Laboratory fatigue evaluation of modified and unmodified asphalt binders in Stone Mastic Asphalt mixtures using a newly developed crack meander technique

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<ul><li><p>Accepted Manuscript</p><p>Laboratory Fatigue Evaluation of Modified and Unmodified Asphalt binders in</p><p>Stone Mastic Asphalt Mixtures using a newly Developed Crack Meander Tech</p><p>nique</p><p>Ratnasamy Muniandy, Nor Azurah Binti Che Md Akhir, Salihudin Hassim,</p><p>Danial Moazami</p><p>PII: S0142-1123(13)00236-3</p><p>DOI: http://dx.doi.org/10.1016/j.ijfatigue.2013.08.021</p><p>Reference: JIJF 3198</p><p>To appear in: International Journal of Fatigue</p><p>Received Date: 7 December 2012</p><p>Revised Date: 16 August 2013</p><p>Accepted Date: 20 August 2013</p><p>Please cite this article as: Muniandy, R., Akhir, N.A.B., Hassim, S., Moazami, D., Laboratory Fatigue Evaluation</p><p>of Modified and Unmodified Asphalt binders in Stone Mastic Asphalt Mixtures using a newly Developed Crack</p><p>Meander Technique, International Journal of Fatigue (2013), doi: http://dx.doi.org/10.1016/j.ijfatigue.2013.08.021</p><p>This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers</p><p>we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and</p><p>review of the resulting proof before it is published in its final form. Please note that during the production process</p><p>errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.</p></li><li><p>1</p><p>Laboratory Fatigue Evaluation of Modified and Unmodified Asphalt binders in Stone Mastic Asphalt Mixtures using a newly Developed Crack Meander Technique </p><p>Ratnasamy Muniandy , Nor Azurah Binti Che Md Akhir, Salihudin Hassim, Danial Moazami </p><p>Department of Civil Engineering, University Putra Malaysia, ratnas@eng.upm.edu.my Department of Civil Engineering, University Putra Malaysia, azurahcma@yahoo.com Department of Civil Engineering, University Putra Malaysia, hsalih@eng.upm.edu.my </p><p>Department of Civil Engineering, University Putra Malaysia, d_moazami@mshdiau.ac.ir </p><p> Corresponding Author E-mail: ratnas@eng.upm.edu.my +60-3-89466373/7847 (+60)123396917 </p></li><li><p>2</p><p>ABSTRACT </p><p>This paper looks into the fatigue evaluation of modified and unmodified asphalt binders in Stone </p><p>Mastic Asphalt (SMA) mixtures using a Crack Meander (CM) technique. Specimens images were </p><p>taken during the repeated load indirect tensile fatigue test (ITFT) and crack initiation, propagation and </p><p>failure were analyzed using a developed "Measurement and Mapping of Crack Meander" (MMCM) </p><p>Software. The results of crack analysis on every SMA specimens were compared with tensile strain </p><p>plots obtained from the ITFT test. It was concluded that, in addition to strain or dynamic modulus </p><p>plots, fatigue behavior can be determined using crack appearance as an alternative method. </p><p>Keywords: Stone Mastic Asphalt; Fatigue Strength; Crack Formation; Crack Meander; Repeated Load Indirect </p><p>Tensile Fatigue Test. </p></li><li><p>3</p><p>1 INTRODUCTION Fatigue cracks are one of the major distresses on the roads worldwide. In fatigue studies, there are </p><p>many approaches to define and evaluate the fatigue strength of asphalt mixtures such as the traditional </p><p>method, by using stress or strain against number of cycles (S-N plot), the dissipated energy approach, </p><p>and visco-elastic continuum damage method. However, there is not a clear or specific standard that </p><p>states which one is the best method to compare the performance between various bituminous mixtures. </p><p>The failure point in the traditional fatigue models considered at 50 percent reduction in the stiffness </p><p>modulus for controlled strain testing [1]. However, Lundstrom et al. [2] reported the traditional failure </p><p>criterion unsuitable, since at that point there is often no sign of real failure leading to inconsistent </p><p>fatigue results. Dissipated energy is another approach used instead of stress or strain while this method </p><p>does not consider progressive damage of material and crack development. Continuum mechanics also </p><p>does not accurately identify the fatigue crack development in the secondary and tertiary stages [3]. </p><p>Therefore, in order to portray the nature of cracks, studying the fatigue crack network and its pattern </p><p>seems necessary. Braz et al. [4] used computed tomography technique to detect crack evolution in </p><p>asphaltic mixtures submitted to fatigue test. Birgisson et al. [5] used a Digital Image Correlation (DIC) </p><p>system to obtain displacement/strain fields and to detect crack patterns. In this study a different </p><p>approach is presented to fully quantify the fatigue strength of asphalt mixtures until failure. Some </p><p>preliminary works were undertaken at Universiti Putra Malaysia (UPM) in 2004 and 2010 to establish </p><p>a protocol for Crack Meander technique (CM) to determine the fatigue strength. Some unique features </p><p>of this method include investigation of all aspects of fatigue distress (crack length, area and density), </p><p>simplicity of the test and the high precision of the image processing technique. In this study the fatigue </p><p>strength of modified and unmodified asphalt binders in Stone Mastic Asphalt mixtures (SMA) were </p><p>evaluated by using the developed crack meander method. The obtained crack data was validated as </p><p>compared to real strain data from the repeated load indirect tensile fatigue test (ITFT). </p><p>2 FATIGUE CRACK MECHANISM </p></li><li><p>4</p><p>In general, fatigue life is defined as the number of load cycles to failure for a bituminous mixture and </p><p>fatigue resistance indicates its ability to resist repeated cyclic loading that cause fracture although </p><p>other stress inducing factors are not mentioned here. Technically, because of continuous cyclic </p><p>loading, the bottom of the pavement layer experiences tensile strains thus forms cracks that continue </p><p>to propagate upward until failure [6, 7]. Fatigue behavior of asphalt mixtures is determined either by </p><p>controlled stress (load) or controlled strain (deflection) mode in the laboratory [8]. Because of the high </p><p>similarity with site conditions, controlled stress mode is widely used [7]. In controlled stress mode, a </p><p>constant amplitude of repeated stress or load causes the increasing strain while in controlled strain </p><p>mode, the amplitude of constant strain is applied in form of repeated deflection which results in stress </p><p>decrease [9]. </p><p>Dynamic reactions are responsible in evaluation of fatigue resistance in bituminous mixtures [10]. </p><p>Dynamic complex modulus is defined as the ratio of sinusoidal amplitude of stress to strain at angular </p><p>frequency for any given time. The dynamic complex modulus (E*) plot is normally used to represent </p><p>the relationship between stress and strain [11, 12]. During a fatigue test, modulus value decreases [13] </p><p>according to Figure 1 [14]. The first phase shows a fall in stiffness modulus due to repetitive load </p><p>excitation. Phase II, shows a quasi-linear decrease in stiffness, after which the sample starts to fracture </p><p>rapidly at the early of phase III due to non-uniformity in the strain field. </p><p> &lt; Insert Figure 1 about here &gt; </p><p>3 STONE MASTIC ASPHALT AND THE MODIFIERS </p><p>SMA is a dense and gap-graded bituminous mixture contains coarse and fine aggregates, filler, and </p><p>bitumen. The binder is typically modified with suitable binder carrier such as fiber or polymer [15, </p><p>16]. Earlier, SMA was known by its great potential to resist rutting and to decrease wear due to the </p><p>studded tires [15, 17]. Cubical, hard, crushed and durable aggregates are adhered with optimum </p><p>quantity of moisture-resistant mortar, and produce stone-on-stone contact. SMA contains about 93 to </p><p>94 percent of aggregates by weight of total mix, less than 1 percent fiber and about 6 percent binder </p><p>[16]. Although SMA is rut resistance, due to high proportions of coarse aggregates, it shows poor </p></li><li><p>5</p><p>performance in fatigue resistance due to the reduced amount of fine aggregates [16]. In total, because </p><p>of its good potential in pavement performance, detailed consideration should be taken in the selection </p><p>of materials to produce suitable mixtures. </p><p>In this study two different common modifiers were selected for use in the SMA mixture in order to </p><p>improve its performance in fatigue strength. Cellulose Oil Palm Fiber (COPF) is widely available in </p><p>Malaysia and therefore it was selected as one of the stabilizers. In addition to COPF, Ethylene Vinyl </p><p>Acetate (EVA) was selected as a traditional asphalt modifier. The cellulose fiber and EVA materials </p><p>are shown in Figures 2 and 3 below. </p><p>&lt; Insert Figures 2 and 3 about here (in one line) &gt; </p><p>COPF is a non-hazardous biodegradable material that is produced from the empty fruit bunch of oil </p><p>palm tree through various pulping methods. It was proven that COPF greatly minimizes drain down of </p><p>asphalt mixtures and tends to improve the fatigue resistance [16]. </p><p>EVA is a type of polymer in plastomer group. For over twenty years, it has been used in pavement </p><p>construction to improve the performance of asphalt mixtures since it has great potential to resist </p><p>permanent deformation [18, 19], thermal cracking [20] as well as fatigue of asphalt mixtures [21]. By </p><p>blending EVA with the original bitumen, the physical properties of binder such as penetration, </p><p>softening point, loss on aging and viscosity improve which indicates the stiffening effect of EVA </p><p>blended binders [22]. </p><p>4 CRACK MEANDER CONCEPT AND APPROACH </p><p>Indirect tensile fatigue test is widely carried out to estimate the resistance of a bituminous mixture </p><p>sample to fatigue failure in accordance with BS EN 12697-24 [23] by using the Universal Testing </p><p>Machine (UTM). Laboratory investigation of fatigue has shown that visual cracks that appear on the </p><p>trimmed test samples seem to have a unique relationship with fatigue resistance. This observation </p><p>leads to the idea of "crack meander" study to be developed. </p><p>The term meander is derived from the river meandering concept with a convoluted path which is </p><p>known as Maiandros or meander by ancient Greeks. According to Oxford dictionary, meander is </p></li><li><p>6</p><p>defined as "to curve a lot rather than being in a straight line" or "to walk slowly and change direction </p><p>often, especially without a particular aim". To summarize, meander in this context can be defined as </p><p>initiation and propagation of cracks, meandering due to crack pinning through the cross section of the </p><p>trimmed specimens. </p><p>The new approach is divided into a few stages. In the first stage, initiation and propagation of cracks </p><p>which appear on the sample surface during the diametral fatigue test is monitored and captured via a </p><p>SLR camera. For this purpose, instead of using the existing frame for indirect tensile fatigue test in </p><p>universal testing machine, the frame was specially fabricated; so that the surface image can be </p><p>captured directly without any barrier as shown in Figure 4. The images were recorded at a </p><p>predetermined interval of cycles depending on the speed of crack migration from start of the test until </p><p>failure. The SLR camera brand Nikon D300 was used to capture images which can capture up to six </p><p>frames per second with 12.3 megapixel resolution. This criterion is important to capture few images in </p><p>one second and to provide more than one image of crack at certain cycle so that the best image can be </p><p>selected for use in the new Measurement and Mapping of the Crack Meander (MMCM) software. The </p><p>diametral surface of the specimen must face the UTM machine glass door. Furthermore a fixed </p><p>distance, between the camera lens and the glass door, and a fixed height, between the camera and the </p><p>ground, must be provided using a tripod. This is important because later the photos will be uploaded </p><p>into the MMCM software to measure and compare the crack development at the same resolution. Each </p><p>image is coded based on the number of load cycles. </p><p>&lt; Insert Figure 4 about here &gt; </p><p>In the second stage, crack analysis and measurement are performed using the MMCM software. </p><p>4.1. Measurement and Mapping of the Crack Meander (MMCM) Software </p></li><li><p>7</p><p>Sample information and test control parameters in MMCM software were designed based on ITFT </p><p>format. This software was developed at UPM [24] based on 2004 original concept [25]. </p><p>The images of samples taken during the fatigue test were inserted as the inputs into this software for </p><p>crack measurement and analysis. Frame size of the picture was set to a standard dimension, by </p><p>changing the pixels (usually 30mm equal to 10 pixels), before any analysis in order to remove the </p><p>possible errors occurred due to slight variation in camera distance. </p><p>In order to specify the initial crack, MMCM used the first image of each specimen before the ITFT </p><p>test as a guide. Since the surface of specimen is painted with white color, MMCM converts each white </p><p>surface to specific number of white pixels. By using image processing and comparing the other images </p><p>with the first image, MMCM is able to recognize any black pixel which represents the initiation of </p><p>crack in any image. As illustrated in Figure 5, crack measurement is based on measuring different </p><p>groups of small cracks which can be highlighted in even different colors. Adding up all the groups of </p><p>cracks leads to the total crack measurement which includes total area, average width and length of </p><p>cracks. This information is presented at the bottom of each sample for comparison purpose. MMCM </p><p>maps all the cracks in each specimen effectively using image processing technique. </p><p> 4.2. The results of each image analysis, include crack length, crack width, crack area and crack density as </p><p>shown in Figure 6, are summarized in Microsoft Excel format as well. Furthermore, as illustrated in </p><p>Figure 7, the software is able to compare the results based on the number of cycles. The image </p><p>comparison among different kinds of samples is a useful tool in crack propagation and samples </p><p>behavior analysis to evaluate the performance as well. </p><p>&lt; Insert Figure 6 about here &gt; </p><p>&lt; Insert Figure 7 about here &gt; </p><p> 5 MATERIALS AND METHODOLOGY </p></li><li><p>8</p><p> In this study granite aggregate from Kajang quarry, Malaysia was used. Non-hydrated calcium </p><p>carbonate powder obtained from the limestone processing plant in Ipoh, Malaysia was the source of </p><p>filler. Asphalt binder with 80/100 penetration grade was used. The aggregate and binder physical </p><p>properties were evaluated which fulfilled the JKR (Malaysia Public Works Department) requirements. </p><p>For the mix design seven different combinations including 1) Control sample; </p><p>2) SMA mix with 0.3% COPF; 3) SMA mix with 0.6% COPF; 4) SMA mix with 0.9% COPF; </p><p>5) SMA mix with 3% EVA; 6) SMA mix with 6% EVA and 7) SMA mix with 9% EVA were used </p><p>which produced 105 Marshall samples (15 samples each). However, the results of mix design stage are </p><p>not presented here since the details are beyond the scope of this paper. In the next stage the Optimum </p><p>Asphalt Content (OAC) was determined and three different types of SMA mixtures including SMA </p><p>Control Samples (CS), SMA mixtures with 0.6 percent of COPF (COPF P0.6) and SMA mixtures with </p><p>6.0 percent of EVA...</p></li></ul>

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