Laboratory evaluation of rutting susceptibility of polymer-modified asphalt mixtures containing recycled pavements

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    binders were the least affected. Aggregate properties of RAP mix had a noticeable effect on rutting results

    cationinder aeclaimes to cor polys of adce to p

    Even with the evident economic and environmental advantagesof adding RAP to virgin HMA mixtures, there is a concern about along-term performance of the HMA pavements containing RAP.RAP characteristics such as increased oxidation levels due to aging,increased RAP binder stiffness, and non-uniformity of aggregatetype and gradation may signicantly affect the fatigue properties,rutting resistance, as well as moisture susceptibility of a RAP-mod-

    the HMA specimen is uneven over time and may cause local con-centrations of shear on the surface of the specimens [4,6].

    Attenuate Total Reection (ATR) Fourier Transform Infrared (FT-IR) spectroscopy enables evaluation of oxidation levels as well aspresence and quantication of additives in asphalt binders by mea-suring the concentration of specic chemical functionalities. Spec-troscopic investigation of the oxidative hardening in asphaltmaterials have been a focus of pavement research for more thanthree decades. Petersen et al. [79] employed IR transmission spec-trometers to study long-term aging in asphalt binders and recog-nized three major products of oxidation: benzylic ketones,

    Corresponding author. Tel.: +1 860 486 2733.E-mail addresses: alex.bernier@engr.uconn.edu (A. Bernier), azofka@engr.uconn.

    Construction and Building Materials 31 (2012) 5866

    Contents lists available at

    B

    evedu (A. Zofka), ily08001@engr.uconn.edu (I. Yut).fatigue cracking, low-temperature cracking, moisture damageand oxidative aging [1].

    RAP has been used in HMA pavements since the 1930s [2]. Withan increase in the number of rehabilitation projects for deterio-rated roadways as compared with new constructions, the amountof RAP generated in the US has been continuously rising. In20062007, the Connecticut Department of Transportation(ConnDOT) used about 260,000 tons out of 420,000 tons (i.e. 62%)of generated RAP in highway construction [3].

    as a means for evaluating in particular modied binders beyondthe standard parameter used in the US in the PG system, i.e. |G|/sind (dynamic shear modulus over sine of phase angle). The As-phalt Pavement Analyzer (APA) is one of several accelerated proto-cols that measure rutting resistance of HMA lab prepared orroadway-cored specimens. Rutting resistance is evaluated by run-ning a steel wheel over pressurized tubing which rests on top ofthe specimens [5]. While the steel wheels have a well-controlledload, previous work has indicated that the load distribution inFourier transform infrared spectroscopyX-ray uorescence spectroscopy

    1. Introduction

    The goal of asphalt binder modibility of Hot Mix Asphalts (HMAs). Brecycled materials, such as old R(RAPs) or crumb rubber from the tiras styrenebutadiene rubber (SBR)Different quantities and combinationto enhance asphalt binders resistan0950-0618/$ - see front matter 2011 Elsevier Ltd. Adoi:10.1016/j.conbuildmat.2011.12.094and adding RAP binder to the mix lead to reduced rutting. 2011 Elsevier Ltd. All rights reserved.

    is to improve the dura-dditives range from theed Asphalt Pavementshemical additives suchphosphoric acid (PPA).ditives have been usedermanent deformation,

    ied HMA. Furthermore, the variability in RAP physical propertiesdue to varying sources of material affects predictability of proper-ties and, therefore, performance of RAP-modied HMA pavements.

    Rutting resistance is one of the primary characteristics that con-trol durability and structural capacity of the pavements. There areseveral testing protocols in Europe and in the US for both asphaltbinders and asphalt mixes that examine rutting resistance. Oneof the most recent developments in binder testing is the MultipleStress Creep and Recovery (MSCR) test [4]. MSCR was developedPolymer-modied bindersRecycling

    employed to verify the mineral content of RAP aggregates. The effect of RAP binder on the APA and MSCRresults showed reasonable correlation with reduced rutting for less-modied binders. Highly-modiedLaboratory evaluation of rutting susceptimixtures containing recycled pavements

    Alexander Bernier, Adam Zofka , Iliya YutUniversity of Connecticut, Department of Civil and Environmental Engineering, 261 Glen

    a r t i c l e i n f o

    Article history:Received 21 October 2011Received in revised form 16 December 2011Accepted 23 December 2011Available online 21 January 2012

    Keywords:Asphalt pavements

    a b s t r a c t

    This paper presents the reasphalt mixtures containinducted in the Asphalt Paveometer in order to constviscoelastic and recovery pand level of oxidation of dTransform Infrared spectr

    Construction and

    journal homepage: www.elsll rights reserved.lity of polymer-modied asphalt

    ok Road, Unit 2037, Storrs, CT 06269-2037, United States

    ts of the laboratory study on rutting susceptibility of polymer-modiedeclaimed Asphalt Pavement (RAP). Accelerated rutting tests were con-nt Analyzer (APA) and binders were evaluated in the Dynamic Shear Rhe-t dynamic shear modulus (|G|) master curves and to evaluate theirerties using the Multi-Stress Creep Recovery Test (MSCR). Polymer contentrent binders were analyzed using an Attenuated Total Reection Fourierter while X-ray diffraction and X-ray uorescence spectrometers were

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  • of known crystalline materials, samples of unknown composition

    from unaged (virgin) materials using a low-shear hand mixer at 60 rpm for1.5 min each at 135 C. Fig. 1 presents an example owchart for one type of RAPsource (basalt-based RAP mix) and one type of virgin binder (PG 58-34).

    The PMBs used in this study were PG 70-28, PG 76-22, PG 58-34, PG 64-28 withunknown modication, and a PPA-modied PG 64-28. RAP binders were recoveredfrom the four different RAP sources using the Quantitative Extraction of Bitumen fromBituminous Paving Mixtures (American Society of Testing Materials (ASTM) D2172-05) [18] and the Abson recovery method (ASTM D1856-95a) [19]. This extractionmethod requires soaking an asphalt mixture in trichloroethylene solvent. The mix-ture is centrifuged to separate the aggregate particles from the solution of asphaltbinder and solvent, which is then distilled to evaporate the solvent out. RAP and vir-gin binders were short-term aged in the laboratory before mechanical and spectro-scopic testing using the Rolling Thin Film Oven Test (RTFOT) according to ASTMD2872-04 [20]. The RTFOT spins up to eight glass bottles on a cradle in an ovenat 163 C for 85 min. Each bottle contains 35 g of asphalt binders that passes overa stream of hot air to simulate a short-term oxidation of the asphalt binder.

    2.2.2. Asphalt mixesIn order to examine the inuence of the RAP binder, two groups of asphalt

    mixes were prepared. In the control mixes, the RAP was rst burned in the ignitionoven at 538 C to remove the RAP binder [21]. Then only the RAP aggregate wasadded to the base batch of virgin binder and aggregate at 10% of the total mixweight with compensatory virgin binder added for the burned RAP binder. In thesecond set of mixes, the complete RAP mix (without burning the binder) was addedat 10% of the total mix weight. This approach produced 40 different mixes, i.e. allcombinations of two mix groups, four RAP sources and ve PMBs. All mixes were

    Building Materials 31 (2012) 5866 59can be identied [16]. X-ray uorescence (XRF) measures the re-sponse when materials are exposed to short-wavelength energies.The resulting energy released from the materials are unique tospecic atoms. The intensity of each unique wave length is directlyrelated to the amount of each element in the material.

    2. Materials and methods

    2.1. Objectives

    The main objective of this laboratory study was to compare rutting resistance ofasphalt binders and asphalt mixes containing different RAP sources and differentpolymer modiers. Rutting resistance was determined by MSCR and APA testing,correspondingly. In this comparison, the following material-related factors wereconsidered:

    RAP aggregate mineral composition (granite, basalt, schist, and limestone), eval-uated by XRD and XRF.

    RAP binder oxidation level (oxidation of RAP binders was evaluated by the ATRFT-IR).

    Polymer modication (type and relative amount of modication were also eval-uated by the ATR FT-IR).

    The research methodology included rheological and spectroscopic testing ofbinder and mixes in laboratory conditions. Rutting resistance of the HMA materialswas determined with the APA. The results of mix rutting susceptibility were com-pared with binder performance in the MSCR and frequency sweeps, both conductedin the Dynamic Shear Rheometer (DSR).

    2.2. Experimental design

    Materials used in this study included four different RAP sources and ve differ-ent virgin binders that constituted 29 binder blends, and 40 different asphalt mixeswhich are presented in details in the following sections.

    2.2.1. Binders and binder blendsThis study contained four RAP binders extracted from the four RAP sources as

    well as ve different virgin asphalt binders. All nine binders were evaluated withthe FT-IR and the DSR to establish their type of modication, chemical aging levels,sulfoxides and free hydroxyl radicals. The latter may interact withketones and form carboxylic acids [7,8]. Glover and Davison [10]have conrmed that an increase in viscosity of aged binders is re-lated to an increase in their carbonyl content. FT-IR techniqueshave also been successfully used for identication and quantica-tion of polymer additives in asphalt binders. Numerous studiesinvestigated effect of styrenebutadienebased polymers (e.g.SBS and SBR) as well as polyphosphoric acid (PPA) on chemicaland physical properties of asphalt [1114]. Recently, a new re-search project in the US titled Evaluating Applications of FieldSpectroscopy Devices to Fingerprint Commonly Used ConstructionMaterials recognized ATR FT-IR as one of the most promisingmethods of spectroscopic analysis of asphaltic materials [15].

    X-ray diffraction (XRD) spectrometry is one of the most power-ful analytical tools available for identifying crystalline substancesin complex mixtures [16]. All crystals are composed of regular,repeating planes of atoms that form a lattice. When concurrentX-rays are directed at a crystal, the X-rays interact with each atomin the crystal, exciting their electrons and causing them to vibratewith the frequency of the incoming radiation. The electrons be-come secondary sources of X-rays, re-radiating this energy and cre-ating interference patterns that depend on the distance betweenatomic layers, chemical composition, and the angle between theX-ray beam and the atomic plane [16]. Traditionally XRD-traces,or diffractograms, are expressed in units of two theta degrees(2h). Since each crystalline structure is unique, the angles of con-structive interference form a unique pattern. By comparing thepositions and intensities of the diffraction peaks against a library

    A. Bernier et al. / Construction anddynamic modulus |G| master curve and MSCRT parameters [17]. Additionally, RAPand virgin binders were mixed in 1:9 proportions to produce 20 different binderblends that underwent MSCRT testing in the DSR. Binder blends were preparedcompacted in the gyratory compactor according to one mix design with 12.5 mmNominal Maximum Aggregate Size (NMAS). All mixes shared one, mainly basaltic,virgin aggregate source. Fig. 2 presents an example owchart for one RAP source(basalt-based) and one type of virgin binder (PG 58-34). One can notice two mixtypes prepared for the APA testing, and RAP aggregate (basalt in that case) preparedfor the XRD/XRF testing.

    A summary of the volumetric mix designs is presented in Table 1. Prior to test-ing, all mixtures were short-term aged in the forced-draft oven for 2 h at 150 C.While American Association of State and Highway Transportation Ofcials(AASHTO) standard call for 4-h aging for loose HMA mixtures it was decided to de-crease the short-term oven aging time. At 2 h in the oven, the loose HMA mix willexperience less oxidative aging and the test will maximize rutting potential of themixes. Upon cooling each specimen was checked for volumetric properties usingAASHTO T-166. In this method, weight of a dry specimen is compared to its weightin water and saturated, surface-dry states to calculate a bulk specic gravity whichis then combined with the maximum theoretical specic gravity (AASHTO T209) todetermine the air voids content. The target air void content was 7 0.5% for allspecimens. All HMA samples with volumetric properties within allowable rangewere tested in the APA under conditions presented in the later sections.

    2.2.3. Characterization of RAP mixes and RAP aggregateFour RAP sources used in this study originated from the pavements located in

    various parts of the northeastern US. All RAP samples were sent to the laboratorywithout any information except for most probable mineral composition of theirFig. 1. Example owchart of virgin binder, RAP binder and binder blend testing andmixing sequence.

  • 2.3.3. FT-IR and XRD/XRF testing

    BuiFig. 2. Example owchart of virgin binder, virgin aggregate and RAP mixes testingand mixing sequence.

    Table 1Summary of mix design.

    Percent (%) mix

    Basalt Granite Schist Limestone

    1/200 20 (21)a 19 (16) 22 (20) 18 (17)3/800 25 (25) 26 (22) 28 (27) 24 (23)Stone sand 35 (34) 35 (37) 35 (35) 38 (38)60 A. Bernier et al. / Construction andaggregates. Once dried in the ambient conditions, appropriate quantities of RAPmixes were designated for the RAP binder extraction/recovery, for the ignition ovenburn (to obtain RAP aggregate for control asphalt mixes) and for the preparation ofthe asphalt mix samples with 10% of RAP. The RAP mix burned in the ignition ovenwas also used to determine asphalt content in each source, as well as to test eachRAP aggregate to establish its Fine Aggregate Angularity (FAA), and Flat and Elongated(FE) parameters together with specic gravity and gradations. Fine Aggregate Angu-larity test (AASHTO T304) measures the uncompacted air voids of an aggregate sam-ple prepared from specic fractions of aggregate from the number 8 to number 50sieves. The sample is prepared by allowing ne aggregate particles to free fall into aknown volume from a particular height. Knowing the specic gravity, the percent ofair voids can then be calculated [22]. On the other hand, the Flat and Elongated test(ASTM D4791) quanties the percent of a coarse aggregate that is greater than a 5:1ratio for length to width [23]. As explained earlier, RAP aggregates from the ignitionoven were used in preparation of 20 control mixes whereas 20 other mixes wereprepared with unprocessed RAP mixes. RAP aggregates from the ignition oven werealso tested using X-ray diffraction (XRD) and X-ray uorescence (XRF) to verifytheir mineral content. The XRD and XRF analysis compared the four RAP aggregateswith the mineral database of similar minerals in the Northeast part of the US fromthe United States Geological Survey (USGS) [24]. The XRD/XRF verication of min-eral content is important because the RAP sources can vary, and do contain outliers.

    2.3. Testing procedures

    2.3.1. Dynamic Shear Rheometer testingAll 29 binders and binder blends were tested with a DSR using the MSCR pro-

    cedure. The MSCR test is conducted by repeatedly applying a load for duration of1 s followed by 9 s recovery period [25]. A 15-min temperature equilibrium periodwas used prior to 10 load cycles at 100 Pa which was followed by 10 cycles at3200 Pa. Data was sampled at 10 Hz and recorded by a data acquisition system con-nected to the DSR. All binders were tested at 64 C except for the PG 58-34 binderand its corresponding blends that were tested at 58 C. Each binder and binderblend was heated to 135 C until viscous and then poured into molds for testingin the DSR. For MSCR testing, the 25 mm plate was used with a 1 mm gap.

    In addition to MSCR testing, ve polymer-modied binders and the four recov-ered RAP binders were also tested in the DSR in the frequency sweep mode in orderto construct dynamic shear modulus |G| master curves. Before frequency sweeptesting, linear behavior ranges were established for all materials at test tempera-

    Natural sand 10 (10) 10 (15) 5 (8) 10 (12)RAP 10 (10) 10 (10) 10 (10) 10 (10)

    a Parentheses indicate control mix design.The ATR FT-IR testing was conducted to verify the presence and the type ofpolymer and to compare levels of oxidation between all RAP-recovered binders,respectively. The ve original PMBs and four RAP-recovered binders were examinedusing a compact FT-IR spectrometer with a single reection diamond ATR accessory.To perform an FT-IR test, approximately 0.1 g of RTFO aged binder was placed di-rectly on the ATR plate and a xed load was applied to the sample to ensure its fullcontact with the crystal. Twenty-four (24) scans were done for each sample withinthe wavenumber range from 4000 to 400 cm1 with resolution of 4 cm1, and theresultant averaged spectra was recorded. Three replicates were prepared and testedfor each binder type. A semi-quantitative analysis of the FT-IR spectra in this studywas performed using a normalized band area approach [26]. This procedure facili-tated identication and quantication of the absorbance peaks related to oxygen-containing functional group and polymer components [7,11,13].

    For the XRD analysis, each RAP aggregate sample was pulverized to a ne pow-der using a mortar and pestle, mounted on a plastic holder. The testing was con-ducted by X-ray diffraction with a Scintag diffractometer with Cu source(k = 1.5418 ). The X-ray tube was operated at 40 kV and 40 mA using a diffractedbeam graphite-monochromator. The data was collected between two-theta valuesof 5 to 75 with a step size of 0.02 and an average counting time of 0.6 s per step.Qualitative analysis of the XRD data was performed using Jade software, version 8.5,with reference to the patterns of the International Centre for Diffraction Data data-base [27].

    For RAP aggregate XRF analysis, 500 g samples were prepared for each of thefour burned RAP aggregates split on the No. 4 sieve. After split, particles were pul-verized to a homogeneous stage, and placed into the XRF device (Innov-X Alpha).The results of the XRF were then condensed to all elements that had detectable lev-els in all eight of the tests run.

    3. Test results and analysis

    3.1. RAP classication and analysis

    Fig. 3 shows the summary of XRD and Table 2 shows a reductionof the XRF results. The XRD data were analyzed using JADEsoftware which compares the measured crystal structure with aseveral national libraries of known crystal structures for matchingmaterial. Characteristic peaks were able to distinctly identifyBasalt and limestone using XRD. The XRF data were used to sup-port XRD data for schist and granite which have almost identicalbase minerals. Because of their formation methods, granite beingigneous and schist being metamorphic, the metamorphic natureof schist introduces various metals from the surrounding environ-ment. The extraneous metal content was noticeably higher in theXRF analysis of schist (Table 2), quantitatively distinguishing be-tween the two minerals.

    The asphalt content of all four RAP sources is shown in Table 3.The statistical analysis using Fishers Least Signicant Differencetures. For |G| master curves, binder specimens were tested on both 8 mm and25 mm plates with the gap of 2 mm and 1 mm, respectively. The 8 mm specimenwas tested from 22 C through 34 C followed by the 25 mm plate from 34 C to6 C above the high PG grade (RAPs were assumed to have a high performance gradeof 64 C). Frequency sweeps were run in the typical 6 increments, however, the lowtemperature of 22 C was due to the limitations of the cooling system attached tothe DSR.

    2.3.2. Asphalt Pavement Analyzer rutting testingThe HMA specimens were tested in the Asphalt Pavement Analyzer (APA) to

    establish rutting susceptibility of considered HMA mixes. The APA test was con-ducted according to AASHTO method TP 63-07 [5]. This method uses 75-mm highHMA specimens which are subjected to repeated loading conditions in the APA. Be-fore APA testing, the specimens were conditioned in the molds at the correspondingbinders high PG temperature for 6 h. During the test, a concave wheel runs overpressurized rubber hosing that is set on top of three gyratory specimens in the tem-perature-controlled chamber. The rubber air lines on the load rack were pressurizedto 0.69 0.03 MPa and the wheel load was set to 0.45 0.02 KN. A total of 8000 cy-cles of wheel loading were applied to the HMA specimens in the chamber. One cycleis equivalent to one forward pass and one backward pass over the specimens. Therut depth for each cycle was recorded in the raw data le by the acquisition systemattached to the APA.

    lding Materials 31 (2012) 5866(LSD) shows that there are two distinct groups at 95% condencelevel but considering the small range of asphalt content (0.5%)and typical RAP mix variability, asphalt content in all RAP sources

  • for schist. A Fishers LSD analysis indicates each sources averageuncompacted air voids is statistically different from the rest. Previ-ous studies have showed a relation between FAA uncompacted airvoids and rutting susceptibility [28]. The higher level of ruttingassociated with low FAA can be explained by the hypothesis thathigher air voids are linked with higher angularity, and aggregatewith high angularity resists rutting better. From the results ofthe FAA analysis, it can be hypothesized that the mixes with basaltRAP aggregate are prone to higher levels of rutting, whereas themixes with schist RAP aggregate are the most rutting resistant.

    The results in Fig. 5 on the FE parameter show that the Lime-stone RAP aggregate has the greatest percent of at and elongatedparticles for both the 9.5 mm sieve and the No. 4 sieve whereasschist and basalt had the overall lowest percentage of at and elon-gated particles for the 9.5 mm and No. 4 sieves respectively. This is

    A. Bernier et al. / Construction and Building Materials 31 (2012) 5866 61Fig. 3. XRD: comparison of XRD spectra results are offset vertically for visualdistinction.

    Table 2can be assumed practically identical. This observation supports theuse of the same asphalt binder compensation for all RAP sources inthe control mixes.

    The results from the FAA analysis are shown in Fig. 4. It can benoticed that RAP aggregates varied in terms of the uncompacted airvoids and FAA increases from 44.9% for basalt aggregate to 49.0%

    showed the lowest FAA value and ner gradation which normally

    Summary of X-ray uorescence results (content in parts per million, ppm). Elementsin bold indicate signicant difference between schist and granite.

    RAPaggregate

    Sievesplita

    K Ca Ti Mn Fe Zn

    Limestone +No. 4 15,742 191,134 2815 732 27,821 51Schist +No. 4 26,357 26,021 4790 595 38,022 50Granite +No. 4 31,928 39,380 1794 267 11,431 33Basalt +No. 4 6717 81,386 5316 1318 83,069 116

    a + On and above sieve No. 4 (4.75 mm).

    Table 3Asphalt content of RAP sources and Fishers LSD grouping.

    RAP Source Mean AC % Statistical group

    Basalt-based RAP mix 5.6256 AGranite-based RAP mix 5.3260 A BSchist-based RAP mix 5.2000 A BLimestone-based RAP mix 5.1167 B

    Fig. 4. Summary of RAP aggregate Fine Aggregate Angularity.suggests increased rutting susceptibility for the mixes with thisRAP source. However, these effects were offset by the low FE valueas well as the highest asphalt content in the basalt-based RAP(assuming RAP binder will have stiffening effect on the APA ruttingperformance). On the other hand, limestone-based mixes could beidentied as potentially prone to rutting due to high FE and low as-phalt content but it was also balanced with fairly high FAA value.The following asphalt mix evaluation in the APA supported withthe DSR and FT-IR asphalt binder testing should shed more lighton which (if any) of the aggregate parameters had deciding inu-ence on rutting susceptibility in this study.

    3.2. |G| frequency sweep results

    In order to construct the |G| master curves, frequency sweepresults were manipulated using the GordonShaw free-shiftingmethod [30] and tted with the sigmoidal approximation [31].Master curve procedures were automated using a computationalroutine created in a MATLAB environment and the results arepresented in Fig. 7. As could be expected, the four RAP recoveredbinders were stiffer than the ve polymer-modied binders.likely related to the weak structure of limestone which is the onlysedimentary aggregate used in this study. Previous studies haveshown at and elongated particles result in aggregate breakdownduring compaction [29]. The gradations of all four RAP aggregatesare displayed in Fig. 6. It can be seen that while granite-, lime-stone- and schist-based RAP aggregates are relatively similar, thebasalt RAP aggregate lie above them which implies ner gradation.

    In summary, the RAP aggregate testing conrmed their mineral-ogical origins but it did not reveal any rm argument that could af-fect the rutting susceptibility of the mixes. Basalt RAP aggregateFig. 5. Summary of RAP aggregate at and elongated content.

  • Fig. 7. Comparison of |G| mastercurves from both PMBs and RAP-recoveredbinders after RTFO aging.

    BuiFurther, all RAP binders produced very similar |G| master curvesexcept for the RAP binder coming from the basalt RAP source. Thisbinder showed signicantly higher |G| values than any other bin-der especially at lower frequencies (or higher temperatures). Onthe other hand, the results of the PMB master curves correlatedwith their corresponding PG grades, with the PG 58-34 binderproducing the lowest |G| values and PG 76-22 having highest|G| values among the PMBs.

    3.3. FT-IR analysis

    In the FT-IR analysis, characteristic peaks associated with oxi-dized functional groups and polymers were rst identied to quan-tify oxidation- and polymer-related changes in the IR absorbance,band areas (ARW) were normalized to the total sum of all bandareas (

    PARWi) and the indices for the oxygen containing and poly-

    mer-related absorbance bands were computed as follows [26]:

    Polymer indices

    PPA index IPPA = AR500/P

    ARWi.Poly-butadiene IPB = AR966-973/

    PARWi.

    Poly-styrene IPS = AR700/P

    ARWi.

    Oxidation indices

    Carbonyl ICO = AR1700/P

    ARWi.Sulfoxide ISO = AR1030/

    PARWi.

    Fig. 6. RAP aggregate gradations.

    62 A. Bernier et al. / Construction andFig. 8 shows the summary of polymer indices for the PMBs. Theresults conrmed that all binders were in fact modied. An exam-ple of this verication is the PG 64-28PPA, which has a unique anddistinct peak for polyphosphoric acid at 500 cm1 and lacks anysignicant amount of styrenebutadiene rubber. The four otherbinders exhibit distinct polystyrene (PS) and/or polybutadiene(PB) peaks at 700 and 966 cm1, correspondingly, which suggestssignicant presence of styrenebutadiene-based polymers. At var-iance with the SBS-modied PG 70-28 and PG 76-22, the PG 64-28shows only one PB peak at 973 cm1, while the expected PS peakexhibited only a shoulder, which suggests modication by SBRLatex.

    In the second part of the FT-IR analysis, oxidation levels werecompared in both the RAP binders and the PMBs. A semi-quantita-tive analysis revealed only short-term binder aging in the vePMBs which was expected as the virgin binders were only exposedto RTFO aging. A summary of the four RAP binders is shown inFig. 9. When comparing the sums of all aging indices for each bin-der it can be found that schist-RAP binder has the greatest amountof oxidative aging and the limestone-RAP binder has the leastlding Materials 31 (2012) 5866amount. However, oxidation results do not explicitly clarify theperformance of the basalt-RAP binder that produced the highest|G| modulus values in Fig. 7. It has to be noted that this RAP binderwas exceptionally difcult to handle and pour, and other analyticalmethods could shed more light on its chemistry, such as Gel Per-meation Chromatography (GPC).

    3.4. Multiple stress creep recovery results and analysis

    The raw MSCR data was processed to determine the averagepercent recovery (R100 and R3200 at creep stress levels of 100 and

    Fig. 8. Summary of polymer indices for PMBs.

  • 3200 Pa, respectively) and the non-recoverable creep complianceJnr [16]. Eqs. (1) and (2) express R and Jnr for each cycle,respectively.

    R100 or R3200 Xi

    n1

    100 e1 e10e1i 1

    where e1 = ec [Strain at the end of cycle loading] e0 [Initial cyclestrain], e10 = er [Strain at the end of cycle recovery] e0

    Jnr e10=rc 2where rc = creep stress

    Figs. 1013 show the average values and corresponding 95%condence intervals bars for all MSCR test parameters. One testper binder and binder blend was conducted with the exception

    due to the much higher stress level, however, the percent differ-ence between linear and non-linear Jnr values varied drastically.The highest increase in Jnr was observed for the PG 70-28 RAPblends and for PG 76-22/limestone RAP-binder blend. The otherbinders and their blends show the increase somewhere between20% and 210%. For comparison, the decrease in percent recovery

    Fig. 10. Summary of linear percent recovery from the MSCR test for PMBs and theirblends with different RAP binders.

    Fig. 11. Summary of non-linear percent recovery from the MSCR test for PMBs andtheir blends with different RAP binders.

    Fig. 12. Summary of linear Jnr (non-recoverable creep compliance) from the MSCRtest for PMBs and their blends with different RAP binders.

    A. Bernier et al. / Construction and Buiof three quality tests to check for test repeatability (not shown).The results in Figs. 1013 are grouped rst by the pure PMB results,and then by the corresponding four binder blends. Visual examina-tion identies several interesting trends. In Fig. 10, heavilySBS-modied binders, PG 70-28 and PG 76-22 show signicantlygreater percent recovery as compared to other PMBs. Furthermore,addition of any RAP binder to PG 64-28PPA and PG 70-28 consis-tently increased the linear percent recovery as compared to thecorresponding pure PMB results. The remaining PMBs and theircorresponding blends do not exhibit similar trends.

    Fig. 11 illustrates again the advantages of SBS modication: PG70-28 and PG 76-22 show signicantly greater non-linear percentrecoveries than the other three binders regardless the presence andtype of the RAP-binder in the blend. DAngelo (2009) reported asimilar sensitivity in the MSCR output values when comparingblending techniques of PMBs [25]. Another notable result inFig. 11 is the evident increase in non-linear percent recovery withthe addition of RAP binders to the PG 64-28PPA and PG 70-28which was also observed in Fig. 10.

    For all PMBs but PG 76-22, the addition of 10% RAP binder dem-onstrated a reduction in linear Jnr values (Fig. 12), which suggestsgreater resistance to rutting. This improvement in Jnr supportsthe results of |G| master curve analysis (Fig. 7) where RAP bindershad higher stiffness than all original PMBs. Fig. 12 also shows thatPG 70-28 and PG 76-22 binders and their blends show signicantlylower Jnr values relative to the PG 58-34, 64-28 and 64-28PPA andtheir blends. Considering that the FT-IR analysis indicated signi-cant SBS content in the PG 70-28 and 76-22 binders and knowingthat Jnr values have positive correlation with the asphalt pavementrut depths [4], this supports polymer modication as a means ofimproving rutting susceptibility.

    The results of non-linear Jnr at 3200 Pa (Fig. 13) show muchgreater inconsistency than any other MSCR gure. In general,non-linear Jnr values of all binders and binder blends increasedFig. 9. Summary of spectroscopic analysis of RAP binders.lding Materials 31 (2012) 5866 63from linear to non-linear was signicantly more consistent havingvalues around 1020% for PG 70-28 and PG 76-22 and approxi-mately 80% for all other binders and their blends.

  • two RAP binder sources relative to the other RAP-blended binders.

    BuiFurthermore, one can notice in Figs. 12 and 13 higher Jnr values forthe granite-RAP binder blends when compared to all other RAPblends for a particular PMB. Similar performance was also ob-served in the APA results in both the control and test mixes (dis-cussed subsequently). This inconsistency can be caused byseveral factors, such as relatively low RAP binder content in theblends (10%) or uniformity of the binder blend samples. It is alsopossible that two DSR binder tests |G| master curve and MSCRare sensitive to different phenomena especially in the case of heav-ily modied binders.

    3.5. Mix testing results

    The average APA results of rutting at 8000th cycles are pre-sented in Fig. 14. The control mixes containing 10% RAP aggregatewith no RAP binder are presented on the left while the results with10% RAP mix are shown on the right. The data show mixed effectsof RAP aggregate minerals on the APA rutting. An overall visualAs shown earlier, the FT-IR results indicated that schist-RAPbinder had the highest relative levels of oxidation among all RAPbinders. The |G| master curve results, however, showed that ba-salt-RAP binder had the highest stiffness. In any case it could be ex-pected that these two RAP-binders would show the most stiffeningeffect when blended with the original PMBs. Conversely, none ofthe MSCR-based gures indicates outstanding stiffness for these

    Fig. 13. Summary of non-linear Jnr (non-recoverable creep compliance) from theMSCR test for PMBs and their blends with different RAP binders.

    64 A. Bernier et al. / Construction andanalysis indicates that the control mixes had higher rutting depthsthan those containing RAP binder which support stiffening theorycaused by addition of RAP binders. However, this improvement inrutting resistance is not uniform across all PMB/RAP combinations.Limestone RAP control mixes had the highest rutting values for allof the ve binders but when combined with RAP binder, had thehighest rutting only for 58-34 this is likely due to the higher FAAvalues in conjunction with the greatest percent FE measured fromthe limestone RAP aggregate. For granite RAPmixes, the addition ofRAP binder had little effect on its rutting performance which can beattributed to the better performing RAP aggregate as well as theleast stiff RAP binder. For the PG 64-28 and PG 64-22PPA bindersevery mix had improved rutting resistance, especially basalt andschist RAP mixes. Alternately, the highly modied PG 76-22 hadvery little performance change between the control mixes andspecimens containing RAP binder, though the variability betweenthe mixes decreased with the addition of RAP binder for this highlymodied binder.

    In order to quantitatively capture the RAP binder effect the RAPbinder effect parameter was determined using APA results asfollows:RAP binder effecti 100 d8000control d800010% RAPi

    d8000controli3

    In the rst step to calculate the RAP binder effect parameter,APA results coming from each mix were assumed as normallydistributed, and mean and standard deviation values were calcu-lated for each mix. Then Monte Carlo simulation was used to ran-domly sample rut depth values from calculated means andstandard deviation to determine the RAP binder effect parameteraccording to Eq. (3). The calculation was repeated ten thousandtimes (i = 10,000) which produced the mean and standard devia-tion of the RAP binder effect for each binder/RAP aggregate com-bination. If the RAP binder effect parameter is positive it suggestsstiffening effect of the RAP binder and less APA rutting, and con-sequently if the RAP binder effect is negative it suggests softeningand more rutting in the total mix. These results were used to testthe hypothesis at a = 0.05 that the RAP binder effect is statisti-cally different than zero, i.e. if no signicant effect was observed.The results of testing such hypotheses for all mixes are shown inFig. 15. The bars represent the mean RAP binder effect and thebolded bars highlight the mixes for which the RAP binder effectis statistically different than zero.

    In Fig. 15, the 64-28PPA binder shows statistically signicantpositive improvement to rutting susceptibility with the additionof RAP binders for all mixes. The same performance improve-ments hold true for the 64-28 binder, excluding the graniteRAP. The PG 58-34, PG 70-28 and PG 76-22 mixes do not supportthis trend. These binders showed positive rutting improvement

    Fig. 14. Average APA rut depth at 8000 cycles for all 40 HMA mixes.

    lding Materials 31 (2012) 5866for some RAP sources. In general, it can be seen that the hea-vier-modied PMB mixes had minimal rutting improvementsfor a majority of the RAP sources. This can be linked to the en-hanced performance of polymer modied mixes in rutting resis-tance that cannot be affected (positively or negatively) by theaddition of 10% RAP.

    3.6. Comparison of MSCR and APA

    In DAngelo et al. (2007) a comparison between rutting perfor-mance evaluated with an accelerated loading facility (ALF) andthe Jnr had an R2 value of over 0.80 a strong correlation betweenthe mix performance in the eld and the binder performance inlaboratory tests [4]. This relationship between ALF rutting andJnr results was clearly non-linear. In order to account for thenon-linear relationship between APA rutting and different MSCRparameters, a Spearmans rank correlation coefcient was used.Table 4 shows the results of this analysis including Spearmansand Pearson (linear) coefcients, and their corresponding p-val-ues. None of the MSCR parameters seem to have a statistically

  • Fig. 15. RAP binder effect (bolded bars imply that effect is statistically differentthan zero).

    Table 4Spearman and Pearson correlation coefcients between APA rutting depth at 8000cycles and different MSCR parameters.

    Spearman Pearson

    Coeff. value p-value Coeff. value p-value

    Linear % Rec 0.045 0.829 0.122 0.560Non-linear % Rec 0.110 0.601 0.146 0.485Linear Jnr (Pa1) 0.164 0.434 0.007 0.972Non-linear Jnr (Pa1) 0.143 0.495 0.279 0.177Rec % diff. 0.074 0.726 0.092 0.663Jnr % diff. 0.026 0.901 0.197 0.344

    Fig. 16. Linear Jnr vs. APA rutting results.

    Fig. 17. Non-linear Jnr vs. APA rutting results.

    A. Bernier et al. / Construction and Buisignicant correlation with the APA rutting depths. As the exam-ples, linear Jnr and non-linear Jnr were plotted against APA resultsin Figs. 16 and 17. Fig. 16 presents the relationship between lin-ear Jnr and APA rutting. A similar relationship was previouslyidentied by DAngelo et al. (2007) who noted that in the caseof the PMB, stress dependency is due at least in part to thenon-linear response of polymers at high strain. Although thereis no apparent trend in the RAP mineral origin, the trend seemsto be more distinct for less modied mixes (open marks in Figs. 16and 17). As observed earlier in the MSCR results, the PG 70-28and 76-22 mixes had very uniform Jnr values which translatedin Fig. 16 to a at horizontal relationship with the APA rutting.In Fig. 17, the correlation between non-linear Jnr and APA resultsis less distinct for all the mixes conrming insignicant statisticalcorrelation coefcients values from Table 4.

    4. Conclusions

    This paper investigated the rutting susceptibility for the HMAmixes and corresponding binder blends containing ve differentpolymer-modied binders and 10 wt.% of RAP from four differentsources. All PMB/RAP binder blends were RTFO-aged and thenevaluated by DSR testing. The presence of polymers and level ofoxidation were examined by FT-IR spectroscopy. HMA mixes con-taining combinations of one PMB and one RAP source were testedfor rutting resistance using the APA procedure. Based on the exper-imental results for the binders and the mixes, the following obser-vations can be made:

    1. XRD and XRF can be used to differentiate between mineralsources and identify the predominant constituent mineral ofan unknown aggregate blend.

    2. At 10% RAP in HMA mixes, the RAP aggregate properties (FAAand FE) affected APA performance for the control samples, beingthe most noticeable in limestone. With the addition of RAP bin-der, consensus aggregate properties were much less apparentdifferentiating the rutting performance.

    3. Sigmoid approximation and GordonShaw free shifting methodwere effective to visually differentiate the binders tested in fre-quency sweeps. For the RTFO-aged PMBs, master curves werealso useful for ordering the binders by their relative stiffness.

    4. FT-IR analysis of the PMBs was helpful in identifying the pres-ence of modiers and estimating relative levels of oxidationamong the RAP binders.

    5. PG 64-28 PPA and PG 70-28 binders were very sensitive to addi-tion of 10% RAP binders in the MSCR testing. For both binders,the results signicantly changed with addition of RAP binders.

    6. PG 70-28 and PG 76-22 had the lowest linear Jnr parameter inthe MSCR which could be explained by their high modicationlevel conrmed in the FT-IR analysis.

    7. The addition of RAP binder to less modied mixes signicantlyreduced the rutting susceptibility measured in the APA. Poly-mer-modied mixes were much less sensitive to additions ofthe low level of RAP.

    8. No statistically signicant correlation was observed betweenthe APA results and any of the MSCR parameters.

    In order to determine the best indicator of the eld rutting sus-ceptibility, more research is needed that will compare MSCR and/or APA results with the rutting measured in the eld. Field studiesreported thus far in the literature [25,32] provide often inconclu-sive outcomes based on limited eld data. Although the resultsof this study were able to highlight differences between mixes

    lding Materials 31 (2012) 5866 65with different RAP sources, it is believed that higher RAP contentwould have provided larger effects which would make the differ-ent blends more distinguishable.

  • Acknowledgments

    The work in this paper was partially sponsored by the NewEngland Transportation Consortium (NETC), this support is grate-fully acknowledged. The results and opinions presented are thoseof the authors and do not necessarily reect those of thesponsoring agencies. The authors would like to thank Dr. MariaChrysochoou and Chad Johnston for their assistance with theXRD/XRF testing. Additionally the authors also acknowledge JamesMahoney and John Dadalt from the Connecticut AdvancedPavement Laboratory (CAP Lab) for their substantial role in thetesting effort.

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    Laboratory evaluation of rutting susceptibility of polymer-modified asphalt mixtures containing recycled pavements1 Introduction2 Materials and methods2.1 Objectives2.2 Experimental design2.2.1 Binders and binder blends2.2.2 Asphalt mixes2.2.3 Characterization of RAP mixes and RAP aggregate

    2.3 Testing procedures2.3.1 Dynamic Shear Rheometer testing2.3.2 Asphalt Pavement Analyzer rutting testing2.3.3 FT-IR and XRD/XRF testing

    3 Test results and analysis3.1 RAP classification and analysis3.2 |G*| frequency sweep results3.3 FT-IR analysis3.4 Multiple stress creep recovery results and analysis3.5 Mix testing results3.6 Comparison of MSCR and APA

    4 ConclusionsAcknowledgmentsReferences

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