Investigation of rheological and fatigue properties of asphalt mixtures containing polyester fibers

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<ul><li><p>dng</p><p>ns</p><p>try</p><p>d fo4 S</p><p>The eects of polyester ber on the rheological characteristics and fatigue properties of asphalt and its mixture are investigated in this</p><p>Bituminous binders have been widely used in exible</p><p>should have a viscosity which permits its use in standardmaterial manufacturing and paving equipments. Moreover,</p><p>available [47].</p><p>erties of asphalt, and the test results indicated that goodadhesion between bers and bitumen enhances the load-carrying ability of asphalt-ber mastics. Wu et al. [13] con-ducted dynamic shear rheometer (DSR) test to study therheological properties of asphalt with various bers. Theirresults indicated that the rutting-resistance property of</p><p>* Corresponding author. Tel./fax: +86 27 8716 2595.E-mail address: yeqs@whut.edu.cn (Q. Ye).</p><p>Available online at www.sciencedirect.com</p><p>Construction and Building Materia</p><p>Constructionpavements because of their good adhesion to mineralaggregates and viscoelastic properties [13]. Unfortunately,asphalt mixture or coating layer shows severe temperaturesusceptibility such as high-temperature rutting, mediumtemperature fatigue and low temperature cracking damage.Therefore, asphalt mixture should be modied in some wayto promote their further application.</p><p>Ideally, a modifying agent of bitumen should be easilyincorporated to yield a highly viscous mixture at in-servicetemperatures which remains homogenous on storage, and</p><p>Among various modiers for asphalt, bers have gottenmuch attention for their excellent improvement eects.Various ber modiers, such as cellulous ber, polyesterber and mineral ber, have been widely used in dierentasphalt mixtures. These include Stone Mastic Asphalt(SMA), Open Grade Friction Concrete (OGFC), etc. [811]. Many earlier research projects focus on the inuenceof ber additives on the engineering properties of asphaltor asphalt mixture. Chen and Lin [12] investigated cellu-lose, rock wool and polyester ber on the engineering prop-paper. The viscosity, rheological and fatigue tests are conducted to characterize such related properties of asphalt binder and mixturewith dierent ber contents. Test results indicate that the viscosity of asphalt binder is increased with increasing polyester ber contents,especially at lower temperature. With dierent polyester ber contents, the complex modulus and loss modulus of asphalt binders aredecreased at 15 C and 0.1100 rad/s frequency range. The dynamic modulus test results for asphalt mixture with 0.3% polyester bercontent also reveal that the dynamic modulus and phase angle are decreased at the same temperature, which leads to a decrease of fatigueparameter for asphalt mixture. When compared with the control asphalt mixture, the cycle numbers to fatigue failure of ber modiedasphalt mixture are increased with 1.9, 2.9 and 3.6 times at 0.5, 0.4 and 0.3 stress ratios, respectively. The parameters of fatigue functionsfor asphalt mixture with or without polyester ber are obtained and compared, and it conrms that the fatigue property of asphalt mix-ture can be improved by ber addition, especially at lower stress levels. 2007 Elsevier Ltd. All rights reserved.</p><p>Keywords: Asphalt mixture; Binder; Rheological characteristics; Fatigue property; Stress level</p><p>1. Introduction it should be highly resistant to ultraviolet light, thermalactions, water damage, environmental friends, and beInvestigation of rheological anmixtures containi</p><p>Shaopeng Wu, Qu</p><p>Key Laboratory of Silicate Materials Science and Engineering of Minis</p><p>Received 1 June 2007; received in reviseAvailable online</p><p>Abstract0950-0618/$ - see front matter 2007 Elsevier Ltd. All rights reserved.doi:10.1016/j.conbuildmat.2007.07.018fatigue properties of asphaltpolyester bers</p><p>han Ye *, Ning Li</p><p>of Education, Wuhan University of Technology, Wuhan 430070, China</p><p>rm 18 July 2007; accepted 21 July 2007eptember 2007</p><p>www.elsevier.com/locate/conbuildmat</p><p>ls 22 (2008) 21112115</p><p>and Building</p><p>MATERIALS</p></li><li><p>asphalt with bers could be improved to a large extent.Putman and Amirkhanian [14] compared the performanceof SMA mixtures containing waste tire and carpet berswith mixes made with commonly used cellulose and polyes-ter bers. The results revealed that the tire, carpet andpolyester bers signicantly improved the toughness ofthe mixtures, but no signicant dierence in permanentdeformation or moisture susceptibility was found.</p><p>Polyester ber modied asphalt binder and mixture havebeen successfully applied in construction practice. How-ever, the eect of polyester ber on the pavement engineer-ing performances is profound, and the mechanism of theber eect on the bitumen is complex. The main objectiveof this research is to investigate the related properties ofpolyester ber modied asphalt binder and mixture; suchas viscosity, rheological characteristics, dynamic property,and fatigue performance.</p><p>2. Materials and experimental designs</p><p>binder or mixes. The microscopic morphology of polyesterber is shown in Fig. 1. It can be seen that the cross-sectionof these bers is quite round and their surface is smooth.</p><p>Asphalt mixtures were obtained with a 12.5 mm Super-Pave gradation. Basalt coarse aggregate and ne aggregatewere used in the specimens preparation, properties ofbasalt aggregate are shown in Table 1. Limestone was usedas mineral ller. Table 2 presents the selected mixgradation.</p><p>2112 S. Wu et al. / Construction and Building Materials 22 (2008) 211121152.1. Raw materials and mix gradation</p><p>A base asphalt (AH-70), provided by KOCH AsphaltCo. Ltd. (Hubei Province, PR China) was used for polyes-ter ber modication, with a penetration of 69 (0.1 mm at25 C, 100 g and 5 s), ductility of more than 100 cm (at15 C) and softening point of 48 C according to ASTMD 3381.</p><p>The polyester ber adopted in this research is a commer-cial product (Tianhui Fiber Materials Co., Ltd., Wuhan,PR China), which is made of polypropylene and with anaverage length and diameter of 6 mm and 20 lm, respec-tively. The specic gravity of polyester bers is 1.35 g/cm3, and the tension strength is 520 MPa. The meltingpoint of polyester ber is 248 C, thus remaining intactduring high mixing temperatures for preparation of asphaltFig. 1. SEM morphological image of polyester ber.2.2. Specimens preparation and test procedure</p><p>The polyester ber modied asphalt binder wasobtained by a constant mixer at 165 C. Fiber contents of0.1, 0.3 and 0.5 percent by weight of the asphalt. To obtainhomogenous bitumen-ber mastics, the polyester berswere added slowly into the preheated pure asphalt andmixed for 2 h. Next, the viscosity test and dynamic sheartest were carried out to investigate the viscosity and rheo-logical properties of the ber modied asphalt binder andthe control sample. The binders were aged in the RTFOand frequency sweep dynamic shear tests were conductedat 15 C.</p><p>Standard SuperPave mix procedures were employed toprepare the dynamic modulus test specimen with 170 mmheight and 150 mm diameter after the mixtures have beenshort-term oven aged for 4 h at 135 C, Then such speci-mens were sawed and polished to the required specimengauge for dynamic modulus test and fatigue test. The diam-eter and height of specimens for dynamic modulus testwere 100 mm and 150 mm, and for indirect tension fatiguetest were 150 mm and 38 mm. The optimum binder contentfor mixtures without ber was found to be 4.8%, while formixtures with 0.3 percent polyester ber (by weight of theasphalt mixture) the optimum binder content was 5.0%.The desired air voids for all specimens was approximately3.0%. When compared with conventional asphalt mixes,the dierences for preparation of polyester ber asphaltmixes are the mixing procedure and the mixing time. Inlaboratory study, the polyester bers must be mixed withdry aggregates for about 30 s prior to the mixing withasphalt and mineral ller. In eld application, the polyesterber can be blasted into the mixer plant, and the dry mix-ing time for bers and aggregates is about 8 s. The layingand compaction for polyester ber asphalt mixes are thesame with the conventional asphalt mixes.</p><p>Table 1Properties of basalt aggregate</p><p>Test items Measured values Standard</p><p>Specic gravity (g/cm3) 2.96 ASTM C-127Water absorption (%) 0.65 ASTM C-127Frost action (%) (with Na2SO4) 7.05 ASTM C-88</p><p>Abrasion loss (%) (Los Angles) 15.6 ASTM DC-131Polishing value 0.62 BS-813</p></li><li><p>mixed with asphalt are shown in Fig. 3 For clarity, curvesof complex modulus are plotted as solid line. It can be seenthat the values of complex modulus of asphalt mastic aredecreased with the increase of ber contents and frequen-cies, but the change of phase angles with or without bersare limited, which indicates that the addition of polyesterber increases the exibility of asphalt mastic, results in</p><p>2.36 1.18 0.6 0.3 0.15 0.075</p><p>3.2 23.1 16.8 12.0 8.7 5.3</p><p>1.E+01</p><p>1.E+02</p><p>1.E+03</p><p>1.E+04</p><p>1.E+05</p><p>1.E+06</p><p>1.E+07</p><p>Visc</p><p>osity</p><p> / Pa</p><p>s</p><p>0.10%0.30%0.50%Origin</p><p>2.E+07</p><p>2.E+07</p><p>3.E+07</p><p>3.E+07</p><p>4.E+07</p><p>G*/</p><p>Pa</p><p>45</p><p>50</p><p>55</p><p>60 /</p><p> Deg</p><p>ree</p><p>Origin PF-0.1%PF-0.3% PF-0.5%Origin PF-0.1%PF-0.3% PF-0.5%</p><p>ilding Materials 22 (2008) 21112115 2113The viscosity tests of asphalt mastic with and withoutpolyester ber were conducted by a Brookeld viscometer(model DV-II+Pro) according to ASTM D 2170. The vis-cosity test temperatures covered a range of 60180 C.</p><p>A strain-controlled rheometer (Anton Paar, Austrilia)with parallel plate geometry (8 mm in diameter) was usedto determine the rheological characteristics of asphalt mas-tics. A frequency sweep was applied over the range 0.1100 rad/s at a xed temperature of 15 C. An approximately1.0 g sample was put onto the lower plate. After the samplewas heated to ow, the upper parallel plate was lowered tocontact tightly with the sample and the sample trimmed.The nal gap was adjusted to 1.0 mm. All the samples wereheld at the dened temperature for 10 min and then con-ducted the frequency sweep from higher levels to the lowerones. Various viscoelastic parameters, such as, G 0, G00, and dwere collected automatically by the software.</p><p>Dynamic modulus test and indirect tension fatigue testin the simple performance test (SPT) of SuperPave wereperformed using the Universal Testing Machine (UTM-25) with an environmental chamber [15]. The dynamicmodulus test was conducted at 15 C and nine frequencies(0.1 Hz, 0.2 Hz, 0.5 Hz, 1 Hz, 2 Hz, 5 Hz, 10 Hz, 20 Hz,25 Hz). The loading pattern used in the indirect tensile fati-gue test was a haversine load with a loading time of 0.1 sand rest period of 0.4 s. The fatigue test was also conductedat the same temperature at 0.3, 0.4, 0.5 stress levels accord-ing to the splitting strength of asphalt mixtures. All sam-ples were conditioned at the test temperature so that thetest temperature was uniform throughout the mass of thespecimen.</p><p>3. Results and discussion</p><p>3.1. Viscosity</p><p>As shown in Fig. 2, the viscosity of asphalt bindersincreases with increasing polyester ber contents. Therewas a limited increase in viscosity at a content of 0.1%because the polyester bers act only as a dispersing mate-rial. If the ber content was increased, the viscosityincreased by two to three times because the polyester bersbegan to form a localized network structure. When the</p><p>Table 2Selected mix gradation</p><p>Sieves [mm] 19 13.2 9.5 4.75</p><p>Passing [%] 100 93.0 79.6 50.6 3</p><p>S. Wu et al. / Construction and Buber content was up to 0.5%, the local networks graduallybegan to interact to initiate a continuous network through-out asphalt, this leads to a 10-fold increase or more in vis-cosity. The network acts as a support structure, reinforcingthe asphalt and resisting deformation. As seen in Fig. 2,these reinforcement eects are more signicant at lowertemperatures (60135 C) than at higher temperatures(135180 C).3.2. Rheological characteristics of asphalt binder</p><p>At any combination of time and temperature within thelinear range, the visco-elastic behavior is usually character-ized by the shear modulus, G*, which is calculated as theratio of the maximum shear stress to the maximum shearstrain. The complex shear modulus (jG*j) and phase angle(d) at 15C for dierent concentrations of polyester bers</p><p>1.E+0040 60 80 100 120 140 160 180 200</p><p>Temperature / C</p><p>Fig. 2. Viscosity of asphalt mixing with polyester bers versustemperatures.0.E+00</p><p>5.E+06</p><p>1.E+07</p><p>1.00E-01 1.00E+00 1.00E+01 1.00E+02Angular Frequency / rad/s</p><p>35</p><p>40</p><p>Fig. 3. Complex modulus and phase angle versus angular frequency fororiginal and polyester ber modied asphalt.</p></li><li><p>the improvement of cracking and fatigue resistance forasphalt mixtures.</p><p>Fatigue is one of the most severe damage for asphaltpavement. Typically, the initiation and propagation ofcracks are always related to the magnitude of lost energyproduced by outer loading [16]. The loss modulus(jG*jsind) mentioned by the Strategic Highway ResearchProgram (SHRP) is an eective parameter to characterizethe resistance to fatigue cracking of asphalt mixtures.Fig. 4 depicts the loss modulus of various asphalt binders.It also can be found that the loss modulus decreases withthe increase of polyester ber contents, especially at higherfrequency range (1100 rad/s). Such results indicate thatthe resistance to fatigue damage of asphalt mixtures is</p><p>tion of fatigue parameter implies an improvement of resis-tance to fatigue damage for asphalt mixtures.</p><p>3.4. Fatigue properties</p><p>Fatigue test results of asphalt mixtures at dierent stresslevels are shown in Fig. 7 and Table 3. Compared with the</p><p>5000</p><p>7000</p><p>9000</p><p>11000</p><p>13000</p><p>15000</p><p>17000</p><p>19000</p><p>21000</p><p>0.1 0.2 0.5 2 10 20 25Frequency / Hz</p><p>Dyn</p><p>amic</p><p> Mod</p><p>ulus</p><p> / M</p><p>Pa0</p><p>5</p><p>10</p><p>15</p><p>20</p><p>25</p><p>Phas</p><p>e an</p><p>gle </p><p>/ Deg</p><p>ree</p><p>E*-Control E*-PF0.3%-Control -PF0.3%</p><p>51</p><p>Fig. 5. Dynamic modulus and phase angles of asphalt mixtures with andwithout polyester ber.</p><p>1000.0</p><p>1500.0</p><p>2000.0</p><p>2500.0</p><p>3000.0</p><p>3500.0</p><p>4000.0</p><p>4500.0</p><p>0.1 10 100Reduced Frequncy / Hz</p><p>Fatig</p><p>ue p</p><p>aram</p><p>eter</p><p> / M</p><p>Pa</p><p>ControlPF0.3%</p><p>3000.0</p><p>3500.0</p><p>4000.0</p><p>Fatig</p><p>ue P</p><p>aram</p><p>eter</p><p> / M</p><p>Pa</p><p>Control PF-0.3%</p><p>1</p><p>Fig. 6. Fatigue parameters of asphalt mixtures.</p><p>1.E+04</p><p>1.E+05</p><p>failu</p><p>re / </p><p>Tim</p><p>es Control PF-0.3%</p><p>2114 S. Wu et al. / Construction and Building Materials 22 (2008) 21112115improved when the ber modiers are used. It may be thatthe polyester ber dispersing in the asphalt can transfer anddisperse the stress caused by loading, which can hold theinitiation of fatigue cracks and their propagations.</p><p>3.3. Dynamic properties of asphalt mixture</p><p>Fig. 5 shows the changes of dynamic modulus (jE*j) andphase angle (d) at 15 C for asphalt mixture with bers andthe control mixture, these cover the frequency range from0.1 Hz to 25 Hz. This illustrates that the dynamic modulusand phase angle decrease with the increase of frequency atthis temperature. The test results indicate that the visco-elastic properties of asphalt mixtures could be changedby the ber modiers. Such ber modiers can enhancethe viscous property of asphalt mixtures at medium tem-peratures, which result in the reduction of fatigue damagefor asphalt mixtures during their service life. Just like theloss modulus of asphalt mastic, we can dene the doubleof dynamic modulus and sine phase angle jE*jsind as thefatigue para...</p></li></ul>