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Construction and Building Materials 64 (2014) 141149

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Construction and Building Materials

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Laboratory performance of warm mix asphalt containing recycledasphalt mixtures

http://dx.doi.org/10.1016/j.conbuildmat.2014.04.0020950-0618/ 2014 Elsevier Ltd. All rights reserved.

Corresponding author at: Institute of Road and Bridge Engineering, DalianMaritime University, Dalian, Liaoning 116026, China.

E-mail addresses: [email protected], [email protected] (N. Guo).

Naisheng Guo a,b,, Zhanping You b, Yinghua Zhao a, Yiqiu Tan c, Aboelkasim Diab ba Institute of Road and Bridge Engineering, Dalian Maritime University, Dalian, Liaoning 116026, Chinab Department of Civil and Environmental Engineering, Michigan Technological University, Houghton, MI 49931-1295, USAc School of Transportation Science and Engineering, Harbin Institute of Technology, Harbin, Heilongjiang 150090, China

h i g h l i g h t s

WMA mixtures containing high percentage of RAP were produced using different WMA additives. WMA additives lowered the mixing and compaction temperatures of mixtures. Performance evaluation on rutting, low temperature cracking, moisture damage, aging, and fatigue of mixtures. Effect of WMA additives and RAP on the performance of mixtures was pronounced.

a r t i c l e i n f o

Article history:Received 24 December 2013Received in revised form 29 March 2014Accepted 2 April 2014

Keywords:Warm mix asphalt (WMA)Reclaimed asphalt pavement (RAP)Moisture damageAgingFatigueRuttingLow temperature cracking

a b s t r a c t

This study aims to evaluate the laboratory performance of warm mix asphalt containing reclaimedasphalt pavement (WMARAP) materials. The WMA mixtures containing 0% and 40% RAP were producedusing Evotherm-DAT and S-I WMA additives. The laboratory performance tests included rutting, bending,freezethaw splitting, Marshall immersion, aging, freezethaw cycles splitting, and fatigue tests. Themoisture and low temperature cracking resistance were evaluated for aged mixtures. The results showedthe WMA mixtures without RAP performed better moisture and low temperature cracking resistance, andlower rutting resistance than the WMARAP mixtures. The WMA mixtures suffered from the short-termaging exhibited a slight increase as compared to the unaged mixtures, whereas the long-term agingresulted in a distinct reduction in terms of the moisture resistance. After the short- and long-term aging,the WMA mixtures exhibited a greater decrease than the unaged mixtures in terms of the low temper-ature cracking resistance. The tensile strength ratio (TSR) results of the WMARAP mixtures generallydecreased with the increase of freezethaw cycles, while the TSR results showed an obvious increaseafter three freezethaw cycles. The addition of RAP significantly reduced the fatigue resistance of theWMARAP mixtures in comparison with the WMA mixtures without RAP. Based upon the study findings,the moisture resistance under freezethaw cycles conditioning remains an issue to be considered in theWMARAP mixtures.

2014 Elsevier Ltd. All rights reserved.

1. Introduction

Warm mix asphalt (WMA) is a technology that allows produc-ing asphalt mixtures at lower temperature than those in the pro-duction of traditional hot mix asphalt (HMA). The production ofWMA mixtures requires lowering the manufacturing temperaturewithout reducing their level of mechanical performance. Severaladvantages of WMA include reduced greenhouse gas emissions,

better working conditions, lower energy consumption, longerhauling distances, etc. Currently, WMA can be produced by theaddition of organic additives and chemical additives or throughthe foaming technologies (water-bearing additives or water-basedprocesses) with the objective to increase the mixture workabilityat reduced temperatures [1]. The application of organic additiveslowers production temperature by decreasing the asphalt binderviscosity, while the chemical additives reduce the internal frictionbetween aggregate particles without change of binder viscosity[2,3]. The foaming technologies are based on the injection of smallamounts of water along with the liquid asphalt binder during themixing process which in-turn causes the asphalt binder to expand
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142 N. Guo et al. / Construction and Building Materials 64 (2014) 141149

in volume and foam at a given temperature. The foaming processhelps the liquid coat the aggregate at reduced temperatures [4].

Asphalt pavement in need of reconstruction or new overlay is acandidate for recycling. Over the years, a lot of recycling technol-ogies have been developed for reclaimed asphalt pavement (RAP),and each of the technologies is specialized to dispose a given task.The central plant hot recycling technology is widely used due tomany benefits including proper mixture gradation controlling,stable quality, reliable performance, etc. Moreover, the perfor-mance of hot recycled asphalt mixture (HRAM) can be restoredto the equivalent level of HMA, and thus the central plant hotrecycling technology is particularly applicable in recycling of theoverused asphalt pavement [5]. However, in the production ofHRAM, which cannot be heated by the open flame, it is difficultfor RAP to obtain the desired mixing temperature. The higher mix-ing temperature of HRAM tends to make the reclaimed asphaltengender secondary aging, which may be a bottleneck in the ser-vice of the central plant hot recycling technology. The smaller RAPcontent to control the production quality of HRAM is also thetechnology disadvantage in comparison with the higher RAP con-tent in the cold recycling technology. The combination of theWMA technology with the central plant hot recycling technologycan be useful to significantly reduce the mixing and productiontemperatures of warm mix asphalt containing reclaimed asphaltpavement (WMARAP) mixtures. The reduction in temperaturesmeans less energy cost in production, and the decrease in fuelconsumption will lower fumes and greenhouse gas emissions.This may also be beneficial to the mixing of virgin asphalt andaged asphalt at lower temperatures, the high RAP content, andfurthermore, the production quality and workability of reclaimedasphalt mixtures.

In recent years, the research and practical use of WMARAPmixtures have been increasingly performed by researchers andpractitioners. A lot of different WMA additives were employed toobtain WMA binder derived from the mixing of virgin asphaltand RAP [68]. Evotherm and Sasobit WMA additives were usedto investigate the laboratory performance of WMARAP mixturesto seek ways to incorporate as high amount of RAP as possible.Compaction characteristics of the Sasobit WMA containing RAPranged from 0% to 60% was evaluated using different compactiontemperatures [9]. Marshall immersion and freezethaw splittingtests were conducted to evaluate the moisture susceptibility ofWMARAP mixtures produced using the Evotherm, at RAP con-tents of 0%, 30%, 40%, and 50% [10]. The skid resistance testingwas performed using a dynamic friction tester in conjunction witha circular texture meter to evaluate the skid resistance of theEvotherm WMA mixtures containing 0%, 50%, and 100% RAP [11].Laboratory tests including rutting and freezethaw splitting testswere conducted to evaluate the Evotherm WMA mixtures with dif-ferent RAP contents [12]. The rutting, bending, and freezethawsplitting tests were performed for evaluation of the Sasobit WMAmixtures containing RAP content ranged from 0% to 60% [13].The four-point bending beam fatigue test at a controlled-strainmode was conducted to evaluated the fatigue resistance ofWMARAP mixture produced using the Evotherm and 45% RAP[14]. Moreover, the WMA containing reclaimed modified asphaltor reclaimed asphalt with recycled asphalt shingle (RAS) wereevaluated through laboratory performance tests. Marshall mixdesign procedure was utilized to design the recycled SMA (StoneMastic Asphalt) mixture with the Evotherm. Meanwhile, a labora-tory study was carried out to investigate the mixing temperatureand fatigue properties of the mixture with a rejuvenating agent[15]. The bending beam rheometer (BBR) test and asphalt bindercracking device methods were conducted to evaluate the lowtemperature performance of the Sasobit WMA binder materialscontaining RAS, RAP, and bioasphalt [16].

Highway engineers started to use the foaming technologies inWMARAP mixtures construction due to cost-effectiveness. Ingeneral, the foaming technologies do not require any costlyadditives to be added to the mixtures. More importantly, the foam-ing technologies have not very expensive plant modificationsrequirement since the foaming component can be attached to plantsystems for a reasonable price without the need for major changes.In a study, the dynamic modulus and indirect tensile tests of mix-tures compacted using a Superpave gyratory compactor were con-ducted to characterize the mechanical properties of porous asphaltpavement mixtures containing 15% RAP and a water-bearing WMAadditive (Advera) [17]. The freezethaw tensile strength, Super-pave indirect tension, dynamic modulus, and Hamburg wheeltracking tests were conducted to evaluate the moisture susceptibil-ity of plant-produced foamed (water-based) WMA containing up to50% RAP [18]. Moreover, the stiffness characteristics, moisturesusceptibility, rutting, and fatigue resistance of plant-producedfoamed (water-based) WMA mixtures with RAP content rangedfrom 15% to 40% were evaluated using laboratory tests [19,20].

One classification of WMA differentiates those mixtures men-tioned above according to the temperature reduction achievedand divides them into two groups: WMA and Half-WMA. A labora-tory study was carried out to evaluate the moisture susceptibility,rutting, and fatigue resistance of laboratory-produced Half-WMAmixtures containing moist aggregates, RAS, and RAP [21].

Although previous studies shown above which mainly focusedon evaluating WMARAP mixtures in terms of moisture suscepti-bility, rutting and low temperature cracking resistance as mea-sured in the laboratory, the durability concerns such as aging andmoisture remain in WMARAP technology, and then the long-termperformance of the field pavement could not be evaluated.Presently, the WMA additives used mostly in China are producedby the U.S. and some countries in Europe. Although the WMA addi-tives can efficiently reduce fabrication temperatures of WMARAPmixtures, higher cost and more complicated addition processes tosome WMA additives result in a impediment to practical use ofWMARAP mixtures to some degree at least. In order to gain morebenefits from WMARAP technology, WMA additives that are cost-effective, workability-efficient, and appropriate for the appointedregion have been developing in China. Additionally, the percent-ages are selected based upon the Chinese technical specifications(Technical Specifications for Recycling of Highway Asphalt Pave-ment (JTG F41-2008)), which define and specify the design require-ments of HRAM with RAP contents as not more than 30%.Therefore, the laboratory performance of WMA mixtures contain-ing high percentage of RAP should be considered as the main con-cern of interest covered in this study.

2. Objectives and scope

Based on the reconstruction project of a highway asphaltpavement in Liaoyang China, the selected WMA additives and reju-venating agent were added into hot recycled asphalt to lower themixing and compaction temperatures and increase the RAP con-tent. The objective of this study is to evaluate the laboratory per-formance of WMA mixtures containing 0% and 40% RAP throughthe rutting, bending, freezethaw splitting, Marshall immersion,aging, freezethaw cycles splitting, and fatigue tests. The mixingand compaction temperatures of mixtures would significantlyaffect the compaction characteristics and mechanical propertiesof the WMARAP mixtures. Therefore, the analysis of the compac-tion characteristics was performed to obtain the fabrication tem-peratures of the WMARAP mixtures. Aging processes haveconsiderable impact on the field performance of the mixtures.The short- and long-term aging tests were used to evaluate the

Table 2Screening test results and volumetric properties of extracted aggregates.

Sieve size(mm)

RAP (010 mm)percent passing (%)

RAP (1020 mm)percent passing (%)

RAPproperties

N. Guo et al. / Construction and Building Materials 64 (2014) 141149 143

resistance to aging during construction and service, respectively.Then, the freezethaw splitting and bending tests were conductedto expose the moisture susceptibility and low temperature crack-ing resistance in terms of aged mixtures.

19 100 10016 100 9913.2 100 94 RAP (0

10 mm):9.5 100 74 Gsb = 2.6724.75 79 40 AC = 5.5%2.36 56 26 RAP (10-

20 mm):1.18 40 19 Gsb = 2.7070.6 33 16 AC = 3.4%0.3 21 120.15 14 90.075 10 8

3. Materials

An innovative WMA additive S-I developed in China, as a chemical additive con-sisting of surfactant, along with Evotherm-DAT was used to prepare the WMARAPmixtures samples. The content of each WMA additive was selected to comply withthe manufacturer recommendations. The Evotherm-DAT is a brown solution, and itwas added at a rate of 11% by weight of the asphalt binder. The S-I is a white con-centrated solution, the solution must be diluted with water in the proportion 7.6parts concentrated solution to 100 parts water while used, and then it was addedat a rate of 5.3% by weight of the asphalt binder. As a result of the residual amountof the WMA additives added into the mixtures is not more than 1% in comparisonwith asphalt content, thus it is not essential to count the amount of the WMA addi-tive in the asphalt content. This means the aggregate gradation, optimum asphaltcontent, and target volume of air voids of the WMARAP mixtures may be consid-ered to be consistent with that of the HRAM in mix design need not be changed aswell.

The grade of virgin asphalt binder labeled as AH-90 was used in this study. Theproperties of the asphalt binder are shown in Table 1. The asphalt binder is com-monly used across Liaoning and much of China in application with the northernregions.

Aggregates were sampled from a central HMA producer of Liaoyang, includingcoarse aggregates, stone chips, and limestone-based mineral filler. The RAP wassampled from a stockpile of pavement materials reclaimed through milling of theasphalt concrete layer of Xiaoxiao Highway in Liaoyang. The particle sizes of theRAP were fractionated into two sieve sizes: 1020 mm and 010 mm. The screeningtest results of extracted aggregates with bulk specific gravity (Gsb), and asphalt con-tent (AC) are listed in Table 2. The overall technical properties of the RAP and virginmaterials met the requirements of the technical specifications (JTG F40-2004).

Rejuvenating agents are used to restore the reclaimed asphalt binder propertiesto a consistency level appropriate to construction purposes and pavement perfor-mance, and to optimize the chemical characteristics with regard to durability.The rejuvenating agents should also provide sufficient additional binder to coatany new aggregates that are added to the recycled mixture, meet mix designrequirements, and disperse in the aged asphalt binder easily. Normally, rejuvenat-ing agents are added for the purpose of restoring physical and chemical propertiesof the RAP binder in China. A rejuvenating agent labeled LKJ-II was obtained fromLiaoning Shihua University, and was developed based upon the aged asphalt binderproperties in the RAP. It was added at a rate of 7% by weight of the aged asphaltbinder.

The mix design procedure of the WMARAP mixtures is basically consistentwith that of the HRAM. The WMA additive properties are necessary to be consid-ered, so are the RAP properties in the mix design of the WMARAP mixtures. In thisstudy, the mix design procedure of the WMARAP mixtures can be summarized asfollows: (1) determine the RAP content; (2) determine the target grade of asphaltblend derived from virgin asphalt (and rejuvenating agent), and reclaimed asphalt;(3) determine the grade and content of virgin asphalt (and rejuvenating agent); (4)determine the optimum asphalt content of the WMARAP mixtures; (5) determinethe mixing and compaction temperatures of the WMARAP mixtures; and (6) con-duct needed laboratory performance tests for evaluating the WMARAP mixturesaccording to different mix design methods. In production of the WMARAP mix-tures, a maximum RAP content is limited by the technical requirements of its prod-ucts, and moreover, it is strongly tied with mixing equipment standards, mixturedesign requirements, asphalt binder properties, WMA additive properties, etc.According to the factors mentioned above that have been taken into account in thisstudy, the 40% RAP content was used to produce the WMARAP mixtures for the

Table 1Properties of the asphalt binder.

Technical indices Testresults

Specificationa

requirements

Virgin asphalt binderPenetration (0.1 mm) (25 C, 100 g, 5 s) 86 80100Softening point (C) 45.5 P44Ductility (cm) (5 cm/min, 15 C) >100 P100

Thin Film Oven Test (TFOT) (163 C, 5 h)Change of mass (%) 0.16 60.8Retained penetration ratio after TFOT (%) 62.1 P57Retained ductility after TFOT (cm) (5 cm/

min, 10 C)31.7 P8

a Chinese technical specifications for construction of highway asphalt pavement(JTG F40-2004).

mix design. The grade of asphalt blend was determined to be the AH-90 as thatof virgin asphalt in accordance with weather and construction conditions, volumeof traffic, highway classification, etc. The design method for selecting the grade ofvirgin asphalt was based upon the harmonic method of asphalt binder viscosity.Grading of aggregate had been chosen in conformity with the type HRAM-16 ofthe technical specifications (JTG F41-2008). The designed gradation curve for theHRAM is shown in Fig. 1.

In this study, Marshall mix design method was employed to determine the opti-mum asphalt content of the HRAM. The mixing and compaction temperatures of theHRAM were determined as 160 C and 150 C, respectively. The asphalt content thatwas represented by the percentage of the weight of the mixtures (approximately4.5%), as a median, was determined by the experiential equation from the technicalspecifications (JTG F41-2008), and the asphalt content related to the HRAM at 3.5%,4%, 4.5%, 5%, and 5.5% were chosen for producing Marshall samples. The mechanicalindices are determined on the basis of the Marshall test, as shown in Table 3. Thevacuum test from the Chinese standard test methods (Standard Test Methods ofBitumen and Bitumen Mixtures for Highway Asphalt Pavement (JTG E20-2011, T0711)) was used to obtain maximum theoretical specific gravity of the HRAM.The bulk specific gravity of the compacted HRAM was determined by the saturatedsurface dry test following the standard test method JTG E20-2011, T 0705. The vol-umetric indices obtained through analysis of the test results of the HRAM are givenin Table 3. The target volume of air voids of the HRAM was determined to be 4.5%according to the requirement of the technical specifications (JTG F40-2004). Theoptimum asphalt content corresponding to 4.5% air void level is taken into accountin the dense graded asphalt mixtures in application with the northern regionsacross China. Based on the technical requirements of the Marshall mix design fol-lowing the technical specifications (JTG F40-2004), the optimum asphalt contentof the HRAM containing 40% RAP determined was 4.47% through the analysis onthe indices listed in Table 3.

Based on the NCHRP project 09-43 [22], a stand-alone WMA mix design proce-dure is not necessary, and therefore mix design of the control mixture was used forthe WMA virgin mixtures (without RAP). The WMA virgin mixtures were mixed andcompacted at temperatures of 120 C and 110 C, respectively to comply with themanufacturer recommendations.

4. Experimental methods

4.1. Determination of mixing and compaction temperatures

The equivalent principle of volumetric parameter of the com-pacted mixtures samples was employed to determine the mixing

0

20

40

60

80

100

120

0.075 0.15 0.3 0.6 1.18 2.36 4.75 9.5 13.2 16 19

Sieve Size (mm)

Perc

ent P

assi

ng (

%) Upper Limit

Lower Limit

Median

Selected Gradation

Fig. 1. Gradation curve for HRAM.

Table 3Mechanical and volumetric indices of HRAM.

Asphaltcontent (%)

Maximum theoreticalspecific gravity

Bulk specificgravity

Volume of airvoids (%)

Voids in mineralaggregate (%)

Voids filled withasphalt (%)

Marshallstability (kN)

Flow(mm)

3.5 2.586 2.382 7.9 14.6 46.1 11.68 2.794.0 2.557 2.427 5.1 13.5 62.2 13.38 3.324.5 2.543 2.444 3.9 13.3 70.6 10.61 3.805.0 2.521 2.469 2.1 12.9 84.0 10.13 4.225.5 2.509 2.464 1.8 13.5 86.9 8.55 4.85


and compaction temperatures of the WMARAP mixtures. It isbecause the WMA additives investigated in this study decreaseproduction temperatures by reducing the internal friction betweenaggregate particles without change of asphalt binder viscosity (i.e.,chemical additives) basically [3]. The Marshall hammeringcompaction method was used to produce the WMARAP mixturessamples. The target volume of air voids of the HRAM sample, as thecontrolling volumetric parameter, was used to determine themixing and compaction temperatures of the WMARAP mixtures.In the process of determining the mixing and compaction temper-atures of the WMARAP mixtures in the laboratory, the compac-tion temperatures ranged from 100 C to 140 C at 10 Cincrements. The mixing temperatures increased by 10 C morethan the corresponding compaction temperatures. The fabricationtemperatures of the WMARAP mixtures including heating tem-peratures of the virgin asphalt, aggregate, and RAP are given inTable 4.

The bulk specific gravity and maximum theoretical specificgravity of the WMARAP mixtures at different fabrication temper-atures were determined by the tests in the same way as that of theHRAM. Then, the volume of air voids of the WMARAP mixturessamples was obtained from the test results.

4.2. Performance tests

The rutting, bending, freezethaw splitting, and Marshallimmersion tests are necessarily conducted to evaluate the labora-tory performance of the dense graded asphalt mixtures in the Mar-shall mix design according to the requirements of the technicalspecifications (JTG F40-2004).

4.2.1. Rutting testThe rutting test evaluates the high temperature stability

(rutting resistance) associated with the dynamic stability of themixture using the standard test method JTG E20-2011, T 0719.The samples are produced to a length of 300 mm, a width of300 mm, and a height of 50 mm. The test produces damage byrolling a rubber wheel across the surface of a sample at 60 Cand the sample is loaded for 60 min, or rut deformation reaches25 mm before 60 min. The dynamic stability (DS) can be calculatedas follows:

DS t2 t1 Nd2 d1

C1 C2 1

Table 4Fabrication temperatures of WMARAP mixtures.

Mixingtemperature (C)

Compactiontemperature (C)

Heating temperature oaggregate (C)

110 100 120120 110 130130 120 140140 130 150150 140 160

where DS = dynamic stability; d1 = deformation related to t1; d2 -= deformation related to t2; t2 = 60 min, or time related to deforma-tion reaching 25 mm before 60 min; t1 = 45 min, or 15 min beforethe time related to deformation up to 25 mm; C1 = coefficient of testmachine; and C2 = coefficient of sample.

4.2.2. Bending testThe bending test was conducted to evaluate the mixtures for

low temperature cracking resistance following the standard testmethod JTG E20-2011, T 0715. In the test, the beam samples areproduced to the dimensions of 250 mm in length, 30 mm in width,and 35 mm in height. The samples are monotonically loaded tofailure along the midpoint of span at the constant rate of 50 mm/min, and the test temperature is controlled at 10 C. The samplesare immersed in a solution with the proportion 1.0 part methanolsolution to 1.0 part water for 45 min at the test temperature beforetesting. During testing, the load and deformation are continuouslyrecorded. Maximum load carried by the sample and deformationassociated with the load are obtained and used to computebending tensile strength, bending tensile stiffness, and maximumbending tensile strain at failure. The bending test evaluates thelow temperature cracking resistance associated with maximumbending tensile strain. Then, it is calculated using the followingequation:

eB 6 h d

L22

where eB = maximum bending tensile strain; h = height of cross sec-tion at midpoint of span; d = deformation related to maximum loadat midpoint of span; and L = span of sample.

4.2.3. Freezethaw splitting testThe freezethaw splitting test was performed to evaluate the

moisture susceptibility using the standard test method JTGE20-2011, T 0729 based on the AASHTO T 283 procedure [23].The samples are produced using the Marshall hammer compactionfor 50 blows. Half of all samples of the mixtures are water-condi-tioned by vacuum saturation with a vacuum pressure no less than730 mm Hg for 15 min, and then the samples are immersed inwater for 0.5 h at the normal air pressure. In the freezethaw con-ditions, the previously conditioned samples are placed in a freezerfor 16 h at 18 C and subsequently thawed for 24 h at 60 C.Afterwards, the conditioned and unconditioned samples were

f Heating temperature of virginasphalt (C)

Heating temperatureof RAP (C)

115 110125 110135 110145 110155 110


brought to 25 C for 2 h prior to measuring their splitting tensilestrengths (indirect tensile strengths). Furthermore, the tensilestrength ratio can be determined with the following equation:

TSR RT2RT1

3

where TSR = tensile strength ratio; RT2 = average of indirect tensilestrengths of conditioned samples; and RT1 = average of indirect ten-sile strengths of unconditioned samples.

4.2.4. Marshall immersion testThe residual Marshall stability (MS0) obtained from Marshall

immersion test was also selected to characterize the moisture sus-ceptibility in this study. The MS0 is the ratio of the Marshall stabil-ity of samples immersed in water for 48 h at 60 C to the standardMarshall stability.

4.2.5. Freezethaw cycles splitting testThe freezethaw splitting test is used to evaluate the moisture

susceptibility of asphalt mixtures subjected to one freezethawcycle. However, asphalt mixtures may suffer severe environmentalconditioning in the field due to the extreme weather conditions. Inaddition, the WMA additives used in this study to introduce waterto the mixtures may increase the potential to moisture damage.The lower fabrication temperatures may result in an inadequatedrying of the aggregates, trapping water in the coated aggregatesincreasing the susceptibility to moisture damage. Thereby, the rig-orous tests for evaluating the moisture susceptibility need to beperformed to investigate the moisture resistance of the WMARAP mixtures. In this study, the freezethaw cycles splitting testwas conducted to evaluate the moisture susceptibility at succes-sive freezethaw cycles. Half of the prepared samples were sub-jected to five freezethaw cycles. Each cycle complies withfreezethaw conditions in the freezethaw splitting test. The TSRwas determined after each cycle.

4.2.6. Aging testAging processes of asphalt mixtures in the field application may

be divided into short- and long-term aging. The aging method ofHMA is presented in the standard test method JTG E20-2011, T0734 based upon the oven aging proposed by AASHTO [24]. Accord-ingly, in this study, the short- and long-term aging processes (dur-ing construction and service) of the WMA mixtures were simulatedby the short- and long-term oven aging, respectively. The short-term oven aging produces aging by putting the loose mixture in aforced-draft oven for 4 h at 135 C. The long-term oven aging is toage compacted mixture samples derived from the mixture sub-jected to the short-term oven aging in a forced-draft oven for fivedays at 85 C, also, the process could be accelerated for two daysat 100 C which could possibly achieve aging effect alike. The com-pacted mixture samples were produced based on the technicalrequirements of dimensions associated with the compaction meth-ods. The samples along with moulds need to be placed at room tem-perature for more than 16 h before the long-term oven aging.Thereafter, the moisture susceptibility and low temperature crack-ing resistance of the aged WMA mixtures were evaluated using thefreezethaw splitting and bending tests, respectively.

4.2.7. Fatigue testThe fatigue resistance of asphalt mixture can be evaluated using

different laboratory tests. The bending beam fatigue test is widelyused, and loading modes of the fatigue test may be either con-trolled-stress or controlled-strain. The most used standards toevaluate the fatigue resistance of asphalt mixtures include theAASHTO T 321-03 through four-point bending beam tests at

controlled-strain mode or at controlled-stress mode [25]. Experi-ence had shown that thick HMA layers (>125 mm) generally per-formed closer to a constant stress mode in the field, while thinHMA layers (130 mm) widely used in China [27]. Inconsideration of the reconstruction project of asphalt pavementrelied on (asphalt concrete layer thickness was 150 mm) in thisstudy, and the higher requirements of testing equipment for thefour-point bending beam fatigue tests, the one-third point bendingbeam fatigue test with the controlled-stress mode was adopted toinvestigate the fatigue properties of the WMARAP mixtures. Inthis test, the beam samples were fabricated to a length of250 mm, a width of 50 mm, and a height of 50 mm. The fatigue testwas conducted at a temperature of 15 C by applying the compres-sive uniaxial half-sinusoidal load at a loading frequency of 10 Hz.The beam samples were conditioned at the test temperature for6 h before testing. The applied constant stress amplitudes wereobtained from four stress ratios of 0.1, 0.2, 0.3, and 0.4 (the ratioof stress amplitudes to bending tensile strengths). The failure loadis determined by the test that the samples are monotonicallyloaded to failure. Then, the bending tensile strength is obtainedfrom the failure load and deformation related to the load.

For a controlled-stress mode, the fatigue equation can be repre-sented as follows:

Nf k1r

n4

where Nf = the number of sample subjected to constant stress tofailure, or fatigue life; r = applied constant stress amplitude; andk, and n = test-related parameters.

In fact, there exists a linear relationship between Nf and r in thelogarithmic scale. Eq. (4) can be rewritten in the following form:

lg Nf k n lgr 5

Alternatively, the relationship can be written as:

lg Nf k nr=rB 6

where rB = bending tensile strength; and r/rB = stress ratio.

5. Results and discussion

5.1. Determination of mixing and compaction temperatures

The relationship between volume of air voids and compactiontemperature is shown in Fig. 2. The compaction temperatures ofthe WMARAP mixtures were determined by the target volumeof air voids of 4.5%. From Fig. 2, the volume of air voids decreasedwith the increase of compaction temperatures. The compactiontemperatures of the WMARAP mixtures with the S-I andEvotherm-DAT were 122 C and 127 C, respectively, and thecorresponding mixing temperatures were 132 C and 137 C.Consequently, the mixing and compaction temperatures of theWMARAP mixtures were 2030 C less than that of the HRAM.If only from the point of the mixing and compaction temperatures,the S-I resulted in an appreciable decrease over the Evotherm-DAT.

5.2. Performance tests

5.2.1. Rutting testFig. 3 shows the results from the rutting test of the WMA virgin

(without RAP) and WMARAP mixtures. It can be seen that theWMARAP mixtures performed a greater dynamic stability (DS)than the corresponding WMA virgin mixtures. The RAP played a

100 110 120 130 140

4.0

4.5

5.0

5.5

6.0

6.5

7.0

Target Volume of Air Voids

Vol

ume

of a

ir v

oids

(%

)

Compaction temperature (C)

Evotherm-DAT

S-I

Fig. 2. Relationship between volume of air voids and compaction temperature.

WMA Virgin WMA-RAP0

400

800

1200

1600

2000

2400

2800

3200

3600

4000

Minimum B Requirement

Minimum DS Requirement

B (Evotherm-DAT)B(S-I)

DS

(cyc

le/m

m)

DS (S-I) DS (Evotherm-DAT)

0

400

800

1200

1600

2000

2400

2800

3200

3600

4000 B

()

Fig. 3. Rutting and bending tests results.

WMA Virgin WMA-RAP0

15

30

45

60

75

90

105

120

135

Minimum TSRRequirement

Minimum MS0Requirement

TSR

(%

)

TSR (Evotherm-DAT)TSR (S-I)MS0 (Evotherm-DAT)MS0 (S-I)

0

20

40

60

80

100

120

140

MS

0 (%

)

Fig. 4. Freezethaw and Marshall immersion tests results.


positive role in the rutting resistance when introduced to WMA.This can be attributed to the asphalt binder and mixtures stiffenwith the addition of RAP leading to an exhibited increase in theDS. The S-I WMA mixtures showed slightly better rutting resis-tance than that produced using the Evotherm-DAT regardless ofRAP incorporation. The DS results occurred likely because of thedifference in softening asphalt binder capability of the WMA addi-tives used. Moreover, the DS values of all the mixtures met the 800(cycle/mm) minimum specified in the technical specifications (JTGF40-2004).

5.2.2. Bending testThe results from the bending test of all the mixtures are shown

in Fig. 3. The WMA virgin mixtures eB results showed the Evo-therm-DAT mixture performed 8.71% higher than the S-I mixture.However, the S-I WMARAP mixture performed as well as thatproduced using the Evotherm-DAT in the low temperature crack-ing resistance. This result indicates that the low temperaturecracking resistance of the WMA mixtures containing high percent-age of RAP (40%) is not sensitive to the WMA additives used. TheWMARAP mixtures showed an obvious decrease as compared tothe corresponding WMA virgin mixtures in terms of the eB. Thismeans the introduction of RAP may lead to an increased low tem-perature cracking potential. It was also found that the eB values ofthe WMA virgin and WMARAP mixtures met the specifications(JTG F40-2004) requirement of eB which is 2000 le.

5.2.3. Freezethaw splitting testAs shown in Fig. 4, the Evotherm-DAT WMA virgin mixture per-

formed 3.75% higher than that produced using the S-I in terms of

the TSR. The Evotherm-DAT WMARAP mixture increased theTSR moisture resistance by 7.6% in comparison with that producedusing the S-I. The TSR results may be due to the inherent anti-strip-ping capabilities difference between the S-I and Evotherm-DAT.This also showed that the interaction of RAP and WMA additivesdid not significantly affect the TSR moisture resistance. The useof RAP can increase the concern with low temperature crackingof the WMA mixtures due to the presence of aged binder whichmay cause a stiffening effect. The Evotherm-DAT WMA virgin mix-ture performed the best among all two data sets. The S-I WMARAP mixture exhibited the greatest potential for the TSR moisturedamage at each of the WMA mixtures. The TSR values of the WMAmixtures investigated passed the 75% minimum specified in thetechnical specifications (JTG F40-2004) irrespective of RAPincorporation.

5.2.4. Marshall immersion testThe Marshall immersion test results for evaluation of the WMA

virgin and WMARAP mixtures in terms of the moisture suscepti-bility are shown in Fig. 4. Similar to freezethaw test results, it wasconcluded that the blending of the virgin and RAP asphalt binderresulted in the decreased moisture resistance. The MS0 of theWMA mixtures showed the same trend as the freezethaw testresults exhibited for the TSR. The Evotherm-DAT WMA virgin mix-ture exhibited 4.59% higher than that produced using the S-I interms of MS0. The Evotherm-DAT WMARAP mixture increasedMS0 by 5.1% more than that produced using the S-I. Based uponthe testing findings, the WMA mixtures produced using the Evo-therm-DAT seemed to have more potential to resist moisture dam-age as compared to that produced using the S-I. The MS0 values ofall the mixtures met the specifications (JTG F40-2004) limit whichis 80%.

5.2.5. Aging testAs shown in Fig. 5, the WMA additives and aging processes

exhibited a significant effect on the TSR. It can be seen that theWMA virgin mixtures after the short-term aging showed a slightincrease as compared to the unged mixtures in terms of the TSR.After the short-term aging, the WMARAP mixtures performed6.69% and 14.05% higher than the unaged mixtures, respectivelyin terms of the TSR. This may be beneficial since the short-termaging aides the increase in viscosity of the asphalt binder causingthe improvement of bond between the asphalt binder and aggre-gate, enhancing the moisture resistance. Moreover, after theshort-term aging, the WMARAP mixtures exhibited slightlyhigher TSR moisture resistance than the corresponding WMA vir-gin mixtures. This result is hypothesized the increase of asphaltbinder film thickness due to the increased content of asphalt

Unaged0

15

30

45

60

75

90

105

120

135


TSR

(%

)

Aging Process

Evotherm-DAT WMAVirgin S-I WMAVirgin Evotherm-DAT WMA-RAP S-I WMA-RAP

Long-term AgingShort-term Aging

Fig. 5. The TSR for unaged and short- and long-term aged mixtures.

1 2 3 4 50

15

30

45

60

75

90

105

120

135


TSR

(%

)

Number of Freeze-thaw Cylces

Evotherm-DAT WMAVirginS-I WMAVirginEvotherm-DAT WMA-RAPS-I WMA-RAP

Fig. 7. Effect of freezethaw cycles on the TSR.


binder peeled off the RAP, leading to the increased moisture resis-tance during the short-term aging. However, for all the mixtures,the long-term aging resulted in a distinct reduction in the TSR,and moreover it failed to pass the 75% minimum. This means thatthe embrittlement of asphalt binder caused by the long-term agingmay result in a loss of durability in terms of moisture resistance. Inaddition, the TSR trends of the WMA mixtures produced using theS-I was similar to that produced using the Evotherm-DAT. The Evo-therm-DAT WMA mixtures performed higher moisture resistancethan that produced using the S-I whether the mixtures were sub-jected to aging or not.

As illustrated in Fig. 6, the eB results showed the WMARAPmixtures suffered from the short- and long-term aging exhibiteda greater decrease as compared to the unaged mixtures in termsof the eB. Furthermore, the eB values failed to meet the minimumrequirement. These results are anticipated due to the decrease inthe ductility of asphalt binder. The ductility of asphalt binder haspotential to affect the resistance to bending of mixtures, and thereduced ductility may lead to the decrease of low temperaturecracking resistance. The Evotherm-DAT WMARAP mixture afterthe short- and long-term aging reduced the eB by 23.77% and26.57% as compared to the unaged mixture, respectively. Afterthe short- and long-term aging, the eB of the S-I WMARAP mixturedecreased by 23.02% and 33.09%, respectively more than that of theunaged mixture. Moreover, the Evotherm-DAT WMARAP mixturehad a higher eB value than that produced using the S-I at differentaging processes. The eB trends of the WMA virgin mixtures were

Unaged Short-term Aging Long-term Aging0

400

800

1200

1600

2000

2400

2800

3200

Minimum B Requirement

B(

)

Aging Process


Fig. 6. The eB for unaged and short- and long-term aged mixtures.

consistent with that of WMARAP mixtures. The WMA virgin mix-tures after aging showed an obvious decrease in the eB. After thelong-term aging, the eB values of the WMA virgin mixtures didnot pass the minimum requirement. The WMA virgin mixturesexhibited higher eB low temperature cracking resistance than thecorresponding WMARAP mixtures at different aging processes.This means that the addition of RAP into the WMA virgin mixturesmay lead to the decrease of the low temperature cracking resis-tance with regard to durability.

5.2.6. Freezethaw cycles splitting testFig. 7 presents the effect of freezethaw cycles on the TSR of the

WMA mixtures. The TSR results of the WMA virgin mixturesdecreased with the increase of freezethaw cycles. The TSR valuesof the WMA virgin mixtures failed to pass the minimum after fourfreezethaw cycles. The TSR values of the WMARAP mixturesgenerally decreased as the mixtures were subjected to successivefreezethaw cycles, whereas the TSR values exhibited a remarkableincrease after three freezethaw cycles. The WMARAP mixtureswere subjected to four freezethaw cycles, their TSR remainedabove the 75% minimum. The WMARAP mixtures exhibited a dis-tinct decrease after five freezethaw cycles in terms of the TSR, andit failed to meet the minimum requirement. These results exhib-ited may be due to crystallize structure of interaction among theWMA additives, rejuvenating agent, and RAP during the successivefreezethaw cycles. The mechanism explanation and characteriza-tion of the test results need to be conducted through further micro-scale and chemical tests analysis of materials, to obtain a morefundamental understanding.

The Evotherm-DAT WMA mixtures exhibited a slight increaseas compared to that produced using the S-I at successive freezethaw cycles in terms of the TSR. This means the WMA additivesinvestigated in this study have a slight effect on the TSR moistureresistance of the WMA mixtures subjected to successive freezethaw cycles. In addition, the freezethaw cycles splitting testresults further demonstrated that the increased number offreezethaw cycles can lead to a reduced moisture resistance. Thisresult was also supported by the fundamental study on HMAwhich showed that binder components forming the asphalt-aggre-gate bond were easily displaced by water. This displacement mayweaken the interface between the asphalt and aggregate andreduce mixture tensile strength [28].

5.2.7. Fatigue testAs shown in Fig. 8, the Evotherm-DAT WMA mixtures per-

formed higher fatigue resistance than that produced using the S-Iat different stress ratios regardless of RAP incorporation. The

0.1 0.2 0.3 0.40

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

Num

ber

of C

ycle

s

Stress Ratio


Fig. 8. Fatigue life of the mixtures at different stress ratios.


fatigue life of the WMARAP mixture with the Evotherm-DAT per-formed a greater increase, on average of approximately 45%, incomparison with that produced using the S-I at different stressratios. The fatigue test results also indicated the Evotherm-DATWMA virgin mixtures performed best in the fatigue resistancereduction with the addition of RAP causing a negative effect.

It can be found from Fig. 9, the relationship between fatigue lifeand stress ratio produced an excellent correlation in the logarith-mic scale. The correlation coefficients (R2) of 0.960, 0.962, 0.988,and 0.976 are an indication that the two parameters (k, n) can beused to describe the fatigue life laws of all the mixtures. Then,the fatigue life of the mixtures can be estimated by the fatigueequations at any stress ratios. Note that the fatigue life of asphaltmixtures is normally higher at a constant strain mode than at aconstant stress mode. It is because that failure is more difficult todefine due to keeping the strain constant. This also seems thatthe fatigue resistance remains a concern using four-point bendingbeam fatigue test at a constant strain mode to obtain a more com-prehensive understanding of fatigue properties of the WMARAPmixtures. The parameters k and n correspond to the interceptand slope of fatigue line in the logarithmic scale. The lower slopeis more desirable to decrease the sensitivity to stress ratio andenhance the fatigue resistance under the restrained conditions.Based upon the fatigue test results, the n-value of the WMAmixtures was obtained from the fatigue equation. From Fig. 9,the n-value of the S-I WMA mixtures with (without) RAP was sim-ilar to that produced using the Evotherm-DAT.

0.10 0.15 0.20 0.25 0.30 0.35 0.40

1.0E+04

1.0E+03

1.0E+02

R2=0.960

lgNf=3.631-2.828(/B) R2=0.988

lgNf=3.836-2.010(/B) R2=0.962

lgNf=3.490-2.913(/B) R2=0.976

=lgNf 3.891-1.812(/B)


Num

ber

of C

ycle

s

Stress Ratio

Fig. 9. Relationship between fatigue life and stress ratio.

6. Conclusions

In this study, the laboratory performance of WMA mixturescontaining 0% and 40% RAP produced using two different WMAadditives (Evotherm-DAT and S-I) was evaluated using the rutting,bending, freezethaw splitting, Marshall immersion, aging, freezethaw cycles splitting, and fatigue tests. Based upon the resultsobtained through the experimental investigation, the followingconclusions were drawn:

The addition of WMA additives into the HRAM reduced by2030 C in terms of the mixing and compaction temperatures.This effect was more pronounced in the S-I WMARAP mixturethan that produced using the Evotherm-DAT.

The WMARAP mixtures performed a greater dynamic stability(DS), or better rutting resistance than the WMA virgin mixtures.The S-I WMA mixtures showed slightly rutting resistance higherthan that produced using the Evotherm-DAT due to the differencein softening the asphalt binder capability of the two WMAadditives.

The inclusion of RAP led to the decreased eB low temperaturecracking resistance. The Evotherm-DAT WMA virgin mixture per-formed higher low temperature cracking resistance than that pro-duced using the S-I. The low temperature cracking resistance of theWMARAP mixtures was not sensitive to the WMA additives used.

The TSR and MS0 moisture resistance of the WMA mixturesdecreased with the addition of RAP. The MS0 trends of the WMAmixtures were consistent with the freezethaw test results exhib-ited for the TSR. The Evotherm-DAT WMA virgin mixture per-formed the best among the WMA mixtures tested with regard tothe TSR and MS0.

The WMA mixtures showed a slight increase after the short-term aging as compared to the unaged mixtures in terms of theTSR, while these mixtures after the long-term aging exhibited lar-gely reduced TSR. After the short-term aging, the WMARAP mix-tures exhibited slightly higher TSR moisture resistance than thecorresponding WMA virgin mixtures. The eB values of the WMAmixtures after aging decreased much more than that of the unagedmixtures. The Evotherm-DAT WMA mixtures performed better inthe aging resistance than that produced using the S-I.

The TSR values of the WMARAP mixtures generally decreasedwith increasing freezethaw cycles, whereas the TSR values dis-played a remarkable increase after three freezethaw cycles. TheWMARAP mixtures exhibited a distinct decrease after fivefreezethaw cycles in terms of the TSR. The TSR values of theWMA virgin mixtures decreased with the increase of freezethawcycles. The WMA additives investigated performed a slight effecton the TSR of the mixtures subjected to successive freezethawcycles. The freezethaw cycle splitting test results further demon-strated that the increased number of freezethaw cycles can leadto the reduced moisture resistance.

The WMA mixtures significantly reduced the fatigue resistancewith the use of RAP. The Evotherm-DAT WMA mixtures performeda greater increase than that produced using the S-I at differentstress ratios in terms of fatigue life. The fatigue life of the WMAmixtures with each WMA additive had similar sensitivity to stressratio regardless of RAP incorporation.

Acknowledgements

This study was funded by the Liaoning Highway AdministrationBureau under Grant No. 201201 and National Natural ScienceFunding of China under Grant No. 51308084. The authors are alsothankful to Liaoyang Highway Administration Department engi-neers for coordinating the materials preparation so that theresearch team may successfully accomplish this study. The authors


do not endorse any of the materials nor technologies mentioned inthis paper.

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