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

  • Published on
    05-Sep-2016

  • View
    219

  • Download
    4

Embed Size (px)

Transcript

<ul><li><p>bi</p><p>bro</p><p>Creep compliance</p><p>sulg Rmerucropiffeome</p><p>binders were the least affected. Aggregate properties of RAP mix had a noticeable effect on rutting results</p><p>cationinder aeclaimes to cor polys of adce to p</p><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-</p><p>the HMA specimen is uneven over time and may cause local con-centrations of shear on the surface of the specimens [4,6].</p><p>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,</p><p> Corresponding author. Tel.: +1 860 486 2733.E-mail addresses: alex.bernier@engr.uconn.edu (A. Bernier), azofka@engr.uconn.</p><p>Construction and Building Materials 31 (2012) 5866</p><p>Contents lists available at</p><p>B</p><p>evedu (A. Zofka), ily08001@engr.uconn.edu (I. Yut).fatigue cracking, low-temperature cracking, moisture damageand oxidative aging [1].</p><p>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].</p><p>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</p><p>1. Introduction</p><p>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.</p><p>is to improve the dura-dditives range from theed Asphalt Pavementshemical additives suchphosphoric acid (PPA).ditives have been usedermanent deformation,</p><p>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.</p><p>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</p><p>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</p><p>Alexander Bernier, Adam Zofka , Iliya YutUniversity of Connecticut, Department of Civil and Environmental Engineering, 261 Glen</p><p>a r t i c l e i n f o</p><p>Article history:Received 21 October 2011Received in revised form 16 December 2011Accepted 23 December 2011Available online 21 January 2012</p><p>Keywords:Asphalt pavements</p><p>a b s t r a c t</p><p>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</p><p>Construction and</p><p>journal homepage: www.elsll rights reserved.lity of polymer-modied asphalt</p><p>ok Road, Unit 2037, Storrs, CT 06269-2037, United States</p><p>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</p><p>SciVerse ScienceDirect</p><p>uilding Materials</p><p>ier .com/locate /conbui ldmat</p></li><li><p>of known crystalline materials, samples of unknown composition</p><p>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).</p><p>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.</p><p>2.2.2. Asphalt mixesIn order to examine the inuence of the RAP binder, two groups of asphalt</p><p>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</p><p>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.</p><p>2. Materials and methods</p><p>2.1. Objectives</p><p>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:</p><p> RAP aggregate mineral composition (granite, basalt, schist, and limestone), eval-uated by XRD and XRF.</p><p> RAP binder oxidation level (oxidation of RAP binders was evaluated by the ATRFT-IR).</p><p> Polymer modication (type and relative amount of modication were also eval-uated by the ATR FT-IR).</p><p>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).</p><p>2.2. Experimental design</p><p>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.</p><p>2.2.1. Binders and binder blendsThis study contained four RAP binders extracted from the four RAP sources as</p><p>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].</p><p>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</p><p>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.</p><p>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.</p><p>2.2.3. Characterization of RAP mixes and RAP aggregateFour RAP sources used in this study originated from the pavements located in</p><p>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.</p></li><li><p>2.3.3. FT-IR and XRD/XRF testing</p><p>BuiFig. 2. Example owchart of virgin binder, virgin aggregate and RAP mixes testingand mixing sequence.</p><p>Table 1Summary of mix design.</p><p>Percent (%) mix</p><p>Basalt Granite Schist Limestone</p><p>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 mi...</p></li></ul>

Recommended

View more >