA pavement sections.

In another field study conducted in Missouri by Hurley et al.[127], 2100 tons of WMA containing 1.5% Sasobit� was con-structed. In this study, Sasobit�-WMA mixtures were produced,mixed and compacted at temperatures of 135 �C and 121 �C,respectively. After in-place densities and constructability of Sas-obit�-WMA mixtures were proved, Sasobit�-WMA mixtures wereproduced and compacted at 121 �C and 107 �C, respectively. Mix-ing and compaction temperatures of control HMA were also re-ported 160 �C and 149 �C, respectively. The field investigationsshowed that the HMA had rut depths of 0.4 mm and 0.5 mm inthe right and left wheel paths, respectively, while the rut depthof the Sasobit�-WMA mixtures stayed at the constant value of0.8 mm.

A field investigation in Wisconsin showed that the rut depth inSasobit�-WMA after 4 months was less than 1 mm [128].

In Franklin, Tennessee, 250 tons of WMA with PG 70-22 and1.5% Sasobit�-WMA mixtures were produced for overlay [200].After 1 year, the Sasobit�-WMA mixtures showed lower ravelingresults than the other warm mix technologies. In this project, theasphalt binder extracted from the field cores was classified interms of high performance grade after 1 year. A maximum highperformance grade of 82 was reported for the asphalt binder con-taining Sasobit�.

A trial study was also implemented in Ohio by Sargand et al.[201] to investigate the effects of reduced wearing course contain-ing Sasobit� and related structural response under dynamic load-ing at different temperatures. The thicknesses of the wearing andbase courses in the first section of Sasobit�-WMA mixtures were35.6 cm and 20.3 cm, respectively (dense graded aggregate), andthe corresponding values for the second section were 40.6 cmand 15.2 cm. The HMA section had the same thicknesses as thesecond Sasobit�-WMA mixtures section. The wearing course

Table 5Specifications of some Sasobit� WMA pavement constructed in European countries [8,193].

Year Country Name Utility Area(m2)

Sasobit�

(%)Binder type Mix type

2007 Russia Gelendzhik Runway and Taxiway 200,000 3 Pen 60/90 AC 0/85, AC 0/16S2006 Norway Svalbard Runway and Taxiway 170,000 3 Pen 490 AC 0/112005 Austria Linz–Hörsching Runway 50,000 3 PMB 60/90 AC 0/16, BT 0/222005 Germany Frankfurt Runway 250,000 4 PMB 45, PMB 25 and

Pen 30/45SMA 0/11 S, AC 0/22, AC0/32 CS

2005 Slovenia Spodnjibrnik–Moste Road 1800 3 AC 50/70 BT 0/16 SBT 0/22 S, AB 0/11 S

2005 Slovenia Laze Road 1000 3 AC 50/70, Olexobit 45 Abi 0/22, SMA 0/82005 Serbia Belgrad Runway 20,000 3 PMB 60/90 AC 0/8, AC 0/162005 Germany Eurogate (Hamburg) Container Terminal 50,000 4 and 2 PEN 50/70 0/22 incl. 50%RAP

PEN25 PMB 0/8 incl. 20%RAP2004 Germany Tollerort (Humburg) Container Terminal 70,000 4 PEN 25 PMB 0/16S and SMA 0/162004 Germany Airbus Terminal Finkenwerder

(Humburg)Runway 96,000 2.5 PMB Carbit 45 AC 0/11S

PEN 25 PMB2004 Germany Airport Berlin Shonefeld Runway 135,000 3 PEN 45 PMB 0/16S2003 Germany Munich Apron 60,000 3 PMB 45 AC 0/11, AC 0/162003 Sweden Sturoman Apron and runway 110,000 3 Pen 120/160 AC 0/112003 Denmark M23, Oslo–Drammen Motorway 100,000 3 B 85 SMA 152003 Sweden Umea (near Arctic Circle) Military Airport 110,000 3 B 120/160 ABTS 112003 Denmark M30, Rodby (Heavy traffic side) Motorway 30,000 2 AC 40/60 ABB2003 Denmark M11, Holbaek (Heavy traffic side) Motorway 15,000 2 AC 40/60 ABB2003 Denmark M70, Alborg South Motorway 81,000 1.5, 3 SMA 11, ABB AB 602003 Germany A25 Hamburg Motorway 25,000 1.5 SMA 0/8 S 0/16S, Caribit 25 RC

Caribit 452003 Czech Brno Road 3000 3 PMB 45 SMA 0/11 S2003 Germany Fraport (Frankfurt) Runway 100,000 4 0/22 S SMA 0/11 S

Carbit 25 RC, Carbit 25/45

ATS CS 0/32

2002 Norway Drammen–Westfall Road 10,000 3 B 85 SMA 11 + 152002 Norway Oslo–Drammen Motorway 100,000 3 B85 SMA 152002 Germany Rendsburg Bridge Pavement 16,500 3 Olexobit 45 Gussasphalt 0/11 S2001 UK Cambridge Apron 3000 3 PMB 65 AC 0/162001 Italy Piemont, Turin Road 4000 3 AC50/70 AC 0/162001 Hungry Szekesfehervar Road 3000 3 AC 50/70 SMA 0/112001 Germany Veddeler Damm–Hamburg Industrial road in the port of

Homburg5000 3 PEN 45 PMB 0/16HS

SMA 0/82001 Germany Hamburg Airport Runway 60,000 3 AC 50/70 SMA 0/112000 Germany A1, Maschen – Harburg Motorway 25000 3 SMA 0/5 Caribit 452000 Germany B 83, Bad Eilsen (A-Road) Road 25000 3 SMA 0/5 Caribit 452000 Denmark Aarhus Road 22,000 3 SMA 0/8 AC50/702000 France Misc. streets Road 20,000 3 Gussasphalt AC 30/502000 Netherland Docking station Schoitema,

WoerdenRoad 15,000 2 and 6 Gussasphalt AC 20/30

2000 Germany Neuhöfer Straße, (Hamburg) Waste disposal site 80,000 4 AC 50/70 0/16 SMA 0/11


consisted of surface and levelling layers and intermediate and fati-gue resistant asphalt concrete layers. More details regarding thethicknesses of the individual layers can be found in a technical doc-ument by Sargand et al. [202].

The test temperatures were 4.4 �C, 21.1 �C and 40 �C. Therewere similar strain levels in the fatigue resistant layers of theHMA and Sasobit�-WMA mixtures sections using acceleratedpavement loading facility (APLF). This implies that the reductionin the perpetual pavement thickness from 40 cm to 35.6 cm wasaccompanied by a corresponding increase in the thickness of thebase layer, which has a similar response to loads.

Furthermore, data obtained using the falling weight deflectom-eter (FWD) showed that the measured deflection in the HMA sec-tion is less than the reduced thickness of the Sasobit� WMA sectionat various test temperatures [202]. This trial test confirmed thatthe thickness of the asphalt concrete wearing cannot be reducedwhen Sasobit� is employed. This trend was also present for theSasobit�-WMA section, which had the same thickness as theHMA section at 4.4 �C, while the deflections in the HMA were re-ported as higher than that in the Sasobit�-WMA at 40 �C. Eq. (7)shows that the range of the pavement deflection percentage differ-

ence (Eq. (6)) between the Sasobit�-WMA mixtures and HMA sec-tions with equal thicknesses at different test temperaturesdepended on the position of the geophone from the plate centreof the FWD test.

PPDD ¼ DDHMA=WMA

dHMA¼ dHMA � dWMA

dHMAð6Þ

Ranges of PPDD¼0�PPDD�16:22% T¼4:4 �C�9:04%�PPDD�5:15% T¼21:1 �C�20:50%�PPDD��4:18% T¼40 �C

8><>: 0�L�152:4

ð7Þ

where PPDD is pavement deflection; DDHMA/WMA means differenceof measure pavement deflection between HMA and Sasobit�-WMA in each location; dHMA and dWMA are deflection in individualpoint of HMA and WMA, respectively.

From Eq. (7), PPDD ranging from 0% to 16.22% at 4.4 �C are con-verted to �4.18% and �20.50% at 40 �C, indicating that the Sas-obit�-WMA mixtures have lower deflections than the HMA. Afield study conducted in Ohio by Hurley et al. [203] reported that


Sasobit�-WMA containing 15% RAP showed the maximum degreeof ravelling.

Another field study by West et al. [186] showed that the rutdepth of Sasobit�-WMA mixtures constructed using PG 76-22and 45% RAP was 64% lower than that of the control sample (PG67-22 without RAP and Sasobit�) after loading by 9.4 million 8.2ton equivalent single axle loads (ESAL). The use of any mix or bin-der additive may affect the mode and development of failures un-der traffic and environmental loadings. For example, West et al.[186] investigated the international roughness index (IRI) for pave-ment sections constructed using Sasobit�-WMA containing RAP.The IRI of the Sasobit�-WMA mixtures constructed using PG 76-22 and 45% RAP fluctuated approximately 80 in./mi, while anincreasing trend was observed for the control sample (HMA con-structed using PG 67-22 without RAP and Sasobit�) after 9.4 mil-lion ESAL repetitions. Thus, the pavement failures that occurredin asphalt mixes constructed using PG 76-22, 45% RAP and Sasobit�

were almost constant over traffic loading, while those that oc-curred in the control samples increased significantly over pave-ment loading.

In 2008, 23,000 tons of Sasobit�-WMA mixtures constructedusing polymer PG 58-28 was used to upgrade the southern portionof Alaska’s Petersburg-Mitkof Highway [138]. In Alaska, asphaltmixture compaction can be very difficult, especially for thin as-phalt pavement layer and when the weather is cold [44,138]. Theassigned traffic level was low, and there was a particular field con-dition due to the low temperature. Using FWD back calculations,the field investigation revealed that the Sasobit�-WMA mixtureshas a higher modulus than HMA. There was no low temperaturecracking for the constructed Sasobit�-WMA pavement after 1 year;the condition of the asphalt appeared to be that of newly con-structed pavement.

6.2.3. CanadaThe results of two Sasobit�-WMA projects conducted in Canada

by Aurilio and Michael [11] are summarized below.In 2007, a trial paving project was conducted to demonstrate

the efficiency of Sasobit� to Ontario’s Ministry of Transportation(MOT). The trial project’s aim was to rehabilitate the pavementof Victoria Street in Ottawa, which was in poor condition due totransverse cracking and rutting.

The mixing temperature and range of compaction temperatureswere 130 �C and approximately 90–110 �C, respectively. Theamount of mix, asphalt binder type, and Sasobit� content were950 tons, PG 58-34, and 1.5% Sasobit�, respectively. The ambienttemperature fluctuated from 3 to 10 �C. Asphalt paving groups re-ported no observed fumes as the mix was laid down and com-pacted. They also reported that the mix was ready to work, andneither shoving nor pushing of the mat was verified during com-paction. Fuel use was reduced by 30% by the use of WMA on Victo-ria Street; this reduction was the main motivation for using WMAin cold climates [204].

These promising results encouraged the use of more Sasobit�-WMA mixtures in Canada. In this regard, 300 tons of Sasobit�-WMA mixtures was used to pave Old Finch Road. The asphaltbinder type and Sasobit� content were PG 64-28 and 1.5%,respectively. The fuel type of the asphalt mixing plant wasnatural gas, and the productions of Sasobit�-WMA mixturesand traditional HMA had fuel consumptions of 5 m3/ton and6–7 m3/ton, respectively.

6.2.4. Australia and New ZealandIn 2006, the Roads and Traffic Authority (RTA) and Boral Asphalt

in New South Wales (NSW) jointly implemented several field trialson Sasobit�-WMA [205]. The mix type and Sasobit� content weredense (AC 14 and AC 20) and 1.5%, respectively. Although the

mixing temperatures were as low as 130–140 �C, and the compac-tion temperatures ranged from 90 �C to 120 �C, satisfactory com-paction was achieved resulting in field air voids of approximately5–6%. It is important to note that these trials focused on the effectsof temperature reduction and longer haulage rather than on struc-tural performance evaluation (e.g., rutting) under service condi-tions. The long distance haulage of WMA can provide advantages,such as the use of WMA for paving projects in neglected areas lo-cated far away from the asphalt mixing plants. Another importantadvantage of WMA is that it can be produced and hauled for theemergency construction and rehabilitation of severely damagedpavements in disaster areas where electricity may not be availablein the asphalt mixing plants for a week or more [206]. Bornmannet al. [205] also reported a long haulage trial carried out in BrokenHill, NSW. In this case, the Sasobit�-WMA mixtures were producedat an asphalt mixing plant and loaded into trucks at 180 �C. Thetrucks were equipped with heat shields over the top of the asphaltassociated with three layers of carpet under felt, as well as the typ-ical tarpaulin covers used to prevent significant asphalt mix loss.The shipping time was approximately 9.5–12 h before the mixwas loaded into the pavers. By that time, the mix temperaturemeasured near the side walls was as low as 100 �C, while the sur-face and core temperatures were 115–135 �C. However, Sasobit� isa compaction aid material; the viscosity of Sasobit�-warm asphaltbinder starts to increase once the Sasobit�-WMA mixture coolsdown [23], and more effort is required to compact the WMA mix-tures. Therefore, there should be no delay in the mix lay down andbreaking down in compaction. The trial appeared to be successfulbecause Sasobit�-WMA mixtures were shipped, placed and com-pacted without any of the traditional challenges or defects associ-ated with long shipping asphalt mixes; this result can be veryhelpful for paving projects located far away from asphalt mixingplants. In Australia, 750 km of asphalt paving road was coveredby Sasobit�-WMA mixtures by 2007 [207].

There are no detailed published data available for Sasobit�-WMA mixtures performance in New Zealand. Table 6 shows thespecifications of two roads constructed using Sasobit�-WMAmixture.

6.2.5. South AfricaIn 2008, a trial paving project was performed on Sasobit�-WMA

mixtures in Brackenhill Road in eThekwini, located near Durban[208]. The trial project’s aim was to repave an old roadway thatwas severely distressed. The length of the road was divided into6 sections, 2 of which were paved using Sasobit�-WMA mixtures.The required asphalt mixes for each section, the binder type, andthe Sasobit� content were 200 tons, AC 40/50, and 1.5%, respec-tively. Furthermore, the Sasobit�-WMA mixtures of one sectioncontained 10% RAP. The results indicated that the temperature atwhich the Sasobit�-WMA mixtures can be compacted is at least20 �C lower than for the traditional HMA (at the same density).The Sasobit�-WMA reduced fuel consumption by 15–20% com-pared to the HMA. The results confirmed that a minimum of 10%RAP could be used to produce the Sasobit�-WMA.

The taxiways and runways of King Shaka International Airport(KSIA) near Durban and the apron, taxiways and taxi-lanes of theOR Tambo Airport (ORTIA) in Johannesburg were repaired usingSMA containing 1.5% and 4% Sasobit� [8,101]. The Sasobit�-WMAmixtures was employed in ORTIA to extend the required time forcompacting (because the paving operations needed to be con-ducted at night with low ambient temperatures) and improvethe strength required against deformation. Hofsink and Barnard[101] also reported that the viscosity depressant characteristicsof Sasobit� led the dispersion temperature of the SBS binder tobe reduced by at least 10 �C. In this regard, the SBS-Sasobit� ratiocan be selected to deliver the precise final modified asphalt binder

Table 6Specifications of some Sasobit� Warm pavement constructed in New Zealand [8].

Year Name Utility Area (m2) Sasobit� (%) Binder type Mix type

2003 Taranaki Region Road 2800 3 B80/100 AC 0/102003 Taranaki Region Car park 1400 3 B80/100 AC 0/10


properties and required performance; the optimal ratio to fulfillthe specifications of SMA according to KSIA requirements was65:25 (SBS:Sasobit�). Table 7 exhibits some paving projects thatwere constructed using the Sasobit� WMA mixtures in SouthAfrica.

6.2.6. AsiaThere is no available English literature regarding the field per-

formance of pavements using Sasobit�-WMA mixtures with vari-ous utilities in Asia. Table 8 presents some road projects andtheir specifications that were constructed in two Asian countries.

7. LCA analysis, energy savings and GHG emissions reductions ofSasobit�-WMA

7.1. LCA analysis and of Sasobit� WMA

In this section, the effects of Sasobit� on asphalt mix productionin the terms of its life-cycle assessment (LCA), energy savings po-tential and greenhouse gas (GHG) emission reduction potentialare reviewed. It concludes with a suggestion on an approach formaterials selection to produce cleaner, more energy efficient as-phalt mixes in Superpave™. The suggestion can be used for bothwarm and hot mix asphalts. Areas in which further research onSasobit�-WMA mixtures is required, are also recommended.

Sustainable development implies equilibrium between environ-mental, political, social, political and economic objectives to pro-tect the world for future generations [209–211]. In this regard, agreen rating system is required to measure the environmental im-pact during the service life of a product or system. The rating sys-tem can also provide strategies for material selection, constructionmethod, production utility, recycling and reusing of materials withminimum environmental loads. LCA and Leadership in Energy andEnvironmental Design (LEED) are typical rating systems. Althoughthere is a lack of in-depth data available on the LCA and/or LEEDratings of mixes constructed using Sasobit�, some useful informa-tion exists regarding the total WMA technology. Cheng et al. [212]performed a LCA analysis, which showed that the WMA reducedthe Photochemical Ozone Formation (POF) and fuel consumptionby 70% and 22.4%, respectively, when compared to the HMA. Has-san [2,213] also used a LCA analysis to evaluate the environmentalimpact of WMA using the Building for Environmental and Eco-nomic Sustainability (BEES) model. The output revealed reductionsin fuel consumption, air pollutants, and smog formation of 18%,24%, and 10%, respectively, which led the overall environmentalimpact of the WMA to be 15% less than that of the HMA.

Tatari et al. [214] developed a hybrid LCA model to compareenvironmental benefits of pavements constructed with different

Table 7Specifications of some Sasobit� WMA pavement constructed in South Africa [8].

Year Name Utility Area (m2)

2004 K 103 Rigel Road 70002004 K 69 Hans Strijdom Road 150002004 South Coast Road Road 12,0002004 M4 Southern Road 60,0001997 Jean Avenue Road 2700

types of WMA. The result showed that Sasobit�-WMA emit theleast pollutants as compared to the other additives according to to-tal the life-cycle emission results. Tatari et al. [214] also comparedthe sustainability of Sasobit�-WMA mixture and HMA using thehybrid LCA model in the terms of ratio (ECEC/ICEC) of ecologicalcumulative exergy consumption (ECEC) and industrial cumulativeexergy consumption (ICEC). The results showed that value ofECEC/ICEC for the Sasobit�-WMA mixtures 41% lower than HMA,indicating Sasobit�-WMA has less dependency to non-renewableresources over whose life-cycle.

Although mixing aggregate and asphalt binder is very impor-tant phase in the terms of fuel consumption GHG emission, outputsbased on Mont Carlo simulation indicated that the just mixingphase should not be evaluated in reduction in GHG emission inWMA life-cycle [214]. For example, further technologies are re-quired to obtain lower emissions in the asphalt mix production(i.e., heavy trucks and construction machines equipped with hy-brid technology can increase fuel efficiency by 35%) [2].

7.2. Energy savings and GHG emissions reductions

Asphalt industries and asphalt mixing plants should be mademore environmentally efficient by optimizing energy consumptionor fuel requirements and GHG emissions. Currently, crude oil isconsumed one million times quicker than it is made, and the peakpoint global oil production may have already occurred or may oc-cur in the near future (i.e., 2010, 2030) [215]. Therefore, energycosts increase as the depletion of crude oil is coupled with anincreasing demand for energy. For instance, the United States En-ergy Administration (USEA) predicted that by 2020, the total en-ergy consumption from petroleum, natural gas, coal, electricityand renewable energy will increase by 32%, 33%, 62%, 22%, 45%,and 26%, respectively [216].

Furthermore, CO2 (the most important type of GHG because offuel burning) is a good heat absorber and may act as a blanket towarm the globe. Thus, environmental policy makers should inves-tigate any method through which CO2 can be further reduced inthe production of asphalt mix.

Asphalt pavements can produce CO2 when energy is consumedduring the mixing and compaction processes and when the asphaltbinder oxidizes the hydrocarbon molecules during construction.Therefore, asphalt mixes made with high binder contents are likelyto emit more CO2. Because Sasobit� is a hydrocarbon, it may alsoemit CO2 during the construction of the asphalt pavement. Mallickand Bergendahl [217] found that the mixing temperature had themost significant effect on CO2 emissions, while asphalt binder con-tents and the amount of Sasobit� showed no strong correlationswith emissions. In a field study, Sargand et al. [202,218] and Hurley

Sasobit� (%) Binder type Mix type

3 AC 60/70 Med. Cont. Grade3 AC 60/70 Med. Cont. Grade3 AC 60/70 Med. Cont. Grade3 AC 60/70 Med. Cont. Grade3 AC 80/1000 SMA

Table 8Specifications of some Sasobit� WMA pavements constructed in two Asian countries [8].

Year Country Name Utility Area (m2) Sasobit� (%) Binder type Mix type

2004 China Trial Road Jiangsu Road 30,000 3 AH 70 SMA2004 Malaysia NS Expressway Road 40,000 3 SMB 35 SMA2004 Malaysia Perak Road 35,000 3 PMB 45 SMA2003 China Shandong Road 500,000 1 Chun Hai 36-1 + 3% SBS AK 162003 Malaysia Seri Kembangan, Selangor Road 1500 3 AC80/100 ACW 202002 China Guangdong Province Road 6000 2 and 3 Moaming #70 + 3.5% SBR AK 162002 Malaysia Kuching-Sri Aman, Sarawak Road 4700 3 AC80/100 ACW 202001 China Shi-Jia Zhuang, Hebei Province Road 5000 4.5 AH 90 AK-1312001 China Wuxi Jiangsu Province Road 4500 3.5 AH 70 AK-1312000 China Guangdong Province Road 4500 3 AH 70 + 1.5% SBR AK-16A, AC-2512000 China Guangdong Province Road 20,000 3 AH 70 + 1.5% SBR AK 1311999 Malaysia Seremban, Negei Sembilan Road 8500 4 AC80/100 ACW 20

Fig. 4. Modification in Superpave™ by including C coefficient of aggregate to aggregate properties.


et al. [203] reported that the air pollutants of Sasobit� WMA interms of total particulate emissions (TPEs), sulfur dioxide (SO2), ni-tric oxide (NOx), carbon monoxide (CO), carbon dioxide (CO2) andVolatile Organic Compounds (VOCs), and benzene soluble matter(BSM). The use of WMA incorporated with Sasobit� reduced TPE,SO2, NOx, CO, CO2, VOC, and BSM levels by 74%, 83.30%, 21.20%,63.20%, 42.9%, 51.30%, and 80%, respectively, compared to thosefrom HMA. Hurley et al. [130,203] also reported that the amountof natural gas and reclaimed oil as industrial fuels that were usedin an asphalt mixing plant to produce Sasobit� WMA decreased by17.90% and 10%, respectively.

Hamzah et al. [55] showed that the specific heat capacity ofaggregate materials is a significant factor affecting the fuel require-ments and CO2 emissions of Sasobit�-WMA mixture and HMA. Thesame aggregate types extracted from different sources may have adifferent specific heat capacity even if their specific gravities or theother specifications are similar. For example, they found that thespecific heat capacity of the granite aggregate from one source(first source) was 95% higher than that of the granite aggregatefrom another source (second source). The granite aggregate fromthe first source required 87% more heat energy or more fuel thanthe second source to go from the ambient temperature to the mix-ing temperature, despite the fact that their specific gravities werealmost identical [55]. The effect of the specific heat capacity onthe same type of aggregate from different sources can be consider-able in terms of fuel requirements and CO2 emissions. Meanwhile,the costs of mining and transportation of the aggregate from

sources with low specific heat capacity should be considered asthe total costs of the paving project to evaluate whether the sug-gested strategies can be economical.

8. Suggested Superpave™ modification based on the resultsoutlined in the literature

While aggregate characteristics and the rheological propertiesof asphalt binder play increasingly important roles in the asphaltmix performance, another parameter is required to evaluate theEnvironmental Polluting Potentials (EPPs) of materials in the as-phalt mixes. In current technical documents [195,219–227], thereis a lack of detailed knowledge on a particular parameter with en-ough potential to assess the environmental pollution level of thematerials used to produce the asphalt mix. Neither the mix designmethods of Marshal and Hveem nor Superpave™, which is catego-rized as the most advanced mix design method, have provided de-tailed recommendations on how to compare EPP in the process ofmaterial selection because the technical documents and mix de-sign methods were established before the current energy crisisand global warming disaster.

The parameter for defining the EPP should enable pavementengineers and environmental policy makers to quantify and com-pare the environmental impacts of different materials and selectoptimal sources and material types considering the environmentalpollution’s effects. However, the parameter should be simpleenough to analyze and measure using available technologies.

Fig. 5. Plan of block laying patterns of containers and stresses distribution induced by container weights on an asphalt pavement surface course.


Furthermore, the parameter should be sensitive enough to thermalchanging, material mass, and energy. For these reasons, the param-eter proposed as the indicator for EPP of materials in the asphaltmixes is the specific heat capacity (C) (kJ kg�1 �C), which can beused to calculate the required heat energy, fuel requirement, andGHG emissions required to heat materials up to the mixing

temperature based on different industrial fuel types in the asphaltmixing plants. The C coefficient is a physical property showing thematerials’ thermal characteristics in terms of energy absorbanceand release properties. Hence, a higher C coefficient indicates high-er energy or fuel requirements and higher GHG emissions (i.e., asmore heat is realized by the aggregate, more heat is absorbed by

Fig. 6. Schematic sketch showing the overlapping stresses at the aisle due to combined weights of containers and wheel load on an asphalt pavement surface course.


the asphalt binder film). However, the C coefficient did not showany distinct relationships with air void and the amount of courseaggregate in HMA for different aggregate sources [228]. Luca andMrawira [229] also found no relationships between the C coeffi-cient and the resilient modulus, mix density, Marshall stability,and flow.

The mass of the asphalt mix is mainly the aggregate; hence, theC coefficient is suggested for aggregate particles and should be in-cluded in the Superpave™. The Superpave™ would be upgraded asan integrated system incorporating performance-based and as-phalt binder rheological characteristics with design service condi-tions by controlling rutting, fatigue and low temperature cracking;furthermore, the method would have enough potential to assessthe EPP and environmental friendliness of the materials duringtheir selection process as indicated in Fig. 4. Under these circum-stances, beyond consensus and the aggregates’ source characteris-tics concerning the structural consistency of the asphalt mix, the Ccoefficient can be added as an aggregate property dealing with en-ergy or fuel requirements and GHG emission reduction potential(dashed line arrow in Block B in Fig. 4). Consensus properties in-clude course and fine aggregate angularity, flat and elongated par-ticles, and clay content. Source properties consist of toughness,soundness, and deleterious materials [105]. As known, rheologicalproperties of asphalt binder are evaluated in Superpave™ by rota-tional viscometer (RV), dynamic shear rheometer (DSR), bendingbeam rheometer (BBR) with direct tension tester (DTT), at high,intermediate, and low temperatures, respectively.

Consequently, the C coefficient may be used as an indicatorwhen comparing the EPPs of different aggregate sources and typesto select the best ones for a paving project from a fuel requirement

and GHG emission reduction standpoint. Although aggregatematerials with a lower C coefficient are more appropriate for pav-ing projects from the environmental policy maker’s standpoint, theperformance of asphalt mixes constructed with these materialsshould be evaluated in laboratory tests by pavement engineerswith more details. Furthermore, because aggregate quarries withlower C may be less accessible, project managers and environmen-tal engineers should include the total fuel requirement and air pol-lution costs associated with the mining and transpiration of lowerC coefficient aggregate into the asphalt mixing plants in the life-cycle of asphalt paving projects. Engineers should also consult withenvironmental policy makers to specify the C coefficient of aggre-gate from different quarries in a country and record it in an aggre-gate database to be able to judge and select the mostenvironmentally friendly aggregate sources.

9. Conclusion

Sasobit� has advantages and disadvantages. On one hand, it re-duces the viscosity of asphalt binder at high temperatures andthereby reduces construction temperatures and aging, and it in-creases rutting resistance at intermediate temperatures for a givenasphalt binder type and source. Sasobit� also reduces the viscosityof polymer-modified binder and asphalt binders containing agedbinder and crumb rubber. On the other hand, Sasobit� may in-crease the potential for fatigue and low-temperature cracking atintermediate and low temperatures. Therefore, it is essential tooptimize the performance of Sasobit�-modified asphalt bindersat high, low, and intermediate temperature ranges by careful selec-tion of the binder type and source and Sasobit� content.


Laboratory studies have shown that the performance of Sas-obit�-WMA mixtures depend on construction temperatures, Sas-obit� content, aggregate type and source, aggregate gradation,filler type, binder type and source, anti-stripping agent type, andthe type and amount of waste materials such as RAP, RAS, RCA,and crumb rubber.

Because there are different methods for estimating appropriateconstruction temperatures, it is important to select the mostappropriate method, particularly for Sasobit�-WMA mixtures con-taining waste materials. No significant differences were observedbetween Sasobit�-WMA mixtures and HMA in terms of volumetricproperties and OAC.

Because Sasobit� improves asphalt binder, the rutting perfor-mance of Sasobit�-WMA mixtures was often observed to equalor exceed the rutting performance of HMA irrespective of the lab-oratory test method.

Aggregate size, source, type, anti-stripping agent type, size ofsolid anti-stripping particles, and aging time are factors that affectthe moisture resistance of Sasobit�-WMA mixtures.

Less aging due to lower construction temperatures increasesthe fatigue resistance of Sasobit�-WMA mixtures. Use of softer orlower-performance-grade asphalt binder could enhance the resis-tance of Sasobit�-WMA mixtures to fatigue.

Not only does Sasobit� decrease the construction temperaturesof asphalt mixtures containing RAP, RAS, RCA, and crumb rubber,but also production of asphalt mixtures containing high percent-ages of RAP is possible using Sasobit�.

The results gained through field studies showed that generalperformance of the Sasobit�-WMA mixtures were satisfactory.However, more effort is required to assess the long-term perfor-mance of Sasobit�-WMA mixtures.

The motivation of use of Sasobit� to produce asphalt mixes inthe studied fields varied in different countries. The main reasonsfor using Sasobit� were to reduce fuel consumption, reduce GHGemissions, extend paving time, potentially haul the mixes for long-er distances, lower the required curing time and hasten the time atwhich the pavement was opened to traffic.

By including the specific heat capacity of aggregate materials in thematerial selection process of Superpave™, this advanced mix designmethod would be upgraded into an integrated system that enablesthe evaluation of performance-based rheological characteristics ofasphalt binder and aggregate requirements and the evaluation andcomparison of the aggregate material EPPs. From this information,the most environmentally friendly aggregate materials can beselected. This situation would lead to the production of the mostsustainable asphalt mixes meeting Superpave™ specifications.

10. Suggestions for further research

The suggestions for further research on this subject include:

1. The suggested Superpave™ modification should be studied, andthe effects of the selection of aggregate should be evaluatingusing LCA and LEED ratings by considering the specific heatcapacity of the asphalt mixes.

2. More detailed field and laboratory studies are required to eval-uate the structural performance, moisture sensitivity, and agingcharacteristics of Sasobit�-WMA mixtures containing the sameaggregates, gradation, and OAC with different specific heatcapacities. The failures and failure development rates of suchmixes should also be measured and compared in the field.

3. Detailed data are required to fully characterize EEP in terms ofdifferent fuel requirements and GHG emissions for the case inwhich an asphalt mixing plant produces mixes using aggregateswith similar properties but different C coefficients.

4. More research should be conducted on the creep characteristicsand deformation of Sasobit�-WMA mixtures constructed at dif-ferent temperatures under heavy static post loads, particularlyin stacking container yards of ports. The deformation of thepavement in container stacking yards placed in a block layingpattern may be greater than that of pavement in other placesbecause that type of area experiences stresses from the weightof four studs of containers (dashed circle in Fig. 5a). Moreover,the pavements in the aisles are vulnerable because they experi-ence overlapped stresses from the weight of containers viastuds (section B-B in Fig. 5) and stresses from the weight ofvehicle wheels as shown in Fig. 6a and b. Figs. 5 and 6 showthe schematic distribution of stresses in the asphalt concretelayer. The effects of reduced construction temperatures and dif-ferent amounts of warm binder or mix additives on structural/functional performance of such pavements should beinvestigated.

5. Mechanistic-analytical models to predict development patternsof distresses in asphalt concrete pavement containing differentamounts of Sasobit� (or mixtures containing aggregates withsimilar characteristics but different C values) and constructedat various temperatures should be determined. These modelscan be very useful for establishing a program to find optimummaintenance time and the best rehabilitation options in pave-ment management system (PMS). Because this job has multipleobjectives, including optimum rehabilitation time, cost effec-tiveness and structural durability, swarm intelligence (SI) strat-egies are recommended to optimize the aforementionedobjectives.

6. WMA pavements that are constructed now will be RAP materi-als in the future (WMA–RAP). Therefore, RAP materials maycontain Sasobit� and other WMA additives. The structural per-formance, aging characteristics and volumetric properties ofnew asphalt mixes constructed using WMA–RAP should be fur-ther investigated. Moreover, Since Amirkhanian and Williams[230] found that asphalt mixtures containing moisture-dam-aged RAP material increase have higher indirect tensile strength(ITS) and resilient modulus under wet and dry conditioning,evaluation of engineering properties of asphalt mixtures con-taining moisture-damaged WMA–RAP materials can be aninteresting issue.

7. Further research should be conducted on the influences of dif-ferent warm additive amounts and reduced temperatures onthe shape and distribution of cracks compared to HMA at differ-ent test temperatures.

8. Because momentum is a function of the mass and velocity gradi-ent of a moving object, each velocity change from heavy vehicles(including changes in the amount and direction of the velocityvector) can lead to severe momentum. Hence, further researchshould be conducted on the performance of Sasobit�-WMAunder severe momentum due to the acceleration, de-accelerat-ing, braking and rotating maneuvers of heavy vehicles (such aslift trucks, straddle carriers, and transtainers) in terms of typeand distress intensity in ports or other industrial pavements.In addition, the performance of Sasobit�-WMA should be evalu-ated under momentum imposed by airplane wheels with differ-ent main gear configurations when commercial aircrafts touchthe runway pavement, if the point of contact is not constructedby concrete pavement. The nose wheels of heavy aircrafts canalso generate severe momentum after touching.

Acknowledgements

The authors would like to acknowledge all of the researcherswho published the valuable literatures used in this state of the


art. The authors would also like to acknowledge the UniversitiSains Malaysia, which enabled this paper to be written due to itsfunding through the Research University grant scheme.

References

[1] Zapata P, Gambatese JA. Energy consumption of asphalt and reinforcedconcrete pavement materials and construction. J Infrastruct Syst2005;11(1):9–20.

[2] Hassan M. Life-Cycle Assessment of Warm-Mix Asphalt: an environmentaland economic perspective. In: Proceedings of 88th transportation researchboard annual meeting. Washington D.C., USA; 2009. p. 1–15.

[3] Peinado D, De Vega M, Garica-Hernando N, Marugaan-Cruz C. Energy andexergy analysis in an asphalt plant’s rotary dryer. Appl Therm Eng 2011;31(6–7):1039–49.

[4] D’Angelo JA, Harm EE, Bartoszek JC, Baumgardner GL, Corrigan MR, CowsertJE, et al. Warm-Mix Asphalt: European practice; 2008.

[5] Hanz A, Bahia H. Effects of warm mix additives of mixture workability and theperformance implications of reduced binder aging. In: The 7th internationalconference and airfield pavement technology. Thailand; 2011. p. 66–76.

[6] Edwards Y, Isacsson U. Wax in bitumen-State of the art: Part2-Characterization and effects. Road Mater Pavement Des 2005;6(4):1–30.

[7] Lu X, Redelius P. Effect of bitumen wax on asphalt mixture performance.Constr Build Mater 2007;21(11):1961–70.

[8] Sasolwax. Sasobit. Sasolwax; 2008. <www.Sasolwax.com>.[9] Damm KW. Asphalt flow improvers-a new technology for reducing mixing

temperature of asphalt concrete mixes with high resistance againstpermanent deformation. In: 6th international RILEM Symposium. Zurich,Switzerland; 2003. p. 521–6.

[10] Worrel J, Choi Y. Warm mix asphalt (WMA) review. Austroads; 2007.[11] Aurilio V, Michael LL. Sasobit�-warm mix asphalt technology: Victoria Street

Trial in the city of Ottawa. In: Proceedings of the 53th annual conference ofthe Canadian Technical Asphalt Association (CTAA). Saskatoon Saskatchewan,Canada; 2008. p. 249–65.

[12] Sampath A. Comprehensive evaluation of four warm asphalt mixtureregarding viscosity, tensile strength, moisture sensitivity, dynamic modulusand flow number. Iowa University; 2010.

[13] Hurley GC. Evaluation of new technologies for use in warm mix asphalt.University of Auburn, Ms.c thesis; 2006.

[14] Hurley GC, Prowell BD. Evaluation of Sasobit� for use in warm mix asphalt.NCAT t; 2005.

[15] Perkins SW. Synthesis of warm mix asphalt paving strategies for use inMontana highway, construction; 2009.

[16] Hurley GC, Prowell BD. Evaluation of potential processes for use in warm mixasphalt. J Assoc Asphalt Paving Technol 2006;75:41–90.

[17] Kristjansdottir O, Muench ST, Michael L, Burke G. Assessing potential forwarm-mix asphalt technology adoption. Transport Res Rec: J Transport ResBoard 2007;2040(1):91–9. http://dx.doi.org/10.3141/2040-1.

[18] Ji J, Xu S. Study on the impact of Sasobit� on asphalt properties andmicrostructures. J Mater Civ Eng 2010;12.

[19] Edwards Y. Influence of waxes on bitumen and asphalt concrete mixtureperformance. KTH Arquitecture and the built environment, PhD thesis; 2005.

[20] Edwards Y, Isacsson U. Wax in bitumen-State of the art: Part1-Classificationsand general aspects. Road Mater Pavement Des 2005;6(3):281–309.

[21] Bueche N. Warm mix asphalt bituminous mixtures with regards to energy,emissions, and performance. In: Young Researchers Seminar (YRS). Torino,Italy; 2011.

[22] Syroezhko AM, Baranov MA, Ivanov SN, Maidanova NV. Influence of naturaladditives and those synthesized by the Fischer-Tropsch method on theproperties of petroleum bitumen and quality of floated asphalt. Coke Chem2011;54(1):26–31.

[23] Wasiuddin NM, Saha R, King W Jr. Effects of a wax-based warm mix additiveon lower Compaction Temperatures. Advances in geotechnical engineeringproceedings of the geo-frontiers: ASCE; USA; 2011. p. 4614–23.

[24] Wasiuddin N, Saltibus N, Mohammad L. Effects of wax-based warm mixadditives on cohesive strength of asphalt binders. In: T & DI congress: ASCE;USA; 2011. p. 528–37.

[25] Rubio MC, Martinez G, Baena L, Moreno F. Warm mix asphalt: an overview. JCleaner Prod 2012;24(8):76–84.

[26] Zhao G-J, Guo P. Workability of Sasobit� warm mixture asphalt. Energy Proc2012;16:1230–6.

[27] Silva HMRD, Oliveira JRM, Ferreira CIG, Pereira PAA. Assessment of theperformance of warm mix asphalts in road pavements. International Journalof Pavement Research and Technology 2010;3(3):119–27.

[28] Seller BH. Characterization and transition of asphalt cement compositematerials. University North Carolina at Charlotte, Ms.C thesis; 2009.

[29] Xiao F, Amirkhanian SN, Zhang R. Influence of short-term aging on rheologicalcharacteristics of non-foaming WMA binders. J Performan Constr Facilities2011. http://dx.doi.org/10.1061/(ASCE)CF.1943-5509.0000223.

[30] Xiao F, Punith VS, Amirkhanian SN. Effects of non-foaming WMA additives onasphalt binders at high performance temperatures. Fuel 2012;94:144–55.

[31] Ran J, Xu S, Li M, Ji J. Research of warm mix asphalt and warm mix asphaltwith Sasobit�. In: ICCTP integrated transportation system green intelligent-reliable. USA; 2010.

[32] Zaumanis M. Warm mix asphalt investigation. Riga Technical University,Ms.C thesis; 2010.

[33] Biro S, Gandhi T, Amirkhanian SN. Midrange temperature rheologicalproperties of warm asphalt binders. J Mater Civ Eng 2009;21(7):316–23.

[34] FHWA. Quarterly technical progress report. Federal Highway Administration;2009.

[35] Tasdemir Y. High temperature properties of wax modified binders andasphalt mixtures. Constr Build Mater 2009;23(10):3220–4.

[36] Edwards Y, Tasdemir Y, Isacsson U. Rheological effects of commercial waxesand polyphosphoric acid in bitumen 160/220-high and medium temperatureperformance. Constr Build Mater 2007;21(10):1899–908.

[37] Edwards Y, Tasdemir Y, Isacsson U. Effects of commercial waxes on asphaltconcrete mixtures performance at low and medium temperatures. Cold RegSci Technol 2006;45(1):31–41.

[38] Silva HMRD, Oliveira JRM, Peralta J, Zoorob SE. Optimization of warm mixasphalts using different blends of binders and synthetic paraffin waxcontents. Constr Build Mater 2010;24(9):1621–31.

[39] Polacco G, Filipini S, Paci M, Giuliani F, Merusi F. Structural and rheologicalcharacterization of wax modified bitumen. Fuel 2012;95:407–16.

[40] Cao D, Ji J. Evaluation of long-term aged properties of Sasobit� modifiedasphalt. International Journal of Pavement Research and Technology2011;4(6):384–91.

[41] Jamshidi A, Hamzah MO, Aman MY. Effects of Sasobit� content on therheological characteristics of unaged and aged asphalt binders at high andintermediate temperatures. Mater Res 2012;15(4):1–11.

[42] Edwards Y, Tasdemir Y, Isacsson U. Rheological effects of commercial waxesand phosphoric acid in bitumen 160/22– low temperature performance. Fuel2006;85:989–97.

[43] Arega Z, Bhasin A, Motamed A, Turner F. Influence of warm mix additives andreduced aging on the rheology of asphalt binders with different natural waxcontents. J Mater Civ Eng 2011;23(10):1453–9.

[44] Liu J, Saboundjian S, Li P, Connor B, Brunette B. Laboratory evaluation ofSasobit�-modified warm-mix asphalt for Alaskan conditions. J Mater Civ Eng2011;23(11):1498–505.

[45] Wasiuddin NM, Selvamohan S, Zaman MM, Guegan MLTA. Comparativelaboratory study of Sasobit� and Aspha-Min� additives in warm-mix asphalt.Transport Res Rec: J Transport Res Board 2007;1998:82–8. http://dx.doi.org/10.3141/1998-10.

[46] Gandhi T, Akisetty C, Amirkhanian SN. Laboratory evaluation of warm asphaltbinder aging characteristics. Int J Pavement Eng 2009;10(5):353–9.

[47] Gandhi T, Amirkhanian SN. Laboratory investigation of warm asphalt binderproperties: a preliminary investigation. MAIREPAV5 proceedings, vol. 5. ParkCity, Utah, USA; 2007. p. 475–80.

[48] Mogawer PE, Walaa S, Austerman AJ, Bonaquist R. Evaluating effects of warm-mix asphalt technology additive dosages on workability and durability ofasphalt mixtures containing recycled asphalt pavement. In: Proceedings of88th transportation research board annual meeting. Washington D.C., USA;2009. p. 1–9.

[49] Hamzah MO, Jamshidi A, Kanitpong K, Yusri MA. Parameters to characterizethe effects of Sasobit� content on the rheological properties of un-aged andaged asphalt binders. J Road Mater Pavement Des 2012;13(2):368–75.

[50] SP-1. Superpave performance graded asphalt binder specifications andtesting. Asphalt Institute, KY, USA; 2003.

[51] Biro S, Gandhi T, Amirkhanian SN. Determination of zero shear viscosity ofwarm asphalt binders. Constr Build Mater 2009;23(5):2080–6.

[52] Bahia HU, Hanson DI, Zeng M, Zhai H, Khatri MA, Anderson RM.Characterization of modified asphalt binders in Superpave™ mix design; 2001.

[53] Buss AF. Investigation of warm-mix asphalt using Iowa aggregates. Institutefor Transportation Iowa State University Iowa, USA: Iowa State University;2011.

[54] Hossain Z, Bhudhala A, Zaman M, O’Rear E, Cross S, Lewis S. Evaluation of theuse of warm mix asphalt as a viable paving material in the UnitedStates. USA: Federal Highway Administration Turner-Fairbank HighwayResearch Center; 2009.

[55] Hamzah MO, Jamshidi A, Shahadan Z. Evaluation of the potential of SasobitÂ�

to reduce required heat energy and CO2 emission in the asphalt industry. JCleaner Prod 2010;18(18):1859–65.

[56] Lu X, Isacsson U. Laboratory study on the low temperature physical hardeningof conventional and polymer modified bitumens. Constr Build Mater2000;14(2):79–88.

[57] Edwards Y, Tasdemir Y, Isacsson U. Influence of commercial waxes onbitumen aging properties. Energy Fuels 2005;19(6):2519–25.

[58] Claudy P, Letoffe JM, Rondelez F, Germanaud L, King G, Planche JP. A newinterpretation of time-dependent physical hardening in asphalt based on DSCand optical thermoanalysis. Proc Am Chem Soc 1992;37(3):1408–26.

[59] Hilliard JE. Spinodal decomposition. In: Phase transformations. Paperspresented at a seminar of the American Society of Metals. American Societyfor Metals. Metals Park, Ohio, USA; 1970. p. 497–560.

[60] Hossain Z, Zaman M, Wasiuddin NM, Sneed J, Edgar AO. Rheologicalevaluation of warm mix and anti-stripping additives modified performancegrade binders. Road Mater Pavement Des 2011;12(4):875–95.

[61] Liu J, Peng L. Low temperature performance of Sasobit�-modified warm-mixasphalt. J Mater Civ Eng 2012;24(1):57–63.

[62] You Z, Mills Beale J, Fini E, Goh SW, Colbert B. Evaluation of low-temperaturebinder properties of warm-mix asphalt, extracted and recovered RAP andRAS, and bioasphalt. J Mater Civ Eng 2011;23(11):1569–74.

http://www.Sasolwax.com

http://dx.doi.org/10.3141/2040-1

http://dx.doi.org/10.1061/(ASCE)CF.1943-5509.0000223

http://dx.doi.org/10.3141/1998-10


[63] Airey G, Choi Y. State of the art report on moisture sensitivity test methods forbituminous pavement materials. Road Mater Pavement Des2002;3(3):355–72.

[64] Shalaby A. Modelling short-term aging of asphalt binders using the rollingthin film oven test. Can J Civ Eng 2002;29(1):135–44.

[65] Rajan NK, Selvavathi VBS, Krishnan JM. Influence of Asphaltanes on therheological properties of blended paving asphalts. Petrol Sci Technol2010;28(4):331–50.

[66] Gao M, Xiao B, Liao K, Cong Y, Dai Y. Aging behaviour of colored pavingasphalt. Petrol Sci Technol 2006;24(6):331–50.

[67] Lee SJ, Hu J, Kim H, Amirkhanian SN, Jeong KD. Aging analysis of rubberizedasphalt binders and mixes using gel permeation chromatography. ConstrBuild Mater 2011;25(3):1485–90.

[68] Lee SJ, Amirkhanian SN, Kim KW. Laboratory evaluation of the effects ofshort-term oven aging on asphalt binders in asphalt mixtures using HP-GPC.Constr Build Mater 2009;23(9):3087–93.

[69] Doh YS, Amirkhanian SN, Kim KW. Analysis of unbalanced binder oxidationlevel in recycled asphalt mixture using GPC. Constr Build Mater2008;22(6):1253–60.

[70] Wahhab HIAA, Asi IM, Ali FM, Al-Dubabi IA. Prediction of asphalt rheologicalproperties using HP-GPC. J Mater Civ Eng 1999;11(1):6–14.

[71] Kim KW, Burati Jr JL. Use of GPC chromatograms to characterize aged asphaltcements. J Mater Civ Eng 1993;5(1):41–52.

[72] Airey GD. State of the art report on ageing test methods for bituminouspavement materials. Int J Pavement Eng 2003;4(3):165–76.

[73] Xiaohu L, Isacsson U. Effect of aging on bitumen chemistry and rheology.Constr Build Mater 2002;16(1):15–22.

[74] Banerjee A, De Fortier Smit A, Prozzi JA. The effect of long-term aging on therheology of warm mix asphalt binders. Fuel 2012. DOI:10.1016/j.fuel.2012.01.072.

[75] Gandhi T. Effects of warm asphalt additives on asphalt binder and mixtureproperties. Clemson University, Ph.D thesis; 2008.

[76] Putman BJ. Qualification of the effects of crumb rubber in CRMbinder. USA: Clemson University; 2005.

[77] Liu S, Cao W, Fang J, Shang S. Variance analysis and performance evaluation ofdifferent crumb rubber modified (CRM) asphalt. Constr Build Mater2009;23(7):2701–8.

[78] Akisetty CK, Lee SJ, Amirkhanian SN. High temperature properties ofrubberized binders containing warm asphalt additives. Constr Build Mater2009;23(1):565–73.

[79] Akisetty CK, Lee SJ, Rogers W, Amirkhanian SN. Evaluation of engineeringproperties of rubberized laboratory mixes containing warm mix additives.Test Eval ASTM 2009;38(1):1–8.

[80] Lee SJ, Akisetty CK, Amirkhanian SN. The effect of crumb rubber modifier(CRM) on the performance properties of rubberized binders in HMApavements. Constr Build Mater 2008;22(7):1368–76.

[81] Xiao F, Amirkhanian SN, Juang S. Effects of various long-term aging procedureon rheological properties of laboratory prepared rubberized asphalt binders.Test Eval ASTM 2009;37(4):1–8.

[82] Xiao F, Amirkhanian SN, Juang CH. Rutting resistance of rubberized asphaltconcrete pavements containing reclaimed asphalt pavement mixtures. JMater Civ Eng 2007;19(6):475–83.

[83] Xiao F. Development of fatigue predictive models of rubberized asphaltconcrete (RAC) containing reclaimed asphalt pavement (RAP) mixtures.Clemson University, Ms.C thesis; 2006.

[84] Airey GD, Singleton TM, Collop AC. Properties of polymer modified bitumenafter rubber-bitumen interaction. J Mater Civ Eng 2002;14(4):344–54.

[85] Airey GD, Rahman MM, Collop AC. Absorption of bitumen into crumbrubber using the basket drainage method. Int J Pavement Eng 2003;4(2):105–19.

[86] Xiao F, Wenbin Zhao PE, Amirkhanian SN. Fatigue behavior of rubberizedasphalt concrete mixtures containing warm asphalt additives. Constr BuildMater 2010;23(10):3144–51.

[87] Zhengqi Z, Qifeng W, Zhisheng Z. Evaluation of Sasobit� warm mix rubberasphalt properties. In: Proceedings of 3th international conference ontransportation engineering. USA; 2011.

[88] Li M, Anling L, Ran J, Li Q. Testing and evaluation of Sasobit� on theperformances of asphalt rubber. In: ICCTP Integrated transportation system.Green intelligent-reliable. USA; 2011. p. 3502–9.

[89] Akisetty CK, Gandhi T, Lee SJ, Amirkhanian SN. Analysis of rheologicalproperties of rubberized binders containing warm asphalt additives. Can J CivEng 2010;37(5):763–71.

[90] Akisetty CK, Lee SJ, Amirkhanian SN. Laboratory investigation of the influenceof warm asphalt additives on long-term performance properties of CRMbinders. Int J Pavement Eng 2009;11(2):153–60.

[91] Gonzalez V, Martinez-Boza FJ, Navarro FJ, Gallegos C, Perez-Lepe A, Paez A.Thermomechanical properties of bitumen modified with crumb tire rubberand polymeric additives. Fuel Process Technol 2010;91(9):1033–9.

[92] Lee SJ, Amirkhanian SN, Park NW, Kim KW. Characterization of warm mixasphalt binders containing artificially long-term aged binders. Constr BuildMater 2009;23(6):2371–9.

[93] Shrum ED. Evaluation of moisture damage in warm mix asphalt containingrecycled asphalt pavement. University of Tennessee – Knoxville, Ms.C thesis;2010.

[94] Kim H, Lee SJ, Amirkhanian SN. Rheology of warm mix asphalt binders withaged binders. Constr Build Mater 2011;25(1):183–9.

[95] Kim H, Lee SJ, Amirkhanian SN, Park T-S. Performance evaluation of recycledPMA binders containing wma binders containing warm mix asphaltadditives. Test Eval ASTM 2011;39(4):1–8.

[96] Yildirim Y. Polymer modified asphalt binders. Constr Build Mater2007;21(1):66–72.

[97] Kim HK, Lee SJ, Amirkhanian SN. Effects of warm mix asphalt additives onperformance properties of polymer modified asphalt binders. Can J Civ Eng2010;37(1):17–24.

[98] Susana H, Macleod D, Zanzoto L. Our experiences with the application ofSasobit� in polymer modified asphalts. In: Proceedings of the fifty-thirdannual conference of the Canadian Technical Asphalt Association (CTAA).Saskatoon, Saskatchewan, Canada; 2008.

[99] Kanitpong K, Nam K, Martono W, Bahia H. Evaluation of a warm-mix asphaltadditive. Proc Inst Civil Eng Constr Mater 2008;161(1):1–8.

[100] Kanitpong K, Sonthong S, Nam K, Martono W, Bahia H. Laboratory study onwarm mix asphalt additives. In: Proceedings of 86th transportation researchboard annual meeting, Washington D.C., USA; 2007. p. 1–19.

[101] Hofsink W, Barnard M. SMA wearing courses on runways and taxiways-recent experience in South Africa. In: 30th International flexible pavementsconference. Surfers Paradise, Queensland, Australia; 2009.

[102] Kim H, Lee SJ, Amirkhanian SN. Influence of warm mix additives on polymermodified asphalt mixture properties. J Mater Civil Eng 2012:1–32. http://dx.doi.org/10.1061/(ASCE)TE.1943-5436.000040.

[103] Edwards Y, Tasdemir Y, Butt AA. Energy saving and environmental friendlywax concept for polymer modified mastic asphalt. Mater Struct2010;43(1):123–31.

[104] Krupa I, Mikova G, Luyt AS. Phase change materials based on low-densitypolyethylene/paraffin wax blends. Eur Polymer J 2007;43(11):4695–705.

[105] SP-2. Superpave mix design, superpave series. Asphalt Institute, Lexington,KY, USA; 2001.

[106] West RC, Watson DE, Turner PA, Casola JR. Mixing and compactiontemperatures of asphalt binders in hot-mix asphalt. NCHRP; 2010.

[107] Bennert T, Reinke G, Mogawer W, Mooney K. Assessment of workability andcompactability of warm-mix asphalt. Transport Res Rec: J Transport ResBoard 2010;2180:36–47. http://dx.doi.org/10.3141/2180-05.

[108] Bonaquist R. Mix Design Practices for Warm Mix Asphalt: NCHRP; 2011.[109] Sanchez-Alonso E, Vega-Zamanillo A, Castro-Fresno D, DelRio-Prat M.

Evaluation of compactability and mechanical properties of bituminousmixes with warm additives. Constr Build Mater 2011;25(5):2304–11.

[110] Vaitkus A, Kilas M, Tuminiene F, Perveneckas Z. Experience use of warm mixasphalt in Lithuania. In: The 8th Int Conf environment engineering. Vilnius,Lithuania; 2011.

[111] Kilas M, Vaitkus A, Paliukatie M. Warm asphalt research, analysis andevaluation. In: Proceedings of modern building materials, structures andtechniques. Vilnius Gediminas Technical University, Italy; 2010.

[112] Hamzah MO, Jamshidi A, Shahadan Z, Hasan MRM, Yahaya AS. Evaluation ofengineering properties and economic advantages of WMA using localmaterials. J Appl Sci 2010;10(20):2433–9.

[113] Brits C. Sasobit� investigation. South Africa: Geostrada Engineering MaterialsLaboratory; 2004.

[114] Mohammad L, Shadi S, Cooper S. Evaluation of asphalt mixture containingwarm mix additive. In: Proceedings of the airfield and highway pavementsconference. USA; 2008.

[115] Jones D, Rongzung W, Tsai B-W, Lu Q, Harvey JT. Warm-mix asphalt study:test track construction and first- level analysis of phase 1 HVS and laboratorytesting University of California. UC Davis, UC Berkeley, USA: PavementResearch Center; 2008.

[116] Kridan FAM, Arshad AK, Rahman MYA. Development of warm mix asphaltand compliance with the requirements set by specifications. Eur J Sci Res2010;48(1):118–28.

[117] Cooper SB. Evaluation of HMA mixtures containing Sasobit�. LouisianaTransportation Research Center; 2009.

[118] Goh DW, You Z. Warm Mix Asphalt using Sasobit� in Cold Region. Coldregions impacts on research, design, and construction. USA: Cold RegionsEngineering; 2009.

[119] Hearon A, Diefenderfer S. Laboratory evaluation of warm asphalt propertiesand performance. Airfield and highway pavements: efficient pavementssupporting transportation’s a future proceedings on airfield and highwaypavement conference. ASCE, USA; 2008. p. 182–94.

[120] Diefenderfer S, McGhee K, Donaldson BM. Installation of warm mix asphaltprojects in Virginia Transport Research Council. Research report; 2007.

[121] Akisetty CK, Lee SJ, Amirkhanian SN. Volumetric properties of warmrubberized mixes depending on compaction temperature. Airfield andhighway pavements: efficient pavements supporting transportation’s afuture proceedings on airfield and highway pavement conference. ASCE,USA; 2008. p. 205–12.

[122] Akisetty CK, Lee SJ, Amirkhanian SN. Effects of compaction temperature onvolumetric properties of rubberized mixes containing warm-mix additives. JMater Civ Eng 2009;21(8):409–4015.

[123] Kanitpong K, Charoentham N, Likitlersuang S. Investigation on the effects ofgradation and aggregate type to moisture damage of warm mix asphaltmodified with Sasobit�. Int J Pavement Eng 2011. http://dx.doi.org/10(1080/10298436), 2011, 565058.

[124] Edwards Y, Tasdemir Y, Isacsson U. Influence of commercial waxes andpolyphosphoric acid on bitumen and asphalt concrete performance at lowand medium temperatures. Mater Struct 2006;39(7):725–37.

http://dx.doi.org/10.1061/(ASCE)TE.1943-5436.000040

http://dx.doi.org/10.3141/2180-05

http://dx.doi.org/10(1080/10298436),2011,565058

http://dx.doi.org/10(1080/10298436),2011,565058


[125] Shang L, Wang S, Zhang Y. Pyrolyzed wax from recycled cross-linkedpolyethylene as warm mix asphalt (WMA) additive for SBS modifiedasphalt. Constr Build Mater 2011;25(2):886–91.

[126] Xiao F, Amirkhanian SN, Putman BJ. Evaluation of rutting resistance in warm-mix asphalts containing moist aggregate. Transport Res Rec: J Transport ResBoard 2010;2180:75–84. http://dx.doi.org/10.3141/2180-09.

[127] Hurley GC, Prowell BD, Kvasnak AN. Missouri field trial of warm-mix asphalttechnologies: construction summary. NCAT; 2010.

[128] Hurley G, Prowell B, Kvasnak A. Wisconsin field trial of warm-mix asphalttechnologies: construction summary. NCAT; 2010.

[129] Kim YR, Zhang J, Ban H. Implementation of warm-mix asphalt mixtures innebraska pavements. USA: Nebraska Department of Roads (NDOR); 2010.

[130] Hurley GC, Prowell BD, Kvasnak AN. Michigan field trial of warm mix asphalttechnologies: construction summary. NCAT; 2009.

[131] Kvasnak AN, Moore JR, Taylor AJ, Prowell BD. Preliminary evaluation of warmmix asphalt field demonstration. Franklin and Tennessee. NCAT; 2010.

[132] Estakhri C, Button J, Alvarez AE. Field and laboratory investigation of warmmix asphalt in Texas. Texas Transportation Institute and the Texas A&MUniversity, System; 2010.

[133] Solaimanian M, Milander S, Boz I, Stoffels SM. Development of guidelines forusage of high percent RAP in warm-mix asphalt pavements. PennsylvaniaDepartment of Transportation; 2011.

[134] Witczak MW. Specification criteria for simple performance tests for rutting,volume I: dynamic modulus (E⁄) and volume II: flow number and flow time:NCHRP, Report 580; 2008.

[135] Petit C, Millien A, Canestrari F, Pannunzio V, Virdili A. Experimental study onshear fatigue behaviour and stiffness performance of warm mix asphalt byadding synthetic wax. Cornell University, Library; 2012. p. 1–21.

[136] Haggag MM, Mogawer WS, Bonaquist R. Fatigue evaluation of warm mixasphalt mixtures using uniaxial cyclic direct tension compression test.Transport Res Rec: J Transport Res Board 2011;2208:26–32. http://dx.doi.org/10.3141/2208-04.

[137] Yanhai Y, Huaizhi Z, Yaodong W. Laboratory evaluation of the warm mixasphalt performance in Liaoning. In: ICCTP: critical issues in transportationsystems planning, development, and management. USA; 2009.

[138] Saboundjian S, Liu J, Li P, Brunette B. Late-season paving of a low-volumeroad with warm-mix asphalt. Transport Res Rec: J Transport Res Board2011;2205:40–7. http://dx.doi.org/10.3141/2205-06.

[139] Goh SW, You Z. Evaluation of warm mix asphalt produced at varioustemperature through dynamic modulus testing and four point beam fatiguetesting. USA: Geotechnical Special Publication; 2011.

[140] Chapuis RP, Gatien A. Temperature dependent tensile strength of asphaltmixtures in relation to field cracking data. ASTM STP 1995;1265:180–93.

[141] Benert T, Maher A, Sauber R. Influence of production temperature andaggregate moisture content on the initial performance of warm-mix asphalt.Transport Res Rec: J Transport Res Board 2011;2208:97–107. http://dx.doi.org/10.3141/2208-13.

[142] Medeiros Jr MS, Daniel JS, Bolton HL, Meagher WC. Evaluation of moistureand low-temperature cracking susceptibility of warm-mixture asphalt. Int JPavement Eng 2011:1–6.

[143] Curtis CW. A literature review of liquid anti stripping and tests for measuringstripping. DC: National Research Council Washington; 1990.

[144] Caro S, Masad E, Bhasin A, Little DN. Moisture susceptibility of asphaltmixtures, Part 1: mechanisms. Int J Pavement Eng 2008;9(2):81–98.

[145] Caro S, Masad E, Bhasin A, Little DN. Moisture susceptibility of asphaltmixtures, Part 2: characterisation and modelling. Int J Pavement Eng2008;9(2):99–114.

[146] MS-24. Best practice to minimize moisture sensitivity in asphalt mixture.Asphalt Institute, KY, USA; 2007.

[147] Kanitpong K, Bahia H. Relating adhesion and cohesion of asphalts to the effectof moisture on laboratory performance of asphalt mixtures. Transport ResRec: J Transport Res Board 2005;1901:33–43. http://dx.doi.org/10.3141/1901-05.

[148] Buddhala A, Hossain Z, Wasiuddin NM, Zaman M, O’Rear EA. Effects of anamine anti-stripping agent on moisture susceptibility of Sasobit� and Aspha-Min� mixes by surface free energy analysis. J Test Eval 2012;40(1):1–9.

[149] Wasiuddin NM, Zaman MM, O’Rear EA. Effect of Sasobit� and Aspha-Min� onwettability and adhesion between asphalt binders and aggregates. TransportRes Rec: J Transport Res Board 2008;2051:80–9. http://dx.doi.org/10.3141/2051-10.

[150] Wei J, Huang X, Zhang Y. Influence of commercial wax on performance ofasphalt. J Mater Civ Eng 2011;22(8):760–6.

[151] O’Sullivan K, Wall PA. The effects of warm mix asphalt additives on RecycledAsphalt Pavement. Worcester Polytechnic Institute, Ms.C thesis; 2009.

[152] Wasiuddin NM, Saltibus NE, Mohammad LN. Novel moisture-conditioningmethod for adhesive failure of hot-and warm-mix asphalt binders. TransportRes Rec: J Transport Res Board 2012;2208:108–17. http://dx.doi.org/10.3141/2208-14.

[153] Arabani M, Roshani H, Hamedi GH. Estimating moisture sensitivity of warm-mix asphalt modified with Zycosoil as an antistrip agent using surface freeenergy method. J Mater Civ Eng 2011;1:392.

[154] Shivaprasad PV, Xiao F, Amirkhanian SN. Evaluation of moisture sensitivity ofstone matrix asphalt mixtures using polymerised warm mix asphalttechnologies. Int J Pavement Eng 2012:1–14.

[155] Hamzah MO, Aman MY, Shahadan Z, Mohd Hassan MR. Laboratory evaluationof the dynamic stripping test on porous asphalt incorporating Sasobit�. In:

Proceedings of the 7th international conference on airfield pavementtechnology. Thailand; 2011.

[156] Lu Q, Harvey JT. Long-term effectiveness of antistripping additives:laboratory evaluation. Transport Res Rec: J Transport Res Board2006;1970:14–24. http://dx.doi.org/10.3141/1970-04.

[157] Mogawer WS, Austerman AJ, Bahia HU. Evaluating the effect of warm-mixasphalt technologies on moisture characteristics of asphalt binders andmixtures. Transport Res Rec: J Transport Res Board 2011;2209:52–60. http://dx.doi.org/10.3141/2209-07.

[158] Xiao F, Zhao W, Gandhi T, Amirkhanian SN. Influence of antistrippingadditives on moisture susceptibility of warm mix asphalt mixtures. J MaterCiv Eng 2010;22(10):1047–55.

[159] Xiao F, Jordan J, Amirkhanian SN. Laboratory investigation of moisturedamage in warm-mix asphalt containing moist aggregate. Transport Res Rec:J Transport Res Board 2009;2126:115–24. http://dx.doi.org/10.3141/2126-14.

[160] Xiao F, Punith VS, Amirkhanian SN. Low-volume road WMA mixtures:moisture susceptibility of mixtures containing coal ash and roofing shinglewith moist aggregate. J Mater Civ Eng 2011;24(1):48–56.

[161] Xiao F, Wenbin Z, Amirkhanian SN. Laboratory evaluation of effects of soakedduration on moisture susceptibility of warm mix asphalt mix. T & DICongress. USA; 2011.

[162] Little DN, Epps J, Sebaaly PE. The benefits of hydrated lime in hot mixasphalt. National Lime Association; 2001.

[163] Shen J, Huang B, Shu X, Tang B. Influence of nano-sized hydrated lime (HL) onselected properties of hot-mix asphalt (HMA). Int J Pavement Res Technol2010;4(4):252–7.

[164] Cheng J, Shen J, Xiao F. Moisture susceptibility of warm mix asphalt mixturescontaining nanosized hydrated lime. J Mater Civ Eng 2011;1:265;Cheng J, Shen J, Xiao F. Moisture susceptibility of warm-mix asphalt mixturescontaining nanosized hydrated lime. J Mater Civ Eng 2011;23(1):1552–9.

[165] Shivaprasad PV, Xiao F, Amirkhanian SN. Moisture susceptibility ofpolymerized stone matrix asphalt using warm mix asphalt technologiesusing moist aggregates. Test Eval ASTM 2011;9(8):1–14.

[166] Akisetty C, Xiao F, Gandhi T, Amirkhanian SN. Estimating correlationsbetween rheological and engineering properties of rubberized asphaltconcrete mixtures containing warm mix asphalt additive. Constr BuildMate 2011;25(2):950–6.

[167] Xiao F, Wenbin Z, Serji NA. Aging influence on fatigue characteristics of RACmixtures containing warm asphalt additives. Adv Civil Eng; 2010.

[168] NAPA. Black and green: sustainable asphalt, now and tomorrow. NationalAsphalt Pavement Association; 2009.

[169] Lee JC, Edil TB, Tinjum JM, Benson CH. Quantitative assessment ofenvironmental and economic benefits of recycled materials in highwayconstruction. Transport Res Rec: J Transport Res Board 2010;2158:138–42.http://dx.doi.org/10.3141/2158-17.

[170] Karlsson R, Isacsson U. Material-related aspects of asphalt recycling: state-of-the-art. J Mater Civ Eng 2006;18(1):81–92.

[171] Chauhan SK, Sharma S, Shukla A, Gangopadhyay S. Recent trends of theemission characteristics from the road construction industry. Environ SciPollut Res 2010;17(9):1493–14501.

[172] Kuo CY, Yang YH, Chao MR, Hu CW. The exposure of temple workers topolycyclic aromatic hydrocarbons. Sci Total Environ 2008;401(1–3):44–50.

[173] Tsai PJ, Shih TS, Chen HL, Lee WJ, Lai CH, Liou SH. Assessing and predicting theexposures of polycyclic aromatic hydrocarbons (PAHs) and their carcinogenicpotencies from vehicle engine exhausts to highway toll station workers.Atmos Environ 2004;38(2):333–43.

[174] Karakaya A, Yucesoy B, Turhan A, Erdem O, Burgaz S, Karakaya AE.Investigation of some immunological functions in a group of asphaltworkers exposed to polycyclic aromatic hydrocarbons. Toxicology1999;135(1):43–7.

[175] Chiu CT, Hsu TH, Yang WF. Life cycle assessment on using recycled materialsfor rehabilitating asphalt pavements. Resour Conserv Recycl2008;52(3):545–56.

[176] Huang Y, Bird RN, Heidrich O. A review of the use of recycled solid wastematerials in asphalt pavements. Resour Conserv Recycl 2007;52(1):58–73.

[177] Jamshidi A, Hamzah MO, Shahadan Z. Selection of reclaimed asphaltpavement sources and contents for asphalt mix production based onasphalt binder rheological properties, fuel requirements and greenhousegas emissions. J Cleaner Prod 2012;23(1):20–7.

[178] Hamzah MO, Jamshidi A, Shahadan Z. Effects of Sasobit� on the required heatenergy and CO2 emission on blended asphalt binder incorporated with agedbinder. Eur J Sci Res 2010;42(1):15–25.

[179] Howard IL, Cooley LAJR, Doyle JD. Laboratory testing and economic analysisof high RAP warm mixed asphalt. Mississippi, USA: Mississippi Departmentof Transportation; 2009.

[180] Tao M, Mallick RB. Effects of warm-mix asphalt additives on workability andmechanical properties of reclaimed asphalt pavement material. TransportRes Rec: J Transport Res Board 2009;2126(-1):151–60.

[181] Mallick RB, Kandhal PS, Bradbury RL. Using warm-wix asphalt technology toincorporate high percentage of reclaimed asphalt pavement material inasphalt mixtures. Transport Res Rec: J Transport Res Board 2008;2051:71–9.http://dx.doi.org/10.3141/2051-09.

[182] Celaya M, Nazarian S. Implementation of quality management of hot-mixasphalt with seismic methods. Transport Res Rec: J Transport Res Board2008;2057:99–106. http://dx.doi.org/10.3141/2057-12.

http://dx.doi.org/10.3141/2180-09

http://dx.doi.org/10.3141/2208-04

http://dx.doi.org/10.3141/2205-06

http://dx.doi.org/10.3141/2208-13

http://dx.doi.org/10.3141/1901-05

http://dx.doi.org/10.3141/1901-05

http://dx.doi.org/10.3141/2051-10

http://dx.doi.org/10.3141/2051-10

http://dx.doi.org/10.3141/2208-14

http://dx.doi.org/10.3141/2208-14

http://dx.doi.org/10.3141/1970-04

http://dx.doi.org/10.3141/2209-07

http://dx.doi.org/10.3141/2126-14

http://dx.doi.org/10.3141/2126-14

http://dx.doi.org/10.3141/2158-17

http://dx.doi.org/10.3141/2051-09

http://dx.doi.org/10.3141/2057-12


[183] Williams RR, Nazarian S. Correlation of resilient and seismic modulus testresults. J Mater Civ Eng 2007;19(12):1026–32.

[184] Bai X. Assessment of relationship between dynamic and seismic moduli ofasphalt mixtures. University of Texas, El Paso, Ph.D thesis; 2004.

[185] Mallick RB, Bradley JE, Bradbury RL. Evaluation of heated reclaimed asphaltpavement material and wax-modified asphalt for use in recycled hot-mixasphalt. Transport Res Rec: J Transport Res Board 2007;1998:112–22. http://dx.doi.org/10.3141/1998/14.

[186] West R, Kvasnak A, Tran N, Powell B, Turner P. Testing of moderate and highreclaimed asphalt pavement content mixes. Transport Res Rec: J TransportRes Board 2009;2126:100–8. http://dx.doi.org/10.3141/2126-12.

[187] Shivaprasad PV, Xiao F, Amirkhanian SN. Performance of warm-mix asphaltmixtures containing recycled coal ash and roofing shingles with moistaggregates for low-volume roads. Transport Res Rec: J Transport Res Board2011;2205:48–57. http://dx.doi.org/10.3141/2205-07.

[188] Robinette C, Epps J. Energy, emissions, material conservation, and pricesassociated with construction, rehabilitation, and material alternatives forflexible pavement. Transport Res Rec: J Transport Res Board2010;2179:10–22. http://dx.doi.org/10.3141/2179-02.

[189] Al-Qadi IL, Wang H, Baek J, Leng Z, Doyen M, Gillen S. Effects of curing timeand reheating on performance of warm stone matrix asphalt. J Mater CivilEng 2012:1–32. http://dx.doi.org/10.1061/(ASCE)MT.1943-5533.0000513.

[190] Al-Qadi IL, Kern J, Baek J, Doyen M. Short-term characterization andperformance of warm mix asphalt. In: Illinois Bituminous pavingconference. Illinois, USA; 2010.

[191] Al-Qadi IL, Baek J, Leng Z, Wang H, Doyen M, Kern J, et al. Short-termperformance of modified stone matrix asphalt (SMA) produced with warmmix additives. Illinois Center for Transportation; 2012.

[192] Chowdhury A, Button JW. A review of warm mix asphalt. USA: TexasTransportation Institute; 2008.

[193] Button JW, Estakhri C, Wimsat A. A synthesis of warm-mixasphalt. USA: Texas Transportation Institute and Texas A&M UniversitySystem; 2007.

[194] Noelting M, Arnold J, Jones B. Heavy duty pavement – new asphalt designsmeet extreme challenges. In: China–Japan paving technology symposium.Nanjing, China; 2005.

[195] Roberts FL, Mohammad LN, Wang LB. History of hot mix asphalt mixturedesign in the United States. J Mater Civ Eng 2002;14(4):279–93.

[196] Keches C, Leblank A. Reducing greenhouse gas emissions from asphaltmaterials. Worcester Polytechnic Institute, Bachelor thesis; 2007.

[197] Choi YK. Warm Mix Asphalt (WMA) review. Sydney, NSW,Australia: Austroads; 2007.

[198] Jones D, Rongzung W, Tsai B-W, Lu Q, Harvey JT. Warm-mix asphalt study:test track construction and first- level analysis of phase 1 HVS and laboratorytesting. UC Davis, UC Berkeley, USA: University of California, PavementResearch Center; 2008.

[199] Aschenbrener T, Schiebel B, West R. Three-year evaluation of the Coloradodepartment of transportation’s warm-mix asphalt experimental feature on I-70 in Silverthorne, Colorado. Auburn, AL, USA: National Center for AsphaltTechnology; 2011.

[200] Kvasnak AN, Moore JR, Taylor AJ, Prowell BD. Preliminary evaluation ofwarm-mix asphalt field demonstration. Tennessee: Franklin NCAT; 2010.

[201] Sargand SM, Edwards WF, Bendana J. Testing of perpetual with warm asphaltconcrete mixes in the Ohio APLF. In: 3th International conference onaccelerated pavement testing apt 2008 impacts and benefits from APTprograms. Madrid, Spain; 2008.

[202] Sargand SM, Figueroa JL, Edwards W, Al-Rawashdeh AS. Performanceassessment of warm mix asphalt (WMA) pavements. USA: Ohio ResearchInstitute for Transportation and the Environment; 2009.

[203] Hurley GC, Prowell BD, Kvasnak AN. Ohio field trial of warm mix asphalttechnologies: construction summary. Auburn, AL: National Center for AsphaltTechnology; 2008.

[204] Kristjonesdottir O. Warm Mix Asphalt for cold weatherpaving. USA: University of Washington; 2006.

[205] Bornmann F, Hiley R, Strydom S. Fischer-Tropsch wax bitumen modifier:overcoming temperature and time, constraints; 2007.

[206] Howard IL, Doyle JD, Hemsley JM, Baumgardner GL, Cooley LA. Use of hot mixwarm compacted asphalt in construction. In: Proceedings of 90thtransportation research board annual meeting. Washington D.C., USA; 2011.

[207] Shaw J. TWG-Warm mix asphalt. Sasolwax; 2007.[208] Sabita. Innovative warm mix asphalt trials completed near Durban; 2011.[209] Brown C. Globalization and environmental challenges, emergent

sustainability: the concept of sustainable development in a complexworld. Netherlands: Springer Publishing Inc; 2008. p. 141–9.

[210] Shackel B. The objective selection of concrete block paving for engineeringprojects. In: Proceedings of the 8th conference concrete block pavement.California, San Francisco, USA; 2006. p. 315–24.

[211] Glasby GP. Concept of sustainable development: a meaningful goal? Sci TotalEnviron 1995;159(1):67–80.

[212] Cheng L, Chen L, Yan G, Zheng H. Life cycle assessment of road surface pavingwith warm mix asphalt (WMA) replacing hot mix asphalt (HMA). In:International conference on e-product e-service and e-entertainment (ICEEE).Henan, China; 2010.

[213] Hassan M. Evaluation of the environmental and economic impacts of warm-mix asphalt using life-cycle assessment. Int J Constr Educat Res2010;6(3):238–50.

[214] Tatari O, Nazzal M, Kucukvar M. Comparative sustainability assessment ofwarm-mix asphalts: a thermodynamic based hybrid life cycle analysis.Resour Conserv Recycl 2012;58(1):18–24.

[215] Armstrong FA, Blundell KM. Energy... beyond oil. UK: Oxford University Press;2007.

[216] USEA. Toward a national energy policy. United States Energy Administration;2004.

[217] Mallick RB, Bergendahl J. A laboratory study on CO2 emission from asphaltbinder and its reduction with the use of warm mix asphalt. Int J Sustain Eng2009;2(4):275–83.

[218] Sargand S, Nazzal MD, Al-Rawashdeh A, Powers D. Field evaluation of warmmix asphalt Technologies. J Mater Civ Eng 2011;1(17):72–9.

[219] White TD, Haddock JE, National Research Council, Transportation Research B,National Cooperative Highway Research P, American Association of State H,Transportation O, et al. Validation of performance-related test of aggregatesfor use in hot-mix asphalt pavements. Transportation Research Board of theNational Academies; 2006.

[220] MS-4. The Asphalt handbook. Asphalt Institute, Lexington, KY, USA; 2007.[221] Cominsky RJ, Huber GA, Kennedy TW, Anderson M. The Superpave mix

design manual for new construction and overlays. Austin, USA: University ofTexas; 1994.

[222] Read J, Whiteoak D. The shell bitumen handbook. Thomas Telford ServicesLtd; 2003.

[223] Roberts FL, Kandhal PS, Brown ER, Lee DY, Kennedy TW. Hot mix asphaltmaterials, mixture design and, construction. 3rd ed. 2009.

[224] Kandhal PS, Mallick RB, Parker F. Aggregate tests for hot-mix asphalt: state ofthe practice. Transportation Research Board; 1997.

[225] Tarrer AR, Wagh V. The effects of the physical and chemical characteristics ofaggregate on boning; 1991.

[226] Barksdale RD. The aggregate handbook. National Stone Association; 1991.[227] Hosking R. Road aggregates and skidding. London: HMSO; 1992.[228] Mrawira DM, Luca J. Effect of aggregate type, gradation, and compaction level

on thermal properties of hot-mix asphalts. Can J Civ Eng2006;33(11):1410–7.

[229] Luca J, Mrawira D. New measurement of thermal properties of superpaveasphalt concrete. J Mater Civ Eng 2005;17(1):72–9.

[230] Amirkhanian SN, Williams B. Recyclability of moisture damaged flexiblepavements. J Mater Civ Eng 1993;5(4):510–30.

http://dx.doi.org/10.3141/1998/14

http://dx.doi.org/10.3141/2126-12

http://dx.doi.org/10.3141/2205-07

http://dx.doi.org/10.3141/2179-02

http://dx.doi.org/10.1061/(ASCE)MT.1943-5533.0000513

Documents

Performance of Warm Mix Asphalt containing Sasobit®: State-of-the-art