Relating Adhesion and Cohesion of Asphalts to the Effect of Moisture on Laboratory Performance of Asphalt Mixtures

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<ul><li><p>33</p><p>Transportation Research Record: Journal of the Transportation Research Board,No. 1901, Transportation Research Board of the National Academies, NationalResearch Council, Washington, D.C., 2005, pp. 3343.</p><p>Antistripping additives and polymer modifications are two common mod-ifiers used to improve the fundamental properties of asphalt binders asthose properties relate to the performance of asphalt mixtures. Adhesionand cohesion are two important related properties of asphalt binders thatcan affect asphalt mixture performance before and after water condi-tioning. The purpose of this study was to quantify the effects of antistrip-ping additives and polymers on the adhesion and cohesion of bindersand to relate these effects to the performance of mixtures as measuredin the laboratory before and after water conditioning. The performancetests of asphalt mixtures included indirect tensile strength, uniaxialcompression permanent deformation, and Hamburg wheel tracking.Asphalt mixtures were produced with different modified binders andwith two aggregate types. The binders were modified with antistrippingadditives and polymers and by chemical treatment and oxidizationmethods. Granite and limestone were selected as two types of aggregatesources. The results indicate that the performance of asphalt mixturesis highly dependent on modification techniques and water conditioning.The overall performance of polymer-modified mixtures is more desir-able than those of unmodified mixtures and of mixtures modified withantistripping additives. Polymers are found to improve rutting perfor-mance, adhesion, and cohesion of an asphalt binder. In contrast, theantistripping additive can improve only the adhesion without changingother properties. The results of this study also illustrate that the adhe-sion and cohesion of an asphalt binder are good indicators of the per-formance of asphalt mixtures in the laboratory when they are conditionedwith water.</p><p>It is well known that antistripping additives and polymers are widelyused modification techniques for improving the performance ofasphalt binders and mixtures. Antistripping additives improve theresistance of asphalt mixtures to moisture damage by reducing thesurface tension of asphalt binders, which increases the adhesion ofbinders to aggregate surfaces (1). The polymers are also success-fully used for modifying binder properties by changing their micro-structure and enhancing the rheological properties and the damageresistance characteristics of asphalt binders and mixtures (2). Most</p><p>research on modification of asphalts has concentrated on evaluatingthe role of polymer-modified asphalt in resisting fatigue cracking,thermal cracking, and permanent deformation; however, few studieshave been done to evaluate the effect of polymer-modified asphaltin reducing moisture susceptibility of asphalt mixtures.</p><p>An attempt was made in a recent study by the authors to predictthe resistance of asphalt mixtures to the moisture damage from theasphalt binder properties. These binder properties include cohe-sion and adhesion, which are directly related to bonding failure inasphaltaggregate systems (3). It was found that that these propertiesare closely related to the indirect tension strength of asphalt mixturesbefore and after water conditioning. This paper expands on the initialstudy by including more mixture testing results and several binderswith various modification techniques, antistripping additives, andtesting conditions. Mixture tests include the Hamburg wheel tracking(HWT) test and the newly developed simple performance test proce-dure. Test conditions include high and intermediate pavement designtemperatures.</p><p>The general objective here was to understand how antistrippingadditives and polymer modification differ in their effects on mixtureperformance before and after water conditioning and what causesthese differences.</p><p>OBJECTIVES</p><p>The specific objectives of this study were the following:</p><p>1. To evaluate and compare the effects of antistripping additiveand polymers on the fundamental properties of asphalt mixturesmeasured in the laboratory before and after water conditioning and</p><p>2. To correlate the adhesion and cohesion properties of as-phalt binders to the performance of asphalt mixtures after waterconditioning.</p><p>MATERIALS</p><p>Two main types of modification techniques were used on theasphalt binders for this study. The first type was the antistripping-additive modification. The original asphalt binder [performancegrade (PG) 5828] was selected as the base asphalt and was modi-fied with three of the most widely used antistripping additives in</p><p>Relating Adhesion and Cohesion of Asphalts to the Effect of Moisture on Laboratory Performance of Asphalt Mixtures</p><p>Kunnawee Kanitpong and Hussain Bahia</p><p>Asphalt Pavement Research Group, Department of Civil and Environmental Engi-neering, University of WisconsinMadison, 2210 Engineering Hall, 1415 Engineer-ing Drive, Madison, WI 53706.</p></li><li><p>34 Transportation Research Record 1901</p><p>TABLE 2 Effect of Antistripping Additives and Polymers on Rutting Resistance of Asphalt Binders</p><p>Testing GV at 1 sec. of Loading (Pa) Strain @ 50 Cycles (mm/mm)</p><p>Temperature COV COVBinder (C) No. 1 No. 2 Avg (%) No. 1 No. 2 Avg (%)</p><p>Antistripping additives</p><p>A 46 1020 1160 1090 9.08 4.93 4.30 4.62 9.65AS1 46 968 941 955 2.00 5.17 5.32 5.25 2.02AS2 46 797 823 810 2.27 6.28 6.08 6.18 2.29AS3 46 867 868 868 0.08 5.78 5.77 5.78 0.12</p><p>Polymers</p><p>A 58 169 164 167 2.12 29.63 30.44 30.04 1.91AP1 64 610 563 587 5.67 8.19 8.88 8.54 5.72AP2 64 3530 4060 3795 9.88 1.32 1.15 1.24 9.73AP3 64 842 849 846 0.59 5.93 5.88 5.91 0.60</p><p>All tests were performed at the stress level of 100 Pa.</p><p>Wisconsin. The second type was the polymer modification. Thesame binder (PG 58 28) was also used as the base asphalt andwas modified with different polymers, including styrenebutadiene(SB), styrenebutadienestyrene (SBS), and Elvaloy. Other modi-fication techniques, such as oxidization (air blown) and chemicaltreatment (acid), were also evaluated. Table 1 shows a list of asphaltbinders used in this study. To produce asphalt specimens for mix-ture testing, granite and limestone aggregates were selected asaggregate sources.</p><p>EXPERIMENTAL TESTING AND RESULTS ANALYSIS</p><p>In this study, the testing was separated into two main parts: asphaltbinder testing and asphalt mixture testing. The binder testing includedbinder creep and recovery testing to determine the rutting resistanceof asphalt binders, cohesion testing to evaluate the resistance of a</p><p>binder to separation within a thin film, and adhesion testing to evalu-ate the bonding strength of an asphalt binder to an aggregate surfacebefore and after water conditioning.</p><p>The mixture testing included the indirect tensile strength test(IDT) (AASHTO T283), the uniaxial compression permanent defor-mation test, and the HWT test. The following sections describe theexperiments conducted and the results collected.</p><p>Asphalt Binder Testing</p><p>Binder Creep and Recovery Test</p><p>The binder creep and recovery test was conducted to measure theresistance of asphalt binders to accumulation of permanent strainunder repeated application of loading. Through selection of theloading time, the stress applied, and the temperature, the trafficspeed and traffic loading conditions can be simulated. The accu-mulated permanent deformation (strain) during each cycle of load-ing, the rate of the accumulation as a function of cycles, and theviscous component (GV) of the creep stiffness can be used as indi-cators of the rutting resistance of asphalt binders. In this study,binders modified with selected antistripping additives and selectedmodifiers were tested. The top of Table 2 shows a comparison ofthe testing results of the original binder and the same binder mixedwith three antistripping additives commonly used in Wisconsin.The creep and recovery tests of these binders were conducted at46C. It was found that the original binder showed lower totalaccumulative strain at 50 cycles and higher GV at 1 s of loadingthan the antistrip-modified binder. It was thus indicated that someantistripping additives could reduce the resistance of binders torutting (higher accumulated strain and lower GV). The bottom ofTable 2 shows a comparison of testing results conducted at 58Cand 64C for the original binder and three polymer-modifiedbinders, respectively. The results show that all three polymer-modified binders perform better (lower accumulated strain andhigher GV) than the original binder, particularly for the SBS-modified binder.</p><p>The conclusions that can be derived from this testing are that theantistripping additives do not appear to have a large effect on the rut-ting resistance of the original binder and in some case can have neg-ative effects. The polymers, in contrast, can significantly improvethe rutting resistance of a binder.</p><p>TABLE 1 Asphalt Binders Used in This Study</p><p>Test Binder ID PG Modifier</p><p>Binder creep and A PG 5828 recovery AS1 PG 5828 Antistripping 1testing AS2 PG 5828 Antistripping 2</p><p>AS3 PG 5828 Antistripping 3AP1 PG 6428 SBAP2 PG 6428 SBSAP3 PG 6428 Elvaloy</p><p>Adhesion/cohesion Group Abinder testing A1 PG 5828 and mixture A2 PG 5828 Antistrippingtesting A3 PG 6428 SB</p><p>A4 PG 6428 SBSA5 PG 6428 ElvaloyA6 PG 7028 SBSA7 PG 7028 OxidizedA8 PG 7628 SBSGroup BB1 PG 5828 (RTFO) B2 PG 6428 (RTFO) AcidB3 PG 6428 (RTFO) ElvaloyB4 PG 6434 (RTFO) ElvaloyB5 PG 7028 (RTFO) Elvaloy</p></li><li><p>Kanitpong and Bahia 35</p><p>Adhesion Testing</p><p>Adhesion can be measured with the pull-off tensile strength test byusing the pneumatic adhesion tensile tester (PATTI). A schematicdiagram of this device is shown in Figure 1a. Details of adhesiontesting using the PATTI can be found in Youtcheff and Aurilio (4) andKanitpong and Bahia (3). The asphalt is applied to a pull stub, whichis then attached to the aggregate surface as shown in Figure 1b.The film thickness of asphalt is controlled by putting two pieces of14- 14- 212-in. metal blocks under the pull stub. The space underboth the pull stub and the aggregate surface is the film thickness ofthe asphalt specimen. PATTI transmits the air pressure to the piston,which is placed over the pull stub and screwed onto the reactionplate (Figure 1a). The air pressure induces formation of an airtightseal between the piston gasket and the aggregate surface. When thepull stub is debonded from the aggregate surface, the pressure atwhich the cohesive or the adhesive failure occurs is measured andconverted to the pull-off strength (kPa), which can be used as anindicator of the adhesive bond strength of the asphalt binder. Stud-ies by Youtcheff and Aurilio (4) and by Kanitpong and Bahia (3)indicated that this test is considered a rapid, low-cost, reproduciblemethod for measuring the adhesion characteristics of asphalt bindersto commonly used aggregate surfaces.</p><p>Two sets of asphalt binders, eight binders in Group A and fivebinders in Group B (including of the original binder), as listed inTable 1, were used in this study. For each binder, eight specimenswere prepared, four under dry conditions and four after water expo-</p><p>sure for 24 h at 25C. The adhesion test was conducted at the ambi-ent temperature (25C). Two sources of aggregate, limestone andgranite, were used. To provide comparable asphaltaggregate adhe-sion in this test to the adhesion characteristic of the asphalt mixtures,the aggregate surface was prepared from the slice of the asphalt mix-ture specimen produced from the same aggregate source. The pull-off strength was measured to represent the adhesion of the asphaltbinder in both dry and water-exposed conditions.</p><p>Figure 2 shows the results for average pull-off strength for allbinders. The numbers above the bar graph represent the ratio of wet-to-dry pull-off strength. Binders in Group A were analyzed sepa-rately from those in Group B because the binders in Group B wereaged to simulate conditions in the mixtures associated with thisgroup. The results in Figures 2a and 2b show that, before water con-ditioning (dry), all binders on the limestone surface had lower pull-off strength than on the granite surface. After water conditioningfor 24 h, all binders lost some pull-off strength, with the exceptionof Asphalts A2, A3, and B4, whose ratios of wet-to-dry pull-offstrength were close to 1. The reduction, however, was dependent onbinder composition and the type of aggregate surface. The decreasein values of pull-off strength after water exposure on the granite sur-face was larger than that on the limestone surface for most bindertypes. The failure modes changed during water exposure on bothlimestone and granite surfaces. When more than 50% of the aggre-gate surface was exposed, the failure was identified as adhesive fail-ure. When the aggregate surface exposed was less than 50%, thefailure was considered cohesive failure (failure within the asphalt</p><p>Metal </p><p>Asphalt Binder </p><p>Pull-Stub</p><p>AggregateSurface</p><p>(b)</p><p>TemperatureChamber</p><p>ProbeAdhesive</p><p>SolidSurface</p><p>0.01 mm/s</p><p>(c)</p><p>(a)</p><p>Pulling Force</p><p>Pull-Stub</p><p>PressureHose</p><p>Reaction Plate</p><p>Coating Substrate</p><p>GasketGasket</p><p>FIGURE 1 Schematic diagram of the devices for adhesion and cohesion testing of asphalt binders: (a) PATTI devicewith cross-section schematic of piston attached to pull stub, (b) specimen preparation for adhesion (pull-off tensilestrength) test, and (c) cohesion (tack) test.</p></li><li><p>36 Transportation Research Record 1901</p><p>(a)</p><p>(b)</p><p>Asphalt</p><p>1500</p><p>2000</p><p>2500</p><p>3000</p><p>3500</p><p>B1 B2 B3 B4 B5</p><p>Limestone-DryLimestone-WetGranite-DryGranite-Wet</p><p>Pu</p><p>ll-o</p><p>ff S</p><p>tren</p><p>gth</p><p> (kP</p><p>a)</p><p>0.81</p><p>0.680.83</p><p>0.96</p><p>0.85</p><p>0.92</p><p>0.91</p><p>1.04</p><p>0.82</p><p>0.86</p><p>0</p><p>1000</p><p>2000</p><p>3000</p><p>4000</p><p>5000</p><p>A1 A2 A3 A4 A5 A6 A7 A8</p><p>Limestone-DryLimestone-WetGranite-DryGranite-Wet</p><p>Pu</p><p>ll-o</p><p>ff S</p><p>tren</p><p>gth</p><p> (kP</p><p>a)</p><p>Asphalt</p><p>0.74</p><p>0.83</p><p>1.02</p><p>1.06 0.99</p><p>1.00 0.73</p><p>0.82</p><p>0.86</p><p>0.851.00</p><p>0.76</p><p>0.94</p><p>0.750.84</p><p>0.85</p><p>FIGURE 2 Pull-off strength of (a) eight asphalt binders in Group A and (b) five asphaltbinders in Group B.</p><p>film). In the unconditioned (dry) state, all failures were cohesive fail-ures; in contrast, in the conditioned (wet) state, the failures appearedto break at the asphaltaggregate interface, which is considered anadhesive failure.</p><p>The statistical analysis of the pull-off strength results for bindersin Group A, which was conducted to evaluate the variables that sig-nificantly affect the pull-off strength values, showed the following:</p><p>Effect P-Value for Pull-Off Strength</p><p>Replicate 0.6472Binder 0.0000Aggregate 0.0000Conditioning 0.2811Binder Aggregate 0.5622Binder Conditioning 0.0000Aggregate Conditioning 0.0308</p></li><li><p>Kanitpong and Bahia 37</p><p>A4, and A5) including SB, SBS, and Elvaloy showed a significantlyhigher tack factor than the original binder (A1) at a given |G*| value.Within the same PG grade and with three different polymer modi-fiers (A3, A4, and A5), Elvaloy resulted in the highest tack factor,while SB and SBS resulted in approximately the same tack factor.Within the same PG grade, the polymer-modified asphalt (A6) alsoshowed a higher tack factor than the oxidized asphalt (A7). Whenthe same modifier (SBS) was...</p></li></ul>

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