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Rutting and moisture damage resistanceof high reclaimed asphalt pavementwarm mixed asphalt: loaded wheeltracking vs. conventional methodsJesse D. Doyle a & Isaac L. Howard ba Airfields and Pavements Branch, Geotechnical and StructuresLaboratory , US Army Engineer Research and Development Center ,3909 Halls Ferry Road, CEERD-GM-A, Vicksburg , MS , 39180-6199 ,USAb Department of Civil and Environmental Engineering , MississippiState University , PO Box 9546, 235 Walker Hall, Mississippi State ,MS , 39762-9546 , USAPublished online: 23 Sep 2013.
To cite this article: Jesse D. Doyle & Isaac L. Howard (2013) Rutting and moisture damageresistance of high reclaimed asphalt pavement warm mixed asphalt: loaded wheel trackingvs. conventional methods, Road Materials and Pavement Design, 14:sup2, 148-172, DOI:10.1080/14680629.2013.812841
To link to this article: http://dx.doi.org/10.1080/14680629.2013.812841
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Road Materials and Pavement Design, 2013Vol. 14, No. S2, 148–172, http://dx.doi.org/10.1080/14680629.2013.812841
Rutting and moisture damage resistance of high reclaimed asphaltpavement warm mixed asphalt: loaded wheel tracking vs.conventional methods
Jesse D. Doylea* and Isaac L. Howardb
aAirfields and Pavements Branch, Geotechnical and Structures Laboratory, US Army Engineer Researchand Development Center, 3909 Halls Ferry Road, CEERD-GM-A, Vicksburg, MS 39180-6199, USA;bDepartment of Civil and Environmental Engineering, Mississippi State University, PO Box 9546, 235Walker Hall, Mississippi State, MS 39762-9546, USA
An increased potential for moisture damage and rutting has been the two main problems withwarm mixed asphalt (WMA) implementation. The use of high reclaimed asphalt pavement(RAP) contents (25% or more) in WMA may alleviate these problems. At present, susceptibilityto the moisture damage and rutting are usually tested for independently; however, these distressmechanisms can be linked for in-service pavements. An enhanced loaded wheel tracking testperformed on dry and wet specimens, the PURWheel, is investigated in this paper to evaluatethe interaction of traffic and moisture. The PURWheel is also compared with conventionalrutting and moisture damage tests. PURWheel results are used to evaluate the performance of25% and 50% RAP–WMA. Rutting and moisture susceptibility of the high RAP–WMA wascomparable with current practice low RAP content hot mixed asphalt.
Keywords: loaded wheel tracking; WMA; RAP; rutting; moisture damage; PURWheel
1. IntroductionAdoption of warm mixed asphalt (WMA) instead of hot mixed asphalt (HMA) by the highwayindustry has progressed rapidly in the last few years. Most state Departments of Transportation(DOTs) have used WMA to some extent or allowed its use as an alternative to HMA; a number ofstate DOTs now use WMA for the majority of their paving projects. In recent years, other changeshave occurred (e.g. mixtures with high amounts of recycled material) that have been consideredin conjunction with WMA. Ever-increasing demands on raw materials and energy have resultedin more new options available to produce asphalt concrete than ever before.
Considerable research has been performed on WMA with generally promising results (Diefend-erfer & Hearon, 2010; Prowell, Hurley, & Crews, 2007). Reduced binder ageing associated withlower WMA mixing temperatures has the potential to result in rutting problems soon after con-struction. Some evidence has been provided in the literature for increased rutting with WMA(Abbas & Ali, 2011; Hurley & Prowell, 2006); however, other studies have indicated the adequateWMA rutting performance (Hurley & Prowell, 2005; Prowell et al., 2007). Numerous researchershave reported increased susceptibility to the moisture damage for WMA in the laboratory test-ing (Hurley & Prowell, 2005, 2006; Kvasnak et al., 2009; Prowell et al., 2007). However, otherstudies have observed improved moisture susceptibility test results with plant-produced WMA(Kvasnak et al., 2009; Prowell et al., 2007), and a survey of state DOTs did not find any evidence
*Corresponding author. Email: [email protected]
© 2013 Taylor & Francis
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of moisture damage problems in field projects based on 30 responses (Mogawer, Austerman,Kassem, & Masad, 2011).
Research has also been performed on WMA with reclaimed asphalt pavement (RAP) contentsin the 20–50% range (Copeland, D’Angelo, Dongré, Belagutti, & Sholar, 2010; Hodo, Kvasnak,& Brown, 2009; Willis, West, Nelson, Taylor, & Leatherman, 2011) in general, these meet thedefinition of high RAP content as 25% or more of total mixture (Copeland, 2011). These mixtureshave been studied for multiple reasons, but alleviation of the rutting and moisture damage seemsto be two of the most prevalent non-economic motivations for adding considerable RAP quantitiesto WMA. Evidence suggests that the use of high RAP in conjunction with WMA may offset anyincreased rutting potential of the WMA (Boggs, 2008; Doyle, Mejías-Santiago, Brown, & Howard,2011; Hodo et al., 2009; Mallick, Kandhal, & Bradbury, 2008). A few studies showed that highRAP–WMA generally has decreased moisture susceptibility relative to low or no RAP–WMAbased on the tensile strength ratio (TSR) testing (Mejías-Santiago, Doyle, Howard, & Brown,2011; Middleton & Forfylow, 2009) and based on Hamburg testing performed at 40◦C (Mogawer,Austerman, Bonaquist, & Roussel, 2011). However, others have found marginal overall moisturedamage performance of high RAP–WMA (Hodo et al., 2009); while Austerman, Mogawer, andBonaquist (2009) reported that 25% RAP HMA performed acceptably, while 25% WMA did notbased on the Hamburg testing at 50◦C. In light of these mixed results, moisture susceptibility ofhigh RAP–WMA should be evaluated while taking rutting resistance into consideration.
The problems of rutting and moisture susceptibility of asphalt mixtures and the difficulty oftranslating laboratory test results to the field performance have been recognised for over 100 years(Richardson, 1912). Although many advances have been made over the last century, the afore-mentioned items are still areas of concern as new mixture types and combinations of materialsare developed. The current state of practice is to independently evaluate the rutting and moisturedamage, but these behaviours can be coupled for in-service pavements. One of the most com-mon methods to measure rutting is the Asphalt Pavement Analyzer (APA) executed accordingto AASHTO T 340 or with agency-specific procedures. One of the most common methods tomeasure the moisture susceptibility is the TSR conducted according to AASHTO T 283, ASTMD4867, or with agency-specific procedures. An additional moisture damage test method that hasgained popularity recently is the Hamburg Loaded Wheel Tester (HLWT) performed accordingto AASHTO T 324 or with agency-specific procedures. The APA, TSR, and HLWT each oper-ate under different principles and each test method’s ability to perform its desired function hasbeen debated. Generally speaking, the moisture susceptibility testing seems to be more of a pointof contention than rut testing. Of the techniques available to characterise the moisture damage,loaded wheel tracking seems to be the most promising.
Kiggundu and Roberts (1988, p. 3) defined the moisture damage as “the progressive functionaldeterioration of a pavement mixture by loss of the adhesive bond between the asphalt cement andthe aggregate surface and/or loss of the cohesive resistance within the asphalt cement principallyfrom the action of water”. The moisture damage in asphalt mixtures falls into two general cate-gories: (1) loss of cohesion within the binder film (i.e. softening of the binder in the presence ofmoisture); and (2) loss of adhesion between the binder film and the aggregate particles (Hicks,1991). Loss of adhesion in a mixture is generally visually apparent (e.g. stripping), whereas loss ofcohesion in a mixture is less readily observed, but it can be measured by loss of mixture strength.An important factor contributing to the moisture damage in the field is the presence of trafficin addition to merely the presence of water (Hicks, 1991; Little & Jones, 2003; Lottman, 1982;Lu, 2005). The moisture damage is often a progressive failure mechanism and, in some situa-tions, manifests itself in the form of accelerated permanent deformation before or without loss ofadhesion (Little & Jones, 2003). A test method capable of detecting any increased rutting in thepresence of moisture as well as the potential for stripping would be useful. The test could provide
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information on two of the most prevalent forms of moisture susceptibility and also informationrelated to rut resistance. Ideally, such a test method could account not only for the interactionbetween water and traffic on an in-service pavement, but also be able to assess the influence ofwater and traffic separately.
The PURWheel laboratory wheel tracker is a test method with the potential to perform the needsdescribed above. The original PURWheel was developed in the 1990s at Purdue University. Theoriginal equipment was donated to Mississippi State University in 2007 where it was renovatedand modified. The equipment now operates under the protocols described in Howard, Doyle,White, Ivy, and Booth (2010). Key items different from the original equipment were an increasein test temperature to simulate the environmental conditions typical of the Southeastern USA,the addition of insulation to maintain the higher test temperatures, and changes to the specimenconditioning protocol to ensure thermal equilibrium during the desired test temperature. Itemsthat remained the same were the load application mechanism and the deflection measurementmethod. One motivation for the renovations was to evaluate Southeastern USA climates and asecond motivation was to update the dry rutting test protocol to more closely match the APA. Thismodified device is still referred to as the PURWheel, although as discussed, notable differencesexist with respect to the approaches previously published (Pan & White, 1999; Stiady et al.,2003). To the author’s knowledge, only two PURWheel devices are in existence. However, thespecific test parameters and testing protocols described in this paper are believed to be unique tothe prototype PURWheel described herein.
The primary objective of this paper was to investigate the rutting and moisture damage using thePURWheel for WMA containing 25–50% RAP. A secondary objective was to compare PURWheeltest results with the commonly used rutting and moisture susceptibility methods (APA, TSR, andHLWT). Loading characteristics of the wheel tracking tests were compared to assess the mixtureresponse. Thereafter, APA, TSR, and PURWheel data were collected in the laboratory and usedto evaluate the performance of WMA with high RAP content relative to current practice mixturesand the relative merits of the PURWheel with respect to conventional practice tests.
2. Review of test method development2.1. History of APA and PURWheel dry protocolThe PURWheel was originally developed at Purdue University for surface mixtures; typical testparameters were 3.8 cm-thick specimens and 50–60◦C test temperatures (Pan & White, 1999;Stiady et al., 2003). Subsequent modifications to the original equipment after its acquisition byMississippi State University (Howard et al., 2010) included additional insulation on the environ-mental chamber, changes to the heating system, and improved air circulation within the chamber;a new specimen conditioning protocol was implemented as well. Afterwards, thermocouples wereimbedded into dummy specimens to monitor temperature. Results indicated that specimen mid-depth temperature was maintained at 64 ± 1◦C for the entire duration of a test and that mid-depthtemperature was uniform along the direction of loading. Temperature of the specimen near thetop surface was observed to vary slightly more due to the cycling of the air heating equipmentand air circulation patterns within the environmental chamber although the variability was notmore than ±2◦C. In addition, the electro-mechanical interface hardware was updated and newcontrol software Hawk was incorporated. This enhanced version of the PURWheel was intendedto evaluate specimens in conditions representative of the Southeastern USA.
Around the same time the original PURWheel was being developed, the Georgia Loaded WheelTester (GLWT) was used as a basis for the development of the APA (Collins, Shami, & Lai, 1996).Extensive additional work (Kandhal & Cooley, 2003) led to the final test parameters in use today.
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Directly, no comparative studies have been performed to relate the APA to the original PURWheelor to the enhanced PURWheel. However, both the APA and the original PURWheel showed tohave reasonable relationships to field rutting measured at the Westrack experiment, with R2 = 0.76for APA and R2 = 0.80 for PURWheel (Federal Highway Administration [FHWA], 1998). Simi-larities between APA and enhanced PURWheel dry (PW-dry) protocol testing consist of specimenthickness (7.6 cm), test temperature (64◦C for LTTPBind PG 64 regions), and specimen condi-tioning time (6 h). Major differences in the test methods are load application method, specimencompaction method, and specimen size. Differences in test parameters will be discussed in moredetail later.
2.2. History of TSR, HLWT, and PURWheel wet protocolThe original research performed by Lottman (1978) to develop the TSR test used CaliforniaKneading (i.e. Hveem) compacted specimens (100 × 63.5 mm) compacted in two lifts; the mix-tures tested were based on in-service pavements in 15 states constructed between 1960 and 1972.None of the mixtures contained RAP and were all typical HMA mixtures for the time with theonly additive being in some cases lime or anti-strip. The use of freeze-thaw cycle(s) as part of theTSR conditioning protocol was simply a method to induce accelerated damage to the specimensto match field conditions and was not intended to relate to the occurrence of freeze-thaw zones(Lottman, 1978). The follow-on field validation study was conducted on in-service pavements,located in seven states, constructed between 1975 and 1977 of conventional HMA without anyadditives other than lime or anti-strip; a minimum TSR value of 0.80 was recommended byLottman (1982).
Since then, Tunnicliff and Root (1984) proposed a similar procedure using 100 by 62.5 mmMarshall Hammer-compacted specimens that led to the ASTM D4867 test method (Tunnicliff& Root, 1995). The follow-on field validation study included eight pavements in eight statesand resulted in a minimum recommended TSR value of 0.75 (Tunnicliff & Root, 1995). Noneof the mixtures contained RAP or any additives other than lime or anti-strip. The current Mis-sissippi DOT (MDOT) test method for the moisture damage is MT-63 and which resemblesASTM D4867 without optional freeze-thaw conditioning except for Superpave gyratory com-pactor (SGC) compaction method and the use of larger specimens; MDOT requires TSR valuesgreater than 0.85.
The original TSR test developed by Lottman (1978) was modified in light of the research byTunnicliff and Root (1984) which eventually led to the AASHTO T 283 test procedure (Eppset al., 2000). The laboratory work was performed by Epps et al. (2000) with mixtures of theknown field performance from five states to refine T 283. Results indicated that the compactionmethod and specimen size were important factors. The 100-mm Marshall compaction and 150-mm SGC compaction resulted in similar TSR values; however, 150-mm SGC compaction resultedin, generally, higher TSR values than 100-mm SGC or 100-mm Hveem compaction. The extent ofloose mixture conditioning, specimen saturation level, and freeze-thaw conditioning also affectedresults. AASHTO T 283 was modified to include 16 h of loose mix ageing and one freeze-thawconditioning cycle based on the study’s recommendations.
Table 1 provides a comparison of the two nationally accepted TSR test methods and MT-63.There are several differences between the test methods, many of which will affect the results (e.g.the compaction method, specimen size, loose mixture conditioning, saturation level, and use of afreeze-thaw conditioning cycle). Since the development of the TSR test, mix design has changedto Superpave (i.e. the SGC), and a variety of new mix types have been introduced; the use ofRAP, WMA, or other modifiers is common. The TSR test is currently used by a majority of stateDOTs to evaluate the moisture damage (Mogawer et al., 2011); yet researchers have observed
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Table 1. Comparison of current TSR test protocols for lab-mixed specimens.
Test method ASTM D4867 AASHTO T 283 MDOT MT-63
Specimen compactionmethods allowed
Marshall, Hveem, orGyratorya
Marshall, Hveem, orSGC
SGC
Specimen sizerequirements
100 × 62.5 mm orlarger
100 × 63.5 mm or150 × 95 mm
150 × 95 mm
Hyd. lime addition Dry or wet Not discussed WetAir void targetb 7 ± 1% 7.0 ± 0.5% 7.0 ± 1%Pre-compaction loose
mixture conditioning1–2 h @ comp temp. Cool for 2 h, 16 h @
60◦C, 2 h @ comptemp.
1.5 h @ comp temp.
Post-compactionconditioning
Cool to room temp formax. of 24 h
Room temperature for24 ± 3 h
Cool to room temp for12–24 h
Saturation range 55–80% 70–80% 55–80%Freeze-thaw cycle Opt., 15 h @ −18◦C Yes, 16 h @ −18◦C NoConditioning 24 h @ 60◦C 24 h @ 60◦C 24 h @ 60◦CTSR single-lab (d2s) None provided 9%c None providedTSR multi-lab (d2s) 23% 25%c None providedMinimum TSR Typically 75% Typically 80% 85%
aMay use either Gyratory Testing Machine or Gyratory Shear Compactor. Does not explicitly allow SGC compactionmethod.bAir voids are determined by the traditional saturated surface dry method (D2726 or T 166).cReported by Azari (2010).
that (1) “TSR is not a reliable indicator of field performance” for AASHTO T 283 (Zaniewski& Viswanathan, 2006, p. 67) and (2) there is no “relationship between the TSR and specificpavement distresses that are known to be related to the moisture damage (such as surface ravelingand rutting)” for ASTM D4867 (Kanitpong & Bahia, 2008, p. 16).
The HLWT was developed in Germany and has been studied by Aschenbrener and Currier(1993) and Aschenbrener (1995). It was observed that the average stripping inflection point (SIP)for mixtures as determined by the Hamburg test provided an excellent correlation to the fieldperformance with respect to the moisture damage. Pavements with the good field performance hadaverage SIPs generally greater than 10,000 passes, and pavements with the poor field performancehad average SIPs lesser than 3000 passes (Aschenbrener & Currier, 1993). Results indicated thatmixture moisture resistance was improved by increasing the binder grade or increasing the short-term ageing time; different binder sources of the same grade were also observed to have differentperformances (Aschenbrener, 1995). The HLWT testing has been observed to better correspond tothe field performance than the AASHTO T 283 TSR testing (Azari, 2010). Nielson (2010) foundthat the moisture damage as evidenced by SIP only occurred above a critical stripping temperature(CST) that was binder grade-dependent. For PG 64 binder and PG 70 binder grades, CST rangeswere reported of 49–54◦C and 54–55◦C, respectively. The HLWT has been adopted by the TexasDOT and a few other agencies; Texas specification criterion is defined as the minimum numberof passes to reach 12.5 mm rut depth when test is performed at 50◦C. The criterion is 10,000 and15,000 passes for PG 64 and PG 70 binders, respectively; however, it has been suggested thatthese are too conservative and alternate criterion can be used of 5000 and 10,000 passes for PG64 and PG 70 binders, respectively (Rand, 2006).
The development of the original PURWheel was an attempt to enhance the original HLWTby (1) incorporating a constant loading speed instead of sinusoidal; (2) using a pneumatic wheelinstead of a solid steel wheel; (3) using larger specimen sizes to minimise boundary effects;(4) measuring rut depths over the entire specimen length during testing; (5) incorporating wheel
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wander; and (6) the flexibility to test in both hot/dry and hot/wet conditions (Pan & White, 1999).The renovations to the original PURWheel have already been described. For the wet test protocol,the same conditioning period before testing and test temperature of the dry protocol was used (6 hand 64◦C). Temperature of the water bath was measured with thermocouples to be uniform fromtop to bottom and to be 64 ± 1◦C (Howard et al., 2010). PURWheel testing has been stated togive a better indication of the moisture damage potential than T 283 TSR testing (Pan & White,1999).
3. Comparison of loaded wheel testersTable 2 summarises loading details for APA, HLWT, and PURWheel tests. Unlike the APA andHLWT, the PURWheel applies loads to specimens through a pneumatic tyre. The load appliedby the PURWheel was directly measured with a scale (Figure 1(a)). Figure 1(b) shows a tyreprint where individual treads are clearly visible. The gross contact area of the tyre print inside theellipse is approximately 2800 mm2. Additional details are provided in Howard et al. (2010).
Initially, a three-dimensional finite element analysis was undertaken to investigate differencesin rutting behaviours measured by the APA, HLWT, and PURWheel tests. However, resultswere not fully developed for the desired comparison purposes and an experimental approachwas undertaken instead. In general, the greater wheel widths of the PURWheel and Hamburgmay be less sensitive to the effects of individual large aggregate particles than the APA. Inaddition, the steel wheel load application of the Hamburg will not conform to the contours of thedeformed specimen surface during the testing, unlike the pneumatic load application of the APAand PURWheel.
In addition to the finite element effort, laboratory testing was conducted to compare ruttingbehaviours of the three tests. Samples of a plant-produced 9.5-mm nominal maximum aggregatesize (NMAS) coarse-graded surface mixture containing 10% RAP designed with 85 gyrations witha polymer-modified PG 76-22 binder (designed properties were Gmm = 2.356, AC% = 5.8%,VMA = 15.0, VFA = 73 and dust to the effective binder ratio of 1.13) were used for testing.Specimens of this mixture were compacted to 7% air voids on an AASHTO T 331 basis for ruttesting in the APA at 50◦C and 64◦C, in the Hamburg in a dry condition at 50◦C and 64◦C andin the PURWheel in a dry condition at 64◦C. Figure 2 shows these rut depth test data plotted asa function of passes. APA testing produced the lowest rut depths for a given temperature, whichis understandable given its considerably higher loading speed. Hamburg testing produced the
Table 2. Comparison of APA, HLWT, and PURWheel test loading parameters.
Parameter APA HLWT PURWheel
Load application Sinusoidal Sinusoidal LinearSpeed (cm/s)a 59 31 33Load application method Pressurised hose Steel wheel Pneumatic tyreLoad (N) 445 705 1750Load area Width (mm) 27.5b 47.0 54.0Strip load (N/mm) 16.2 15.0 32.4Contact area (mm2) 645c 970d 2800 (gross)Contact pressure (MPa) 0.69c 0.73d 0.63 (gross)
aSpeed at the point where specimen deformation is measured.bValue assumes full embedment of the hose; actual width will be narrower at start of test.cReported by Kandhal and Cooley (2003).dReported by FHWA (2012).
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Scale
Contact Print
Gross Area2800 mm2
54.0 mm
(a) (b)
Figure 1. Measurement of load and contact area for the PURWheel. (a) Load and contact measurement.(b) Completed contact area print.
0
4
8
12
16
20
0 4 8 12 16 20
Rut
Dep
th (
mm
)
Thousand Passes
Ham 64°C
PW 64°C
APA 64°C
Ham 50°C
APA 50°C
Figure 2. Experimental APA, dry HLWT, and dry PURWheel rutting data.
greatest rut depths for a given temperature, which can be explained by the slow loading speed andhigh contact pressure. PURWheel testing produced moderately higher rut depths than the APAand considerably smaller rut depths than the Hamburg for the same temperature.
An interesting observation from Hamburg test data was that most of the permanent deformationof this mixture was simply due to rutting since there was 4.8 mm of total deformation in adry test at 50◦C; while the same mixture in a customary Hamburg wet test at 50◦C only had4.9 mm of deformation (data not shown) and no SIP or evidence of the moisture damage. This dryrutting behaviour is not accounted for in traditional wet Hamburg testing, which provides moreof an overall performance assessment since all rutting deformation is grouped together withoutdistinction between dry rutting and moisture-related rutting. On the other hand, dry PURWheeltesting of the same mixture at 64◦C produced 8.8 mm of deformation, while wet PURWheeltesting indicated the moisture damage with an average SIP of about 6000 passes (not shown).
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These results are in line with the findings of Nielson (2010) that little or no moisture damageoccurs at lower test temperatures.
4. Experimental programA research approach was developed to support the objectives of this paper. The specific goal wasto determine if the rutting and moisture susceptibility performance of 25% and 50% RAP–WMAwas similar to the performance of mixtures currently used in Mississippi. With this in mind, controlmixtures were selected to represent a band of performance results for current practice mixtures.The performance of 25% and 50% RAP mixtures was then compared with this band to addressthe primary objective. Results from individual performance tests were compared across mixturesto address the secondary objective. Details of the materials selected, specimen preparation, andtesting methods are provided in the following sections.
4.1. Materials testedAll testing was performed on 9.5-mm NMAS surface mixes where the coarse aggregate typewas predominately crushed gravel. The high-RAP content WMA mixtures evaluated contained25% and 50% RAP; two RAP sources were tested. One warm mix technology (Sasobit�) wasused at 1.0% of the total binder mass including all RAP binder. The performance of these fourmixtures was compared with three control mixtures with 15% RAP selected to encompass typicalbehaviours in Mississippi.
The two RAP materials tested (Figure 3) varied in terms of their binder grades and gradations,and were selected to determine the influence of RAP properties (binder in particular) on ruttingand moisture susceptibility. Figure 3 shows that both gradations have a hump near the 0.6-mmsieve that is often indicative of a high natural sand content. Note, especially, the high viscosityand PG temperature grades for the R1 RAP source. R1 represents a high-design traffic mixture;the material was milled from the surface of a 22.5 km stretch of Interstate 55 near Grenada, MS.The material was originally placed in 1992 and used both polymer-modified and non-polymermodified binders. R2 was selected to represent an intermediate design traffic mixture commonly
Figure 3. Properties of RAP sources tested.
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Table 3. Properties of highway surface mixtures tested.
Mixture ID CM1 CM2 CM3 RM1 RM2 RM3 RM4
WMA No No No Yes Yes Yes YesTMix (◦C) 157 132 160 116 116 116 116TComp (◦C) 116 138 138 116 116 116 116Ndes 50 85 85 65 65 65 65PG gradea 67–22 76–22 67–22 67–22 67–22 67–22 67–22RAP ID Stockb Stockb Stockb R1 R2 R1 R2RAP AC (%) 4.6 5.5 5.6 5.5 5.6 5.5 5.6RAP (%) 15 15 15 25 25 50 50Crushed gravel (%) 43 37 37 56 56 40 40Limestone (%) 0 31 37 8 8 0 0Sand (%) 9 10 10 10 10 9 9Hydrated lime (%) 1 1 1 1 1 1 19.5-mm (%) 92 96 96 93 95 92 96No 4 (%) 67 64 60 59 63 58 65No 8 (%) 40 41 37 40 42 40 45No 200 (%) 5.5 6.1 6.0 7.2 7.5 7.3 7.8Combined Gsb 2.533 2.480 2.518 2.462c 2.469c 2.477c 2.492c
Virgin AC 5.6 5.0 5.0 4.7 4.2 3.7 3.4Total AC 6.3 5.8 5.8 6.1 5.6 6.5 6.2Gmm 2.362 2.332 2.367 2.306 2.334 2.311 2.338
aPG grade of virgin asphalt prior to mixing.bStock of RAP at production facility, properties were not monitored and the source of the stock was different for CM1,CM2, and CM3.cGsb of RAP aggregate used to calculate combined value for the gradation was determined by the procedure recommendedin Doyle, Howard, and Robinson (2012).
used on lower volume roads and state highways. The material was milled from a 12 km stretchof State Highway 25 in Monroe County, Mississippi.
Table 3 summarises the seven mixtures investigated for use on highway surfaces. In general,the relative performance boundaries of asphalt mixtures in Mississippi are represented by 50design gyration and 85 gyration mixtures. The 50 gyration mixtures are intended for low trafficvolumes and have the highest effective asphalt content (AC) for a particular gradation, resultingin a flexible pavement that is more crack resistant but less rut resistant. The 85 gyration mixturesare intended for high traffic volumes and have the lowest effective AC for a particular gradation,resulting in stiff, more rut resistant but less crack resistant pavements. The goal when selectingcontrol mixtures CM1–CM3 for this study was to encompass the range of potential cracking andrutting resistance of current practice mixtures to the best extent possible. These mixtures wereplant-produced and sampled during highway surface paving for MDOT. The 85 gyration mixturescontained neat binder (CM3) and polymer-modified binder (CM2). The 4 high RAP content WMAmixtures were developed in the laboratory with 65 design gyrations. For the 4 recycled mixtures,the same virgin aggregate stockpile percentages were used with each RAP source at the 25% and50% RAP contents to control the effects of virgin aggregate gradation. Virgin PG 67-22 binderwith 1.0% Sasobit� was used for all high RAP mixtures.
4.2. Specimen preparation and testing methodsAfter mixing and short-term conditioning for 1.5 h, SGC specimens were prepared with a PineInstrument model AFGC125X calibrated to an external angle of 1.25 ± 0.02◦. The internal anglewas verified to be within allowable tolerance of 1.16 ± 0.02◦. Slabs were compacted in the Linear
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(a) (b)
(c) (d)
Figure 4. Linear Asphalt Compactor.
Asphalt Compactor (LAC) shown in Figure 4(a). After mixing and short-term conditioning for1.5 h, asphalt mixture was placed in the mould to prevent segregation and a series of 47 steel plateswere placed on top (Figure 4(b)). Compaction parameters were 18 passes and a 2413-kPa systempressure. The rectangular slabs were 29 × 62 cm and a nominal thickness of 7.6 cm (Figure 4(c)).The compacted slabs were then cut into half to produce two PURWheel test specimens referredto as blocks (Figure 4(d)) or were cored to produce specimens for the APA testing. Additionaloperational details are provided in Doyle and Howard (2010), while Howard, Doyle, and Barham(2012) provide an evaluation of the compactor.
Theoretical maximum specific gravity (Gmm) of each mixture was determined on duplicatespecimens according to AASHTO T 209 and the average value was reported. Bulk-specific gravity(Gmb) of compacted cylindrical specimens was determined according to AASHTO T 331 and usedto determine specimen air voids (Va); research by the authors has indicated that this test methodproduces the most reliable and consistent measurements of Gmb over a wide range of specimenair voids (Howard & Doyle, 2012). For slab-compacted specimens, air voids were estimated frommeasurement of the bulk density and correlation to equivalent air voids on an AASHTO T 331basis using the correlation developed in Doyle and Howard (2010).
To evaluate rutting potential, the APA was used to test each mixture in the experimental designaccording to AASHTO TP 63. SGC-compacted specimens were tested at nominal air void levelsof 7% and 10%; LAC-compacted specimens were tested at their respective air void levels. Wheelload was 445 N and hose pressure was 690 kPa; the test was run for 16,000 passes (i.e. 8000 cycles)or 14 mm of rutting, whichever occurred first. A pass was defined as the load wheel moving fromone end of the specimen to the other, i.e. two passes is one cycle. Rut measurements during testingwere recorded automatically by the APA device and rut depth (RDAPA) was defined as downwardpermanent deformation of the specimen surface relative to the original surface, i.e. uplift of the
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158 J.D. Doyle and I.L. Howard
specimen surface was not considered part of the overall rut depth. Rutting rate was determinedby fitting a linear equation to the post-consolidation rut depth data at 2000 and 8000 cycles (i.e.4000 and 16,000 passes); the slope of that line was defined as the rutting rate parameter (RRAPA)with units of mm/1000 cycles.
To evaluate the moisture damage, ASTM D4867 was performed on each high RAP mixture.Six 100-mm-diameter and 62.5-mm-thick specimens were tested. A freeze-thaw cycle was notperformed as part of the conditioning process. Air voids of all specimen sets were between 6%and 8% as by the test method. For control mixtures, TSR values determined by MDOT MT-63during mix design were used.
(a)
Hood and Tank AssemblyShown closed as when a testis conducted
Computer, Control Box
(b) (c)
(d) (e)
Figure 5. PURWheel laboratory wheel tracker.
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Two protocols were used for PURWheel testing: (1) PW-dry protocol, specimen tested at 64◦C;and (2) PURWheel wet (PW-wet) protocol, specimen tested submerged in 64◦C water. The testedLAC-produced specimens were 7.6 ± 0.6 cm thick and approximately 30 cm2, the air voids ofslab specimens were between 6% and 10%. Figure 5 shows key components of the PURWheel.Figure 5(a) shows an overall view where the hood/tank assembly, control box, and computerpowered by Hawk software are visible. Two independently controlled wheel carriages mountedwith four-ply pneumatic tyres load the slabs for 20,000 passes. Figure 5(b) shows a slab plasteredinto the mould and ready to be tracked by one of the two wheel carriages. Figure 5(c) shows anexpanded view of one of the carriages with the pneumatic wheel retracted after a test is complete.Figure 5(d) is a detail view of a PW-dry protocol specimen after testing. Figure 5(e) is a detailview of a PW-wet protocol specimen after testing.
Four slabs (8 test blocks) were compacted per mixture (2 PW-dry and 2 PW-wet). Data fromcorresponding LAC slab test blocks were averaged to create one PW-dry or PW-wet replicate. Dryand wet PURWheel testing was performed according to the procedures in Howard et al. (2010).Specimens were conditioned at the test temperature of 64◦C for 6 h before testing. Test parametersfor PW-wet protocol testing were the same as for the dry protocol test with the addition of sufficient64◦C water to the test chamber to fully submerge the specimens. The tyre inflation pressure was862 kPa, the wheel load was 1750 N, and the gross contact pressure at the beginning of the testwas approximately 630 kPa. The test was run for 20,000 passes or 20 mm of rutting, whicheveroccurred first. A pass was defined as one passage of the load wheel over the specimen. Raw rutmeasurements during testing were recorded by the PURWheel device and adjusted as describedin Howard et al. (2010). Rut depth (RDPW) was defined as downward permanent deformationof the specimen surface relative to the original surface, i.e. uplift of the specimen surface wasnot considered as part of the overall rut depth. The number of passes to 12.5 mm of rutting wasdetermined and denoted as P12.5.
In PW-dry testing, rutting rate was determined by fitting a linear equation to the post-consolidation data between 4000 and 16,000 passes (i.e. 2000 and 8000 cycles); the slope ofthat line was defined as the rutting rate parameter (RRPW) with units of millimetres/1000 cyclesfor comparison with APA data. For PW-wet test data, linear equations were fitted to rut depth datain the creep region and stripping region; slopes of these lines were denoted SC and SS, respectively,with units of millimetres/1000 passes. The calculated intersection of these two equations was SIP.
Air voids of slabs tested in the PURWheel were targeted to be 8 ± 2% on a Corelok® (AASHTOT 331) basis or 7 ± 1.7% on a submerged basis (AASHTO T 166). This air void level is in linewith Southeastern USA DOT specifications where average target, full pay maximum, and removalvoid levels are approximately 7%, 8%, and 10% measured via T 166 (Howard & Doyle, 2012).This criterion allows air voids to be in the range stated by Terrel and Al-Swailmi (1993) tobe favourable to the moisture damage (7–11%). Testing slabs at air void levels representing thehigher end of permissible values is more indicative of cases likely to be susceptible to the moisturedamage in service. If a mixture performs adequately at the upper end of allowable voids, it shouldin turn perform well at the lower end of allowable voids with the same aggregate blend and AC.
5. Test results and analysisTable 4 summarises results of the 28 PURWheel tests performed. Note that mixture CM1 per-formed poorly in both PW-dry and PW-wet tests; the test terminated early when all specimensexhibited excessive rutting prior to 2000 passes. Post-test visual observations of the specimensrevealed failure of the mix in shear as evidenced by the sharp vertical edges of the wheel path.When a mixture did reached 20,000 passes but did not achieve 12.5 mm of rutting or have a SIP,a value of 20,000 passes was used for averaging.
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Table 4. Dry and wet PURWheel test results.
PW-dry PW-wet
RDPW by passes (mm) RDPW by passes (mm)
Mixture ID Rep. Va (%)a P12.5 RRPW 4 k 5 k 10 k 15 k 16 k 20 k Rep. Va (%)a P12.5 SC SS SIP 5 k 10 k 15 k 20 k
CM1 1L&R 9.2 500 – – – – – – – 1L&R 9.1 550 – – – – – – –2L&R 9.1 350 – – – – – – – 2L&R 9.2 450 – – – – – – –Avg. 9.2 425 – – – – – – – Avg. 9.2 500 – – – – – – –
CM2 1L&R 6.9 20,000 0.35 3.1 3.5 4.4 5.1 5.2 5.5 1L&R 7.0 8550 1.02 5.86 8000 6.5 14.1 – –2L&R 8.8 20,000 0.58 4.3 4.8 6.4 7.7 7.8 8.5 2L&R 7.3 20,000 0.22 – 20000 3.5 4.6 5.6 7.7Avg. 7.9 20,000 0.46 3.7 4.1 5.4 6.4 6.5 7.0 Avg. 7.2 14,275 0.62 5.86 14000 5.0 9.4 5.6 7.7
CM3 1L&R 8.0 20,000 0.26 3.1 3.3 4.1 4.7 4.7 5.1 1L&R 7.4 20,000 0.12 – 20000 3.0 3.6 4.2 4.72L&R 11.5 20,000 0.62 4.6 5.1 6.8 8.1 8.3 9.2 2L&R 4.8 13,100 0.72 9.79 12750 5.4 5.7 6.8 7.6Avg.b 8.0 20,000 0.26 3.1 3.3 4.1 4.7 4.7 5.1 Avg.b 7.4 20,000 0.12 – 20000 3.0 3.6 4.2 4.7
RM1 1L&R 10.3 18,200 0.97 4.4 5.1 7.7 9.7 10.2 11.7 1L&R 9.5 10,500 0.95 4.52 11250 6.1 13.0 17.1 –2L&R 9.0 20,000 0.51 3.4 3.8 5.1 6.3 6.5 7.3 2L&R 9.1 15,200 0.64 7.90 15750 4.7 7.7 12.4 –Avg. 9.7 19,100 0.74 3.9 4.4 6.4 8.0 8.4 9.5 Avg. 9.3 12,850 0.79 6.21 13500 5.4 10.4 14.8 –
RM2 1L&R 7.0 17,100 0.81 5.3 5.9 8.1 9.8 10.2 11.7 1L&R 9.1 4500 1.94 9.02 4000 12.0 – – –2L&R 10.4 20,000 0.53 4.4 4.7 6.2 7.3 7.5 8.2 2L&R 8.9 11,400 1.19 7.02 4000 10.0 7.8 10.5 13.6Avg. 8.7 18,550 0.67 4.8 5.3 7.1 8.5 8.8 9.9 Avg. 9.0 7950 1.56 8.02 4000 11.0 7.8 10.5 13.6
RM3 1L&R 8.1 20,000 0.13 1.8 1.9 2.2 2.5 2.5 2.6 1L&R 8.2 12,750 0.54 3.72 11500 3.8 7.5 15.3 –2L&R 8.7 20,000 0.20 2.1 2.3 2.9 3.3 3.4 3.4 2L&R 8.3 14,450 0.37 10.10 8500 3.5 12.7 3.7 4.3Avg. 8.4 20,000 0.16 1.9 2.1 2.6 2.9 2.9 3.0 Avg. 8.8 13,600 0.46 6.91 10000 3.6 10.1 9.5 4.3
RM4 1L&R 6.4 20,000 0.45 3.2 3.6 4.8 5.7 5.9 6.6 1L&R 6.7 10,200 0.65 5.06 9250 4.9 9.9 – –2L&R 8.0 20,000 0.57 3.8 4.2 5.7 6.9 7.2 8.0 2L&R 7.6 14,000 0.60 10.80 7500 4.3 3.2 7.1 10.0Avg. 7.2 20,000 0.51 3.5 3.9 5.2 6.3 6.5 7.3 Avg. 7.2 12,100 0.63 7.93 8375 4.6 6.6 7.1 10.0
Note: Dashes (–) in a column entry indicate that the data in question are not applicable or could not be calculated for that test.aAir voids on a AASHTO T 331 basis.bReplicate 2L&R was not included in average since air voids were outside of desired tolerances.
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0
5
10
15
20
25
-0.2 -0.1 -0.1 0.0 0.1 0.1 0.2
Rel
ativ
e F
requ
ency
(%
)
[LAC RR APA - SGC RR APA] (mm/1000 cycles)
n: 14Mean: -0.016
Std. dev.: 0.083
t0.025 = ± 2.160t = -0.721
RRAPA = 0.0248Va + 0.08
0
0.1
0.2
0.3
0.4
0.5
0.6
0 2 4 6 8 10 12 14
RR
APA
(mm
/100
0 cy
cles
)
Va (%)
SGC data
LAC data
Linear (SGC data)
-0.100
+0.055
(a)
(b)
Figure 6. The effect of compaction method on APA results. (a) Example RRAPA data for CM2.(b) Histogram for rutting rate.
5.1. Effect of compaction method on APA resultsThe effect of the specimen compaction method on the APA rut performance was assessed bycomparing LAC-compacted specimens to SGC-compacted specimens at the same level of airvoids. The comparison consisted of drawing a line between SGC specimen data points to predictthe rutting performance as a function of air voids (Figure 6(a)). Based on the equation of this line,estimates of the rutting performance at the level of air voids of LAC-compacted specimens werecalculated and the difference between measured performance of LAC specimens and predictedperformance of SGC specimens at the same level of air voids was then determined (differenceswere +0.055 and −0.100 for air voids of 6.6% and 6.8%, respectively). The same procedure wasperformed with rut depth data and the process was repeated for all mixtures.
A relative frequency histogram summarising this data is presented in Figures 6(b) forrutting rate; a similar histogram was produced for rut depth data (n = 14, mean = −0.44,Stddev. = 1.89). Based on one sample two-tailed Student’s t-tests at a 5% significance level(t0.025 = ±2.160), the mean of the differences was not statistically different than zero for ruttingrate (t = −0.721) or total rut depth (t = −0.087). Indicating that for this specific data set, meanAPA rutting performance for SGC- and LAC-compacted specimens was similar. A similar dataanalysis approach was taken in Howard et al. (2012) for a larger data set and it was observed that
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162 J.D. Doyle and I.L. Howard
0
2
4
6
8
10
0 2 4 6 8 10
PW
rutti
ng a
t V
a=
8%
with
AP
A s
hift
fact
ors
PW rutting at Va = 8% with PW shift factors
Rut Depth at 5,000 Passes
Rut Depth at 16,000 Passes
Rutting Rate
Plot uses data from mixtures CM2,
RM2, RM3 and RM4 where PW-dry
air voids reasonably bracket 8%
Figure 7. Comparison of shift factors based on APA or PURWheel data.
total rut depths of LAC-compacted specimens were generally similar or slightly higher than forSGC-compacted specimens at similar air void levels.
5.2. Comparison of APA and PW-dry protocol ruttingBased on the observations in the previous section, PW-dry test results for LAC-compacted spec-imens were directly compared with APA results for SGC specimens. Both PW-dry and APAdata were adjusted to 8% air voids on T 331 basis, corresponding to 7% air voids on a T 166basis (Howard & Doyle, 2012). This adjustment was made by assuming that, for a given mix-ture, the change in rut depth or rutting rate per unit change in air voids was the same for APAand PW-dry tests. The shift factor was determined by dividing the change in rutting by thecorresponding change in air voids. For example, mixture CM2 at 16,000 passes had 2.0 mmAPA rutting at 6.8% air voids and 4.4 mm rutting at 9.5% air voids; the shift factor was then(4.4 − 2.0)/(9.5 − 6.8) = +1.037 mm of rutting for each 1% change in air voids. For PW-dryreplicate 1, air voids were 6.9% and rutting was 5.2 mm; the rut depth was then increased by(8 − 6.9) ∗ 1.037 = 1.1 mm for a shifted rut depth of 6.3 mm (5.2 + 1.1 = 6.3). The effect ofusing air void shift factors based on APA data instead of shift factors based on PURWheel datais trivial as shown in Figure 7. For each mixture, shift factors based on APA rut depths at 16,000passes (8000 cycles) were used to shift PW-dry rut depth data at 16,000 cycles and similarly forrut depth data at 5000 passes and rutting rate.
Figures 8–10 are equality plots showing APA and PW-dry data for rut depth at 16,000 passes, rutdepth at 5000 passes and rutting rate, respectively. These figures use data from Table 4 alongside11 additional base mixtures tested and analysed with the same methods of this paper to compareAPA and PURWheel rut depths adjusted to 8% air voids on a T 331 basis. The 11 additional basemixtures consisted of four control mixtures, two 50% RAP mixtures, two 75% RAP mixtures, andtwo 100% RAP mixtures. The same raw materials (R1 and R2 RAP sources, virgin aggregates,and virgin binder) were used as in this paper and the raw data from those mixes are presented inDoyle (2011).
A total of 15 mixes were plotted; CM1 and one of the control mixtures of Doyle (2011) couldnot be used due to early rutting failure, one of the 75% RAP mixtures from Doyle (2011) was anoticeable outlier when the data were plotted (inclusion of this mixture did not change the overall
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0
2
4
6
8
10
0 2 4 6 8 10
RD
PW
Adj
uste
d to
8%
T33
1 A
ir V
oids
(mm
)
RDAPA Adjusted to 8% T331 Air Voids (mm)
9.5 mm (Table 4)
12.5 mm (Doyle, 2011)
Equality Line
Series4
Series5
Intercept Set to Zero:RDPW = 1.47 (RDAPA) R2 = 0.29
Intercept Not Set to Zero:RDPW = 0.90 (RDAPA) + 2.6 R2 = 0.51
Figure 8. 16,000 pass rut depth comparison of APA with PW-dry adjusted to Va = 8%.
0
2
4
6
0 2 4 6
RD
PW
Adj
uste
d to
8%
T33
1 A
ir V
oids
(mm
)
RDAPA Adjusted to 8% T331 Air Voids (mm)
9.5 mm (Table 4)
12.5 mm (Doyle, 2011)
Equality Line
Series4
Series5
Intercept Set to Zero:RDPW = 1.38 (RDAPA) R2 = 0.33
Intercept Not Set to Zero:RDPW = 0.62 (RDAPA) + 2.3 R2 = 0.40
Figure 9. 5000 pass rut depth comparison of APA with PW-dry adjusted to Va = 8%.
0
0.25
0.5
0.75
1
0 0.25 0.5 0.75 1
RR
PW
Adj
uste
d to
8%
T33
1 A
ir V
oids
(mm
/100
cyc
les)
RR APA Adjusted to 8% T331 Air Voids
9.5 mm (Table 4)
12.5 mm (Doyle, 2011)
Equality Line
Series4
Series5
Intercept Set to Zero:RRPW = 1.73(RRAPA) R2 = 0.35
Intercept Not Set to Zero:RRPW = 1.31 (RRAPA) + 0.12 R2 = 0.39
Figure 10. Rutting rate comparison of APA to PW-dry adjusted to Va = 8%.
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164 J.D. Doyle and I.L. Howard
SIP = 8500
Creep Regiony = (0.607E-3)x + 1.48
Strip Regiony = (10.08E-3)x - 78.6
0
5
10
15
20
25
0 5000 10000 15000 20000
(a)
(b)
Rut
Dep
th (
mm
)
Pass
P12.5 = 8900
Mix RM3Replicate 2L
P12.5 = 1.01SIPR² = 0.94
0
5000
10000
15000
20000
0 5000 10000 15000 20000
P12
.5(p
ass)
SIP (pass)
9.5 mm12.5 mm (Doyle, 2011)Equality LineLinear (All data)
Figure 11. Analysis of PW-wet data and comparison with TSR. (a) Example calculation of SIP and P12.5.(b) Relationship of SIP to P12.5.
prediction by a large amount but it was believed the data were more representative without itsinclusion). Figures 8–10 include data for 60 individual PW-dry test specimens (15 mixtures with 4specimens each). The 9.5-mm surface mixes and the 12.5-mm base mixes were plotted separately,but they did not differ by a considerable amount so one set of prediction equations was developed.Figures 8–10 do show the 9.5- and 12.5-mm mixes with different markers. In general, PURWheeldata indicate greater rut depths and higher rutting rates than APA data, a result that aligns withconclusions in the loaded wheel tester comparison discussed earlier. The data in Figure 9 areutilised in the moisture damage analysis presented in the following section.
5.3. Analysis of PURWheel moisture susceptibility dataThe first step in the analysis of PW-wet data is illustrated in Figure 11(a) for mixture RM3and consisted of fitting lines to the data in the first steady-state (creep) region and the secondsteady-state (strip) region. The SIP was calculated as the intersection point of the two lines; thecalculations are demonstrated on the figure and the vertical dashed arrow shows where this occurs.Values were rounded to 500 passes since selection of these line fits are subjective. Determinationof the number of passes to 12.5 mm of rutting (P12.5) was straightforward and is shown by thesolid horizontal and vertical arrows; values were rounded to 100 passes.
It was observed that the values for SIP were generally very similar to values for P12.5.Figure 11(b) investigates this relationship for 17 mixtures from Table 4 and Doyle (2011); mix-ture CM1 from Table 4 failed too quickly to develop any SIP values and was not used. Figure 11
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includes data for 68 individual PW-wet test specimens (17 mixtures with 4 specimens each). Itis apparent that for the specific combination of test temperature and loading conditions in thePW-wet test, P12.5 can safely be used as a surrogate for SIP in the further analysis. Doing soallows for direct comparison of PW-wet and PW-dry data since P12.5 values are obtained in thePW-dry test but SIPs are not.
Three indicators were defined from PURWheel testing to evaluate moisture susceptibility: (1)cohesion ratio for loss of cohesion due to moisture; (2) SIP for loss of adhesion due to moisture;and (3) P12.5 ratio to provide an overall assessment of the mixture performance in the presence ofmoisture. All of these performance measures are used in the next section to assess the performanceof high RAP content WMA.
Cohesion ratio (Equation (1)) is the ratio of PW-wet to PW-dry rut depth (RDPW ) at 5000 passesand was used to evaluate the cohesive (or mastic) response of the specimen to moisture. PW-drydata were shifted to the same air voids of PW-wet data in the manner already discussed. A highercohesion ratio is considered indicative of greater rutting in the presence of moisture without loss ofadhesion. Some in-service pavements experience noticeable moisture damage without strippingor adhesive failure (Little & Jones, 2003). Cohesion of the mastic could be especially importantin high RAP content mixtures since the interaction of aged and virgin binders would affect thecohesion ratio prior to stripping. RAP particles often have a very stiff and tightly bonded coatingthat could protect against stripping. Nevertheless, inadequate partial blending of aged and virginbinders could lead to cohesive problems in some mixtures.
Cohesion ratio = PW-wet RD5000 pass
PW-dry RD5000 pass. (1)
The higher the cohesion ratio, the more affected the specimen is by moisture on a relative scale.However, the overall increase in rut depth due to moisture is also relevant since a specimen couldhave a very high cohesion ratio (e.g. 5) from a largely meaningless change in rut depths (e.g.0.1 mm dry to 0.5 mm wet). These two values should be interpreted together. One criticism ofthe TSR often made is that only the wet-to-dry strength ratio is presented absent the dry or wettensile strength. An example would be a dry tensile strength of 350 kPa and a wet tensile strengthof 327 kPa; the TSR is 93% but the material probably will not perform well with such low valuesof wet and dry tensile strength.
SIP has already been defined and was considered indicative of loss of adhesion for a mixturesince that is when loose aggregate begins to appear with the binder coating removed. A lowerSIP is indicative of poorer adhesion in the presence of moisture. Based on HLWT testing at 50◦C,Aschenbrener and Currier (1993) found that SIP values less than 3000 were indicative of mixtureswith the poor field performance and SIPs greater than 10,000 were indicative of the good fieldperformance. Based on the work of Nielson (2010) and observations made during comparison ofloaded wheel testers, it is expected that SIPs might be more likely to occur with PW-wet testingat 64◦C than for HLWT testing at 50◦C.
Finally, the P12.5 ratio (Equation (2)) is the ratio of PW-wet and PW-dry P12.5 values. It isconsidered to be indicative of the overall mixture performance in the presence of moisture. Thekey difference in the P12.5 ratio and TSR measures of the moisture damage potential is thatthe P12.5 ratio incorporates the effects of traffic in combination with moisture to evaluate thepotential susceptibility of a mixture to the moisture damage. Numerous studies in the literaturehave indicated that the effects of traffic are an important factor in moisture susceptibility ofpavements (Hicks, 1991; Little & Jones, 2003; Lu, 2005; Lottman, 1982).
P12.5 Ratio (%) = PW-wet P12.5
PW-dry P12.5100 (2)
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166 J.D. Doyle and I.L. Howard
11.9
4.7 4.43.5 3.7
2.2
4.7
6.7
4.73.7
9.4
2.4
7.2
0
4
8
12
16
20
CM1 CM2 CM3 RM1 RM2 RM3 RM4
Rut
Dep
th (
mm
)
APA
PW-Dry
Control Mixtures 25% RAP 50% RAP
Not
Ava
ilabl
e
Data Shifted to Va = 8% on T331 Basis
0.48
0.280.22 0.23
0.26
0.16
0.36
0.48
0.26
0.16
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0.0
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CM1 CM2 CM3 RM1 RM2 RM3 RM4
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les) APA
PW-Dry
Control Mixtures 25% RAP 50% RAPN
ot A
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Data Shifted to Va = 8% on T331 Basis
Figure 12. Rutting performance of high RAP content WMA. (a) Rutting rate. (b) Rutting depth at 16,000passes.
5.4. Performance of high RAP content WMABased on the analysis techniques previously discussed, Figure 12 presents rutting performanceresults of all high RAP–WMA surface mixtures tested. Values for CM1 were not available forPW-dry since the mixture failed so quickly in the PURWheel testing. In terms of rutting, theperformance of the high RAP content WMA mixtures was affected by RAP source as well asRAP content. Based on all the data, mixtures made with the R1 RAP source (i.e. RM1 and RM3)generally had better performance than all the controls. On the other hand, the performance ofmixtures made with R2 RAP (i.e. RM2 and RM4) was better than CM1 but similar or not quite asgood as CM2 or CM3. For R1 RAP mixes, 50% RAP had less rutting than 25% RAP as expected;for R2 RAP, PW-dry testing predicted better performance in 50% RAP, but APA testing did notoffer the same prediction. With the one exception, data from APA and PW-dry testing providedthe same rankings and assessments for the mixture performance; PW-dry data provided the morelogical ranking of mixtures in the excepted case. Overall, the rutting performance of the high RAPcontent WMA was similar to or better than current practice mixtures, results in line with recentstudies (Abbas & Ali, 2011; Hurley & Prowell, 2006).
Based on the observations and analysis techniques previously discussed, Figure 13 presentsmoisture damage performance results of all the high RAP content WMA surface mixtures tested.The cohesion ratio and SIP values for CM1 were not available since the mixture failed so quickly inthe PURWheel testing. The cohesion ratio (Figure 13(a)) was less than 1.5 for the control mixturesand rut depths increased no more than 1.3 mm in the presence of moisture. The performance ofmixtures RM1, RM3, and RM4 was similar to the controls with cohesion ratios on the order of
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1.40.9
1.3
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6(a)
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CM1 CM2 CM3 RM1 RM2 RM3 RM4
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ot A
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94 95 95 97 97 98 93
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CM1 CM2 CM3 RM1 RM2 RM3 RM4
P12
.5R
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R (
%)
TSR P12.5 Ratio
Control Mixtures 25% RAP 50% RAP
Figure 13. Moisture damage performance of high RAP content WMA. (a) Cohesion ratio. (b) SIP. (c) P12.5ratio and TSR.
1.5 or less and rut depth increases of 1.5 mm or less. On the other hand, the cohesion ratio ofmixture RM2 was 2.0 and rutting increased by 5.5 mm due to the presence of moisture.
Figure 13(b) provides average SIP values for each mixture. SIP values for the control mixturewere well above the 10,000 pass criterion of Aschenbrener and Currier (1993). Mixtures RM1,RM3, and RM4 have the similar or slightly lower SIP values than control mixtures, but still abovethe 10,000 pass criterion. RM2 has a lower result than the other mixtures of 8000 passes, indicatingpotential for increased susceptibility to the moisture damage relative to the other mixtures.
Figure 13(c) presents the P12.5 ratio and TSR values for all mixtures. All of the TSR valuesrange from 93% to 98%, indicating that the mixtures will likely have similarly good resistance
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to the moisture damage. On the other hand, P12.5 ratios indicate a wider range of the potentialperformance. Values for controls CM1–CM3 were 118%, 71%, and 100%, respectively; however,the 118% for CM1 is misleading since rapid failure of the mix in shear did not provide time forany moisture damage to develop and the overall performance of that mixture in the PURWheeltesting was poor (i.e. the ratio of 500–425 passes is 118% but the mix failed in about 500 passesrelative to the 20,000 passes desired). For the high RAP mixtures, P12.5 ratios were 67%, 68%, and61% for RM1, RM3, and RM4, respectively, indicating the moisture damage performance similartoo or only slightly less than that of control mixtures. Overall, moisture damage data indicate thatthree of the four high RAP content WMA mixtures would have acceptable performance relativeto current practice while the fourth may be slightly more susceptible to moisture.
Based on all the PURWheel data, mixture RM2 may have the potential for increased moisturesusceptibility compared with the control and other high RAP mixtures. This is not evident fromTSR test data, providing evidence that the current PURWheel equipment and test parameters canprovide a more discerning assessment of the mixture performance. Additional research is neededto quantify what PURWheel test values with the enhanced protocols best indicate the good fieldperformance.
6. Summary and conclusionsThe enhanced version of the PURWheel test currently in use was used to assess the rutting andmoisture damage performance of 7 mixtures with up to 50% warm mixed RAP content. Basedon the study results, the following conclusions and recommendations are made:
• PW-dry and APA were equally good indicators of rutting potential. APA rutting perfor-mance was not affected by the compaction method. Using APA dry rut data (since it isreadily available) in conjunction with PW-wet data could be an efficient combination.
• Rutting performance of the high RAP content WMA was similar to or better than currentpractice control mixtures. RAP source influenced the rutting performance.
• PW-wet testing showed a better ability to discern the moisture damage performance poten-tial than the TSR test and also appeared to provide more useful moisture damage informationin terms of cohesion and adhesion.
• The current PURWheel equipment and test parameters are capable of providing moisturedamage assessments while including the effects of traffic.
• Moisture damage performance of high RAP content WMA appeared to be similar to or notgreatly worse than current practice control mixtures.
• Additional research is needed to relate PURWheel parameters to the field performance andfor a wide variety of mixture types.
List of acronyms and variables
AASHTO American association of state highway and transportation officialsAbs water absorption (%)ASTM American society for testing and materialsCM1 control mixture 1CM2 control mixture 2CM3 control mixture 3Gmb bulk-specific gravity of mixtureGmm theoretical maximum specific gravityGsb bulk-specific gravity of aggregate
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GSC gyratory shear compactorGTM gyratory testing machineNdes number of design gyrationsP12.5 number of passes in the PURWheel to 12.5 mm rut depthPG performance gradeR1 RAP source 1R2 RAP source 2RD5000pass rut depth in the PURWheel at 5000 passesRDAPA rut depth measured in APARDPW rut depth measured in the PURWheelRM1 recycled mixture 1RM2 recycled mixture 2RM3 recycled mixture 3RM4 recycled mixture 4RRAPA rutting rate measured in APARRPW rutting rate measured in the PURWheelSC slope of rut depth data in creep regionSS slope of rut depth data in stripping regionTcomp compaction temperatureTmix mixing temperatureVa air voidsVFA voids filled with asphaltVMA voids in mineral aggregate
List of test methods referencedASTM D2726 Standard Test Method for Bulk-Specific Gravity and Density of
Non-Absorptive Compacted Bituminous MixturesASTM D4867 Standard Test Method for Effect of Moisture on Asphalt Concrete Paving
MixturesAASHTO R 29 Standard Practice for Grading or Verifying the Performance Grade (PG) of
an Asphalt BinderAASHTO T 164 Standard Method of Test for Quantitative Extraction of Asphalt Binder
from Hot-Mix Asphalt (HMA)AASHTO T 166 Standard Method of Test for Bulk-Specific Gravity (Gmb) of Compacted
Hot-Mix Asphalt (HMA) Using Saturated Surface-Dry SpecimensAASHTO T 209 Standard Method of Test for Theoretical Maximum Specific Gravity
(Gmm) and Density of Hot Mix Asphalt (HMA)AASHTO T283 Standard Method of Test for Resistance of Compacted Hot Mix Asphalt
(HMA) to Moisture-Induced DamageAASHTO T 316 Standard Method of Test for Viscosity Determination of Asphalt Binder
Using Rotational ViscometerAASHTO T324 Standard Method of Test for Hamburg Wheel-Track Testing of Compacted
Hot Mix asphalt (HMA)AASHTO T 331 Standard Method of Test for Bulk-Specific Gravity and Density of
Compacted Hot-Mix Asphalt Using Automatic Vacuum SealingMethod
AASHTO T 340 Standard Method of Test for Determining the Rutting Susceptibility of HotMix Asphalt (HMA) Using the Asphalt Pavement Analyzer (APA)
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AASHTO TP 63 Standard Method of Test for Determining the Rutting Susceptibility of HotMix Asphalt (HMA) Using the Asphalt Pavement Analyzer (APA)
MT-63 Mississippi Test Method for Resistance of Bituminous Paving Mixtures toStripping (Vacuum Saturation Method)
AcknowledgementsThis research was funded by the Mississippi DOT under State Study 212. Scott Glusenkamp of APACMississippi is thanked for his assistance in the location of field mixtures. Dr. Thomas D. White is thankedfor his assistance in a variety of manners including securing the original PURWheel equipment, and for thetechnical guidance related to wheel tracking and finite element modelling. Permission to publish was grantedby the Director, Geotechnical and Structures Laboratory, US Army Engineer Research and DevelopmentCenter.
ReferencesAbbas, A. R., & Ali, A. (2011). Mechanical properties of warm mix asphalt prepared using foamed asphalt
binders (Report No. FHWA/OH-2011/6). Columbus, OH: Ohio Department of Transportation.Aschenbrener, T. (1995). Evaluation of Hamburg wheel-tracking device to predict moisture damage in
hotmix asphalt. Transportation Research Record: Journal of the Transportation Research Board, 1492,193–201.
Aschenbrener, T., & Currier, G. (1993). Influence of testing variables on the results from the Ham-burg wheel-tracking device (Report No. CDOT-DTD-R-93-22). Denver, CO: Colorado Departmentof Transportation.
Austerman, A. J., Mogawer, W. S., & Bonaquist, R. (2009, January 11–15). Evaluating the effects of warmmix asphalt technology additive dosages on the workability and durability of asphalt mixtures containingrecycled asphalt pavement. Proceedings of transportation research board 88th annual meeting, PaperNo. 09-1279, Washington, DC.
Azari, H. (2010). Precision estimates of AASHTO T 283: Resistance of compacted hot mix asphalt (HMA) tomoisture-induced damage. (NCHRP Web-Only Document No. 166). Washington, DC: TransportationResearch Board.
Boggs, W. (2008). Customers warm up to green system. Warm-Mix Asphalt: Contractor’s Experiences,Information Series 134, National Asphalt Pavement Association, Lanham, MD, pp. 16–17.
Collins, R., Shami, H., & Lai, J. S. (1996). Use of Georgia loaded wheel tester to evaluate rutting of asphaltsamples prepared by Superpave gyratory compactor. Transportation Research Record: Journal of theTransportation Research Board, 1545, 161–168.
Copeland, A. (2011). Reclaimed asphalt pavement in asphalt mixtures: State-of-the-practice (Report No.FHWA-HRT-11-021). Washington, DC: Federal Highway Administration.
Copeland, A., D’Angelo, J., Dongré, R., Belagutti, S., & Sholar, G. (2010). Field evaluation of high reclaimedasphalt pavement-warm mix asphalt project in Florida: Case study. Transportation Research Record:Journal of the Transportation Research Board, 2179, 93–101.
Diefenderfer, S. D., & Hearon, A. J. (2010). Performance of Virginia’s warm-mix asphalt trial sections(Report No. FHWA/VTRC 10-R17). Charlottesville, VA: Virginia Transportation Research Council.
Doyle, J. D. (2011). Characterization of reclaimed asphalt and performance based evaluation of its use inrecycled mixtures (PhD dissertation). Mississippi State University, Mississippi State, MS.
Doyle, J. D., & Howard, I. L. (2010). Linear asphalt compactor operator’s manual, Manual No. CMRCM 10-1 Version 2, Construction Materials Research Center, Mississippi State University, MississippiState, MS.
Doyle, J. D., Howard, I. L., & Robinson, W. J. (2012). Prediction of absorbed, inert, and effective bituminousquantities in reclaimed asphalt pavement. Journal of Materials in Civil Engineering, 24(1), 102–112.
Doyle, J. D., Mejías-Santiago, M., Brown, E. R., & Howard, I. L. (2011). Performance of high RAP-WMA surface mixtures. Asphalt Paving Technology: Journal of the Association of Asphalt PavingTechnologists, 80, 419–457.
Epps, J. A., Sebaaly, P. E., Penaranda, J., Maher, M. R., McCann, M. B., & Hand, A. J. (2000). Compatibilityof a test for moisture-induced damage with Superpave volumetric mix design (NCHRP Report 444).Washington, DC: Transportation Research Board.
Dow
nloa
ded
by [
McG
ill U
nive
rsity
Lib
rary
] at
02:
21 2
0 N
ovem
ber
2014
Road Materials and Pavement Design 171
Federal Highway Administration (FHWA). (1988). Performance of coarse-graded mixes at Westrack-premature rutting (Report No: FHWA-RD-99-134). Washington, DC: Author.
Federal Highway Administration (FHWA). (2012). Hamburg wheel tracking device – equipment – bitumi-nous mixtures laboratory (BML) – labs – research – asphalt – pavements – FHWA. Retrieved July 23,2012, from http://www.fhwa.dot.gov/pavement/asphalt/labs/mixtures/hamburg.cfm
Hicks, R. G. (1991). Moisture damage in asphalt concrete (NCHRP Synthesis of Highway Practice (No.175)). Washington, DC: Transportation Research Board.
Hodo, W. D., Kvasnak, A., & Brown, E. R. (2009, January 11–15). Investigation of foamed asphalt (warmmix asphalt) with high reclaimed asphalt pavement (RAP) content for sustainment and rehabilitation ofasphalt pavement. Proceedings of transportation research board 88th annual meeting, Paper No. 09-3789,Washington, DC.
Howard, I. L., & Doyle, J. D. (2012, January 22–26). Comparison of available density measurement methodsapplicable to design and construction. Proceedings of transportation research board 91st annual meeting,Paper No. 12-0564, Washington, DC.
Howard, I. L., Doyle, J. D., & Barham, J. M. (2012). Uniformity, repeatability, and permanent deformationresistance of slabs produced with the linear asphalt compactor. Advances in Civil Engineering Materials,1(1), 1–17.
Howard, I. L., Doyle, J. D., White, T. D., Ivy, J., & Booth, O. (2010). PURWheel laboratory wheel trackeroperator’s manual, Manual No. CMRC M 10-2 Version 1, Construction Materials Research Center,Mississippi State University, Mississippi State, MS.
Hurley, G. C., & Prowell, B. D. (2005). Evaluation of Sasobit® for use in warm mix asphalt (NCAT ReportNo. 05-06). Auburn, AL: National Center for Asphalt Technology.
Hurley, G. C., & Prowell, B. D. (2006). Evaluation of Evotherm® for use in warm mix asphalt (NCATReport No. 06-02). Auburn, AL: National Center for Asphalt Technology.
Kandhal, P. S., & Cooley, Jr., L. A. (2003). Accelerated laboratory rutting tests: Evaluation of the asphaltpavement analyzer (NCHRP Report 508). Washington, DC: Transportation Research Board.
Kanitpong, K., & Bahia, H. (2008). Evaluation of HMA moisture damage in Wisconsin as it relates topavement performance. International Journal of Pavement Engineering, 9(1), 9–17.
Kiggundu, B. N., & Roberts, F. L. (1988). Stripping in HMA mixture: State-of-the-art and critical review ofthe test methods (NCAT Report No. 88-02). Auburn, AL: National Center for Asphalt Technology.
Kvasnak, A., West, R., Moore, J., Nelson, J., Turner, P., & Tran, N. (2009, January 11–15). Case studyof warm mix asphalt moisture susceptibility Birmingham. Proceedings of transportation research board88th annual meeting, Paper No. 09-3703, Washington, DC.
Little, D., & Jones, D. R. (2003). Chemical and mechanical processes of moisture damage in hot-mix-asphaltpavements. Moisture sensitivity of asphalt pavements: A national seminar, Transportation ResearchBoard, Washington, DC.
Lottman, R. P. (1978). Predicting moisture-induced damage to asphaltic concrete (NCHRP Report No. 192).Washington, DC: Transportation Research Board.
Lottman, R. P. (1982). Predicting moisture-induced damage to asphaltic concrete field evaluation (NCHRPReport No. 246). Washington, DC: Transportation Research Board.
Lu, Q. (2005). Investigation of conditions for moisture damage in asphalt concrete and appropriatelaboratory test methods (PhD dissertation). University of California, Berkeley, CA.
Mallick, R. B., Kandhal, P. S., & Bradbury, R. L. (2008). Using warm mix asphalt technology to incorporatehigh percentage of reclaimed asphalt pavement material in asphalt mixes. Transportation ResearchRecord: Journal of the Transportation Research Board, 2051, 71–79.
Mejías-Santiago, M., Doyle, J. D., Howard, I. L., & Brown, E. R. (2011, October 11–13). Moisture damagepotential for warm mix asphalt containing reclaimed asphalt pavement. Proceedings of 2nd internationalwarm mix conference, St. Louis, MO.
Middleton, B., & Forfylow, R. W. (2009). Evaluation of warm-mix asphalt produced with the double barrelgreen process. Transportation Research Record: Journal of the Transportation Research Board, 2126,19–26.
Mogawer, W. S., Austerman, A. J., Bonaquist, R., & Roussel, M. (2011, January 23–27). Performancecharacteristics of thin lift overlay mixtures containing high RAP content, RAS, and warm mix asphalttechnology. Proceedings of transportation research board 90th annual meeting, Paper No. 11-1859,Washington, DC.
Mogawer, W. S., Austerman, A. J., Kassem, E., & Masad, E. (2011). Moisture damage characteristics ofwarm mix asphalt mixtures. Asphalt Paving Technology: Journal of the Association of Asphalt PavingTechnologists, 80, 491–526.
Dow
nloa
ded
by [
McG
ill U
nive
rsity
Lib
rary
] at
02:
21 2
0 N
ovem
ber
2014
172 J.D. Doyle and I.L. Howard
Nielson, J. (2010). Development of a testing temperature to be used with the Hamburg wheel tracking deviceon asphalt mixtures that utilize performance grade binders (MS thesis), University of Utah, Salt LakeCity, UT.
Pan, C., & White, T. (1999). Conditions for stripping using accelerated testing (Report FHWA/IN/JTRP-97/13). West Lafayette, IN: Joint Transportation Research Program, Purdue University.
Prowell, B. D., Hurley, G. C., & Crews, E. (2007). Field performance of warm-mix asphalt at nationalcenter for asphalt technology test track. Transportation Research Record: Journal of the TransportationResearch Board, 1998, 96–102.
Rand, D. A. (2006). Hamburg wheel test (Technical Advisory Dated August 16, 2006). Austin, TX: TexasDepartment of Transportation Construction and Bridge Division.
Richardson, C. (1912). The modern asphalt pavement (2nd ed.). New York: John Wiley & Sons.Stiady, J. L., Hand, A. J. T., Noureldin, A. S., Galal, K., Hua, J., & White, T. D. (2003). Validation of
SHRP asphalt mixture specifications using accelerated testing (Final Report No. 176). Indianapolis, IN:Indiana Department of Transportation.
Terrel, R. L., & Al-Swailmi, S. (1993). Role of Pessium voids concept in understanding moisture damageto asphalt concrete mixtures. Transportation Research Record: Journal of the Transportation ResearchBoard, 1386, 31–37.
Tunnicliff, D. G., & Root, R. E. (1984). Use of antistripping additives in asphaltic concrete mixtures (NCHRPReport No. 274). Washington, DC: Transportation Research Board.
Tunnicliff, D. G., & Root, R. E. (1995). Use of antistripping additives in asphaltic concrete mixtures: Fieldevaluation (NCHRP Report No. 373). Washington, DC: Transportation Research Board.
Willis, J. R., West, R., Nelson, J., Taylor, A., & Leatherman, K. (2011, October 11–13). Combining warmmix asphalt technologies with mixtures containing reclaimed asphalt pavement. Proceedings of 2ndinternational warm mix conference, St. Louis, MO.
Zaniewski, J., & Viswanathan, A. G. (2006). Investigation of moisture sensitivity of hot mix asphalt concrete(Report Submitted to West Virginia Division of Highways). Charleston, WV: West Virginia Departmentof Highways.
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