The use of CRM-modified asphalt mixtures in Korea: Evaluation of high and ambient temperature performance

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  • es

    Kim

    pared bnicanas founctive in

    ter F/T treatment was found to be very poor. The poor performance of the

    [68,12,20]. However, because of poor adsorption of asphalt bind-ers to granite-base aggregates which are relatively abundant inKorea, a signicant portion of the CRM-modied asphalt mixtures(CRM mixtures) placed in pavements in Korea were disintegratedin earlier age after experiencing a freezing winter. In the followingspring season, signicant stripping in the mixture and raveling inthe surfacing layers were often noted. The reason was thought to

    e summer, manywere visible frome to the sttures [7,8

    It is interesting to note that those problematic CRM mwere typically found to be satisfactory when performancerutting at high service temperature was assessed. This suthat the uncertainty in cracking-related performances of CRMmix-ture at ambient/low temperatures would be the main risk of usingthe material. Therefore, ongoing efforts should be made to estab-lish mitigation/ prevention practices so that the risk can effectivelybe accounted for.

    This study supplements previous studies that investigatedcracking-related property at ambient-temperature and rut-related

    Corresponding author. Tel.: +82 33 250 6467; fax: +82 33 242 2095.E-mail address: asphaltech@hanmail.net (K.W. Kim).

    Construction and Building Materials xxx (2014) xxxxxx

    Contents lists availab

    B

    evThe ground waste tire rubber, or crumb rubber modier (CRM),is widely used as an asphalt modifying material in asphaltpavement in the world [15,11,24]. In Korea, CRMs have beenincreasingly used as an asphalt modier in paving industry

    thawing in spring time and rainy spells during thpotholes were observed at the sites where cracksthe surface. Those distresses are thought to be duof mixtures in ambient or relatively low temperahttp://dx.doi.org/10.1016/j.conbuildmat.2014.02.0740950-0618/ 2014 Elsevier Ltd. All rights reserved.

    Please cite this article in press as: Kim S et al. The use of CRM-modied asphalt mixtures in Korea: Evaluation of high and ambient temperaturemance. Constr Build Mater (2014), http://dx.doi.org/10.1016/j.conbuildmat.2014.02.074ripping].ixturesagainstggestsSDFatigueHydrated limeStrippingTensile strength ratioFreezing and thawing

    CRM mixtures in terms of moisture sensitivity appears to explain the early-life failures experienced inKorea. The study then examined the effectiveness of hydrated lime (HL) in improving the concerned per-formance since the HL is a well-known moisture resistance additive for conventional asphalt mixtures.The test results showed that CRM-mixtures containing the HL had marked improvement in moisturesensitivity.

    2014 Elsevier Ltd. All rights reserved.

    1. Introduction be due to the distress caused by freezing and thawing of waterinltrated through cracks on the pavement surface. FollowingCRMDeformation resistance the moisture resistance afh i g h l i g h t s

    CRM-modied asphalt mixes were pre The fatigue life was improved most sig The moisture resistance of CRM mix w The hydrated lime (HL) was highly effe

    a r t i c l e i n f o

    Article history:Received 16 September 2013Received in revised form 25 February 2014Accepted 26 February 2014Available online xxxx

    Keywords:Asphalt mixturey dry and wet process using CRM contents of 8%, 10% and 12%.tly by CRM modication, compared with SD and ITS.d to be very poor after freezing and thawing treatment.improving the concerned performance of CRM mixes.

    a b s t r a c t

    The asphalt mixtures modied with crumb rubber modier (CRM) were evaluated to estimate the defor-mation resistance at a high service temperature, fatigue resistance and tensile strength at ambient tem-peratures. As a mean to address the early-life failures of the mixtures observed from a number ofpavements in Korea, the study also investigated the moisture susceptibility after freezing-and-thawing(F/T) treatment by indirect tensile strength (ITS) test. A series of CRM-modied asphalt mixtures (CRMmixtures) were prepared by dry process as well as wet process using the CRM contents of 8%, 10% and12% by weight of total binder, respectively. The test results showed that fatigue resistances of CRMmixtures were signicantly improved, compared with the normal mixture (control) without CRM, butDepartment of Regional Infrastructures Engineering, Kangwon National University, Chuncheon 200-701, Republic of KoreaThe use of CRM-modied asphalt mixturand ambient temperature performance

    Sungun Kim, Sung-Jin Lee, Yeo-Bin Yun, Kwang W.

    Construction and

    journal homepage: www.elsin Korea: Evaluation of high

    le at ScienceDirect

    uilding Materials

    ier .com/locate /conbui ldmatperfor-

  • property at high-temperature [5,7,12,13]. Several treating agents

    2 S. Kim et al. / Construction and Buildinwere used for improving properties of the CRM mixtures [1,6].From those studies, it was observed that the hydrated lime (HL)would be the best choice as an anti-stripping additive for normalasphalt concrete. However, few studies dealing with CRMmixtureswere conducted in depth in Korea where humid-and-hot summerand freezing winter are expected. Therefore, the HL was used asan anti-stripping additive for CRMmixture in this study. The objec-tive of this study was to evaluate the fatigue resistance as a crack-ing-related property at ambient-temperature and the deformationstrength (SD) as a rut-related property at high-temperature[9,15,18] with particular emphasis given to moisture susceptibilityof CRM mixtures.Fig. 1. CRM powder passing #30 mesh.2. Materials and methods

    A source of a PG 64-22 asphalt binder (AP5), which is most widely used in SouthKorea was used as a base binder in this study. A size of minus 30 mesh of CRM,produced by the mechanical shredding in ambient temperature, was prepared forthis study as shown in Fig. 1. The CRM contents were 8%, 10% and 12% by weightof total binder. Granite coarse and ne aggregates were used for 13 mm dense-graded surface course, as shown in Fig. 2. Limestone powder was used as mineralller. As an anti-stripping additive, the hydrated lime (HL) was used. Table 1 showsphysical properties of aggregate and ller materials together with the specicationlimits given by the Ministry of Land, Infrastructure and Transport, South Korea.

    Fig. 2. Gradation of combined aggregates.

    Please cite this article in press as: Kim S et al. The use of CRM-modied asphamance. Constr Build Mater (2014), http://dx.doi.org/10.1016/j.conbuildmat.2012.1. Preparation of sample

    For wet process, the rubber-modied binder was prepared by slowly adding theCRM into the binder while mixing at 5000 rpm with a homogenizer at 180 C for30 min. The reaction time of 30 min were selected based on previous study results[3,5,13]. For dry process, the CRMwas directly added into asphalt mixture while theheated binder and aggregates were blended in the mixer.

    The optimum binder content (OBC) was determined based on 4% air void foreach CRM mixture by mix design using 100 mm diameter specimens compactedusing a Superpave gyratory compactor (SGC). The 75 and 100 gyrations were ap-plied for compaction of the normal mixtures and CRM modied mixtures, respec-tively. The specimens for moisture susceptibility test were compacted only up to20 gyrations so that a higher air voids of 7% could be achieved as required by thetest method. Since the HL is ne powder (more than 90% passing #200 sieve), the1/2 of mineral ller was replaced with HL. HL was only added to the specimens pre-pared for the moisture susceptibility testing.

    2.2. Tensile strength ratio

    The moisture susceptibility was evaluated by the indirect tensile strength (ITS)test before and after F/T treatment. The vacuum-saturated specimen to the degreeof 7080% was covered with a plastic lm and each wrapped specimen was sealedin a plastic bag containing 10 g of water. The plastic bag containing each specimenwas placed in a freezer at a temperature of18 C for 16 h. The frozen specimen bagwas submerged in a water container at 60 C, and the plastic bag and wrap were re-moved from the specimen as soon as it was submerged into the water. After 24 h inthe 60 C water bath, the specimen was removed and placed in a water bath at 25 Cfor 2 h according to the guideline of ASHTO T283-07 [27]. The specimen was re-moved from the water bath, and ITS was measured by applying 50 mm/min staticloading through the steel loading strips at 25 C.

    The retained tensile strength ratio (TSR) was calculated from the test results be-fore and after conditioning by the equation below.

    TSR % ITSwITSD

    100 1

    where ITSW is ITS after F/T treatment and ITSD is ITS without F/T treatment.

    2.3. Deformation strength

    The deformation strength (SD] is a measure of resistance against deformationinduced by a static-mode loading applied on top of a briquette specimen of asphaltmixture at a high temperature [15]. The test procedure, designated as Kim Test,uses the specimen (100 or 150 mm diameter) heated in 60 C water for 30 min be-fore placing in the specimen holder, as shown in Fig. 3(a). A static loading at thespeed of 30 mm/min is applied through the loading head, a steel rod, with a40 mm diameter and 10 mm radius of round cut at the bottom edge. Since the SDwas found to have a good correlation with rut characteristics of dense gradeHMA mixtures when correlate to the conventional wheel tracking test[9,15,17,18,22], it was adopted as a standard criterion in Korean mix-design guide[26]. The peak load, Pmax, and vertical deformation, v, at Pmax, were read from thecurve (Fig. 3(b)) and used for SD calculation using Eq. (2).

    SD 0:32Pmax10

    20v v2p

    22

    Table 1Physical properties of materials.

    Property Specication 13 mmagg.

    Fine agg.(screenings)

    Filler

    Apparent specic gravity >2.45 2.686 2.696 2.75Absorption (%)

  • ildinS. Kim et al. / Construction and Buof cycle to failure (Nf) was determined at the inection point at the end of the 2ndstage and beginning of the 3rd stage, as shown in Fig. 4.

    The briquette specimen (100 mm diameter) was used for ITS mode fatigue test.The specimen was conditioned at a 20 C chamber for 72 h before test. The 20%stress level of the static ITS was applied on each specimen for fatigue test. The peakof repeated load (force) was 2 kN, which induced 20% of stress level for the samediameter specimen of a relatively high quality asphalt concrete showing approxi-mately 1.0 MPa of static ITS. The 10% of the peak load was used for a minimum load.The speed of load cycle in a harversine wave form was 1 Hz (0.1 s loading and 0.9 srest period), making 1 cycle per second of dynamic loading, as shown in Fig. 5.

    The horizontal expansion and vertical deformation of a specimen were mea-sured by an extensometer and load cell position, respectively, as shown in Fig. 6.The max range of clip- on extensometer used in this study was 50 mm. The testwas conducted in an environmental chamber, as shown in Fig. 7. More detailedprocedures are given elsewhere [14,16,19,21]

    (a)Fig. 3. (a) Kim Test setting for SD and (b)

    Fig. 4. Schematics of a fatigue test curve.

    Fig. 5. Load-time pulse for fatigue test.

    Please cite this article in press as: Kim S et al. The use of CRM-modied asphamance. Constr Build Mater (2014), http://dx.doi.org/10.1016/j.conbuildmat.201g Materials xxx (2014) xxxxxx 33. Results and discussion

    The PG of the base binder (control) was 6422, and the wet-processed CRM-modied binder observed to be 7622 in all threeCRM contents as shown in Table 2. The 7622 performance gradewas achieved using CRM from the content of 8%, a little lower levelof CRM content used in previous studies [3,5,13]. The mix-designresults of 7 mixtures including control showed that the CRMmixture required higher optimum binder content (OBC) thancontrol mix. But there was not much difference in OBC between

    (b)P-v curve acquired from a Kim Test.

    Fig. 6. Schematics setup for fatigue test.

    Fig. 7. Environment chamber installed in an Instron loading frame.

    lt mixtures in Korea: Evaluation of high and ambient temperature perfor-4.02.074

  • Table 2PG and mix-design results.

    Property Spec. Control (AP5) CRM content (%)

    Dry process Wet process

    8 10 12 8 10 12

    PG (C) 6422 7622 7622 7622OBC (%) 4.9 5.3 5.4 5.6 5.3 5.5 5.7Air void (%) 35 4.1 4.3 3.9 4.7 3.8 3.9 4.3VFA (%) 6580 73.6 73.8 77.2 76.1 76.5 76.9 75.3Stability (kN) >7.5 12.4 15.1 16.9 18.0 17.1 17.6 18.1Flow (0.1 mm) 2040 28.0 32.0 38.0 39.0 34.0 36.0 35.0

    Table 3SD, ITS and fatigue (Nf) test results.

    Property Control (AP5) CRM content (%)

    Dry process Wet process

    4 S. Kim et al. / Construction and Building Materials xxx (2014) xxxxxx8

    SD Value (MPa) 3.51 3.91Ratioa 1.00 1.11

    ITS Value (MPa) 0.96 1.10Ratioa 1.00 1.15

    Nf Value (cycle) 2630 3965Ratioa 1.00 1.51dry and wet-processedmixtures. The CRMmixtures showed higherincrease in Marshall Stability and ow values than control mix.

    Table 3 shows the measured values of SD, ITS and fatigue life (Nf)of CRM mixtures in comparison with those of control. The CRMmixtures showed the most signicant increase in fatigue life andleast increase in indirect tensile strength (ITS). The high-temperature

    a Increasing ratio based on control value.

    Table 4Comparison of fatigue resistance (Nf) results.

    CRM content (%) Nf (cycle) Increase ratio Note

    Dry mix Wet mix Mean

    0 r 2630 1.00 control8 3965 4325 s 4145 s/r = 1.5810 5381 4522 t 4951 t/r = 1.8812 4610 5218 u 4914 u/r = 1.87Total 13,956 14,065

    Table 5Tensile strength ratio (TSR) of CRM mixtures with and without HL.

    Anti-stripping additive Method CRM content (%) Air void (%) ITS

    No additive 0 6.87 0.9Dry 8 7.27 1.1

    10 7.57 1.012 7.06 0.9

    Wet 8 6.96 1.110 7.40 1.112 6.93 1.1

    Mean 1.0

    Hydrated lime (HL) 0 6.77 0.9Dry 8 7.36 1.1

    10 7.39 1.112 7.54 1.0

    Wet 8 7.70 1.010 7.79 1.012 7.65 1.0

    Mean 1.0

    Please cite this article in press as: Kim S et al. The use of CRM-modied asphamance. Constr Build Mater (2014), http://dx.doi.org/10.1016/j.conbuildmat.201property (SD) showed relatively moderate increase among the threeproperties. The wet processed CRM mixtures were stronger thandry mixtures in SD and also in ITS, indicating that the wet processcould be a better manufacturing method of CRM mixtures. As forthe fatigue resistance of the two CRM mixture groups, not muchdifference was observed in Nf values.

    Since the fatigue test showed the most signicant improvementover the control mixture among the three properties due to CRM

    10 12 8 10 12

    4.21 4.43 4.48 4.62 4.71.20 1.26 1.28 1.32 1.341.06 0.97 1.17 1.13 1.131.10 1.01 1.22 1.18 1.185381 4610 4325 4522 52182.05 1.75 1.64 1.72 1.98modication, Nf data were further analyzed. As sown in Total inTable 4, almost no Nf difference was observed between dry andwet groups, as mentioned previously. The CRM contents of the10% and 12% showed almost no difference in fatigue life increaseratio, but the 8% showed somewhat lower ratio. In addition, thePG of CRM 10% was measured to be 7622, the SD and ITS ofCRM 10% were almost the same with 12% of CRM. Therefore, 10%of CRM appears to be an appropriate content in terms of fatigueresistance and ot...

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