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Laboratory fatigue evaluation of modified and unmodified asphalt binders in Stone Mastic Asphalt mixtures using a newly developed crack meander technique
Accepted Manuscript Laboratory Fatigue Evaluation of Modified and Unmodified Asphalt binders in Stone Mastic Asphalt Mixtures using a newly Developed Crack Meander Tech‐ nique Ratnasamy Muniandy, Nor Azurah Binti Che Md Akhir, Salihudin Hassim, Danial Moazami PII: DOI: Reference:
S0142-1123(13)00236-3 http://dx.doi.org/10.1016/j.ijfatigue.2013.08.021 JIJF 3198
To appear in:
International Journal of Fatigue
Received Date: Revised Date: Accepted Date:
7 December 2012 16 August 2013 20 August 2013
Please cite this article as: Muniandy, R., Akhir, N.A.B., Hassim, S., Moazami, D., Laboratory Fatigue Evaluation of Modified and Unmodified Asphalt binders in Stone Mastic Asphalt Mixtures using a newly Developed Crack Meander Technique, International Journal of Fatigue (2013), doi: http://dx.doi.org/10.1016/j.ijfatigue.2013.08.021
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Laboratory Fatigue Evaluation of Modified and Unmodified Asphalt binders in Stone Mastic Asphalt Mixtures using a newly Developed Crack Meander Technique Ratnasamy Muniandy , Nor Azurah Binti Che Md Akhir, Salihudin Hassim, Danial Moazami Department of Civil Engineering, University Putra Malaysia, [email protected] Department of Civil Engineering, University Putra Malaysia, [email protected] Department of Civil Engineering, University Putra Malaysia, [email protected] Department of Civil Engineering, University Putra Malaysia, [email protected]
Corresponding Author +60-3-89466373/7847
E-mail: [email protected] (+60)123396917
1
ABSTRACT This paper looks into the fatigue evaluation of modified and unmodified asphalt binders in Stone Mastic Asphalt (SMA) mixtures using a Crack Meander (CM) technique. Specimens images were taken during the repeated load indirect tensile fatigue test (ITFT) and crack initiation, propagation and failure were analyzed using a developed "Measurement and Mapping of Crack Meander" (MMCM) Software. The results of crack analysis on every SMA specimens were compared with tensile strain plots obtained from the ITFT test. It was concluded that, in addition to strain or dynamic modulus plots, fatigue behavior can be determined using crack appearance as an alternative method.
Keywords: Stone Mastic Asphalt; Fatigue Strength; Crack Formation; Crack Meander; Repeated Load Indirect Tensile Fatigue Test.
2
1
INTRODUCTION
Fatigue cracks are one of the major distresses on the roads worldwide. In fatigue studies, there are many approaches to define and evaluate the fatigue strength of asphalt mixtures such as the traditional method, by using stress or strain against number of cycles (S-N plot), the dissipated energy approach, and visco-elastic continuum damage method. However, there is not a clear or specific standard that states which one is the best method to compare the performance between various bituminous mixtures. The failure point in the traditional fatigue models considered at 50 percent reduction in the stiffness modulus for controlled strain testing [1]. However, Lundstrom et al. [2] reported the traditional failure criterion unsuitable, since at that point there is often no sign of real failure leading to inconsistent fatigue results. Dissipated energy is another approach used instead of stress or strain while this method does not consider progressive damage of material and crack development. Continuum mechanics also does not accurately identify the fatigue crack development in the secondary and tertiary stages [3]. Therefore, in order to portray the nature of cracks, studying the fatigue crack network and its pattern seems necessary. Braz et al. [4] used computed tomography technique to detect crack evolution in asphaltic mixtures submitted to fatigue test. Birgisson et al. [5] used a Digital Image Correlation (DIC) system to obtain displacement/strain fields and to detect crack patterns. In this study a different approach is presented to fully quantify the fatigue strength of asphalt mixtures until failure. Some preliminary works were undertaken at Universiti Putra Malaysia (UPM) in 2004 and 2010 to establish a protocol for Crack Meander technique (CM) to determine the fatigue strength. Some unique features of this method include investigation of all aspects of fatigue distress (crack length, area and density), simplicity of the test and the high precision of the image processing technique. In this study the fatigue strength of modified and unmodified asphalt binders in Stone Mastic Asphalt mixtures (SMA) were evaluated by using the developed crack meander method. The obtained crack data was validated as compared to real strain data from the repeated load indirect tensile fatigue test (ITFT).
2 FATIGUE CRACK MECHANISM
3
In general, fatigue life is defined as the number of load cycles to failure for a bituminous mixture and fatigue resistance indicates its ability to resist repeated cyclic loading that cause fracture although other stress inducing factors are not mentioned here. Technically, because of continuous cyclic loading, the bottom of the pavement layer experiences tensile strains thus forms cracks that continue to propagate upward until failure [6, 7]. Fatigue behavior of asphalt mixtures is determined either by controlled stress (load) or controlled strain (deflection) mode in the laboratory [8]. Because of the high similarity with site conditions, controlled stress mode is widely used [7]. In controlled stress mode, a constant amplitude of repeated stress or load causes the increasing strain while in controlled strain mode, the amplitude of constant strain is applied in form of repeated deflection which results in stress decrease [9]. Dynamic reactions are responsible in evaluation of fatigue resistance in bituminous mixtures [10]. Dynamic complex modulus is defined as the ratio of sinusoidal amplitude of stress to strain at angular frequency for any given time. The dynamic complex modulus (E*) plot is normally used to represent the relationship between stress and strain [11, 12]. During a fatigue test, modulus value decreases [13] according to Figure 1 [14]. The first phase shows a fall in stiffness modulus due to repetitive load excitation. Phase II, shows a quasi-linear decrease in stiffness, after which the sample starts to fracture rapidly at the early of phase III due to
non-uniformity in the strain field. < Insert Figure 1 about here >
3
STONE MASTIC ASPHALT AND THE MODIFIERS
SMA is a dense and gap-graded bituminous mixture contains coarse and fine aggregates, filler, and bitumen. The binder is typically modified with suitable binder carrier such as fiber or polymer [15, 16]. Earlier, SMA was known by its great potential to resist rutting and to decrease wear due to the studded tires [15, 17]. Cubical, hard, crushed and durable aggregates are adhered with optimum quantity of moisture-resistant mortar, and produce stone-on-stone contact. SMA contains about 93 to 94 percent of aggregates by weight of total mix, less than 1 percent fiber and about 6 percent binder [16]. Although SMA is rut resistance, due to high proportions of coarse aggregates, it shows poor 4
performance in fatigue resistance due to the reduced amount of fine aggregates [16]. In total, because of its good potential in pavement performance, detailed consideration should be taken in the selection of materials to produce suitable mixtures. In this study two different common modifiers were selected for use in the SMA mixture in order to improve its performance in fatigue strength. Cellulose Oil Palm Fiber (COPF) is widely available in Malaysia and therefore it was selected as one of the stabilizers. In addition to COPF, Ethylene Vinyl Acetate (EVA) was selected as a traditional asphalt modifier. The cellulose fiber and EVA materials are shown in Figures 2 and 3 below. < Insert Figures 2 and 3 about here (in one line) >
COPF is a non-hazardous biodegradable material that is produced from the empty fruit bunch of oil palm tree through various pulping methods. It was proven that COPF greatly minimizes drain down of asphalt mixtures and tends to improve the fatigue resistance [16]. EVA is a type of polymer in plastomer group. For over twenty years, it has been used in pavement construction to improve the performance of asphalt mixtures since it has great potential to resist permanent deformation [18, 19], thermal cracking [20] as well as fatigue of asphalt mixtures [21]. By blending EVA with the original bitumen, the physical properties of binder such as penetration, softening point, loss on aging and viscosity improve which indicates the stiffening effect of EVA blended binders [22]. 4 CRACK MEANDER CONCEPT AND APPROACH Indirect tensile fatigue test is widely carried out to estimate the resistance of a bituminous mixture sample to fatigue failure in accordance with BS EN 12697-24 [23] by using the Universal Testing Machine (UTM). Laboratory investigation of fatigue has shown that visual cracks that appear on the trimmed test samples seem to have a unique relationship with fatigue resistance. This observation leads to the idea of "crack meander" study to be developed. The term ‘meander’ is derived from the river meandering concept with a convoluted path which is known as Maiandros or meander by ancient Greeks. According to Oxford dictionary, meander is 5
defined as "to curve a lot rather than being in a straight line" or "to walk slowly and change direction often, especially without a particular aim". To summarize, meander in this context can be defined as initiation and propagation of cracks, meandering due to crack pinning through the cross section of the trimmed specimens. The new approach is divided into a few stages. In the first stage, initiation and propagation of cracks which appear on the sample surface during the diametral fatigue test is monitored and captured via a SLR camera. For this purpose, instead of using the existing frame for indirect tensile fatigue test in universal testing machine, the frame was specially fabricated; so that the surface image can be captured directly without any barrier as shown in Figure 4. The images were recorded at a predetermined interval of cycles depending on the speed of crack migration from start of the test until failure. The SLR camera brand Nikon D300 was used to capture images which can capture up to six frames per second with 12.3 megapixel resolution. This criterion is important to capture few images in one second and to provide more than one image of crack at certain cycle so that the best image can be selected for use in the new Measurement and Mapping of the Crack Meander (MMCM) software. The diametral surface of the specimen must face the UTM machine glass door. Furthermore a fixed distance, between the camera lens and the glass door, and a fixed height, between the camera and the ground, must be provided using a tripod. This is important because later the photos will be uploaded into the MMCM software to measure and compare the crack development at the same resolution. Each image is coded based on the number of load cycles. < Insert Figure 4 about here >
In the second stage, crack analysis and measurement are performed using the MMCM software.
4.1.
Measurement and Mapping of the Crack Meander (MMCM) Software 6
Sample information and test control parameters in MMCM software were designed based on ITFT format. This software was developed at UPM [24] based on 2004 original concept [25]. The images of samples taken during the fatigue test were inserted as the inputs into this software for crack measurement and analysis. Frame size of the picture was set to a standard dimension, by changing the pixels (usually 30mm equal to 10 pixels), before any analysis in order to remove the possible errors occurred due to slight variation in camera distance. In order to specify the initial crack, MMCM used the first image of each specimen before the ITFT test as a guide. Since the surface of specimen is painted with white color, MMCM converts each white surface to specific number of white pixels. By using image processing and comparing the other images with the first image, MMCM is able to recognize any black pixel which represents the initiation of crack in any image. As illustrated in Figure 5, crack measurement is based on measuring different groups of small cracks which can be highlighted in even different colors. Adding up all the groups of cracks leads to the total crack measurement which includes total area, average width and length of cracks. This information is presented at the bottom of each sample for comparison purpose. MMCM maps all the cracks in each specimen effectively using image processing technique.
4.2. The results of each image analysis, include crack length, crack width, crack area and crack density as shown in Figure 6, are summarized in Microsoft Excel format as well. Furthermore, as illustrated in Figure 7, the software is able to compare the results based on the number of cycles. The image comparison among different kinds of samples is a useful tool in crack propagation and samples behavior analysis to evaluate the performance as well. < Insert Figure 6 about here > < Insert Figure 7 about here >
5
MATERIALS AND METHODOLOGY 7
In this study granite aggregate from Kajang quarry, Malaysia was used. Non-hydrated calcium carbonate powder obtained from the limestone processing plant in Ipoh, Malaysia was the source of filler. Asphalt binder with 80/100 penetration grade was used. The aggregate and binder physical properties were evaluated which fulfilled the JKR (Malaysia Public Works Department) requirements. For
the
mix
design
seven
different
combinations
including
1)
Control
sample;
2) SMA mix with 0.3% COPF; 3) SMA mix with 0.6% COPF; 4) SMA mix with 0.9% COPF; 5) SMA mix with 3% EVA;
6) SMA mix with 6% EVA and 7) SMA mix with 9% EVA were used
which produced 105 Marshall samples (15 samples each). However, the results of mix design stage are not presented here since the details are beyond the scope of this paper. In the next stage the Optimum Asphalt Content (OAC) was determined and three different types of SMA mixtures including SMA Control Samples (CS), SMA mixtures with 0.6 percent of COPF (COPF P0.6) and SMA mixtures with 6.0 percent of EVA (EVA P6.0) were selected for fatigue performance test. Percentages of COPF and EVA were by weight of mix and by weight of original binder, respectively. The selected quantities were based on the performance comparison among the various percentages. Performance comparisons were with respect to stability, flow, resilient modulus and optimum asphalt content. Finally 6 control samples, 6 COPF P0.6 and 6 samples with EVA P6.0 were cored from the three prepared slabs. Table 1 summarizes the specimens for fatigue performance testing. All the mixtures were prepared according to the middle boundary of JKR- SMA 14 specification as shown in Table 2. < Insert Table 1 about here > < Insert Table 2 about here >
Samples with 150 mm diameter, instead of 100 mm in common diametral fatigue tests, were used since the bigger surface is easier and more precise for crack analysis. To produce the 150 mm diameter samples, three slabs were prepared using an in-house automatic Turamesin slab compactor [26] in Figure 8. The Turamesin roller compactor can compact a slab with maximum dimensions of 8
750×600×90 mm. In this study, from each slab only six core samples were needed based on the experimental design. Therefore, by using the additional already designed plates in Turamesin, the mould size was reduced to 600×450×80 mm (separated area in Figure 8) to avoid any wastage of materials. Specimens were cored and trimmed to the desired size of 150 mm diameter and 60 mm thickness. The surfaces of the trimmed samples were then painted with a very thin white color so that the crack line can be appeared clearly during the test. Moreover, the very thin and light paint causes the hairline cracks to penetrate through the coating and reduces the paint coating cracks which are not the reflection of cracks in the specimen. < Insert Figure 8 about here >
Following parameters in Table 3 were used in the indirect tensile fatigue test. Critical situations were selected including loading frequency of 2 Hz for very high trafficked volume roads, and the rise time of 100 ms for low speed operation. Poisson’s Ratio of 0.35 was selected since this value is reasonable and common for asphalt mixtures [27]. < Insert Table 3 about here >
6
RESULTS AND ANALYSIS
Fatigue analysis using two approaches were presented. Indirect tensile fatigue test with tensile strain plot and crack meander method using crack appearance were compared. 6.1.
Indirect Tensile Fatigue Test Result
There are two main results that are important in the indirect tensile fatigue study including tensile strain and dynamic modulus. Figure 9 shows the tensile strain and dynamic modulus graphs plotted against the number of load cycles for all the three mixes. Strain plots against the number of cycles indicate that high value of strain; results in stiffness reduction to a large extent and induces changes in bituminous internal structure which lead to damage. < Insert Figure 9 about here >
The trend line patterns were different for each type of SMA mixture. It was observed that after certain number of cycles, the tensile strain gradient for EVA P6.0 changed drastically and became bias to 9
vertical axis just before the fracture point, while the control samples and COPF P0.6 samples’ trend line patterns looked normal. It means that although EVA mixture has a long fatigue life it fractures in a short period after the failure point rather than slower trend in control samples and COPF. 6.2.
Crack Measurement and Mapping Result
In crack measurement and analysis, the graphs of crack length, crack area and crack density were plotted as shown in Figures 10, 11 and 12, respectively. Every mixture displayed the same trend and the same sequence in all aspects of crack length, crack area and crack density. The control sample had the longest crack length, the highest crack area and crack density followed by COPF P0.6 and EVA P6.0, respectively. The reason could be that the unmodified control sample did not provide any barrier to pin down or block the crack movement in the structure whereby the cracks propagated freely. EVA had the longest fatigue life, the lowest crack length, crack area and density. Based on earlier research, modification of the original binder with an optimum content of EVA produced a crystallization of rigid three-dimensional networks which could increase the complex modulus, storage modulus and the elastic behavior of the specimen [28]. Therefore, the EVA P6.0 exhibited the longest fatigue life and the lowest appearance of cracks on the sample. < Insert Figure 10 about here > < Insert Figure 11 about here > < Insert Figure 12 about here >
It was also observed that the trend line pattern and the sequence of the three graphs in Figure 13 were obviously consistent with the plots from the crack meander technique. The crack analysis (visual) exhibits a similar movement as the tensile strain trend progresses with the increasing number of cycles. The similarity of the trend line patterns shows a relationship between the crack analysis and the tensile strain in bituminous mixtures. This observation shows that the fatigue behavior of a bituminous mixture can be investigated by using the crack analysis although a continuous research is expected for precision. 10
< Insert Figure 13 about here >
6.3.
Fatigue life evaluation analysis
In order to evaluate the fatigue resistance of the SMA mixtures in both methods, the ratio of number of cycles to increase one unit of strain ( crack length (
and the ratio of number of cycles to cause one millimeter of
were determined for different load cycle intervals as illustrated in Table 4 and
Figure 14.
Bivariate pearson correlation and partial correlation were performed on the parallel data points. Pearson correlation of 0.906 was obtained between the data from ITFT and data from CM approach which shows a very high positive relationship. Partial correlation is an extension of pearson correlation which removes the effect of the confounding variable, to get a more accurate picture of the relationship between two variables of interest. Controlling for sample type a partial correlation of 0.879 was obtained which again shows a high positive relationship between the obtained data from both methods. In order to evaluate the fatigue results further analysis was done to compare the ratio of in both ITFT and CM methods. For this analysis
number of cycles to increase one unit of strain (
the comparison was done starting from critical fatigue point until the failure point. For control stress mode of ITFT the critical fatigue point was considered at the cycle where the linear trend line was followed by an abrupt change as shown in Figure 15. At that point, constant rate of increase in the horizontal tensile strain is replaced by a faster rate of increase. < Insert Figure 15 about here >
For the crack meander approach, the critical fatigue point was considered as the number of cycles where crack began to appear which was detected by MMCM software.
In order to make the comparison meaningful the failure point for both methods was considered at the cross tangents in tensile strain plot against the number of cycles. At this point, the sample is said to be 11
at the end of fatigue life. Table 5 and Figure 16 show the number of cycles that were needed to increase one unit of strain. Fatigue strength for the three mixtures was combined into one line to study the trend of crack meander approach and to compare with the line obtained from tensile strain plot. It was observed that both lines were parallel and based on the one-way ANOVA test results there was no significant difference between (
values in both methods.
Finally it was concluded that the data from the crack meander seems to be quite reliable to be used in the fatigue study although more advanced research is needed to validate the new approach. < Insert Table 5 about here > < Insert Figure 16 about here >
7
CONCLUSION
This paper studies the fatigue strength of SMA mixtures using a new approach called crack meander technique. In the fatigue study using visual crack appearance, the images of the specimen were taken during the repeated load indirect tensile fatigue test at various intervals of the test duration. The tool used in this study was the newly developed MMCM software which is able to measure and map the crack initiation and propagation. The software is able to make comparison between the crack images, captured at different cycles, for one sample as well as comparison between various samples to evaluate the performance. It was observed that CM method can be used as an alternative way to study the fatigue performance by mapping the cracks especially when full fatigue strength of asphalt mixtures is desired. Crack analysis exhibits the same movement as the tensile strain trend progresses with the increasing number of cycles. Moreover, the sequence of maximum tensile strain value and maximum crack value (crack length, crack area and crack density) for the three SMA mixes were comparable. It was concluded that comparison of fatigue performance and behavior between different mixes can be determined by using this new approach in the laboratory. Based on the obtained results, the control sample had the longest crack length, the highest crack area and crack density followed by COPF P0.6 and EVA P6.0, respectively. The reason could be that the binder used in the control sample was unmodified so that 12
the cracks propagated freely without any barrier to pin down or block the crack movement in the structure. EVA-blended samples had the longest fatigue life and the lowest crack length, crack area and density. Therefore, modification of the original binder with an optimum content of EVA produced a crystallization of rigid three-dimensional networks which could increase the complex modulus and fatigue resistance of the specimen. Significant difference was found between the crack paths of the tested samples. EVA P6.0 sample which had the longest fatigue life obviously showed the macrocrack appearance rather than microcrack. Meanwhile, control sample which placed second in fatigue life exhibited balanced micro and macro cracks. The COPF P0.6 which had the shortest fatigue life obviously had more microcracks compared to the other two types of mixtures.
8
RECOMMENDATION
This study is just a beginning in evaluating the fatigue strength from crack images and appearance. Since the study was limited to three types of mixtures only, it is recommended to explore more mixture varieties in the future studies to improve the confidence of using this approach. Since this paper only looked into the crack on ITFT samples, it might be precious to try other types of fatigue test plus the MMCM software to measure and map the cracks.
REFERENCES [1] Ghuzlan KA, Carpenter SH. Traditional fatigue analysis of asphalt concrete mixtures. Urbana 2002;51:61801. [2] Lundstrom R, Isacsson U. Asphalt fatigue modelling using viscoelastic continuum damage theory. Road materials and pavement design 2003;4(1):51-75. [3] Nguyen MT, Lee HJ, Baek J. Fatigue Analysis of Asphalt Concrete under Indirect Tensile Mode of Loading Using Crack Images. Journal of Testing and Evaluation;41(1):148-158. [4] Braz D, Lopes R, Motta L. Research on fatigue cracking growth parameters in asphaltic mixtures using computed tomography. Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms 2004;213:498-502. [5] Birgisson Br, Montepara A, Romeo E, Roncella R, Napier J, Tebaldi G. Determination and prediction of crack patterns in hot mix asphalt (HMA) mixtures. Engineering Fracture Mechanics 2008;75(3):664-673. [6] Nejad FM, Aflaki E, Mohammadi MA. Fatigue behavior of SMA and HMA mixtures. Construction and Building Materials 2010;24(7):1158-1165. [7] Pell PS. Characterization of fatigue behavior. Highway Research Board Special Report 140; Proceedings of a Symposium on Structural Design of Asphalt Concrete Pavements to Prevent Fatigue Cracking;Washington, 1973:49-64. 13
[8] Khalid HA. A comparison between bending and diametral fatigue tests for bituminous materials. Materials and Structures 2000;33(7):457-465. [9] Brown SF. Material characteristics for analytical pavement design. Development in Highway Pavement Engineering-1 1978;P.S. Pell,ed. Applied Science, London:41-92. [10] Ye Q, Wu S, Li N. Investigation of the dynamic and fatigue properties of fiber-modified asphalt mixtures. International Journal of Fatigue 2009;31(10):1598-1602. [11] Polacco G, Muscente A, Biondi D, Santini S. Effect of composition on the properties of SEBS modified asphalts European Polymer Journal 2006;42(5):1113-1121. [12] Krishnan J, Rajagopal K. On the mechanical behavior of asphalt. Mechanics of Materials 2005;37(11):1085-1100. [13] Di Benedetto H, Soltani A, Chaverot P, Benedetto D. Fatigue damage for bituminous mixtures: A Pertinent Approach Association of Asphalt Paving Technologists 1996;65:142-158. [14] Castro M, Sánchez JA. Estimation of asphalt concrete fatigue curves - A damage theory approach. Construction and Building Materials 2008;22(6):1232-1238. [15] Richardson J. Stone Mastic Asphalt in the UK. Society of Chemical Industry Lecture Papers Series, Symposium on Stone Mastic Asphalt and Thin Surfacings,Wolverhampton, West Midlands, UK 1997. [16] Muniandy R, Huat BBK. Laboratory Diametral Fatigue Performance of Stone Matrix Asphalt with Cellulose Oil Palm Fiber. American Journal of Applied Sciences 2006;3(9):2005-2010. [17] Asi IM. Laboratory comparison study for the use of stone matrix asphalt in hot weather climates. Construction and Building Materials 2006;20(10):982-989. [18] Goos D, Carre D. Rheological modelling of bituminous binders- a global approach to road technologies. Proceedings of the Eurasphalt & Eurobitume Congress, Session 5: Binders-Functional Properties and Performance Testing,E&E5111, Strasbourg,1996. [19] Cavaliere M, Diani E, Sacconi LV. Polymer modified bitumens for improved road application. Proceedings of the 5th Eurobitume Congress, Stockholm 1993;1A(1.23):138-142. [20] González O, Muñoz ME, A.Santamarı́a, Garcı́a-Morales M, Navarro FJ, Partal P. Rheology and Stability of Bitumen/EVA blends. European Polymer Journal 2004;40(10):2365-2372. [21] Yildirim Y. Polymer modified asphalt binders. Construction and Building Materials 2007;21(1):66-72. [22] Sengoz B, Isikyakar G. Evaluation of the properties and microstructure of SBS and EVA polymer modified bitumen. Construction and Building Materials 2008;22(9):1897-1905. [23] British Standards Institution–BS EN 12697-24. Bituminous mixtures - Test methods for hot mix asphalt. In: Part 24: Resistance to fatigue London 2004. [24] Radkeya S. Development of crack meander protocol for the fatigue resistance of stone mastic asphalt mixture using cellulose fibers In: Civil Engineering: Ph.D.dissertation, University Putra Malaysia, 2010. [25] Muniandy R, Selim AA, R.Schaefer V. Effect of the Newly Developed Cellulose Oil Palm Fiber in the Fatigue Cracking of Stone Mastic Asphalt. Transportation Research Board Washington, D.C., 2004. [26] Muniandy R, Hassim S, Jakarni FM, Selim A. Determination of SMA Slab Properties Using a Newly Developed Roller Compactor (Turamesin). In: Transportation and Development, 2008, pp. 505-510. [27] Huang Y. Pavement Design and Analysis. Pearson/Prentice Hall, 2004. [28] Airey GD. Rheological evaluation of ethylene vinyl acetate polymer modified bitumens. Construction and Building Materials 2002;16(8):473-487.
14
PHASE I
PHASE III
PHASE II
Modulus
Number of Cycles
Figure 1: Modulus variation during a fatigue test
Figure 2: Cellulose Oil Palm Fiber
Figure 3: Ethylene Vinyl Acetate
15
Figure 4: A 150 mm diameter specimen under the crack meander mapping jig
Figure 5: MMCM schematic surface plan of a cracked specimen
16
Figure 6: The output from MMCM software for the control sample after 19000 of load cycles
17
Figure 7: Example of crack comparison among various number of load cycles for the control sample
18
150 mm
150 mm
150 mm
600 mm
150 mm
750 mm Figure 8: Slab roller compactor (Turamesin) and 150 mm coring plan
19
(a) Control Sample
(b) COPF P0.6
(c) EVA P6.0
Figure 9: Tensile strain and dynamic modulus versus number of load cycles for various samples
20
Figure 10: Comparison of crack length among control, COPF P0.6 and EVA P6.0 samples
Figure 11: Comparison of crack area among control, COPF P0.6 and EVA P6.0 samples
Figure 12: Comparison of crack density among control, COPF P0.6 and EVA P6.0 samples
21
Figure 13: Comparison of tensile strain plots among control, COPF P0.6 and EVA P6.0 samples
Figure 14: Comparison of trend lines between ∆N/∆ɛ and ∆N/∆CL for all tested samples
22
Figure15: Example of difference between two points in tensile strain graph for ITFT
Figure 16: Comparison of fatigue strength power curves for the Crack Meander and ITFT approaches
23
Table 1: Cylindrical cored samples for fatigue performance test
SMA mixtures Control COPFPO.6 EVAP6.0
No. of cored samples 6 6 6
OAC (%) 5.50 5.86 5.78
Desired air void content (%) 4±0.3 4±0.3 4±0.3
Asphalt binder grade 80/100 80/100 80/100
Table 2: Aggregate gradation for SMA 14, JKR specification
Sieve size (mm) 19.0 12.5 9.5 4.75 2.36 0.6 0.3 0.075 filler
Percentage passing 100 100 72-83 25-38 16-24 12-16 12-15 8-10
Desired (% retained) 0 0 22.5 46 11.5 6 0.5 4.5 9
Table 3: Test parameters for the repeated load indirect tensile fatigue test
Test parameters
Value
Seating force Cyclic loading force Cycle width Loading frequency Temperature Estimated Poisson’s ratio
24
100 N 2500 N 200 ms 2 Hz 20°C 0.35
Table 4: Comparison between ∆N/∆ɛ ITFT and ∆N/∆CL from CM approach Interval (No. of Cycles, N) Control Sample 200-5000 5000-10000 10000-15000 15000-20000 20000-21000 COPF P0.6 500-1000 1000-1500 1500-1900 EVA P6.0 15000-20000 20000-25000 25000-30000 30000-34000
Center Point
∆N/∆ɛ
Interval (No. of Cycles, N)
Center Point
∆N/∆CL
2600 7500 12500 17500 20500
4.04E+06 8.52E+06 7.68E+06 4.68E+06 3.18E+06
2000-5000 5000-10000 10000-15000 15000-20000 20000-21000
4000 7500 12500 17500 20500
64.79 67.49 56.80 62.12 155.38
750 1250 1700
6.86E+05 6.06E+05 4.23E+05
500-1000 1000-1500 1500-1900
750 1250 1700
12.27 6.97 5.17
17500 22500 27500 32000
2.68E+07 1.96E+07 1.09E+07 3.01E+06
15000-20000 20000-25000 25000-30000 30000-34000
17500 22500 27500 32000
924.47 1153.14 391.54 131.75
Table 5: Fatigue evaluation for ITFT and CM analyses
ITFT
∆Nf Control Sample COPF P0.6 EVA P6.0
CM
5.55E+03
1.70E+04
∆Nf / ∆ɛ 6.47E+06
3.55E+02 1.36E+04
3.73E+05 9.03E+06
1.33E+03 2.58E+04
5.84E+05 1.09E+07
25
∆Nf
∆Nf/∆ɛ 4.93E+06
Fatigue evaluation of SMA mixtures using crack meander technique was introduced. ‘Measurement and Mapping of crack Meander’ (MMCM) Software was developed. Crack initiation, propagation and failure were analyzed by MMCM tool. Control sample indicated the maximum crack length, crack area and crack density. Same results were followed by COPF P0.6 and EVA P6.0, respectively.
26
S0142-1123(13)00236-3 http://dx.doi.org/10.1016/j.ijfatigue.2013.08.021 JIJF 3198
To appear in:
International Journal of Fatigue
Received Date: Revised Date: Accepted Date:
7 December 2012 16 August 2013 20 August 2013
Please cite this article as: Muniandy, R., Akhir, N.A.B., Hassim, S., Moazami, D., Laboratory Fatigue Evaluation of Modified and Unmodified Asphalt binders in Stone Mastic Asphalt Mixtures using a newly Developed Crack Meander Technique, International Journal of Fatigue (2013), doi: http://dx.doi.org/10.1016/j.ijfatigue.2013.08.021
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Laboratory Fatigue Evaluation of Modified and Unmodified Asphalt binders in Stone Mastic Asphalt Mixtures using a newly Developed Crack Meander Technique Ratnasamy Muniandy , Nor Azurah Binti Che Md Akhir, Salihudin Hassim, Danial Moazami Department of Civil Engineering, University Putra Malaysia, [email protected] Department of Civil Engineering, University Putra Malaysia, [email protected] Department of Civil Engineering, University Putra Malaysia, [email protected] Department of Civil Engineering, University Putra Malaysia, [email protected]
Corresponding Author +60-3-89466373/7847
E-mail: [email protected] (+60)123396917
1
ABSTRACT This paper looks into the fatigue evaluation of modified and unmodified asphalt binders in Stone Mastic Asphalt (SMA) mixtures using a Crack Meander (CM) technique. Specimens images were taken during the repeated load indirect tensile fatigue test (ITFT) and crack initiation, propagation and failure were analyzed using a developed "Measurement and Mapping of Crack Meander" (MMCM) Software. The results of crack analysis on every SMA specimens were compared with tensile strain plots obtained from the ITFT test. It was concluded that, in addition to strain or dynamic modulus plots, fatigue behavior can be determined using crack appearance as an alternative method.
Keywords: Stone Mastic Asphalt; Fatigue Strength; Crack Formation; Crack Meander; Repeated Load Indirect Tensile Fatigue Test.
2
1
INTRODUCTION
Fatigue cracks are one of the major distresses on the roads worldwide. In fatigue studies, there are many approaches to define and evaluate the fatigue strength of asphalt mixtures such as the traditional method, by using stress or strain against number of cycles (S-N plot), the dissipated energy approach, and visco-elastic continuum damage method. However, there is not a clear or specific standard that states which one is the best method to compare the performance between various bituminous mixtures. The failure point in the traditional fatigue models considered at 50 percent reduction in the stiffness modulus for controlled strain testing [1]. However, Lundstrom et al. [2] reported the traditional failure criterion unsuitable, since at that point there is often no sign of real failure leading to inconsistent fatigue results. Dissipated energy is another approach used instead of stress or strain while this method does not consider progressive damage of material and crack development. Continuum mechanics also does not accurately identify the fatigue crack development in the secondary and tertiary stages [3]. Therefore, in order to portray the nature of cracks, studying the fatigue crack network and its pattern seems necessary. Braz et al. [4] used computed tomography technique to detect crack evolution in asphaltic mixtures submitted to fatigue test. Birgisson et al. [5] used a Digital Image Correlation (DIC) system to obtain displacement/strain fields and to detect crack patterns. In this study a different approach is presented to fully quantify the fatigue strength of asphalt mixtures until failure. Some preliminary works were undertaken at Universiti Putra Malaysia (UPM) in 2004 and 2010 to establish a protocol for Crack Meander technique (CM) to determine the fatigue strength. Some unique features of this method include investigation of all aspects of fatigue distress (crack length, area and density), simplicity of the test and the high precision of the image processing technique. In this study the fatigue strength of modified and unmodified asphalt binders in Stone Mastic Asphalt mixtures (SMA) were evaluated by using the developed crack meander method. The obtained crack data was validated as compared to real strain data from the repeated load indirect tensile fatigue test (ITFT).
2 FATIGUE CRACK MECHANISM
3
In general, fatigue life is defined as the number of load cycles to failure for a bituminous mixture and fatigue resistance indicates its ability to resist repeated cyclic loading that cause fracture although other stress inducing factors are not mentioned here. Technically, because of continuous cyclic loading, the bottom of the pavement layer experiences tensile strains thus forms cracks that continue to propagate upward until failure [6, 7]. Fatigue behavior of asphalt mixtures is determined either by controlled stress (load) or controlled strain (deflection) mode in the laboratory [8]. Because of the high similarity with site conditions, controlled stress mode is widely used [7]. In controlled stress mode, a constant amplitude of repeated stress or load causes the increasing strain while in controlled strain mode, the amplitude of constant strain is applied in form of repeated deflection which results in stress decrease [9]. Dynamic reactions are responsible in evaluation of fatigue resistance in bituminous mixtures [10]. Dynamic complex modulus is defined as the ratio of sinusoidal amplitude of stress to strain at angular frequency for any given time. The dynamic complex modulus (E*) plot is normally used to represent the relationship between stress and strain [11, 12]. During a fatigue test, modulus value decreases [13] according to Figure 1 [14]. The first phase shows a fall in stiffness modulus due to repetitive load excitation. Phase II, shows a quasi-linear decrease in stiffness, after which the sample starts to fracture rapidly at the early of phase III due to
non-uniformity in the strain field. < Insert Figure 1 about here >
3
STONE MASTIC ASPHALT AND THE MODIFIERS
SMA is a dense and gap-graded bituminous mixture contains coarse and fine aggregates, filler, and bitumen. The binder is typically modified with suitable binder carrier such as fiber or polymer [15, 16]. Earlier, SMA was known by its great potential to resist rutting and to decrease wear due to the studded tires [15, 17]. Cubical, hard, crushed and durable aggregates are adhered with optimum quantity of moisture-resistant mortar, and produce stone-on-stone contact. SMA contains about 93 to 94 percent of aggregates by weight of total mix, less than 1 percent fiber and about 6 percent binder [16]. Although SMA is rut resistance, due to high proportions of coarse aggregates, it shows poor 4
performance in fatigue resistance due to the reduced amount of fine aggregates [16]. In total, because of its good potential in pavement performance, detailed consideration should be taken in the selection of materials to produce suitable mixtures. In this study two different common modifiers were selected for use in the SMA mixture in order to improve its performance in fatigue strength. Cellulose Oil Palm Fiber (COPF) is widely available in Malaysia and therefore it was selected as one of the stabilizers. In addition to COPF, Ethylene Vinyl Acetate (EVA) was selected as a traditional asphalt modifier. The cellulose fiber and EVA materials are shown in Figures 2 and 3 below. < Insert Figures 2 and 3 about here (in one line) >
COPF is a non-hazardous biodegradable material that is produced from the empty fruit bunch of oil palm tree through various pulping methods. It was proven that COPF greatly minimizes drain down of asphalt mixtures and tends to improve the fatigue resistance [16]. EVA is a type of polymer in plastomer group. For over twenty years, it has been used in pavement construction to improve the performance of asphalt mixtures since it has great potential to resist permanent deformation [18, 19], thermal cracking [20] as well as fatigue of asphalt mixtures [21]. By blending EVA with the original bitumen, the physical properties of binder such as penetration, softening point, loss on aging and viscosity improve which indicates the stiffening effect of EVA blended binders [22]. 4 CRACK MEANDER CONCEPT AND APPROACH Indirect tensile fatigue test is widely carried out to estimate the resistance of a bituminous mixture sample to fatigue failure in accordance with BS EN 12697-24 [23] by using the Universal Testing Machine (UTM). Laboratory investigation of fatigue has shown that visual cracks that appear on the trimmed test samples seem to have a unique relationship with fatigue resistance. This observation leads to the idea of "crack meander" study to be developed. The term ‘meander’ is derived from the river meandering concept with a convoluted path which is known as Maiandros or meander by ancient Greeks. According to Oxford dictionary, meander is 5
defined as "to curve a lot rather than being in a straight line" or "to walk slowly and change direction often, especially without a particular aim". To summarize, meander in this context can be defined as initiation and propagation of cracks, meandering due to crack pinning through the cross section of the trimmed specimens. The new approach is divided into a few stages. In the first stage, initiation and propagation of cracks which appear on the sample surface during the diametral fatigue test is monitored and captured via a SLR camera. For this purpose, instead of using the existing frame for indirect tensile fatigue test in universal testing machine, the frame was specially fabricated; so that the surface image can be captured directly without any barrier as shown in Figure 4. The images were recorded at a predetermined interval of cycles depending on the speed of crack migration from start of the test until failure. The SLR camera brand Nikon D300 was used to capture images which can capture up to six frames per second with 12.3 megapixel resolution. This criterion is important to capture few images in one second and to provide more than one image of crack at certain cycle so that the best image can be selected for use in the new Measurement and Mapping of the Crack Meander (MMCM) software. The diametral surface of the specimen must face the UTM machine glass door. Furthermore a fixed distance, between the camera lens and the glass door, and a fixed height, between the camera and the ground, must be provided using a tripod. This is important because later the photos will be uploaded into the MMCM software to measure and compare the crack development at the same resolution. Each image is coded based on the number of load cycles. < Insert Figure 4 about here >
In the second stage, crack analysis and measurement are performed using the MMCM software.
4.1.
Measurement and Mapping of the Crack Meander (MMCM) Software 6
Sample information and test control parameters in MMCM software were designed based on ITFT format. This software was developed at UPM [24] based on 2004 original concept [25]. The images of samples taken during the fatigue test were inserted as the inputs into this software for crack measurement and analysis. Frame size of the picture was set to a standard dimension, by changing the pixels (usually 30mm equal to 10 pixels), before any analysis in order to remove the possible errors occurred due to slight variation in camera distance. In order to specify the initial crack, MMCM used the first image of each specimen before the ITFT test as a guide. Since the surface of specimen is painted with white color, MMCM converts each white surface to specific number of white pixels. By using image processing and comparing the other images with the first image, MMCM is able to recognize any black pixel which represents the initiation of crack in any image. As illustrated in Figure 5, crack measurement is based on measuring different groups of small cracks which can be highlighted in even different colors. Adding up all the groups of cracks leads to the total crack measurement which includes total area, average width and length of cracks. This information is presented at the bottom of each sample for comparison purpose. MMCM maps all the cracks in each specimen effectively using image processing technique.
4.2. The results of each image analysis, include crack length, crack width, crack area and crack density as shown in Figure 6, are summarized in Microsoft Excel format as well. Furthermore, as illustrated in Figure 7, the software is able to compare the results based on the number of cycles. The image comparison among different kinds of samples is a useful tool in crack propagation and samples behavior analysis to evaluate the performance as well. < Insert Figure 6 about here > < Insert Figure 7 about here >
5
MATERIALS AND METHODOLOGY 7
In this study granite aggregate from Kajang quarry, Malaysia was used. Non-hydrated calcium carbonate powder obtained from the limestone processing plant in Ipoh, Malaysia was the source of filler. Asphalt binder with 80/100 penetration grade was used. The aggregate and binder physical properties were evaluated which fulfilled the JKR (Malaysia Public Works Department) requirements. For
the
mix
design
seven
different
combinations
including
1)
Control
sample;
2) SMA mix with 0.3% COPF; 3) SMA mix with 0.6% COPF; 4) SMA mix with 0.9% COPF; 5) SMA mix with 3% EVA;
6) SMA mix with 6% EVA and 7) SMA mix with 9% EVA were used
which produced 105 Marshall samples (15 samples each). However, the results of mix design stage are not presented here since the details are beyond the scope of this paper. In the next stage the Optimum Asphalt Content (OAC) was determined and three different types of SMA mixtures including SMA Control Samples (CS), SMA mixtures with 0.6 percent of COPF (COPF P0.6) and SMA mixtures with 6.0 percent of EVA (EVA P6.0) were selected for fatigue performance test. Percentages of COPF and EVA were by weight of mix and by weight of original binder, respectively. The selected quantities were based on the performance comparison among the various percentages. Performance comparisons were with respect to stability, flow, resilient modulus and optimum asphalt content. Finally 6 control samples, 6 COPF P0.6 and 6 samples with EVA P6.0 were cored from the three prepared slabs. Table 1 summarizes the specimens for fatigue performance testing. All the mixtures were prepared according to the middle boundary of JKR- SMA 14 specification as shown in Table 2. < Insert Table 1 about here > < Insert Table 2 about here >
Samples with 150 mm diameter, instead of 100 mm in common diametral fatigue tests, were used since the bigger surface is easier and more precise for crack analysis. To produce the 150 mm diameter samples, three slabs were prepared using an in-house automatic Turamesin slab compactor [26] in Figure 8. The Turamesin roller compactor can compact a slab with maximum dimensions of 8
750×600×90 mm. In this study, from each slab only six core samples were needed based on the experimental design. Therefore, by using the additional already designed plates in Turamesin, the mould size was reduced to 600×450×80 mm (separated area in Figure 8) to avoid any wastage of materials. Specimens were cored and trimmed to the desired size of 150 mm diameter and 60 mm thickness. The surfaces of the trimmed samples were then painted with a very thin white color so that the crack line can be appeared clearly during the test. Moreover, the very thin and light paint causes the hairline cracks to penetrate through the coating and reduces the paint coating cracks which are not the reflection of cracks in the specimen. < Insert Figure 8 about here >
Following parameters in Table 3 were used in the indirect tensile fatigue test. Critical situations were selected including loading frequency of 2 Hz for very high trafficked volume roads, and the rise time of 100 ms for low speed operation. Poisson’s Ratio of 0.35 was selected since this value is reasonable and common for asphalt mixtures [27]. < Insert Table 3 about here >
6
RESULTS AND ANALYSIS
Fatigue analysis using two approaches were presented. Indirect tensile fatigue test with tensile strain plot and crack meander method using crack appearance were compared. 6.1.
Indirect Tensile Fatigue Test Result
There are two main results that are important in the indirect tensile fatigue study including tensile strain and dynamic modulus. Figure 9 shows the tensile strain and dynamic modulus graphs plotted against the number of load cycles for all the three mixes. Strain plots against the number of cycles indicate that high value of strain; results in stiffness reduction to a large extent and induces changes in bituminous internal structure which lead to damage. < Insert Figure 9 about here >
The trend line patterns were different for each type of SMA mixture. It was observed that after certain number of cycles, the tensile strain gradient for EVA P6.0 changed drastically and became bias to 9
vertical axis just before the fracture point, while the control samples and COPF P0.6 samples’ trend line patterns looked normal. It means that although EVA mixture has a long fatigue life it fractures in a short period after the failure point rather than slower trend in control samples and COPF. 6.2.
Crack Measurement and Mapping Result
In crack measurement and analysis, the graphs of crack length, crack area and crack density were plotted as shown in Figures 10, 11 and 12, respectively. Every mixture displayed the same trend and the same sequence in all aspects of crack length, crack area and crack density. The control sample had the longest crack length, the highest crack area and crack density followed by COPF P0.6 and EVA P6.0, respectively. The reason could be that the unmodified control sample did not provide any barrier to pin down or block the crack movement in the structure whereby the cracks propagated freely. EVA had the longest fatigue life, the lowest crack length, crack area and density. Based on earlier research, modification of the original binder with an optimum content of EVA produced a crystallization of rigid three-dimensional networks which could increase the complex modulus, storage modulus and the elastic behavior of the specimen [28]. Therefore, the EVA P6.0 exhibited the longest fatigue life and the lowest appearance of cracks on the sample. < Insert Figure 10 about here > < Insert Figure 11 about here > < Insert Figure 12 about here >
It was also observed that the trend line pattern and the sequence of the three graphs in Figure 13 were obviously consistent with the plots from the crack meander technique. The crack analysis (visual) exhibits a similar movement as the tensile strain trend progresses with the increasing number of cycles. The similarity of the trend line patterns shows a relationship between the crack analysis and the tensile strain in bituminous mixtures. This observation shows that the fatigue behavior of a bituminous mixture can be investigated by using the crack analysis although a continuous research is expected for precision. 10
< Insert Figure 13 about here >
6.3.
Fatigue life evaluation analysis
In order to evaluate the fatigue resistance of the SMA mixtures in both methods, the ratio of number of cycles to increase one unit of strain ( crack length (
and the ratio of number of cycles to cause one millimeter of
were determined for different load cycle intervals as illustrated in Table 4 and
Figure 14.
Bivariate pearson correlation and partial correlation were performed on the parallel data points. Pearson correlation of 0.906 was obtained between the data from ITFT and data from CM approach which shows a very high positive relationship. Partial correlation is an extension of pearson correlation which removes the effect of the confounding variable, to get a more accurate picture of the relationship between two variables of interest. Controlling for sample type a partial correlation of 0.879 was obtained which again shows a high positive relationship between the obtained data from both methods. In order to evaluate the fatigue results further analysis was done to compare the ratio of in both ITFT and CM methods. For this analysis
number of cycles to increase one unit of strain (
the comparison was done starting from critical fatigue point until the failure point. For control stress mode of ITFT the critical fatigue point was considered at the cycle where the linear trend line was followed by an abrupt change as shown in Figure 15. At that point, constant rate of increase in the horizontal tensile strain is replaced by a faster rate of increase. < Insert Figure 15 about here >
For the crack meander approach, the critical fatigue point was considered as the number of cycles where crack began to appear which was detected by MMCM software.
In order to make the comparison meaningful the failure point for both methods was considered at the cross tangents in tensile strain plot against the number of cycles. At this point, the sample is said to be 11
at the end of fatigue life. Table 5 and Figure 16 show the number of cycles that were needed to increase one unit of strain. Fatigue strength for the three mixtures was combined into one line to study the trend of crack meander approach and to compare with the line obtained from tensile strain plot. It was observed that both lines were parallel and based on the one-way ANOVA test results there was no significant difference between (
values in both methods.
Finally it was concluded that the data from the crack meander seems to be quite reliable to be used in the fatigue study although more advanced research is needed to validate the new approach. < Insert Table 5 about here > < Insert Figure 16 about here >
7
CONCLUSION
This paper studies the fatigue strength of SMA mixtures using a new approach called crack meander technique. In the fatigue study using visual crack appearance, the images of the specimen were taken during the repeated load indirect tensile fatigue test at various intervals of the test duration. The tool used in this study was the newly developed MMCM software which is able to measure and map the crack initiation and propagation. The software is able to make comparison between the crack images, captured at different cycles, for one sample as well as comparison between various samples to evaluate the performance. It was observed that CM method can be used as an alternative way to study the fatigue performance by mapping the cracks especially when full fatigue strength of asphalt mixtures is desired. Crack analysis exhibits the same movement as the tensile strain trend progresses with the increasing number of cycles. Moreover, the sequence of maximum tensile strain value and maximum crack value (crack length, crack area and crack density) for the three SMA mixes were comparable. It was concluded that comparison of fatigue performance and behavior between different mixes can be determined by using this new approach in the laboratory. Based on the obtained results, the control sample had the longest crack length, the highest crack area and crack density followed by COPF P0.6 and EVA P6.0, respectively. The reason could be that the binder used in the control sample was unmodified so that 12
the cracks propagated freely without any barrier to pin down or block the crack movement in the structure. EVA-blended samples had the longest fatigue life and the lowest crack length, crack area and density. Therefore, modification of the original binder with an optimum content of EVA produced a crystallization of rigid three-dimensional networks which could increase the complex modulus and fatigue resistance of the specimen. Significant difference was found between the crack paths of the tested samples. EVA P6.0 sample which had the longest fatigue life obviously showed the macrocrack appearance rather than microcrack. Meanwhile, control sample which placed second in fatigue life exhibited balanced micro and macro cracks. The COPF P0.6 which had the shortest fatigue life obviously had more microcracks compared to the other two types of mixtures.
8
RECOMMENDATION
This study is just a beginning in evaluating the fatigue strength from crack images and appearance. Since the study was limited to three types of mixtures only, it is recommended to explore more mixture varieties in the future studies to improve the confidence of using this approach. Since this paper only looked into the crack on ITFT samples, it might be precious to try other types of fatigue test plus the MMCM software to measure and map the cracks.
REFERENCES [1] Ghuzlan KA, Carpenter SH. Traditional fatigue analysis of asphalt concrete mixtures. Urbana 2002;51:61801. [2] Lundstrom R, Isacsson U. Asphalt fatigue modelling using viscoelastic continuum damage theory. Road materials and pavement design 2003;4(1):51-75. [3] Nguyen MT, Lee HJ, Baek J. Fatigue Analysis of Asphalt Concrete under Indirect Tensile Mode of Loading Using Crack Images. Journal of Testing and Evaluation;41(1):148-158. [4] Braz D, Lopes R, Motta L. Research on fatigue cracking growth parameters in asphaltic mixtures using computed tomography. Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms 2004;213:498-502. [5] Birgisson Br, Montepara A, Romeo E, Roncella R, Napier J, Tebaldi G. Determination and prediction of crack patterns in hot mix asphalt (HMA) mixtures. Engineering Fracture Mechanics 2008;75(3):664-673. [6] Nejad FM, Aflaki E, Mohammadi MA. Fatigue behavior of SMA and HMA mixtures. Construction and Building Materials 2010;24(7):1158-1165. [7] Pell PS. Characterization of fatigue behavior. Highway Research Board Special Report 140; Proceedings of a Symposium on Structural Design of Asphalt Concrete Pavements to Prevent Fatigue Cracking;Washington, 1973:49-64. 13
[8] Khalid HA. A comparison between bending and diametral fatigue tests for bituminous materials. Materials and Structures 2000;33(7):457-465. [9] Brown SF. Material characteristics for analytical pavement design. Development in Highway Pavement Engineering-1 1978;P.S. Pell,ed. Applied Science, London:41-92. [10] Ye Q, Wu S, Li N. Investigation of the dynamic and fatigue properties of fiber-modified asphalt mixtures. International Journal of Fatigue 2009;31(10):1598-1602. [11] Polacco G, Muscente A, Biondi D, Santini S. Effect of composition on the properties of SEBS modified asphalts European Polymer Journal 2006;42(5):1113-1121. [12] Krishnan J, Rajagopal K. On the mechanical behavior of asphalt. Mechanics of Materials 2005;37(11):1085-1100. [13] Di Benedetto H, Soltani A, Chaverot P, Benedetto D. Fatigue damage for bituminous mixtures: A Pertinent Approach Association of Asphalt Paving Technologists 1996;65:142-158. [14] Castro M, Sánchez JA. Estimation of asphalt concrete fatigue curves - A damage theory approach. Construction and Building Materials 2008;22(6):1232-1238. [15] Richardson J. Stone Mastic Asphalt in the UK. Society of Chemical Industry Lecture Papers Series, Symposium on Stone Mastic Asphalt and Thin Surfacings,Wolverhampton, West Midlands, UK 1997. [16] Muniandy R, Huat BBK. Laboratory Diametral Fatigue Performance of Stone Matrix Asphalt with Cellulose Oil Palm Fiber. American Journal of Applied Sciences 2006;3(9):2005-2010. [17] Asi IM. Laboratory comparison study for the use of stone matrix asphalt in hot weather climates. Construction and Building Materials 2006;20(10):982-989. [18] Goos D, Carre D. Rheological modelling of bituminous binders- a global approach to road technologies. Proceedings of the Eurasphalt & Eurobitume Congress, Session 5: Binders-Functional Properties and Performance Testing,E&E5111, Strasbourg,1996. [19] Cavaliere M, Diani E, Sacconi LV. Polymer modified bitumens for improved road application. Proceedings of the 5th Eurobitume Congress, Stockholm 1993;1A(1.23):138-142. [20] González O, Muñoz ME, A.Santamarı́a, Garcı́a-Morales M, Navarro FJ, Partal P. Rheology and Stability of Bitumen/EVA blends. European Polymer Journal 2004;40(10):2365-2372. [21] Yildirim Y. Polymer modified asphalt binders. Construction and Building Materials 2007;21(1):66-72. [22] Sengoz B, Isikyakar G. Evaluation of the properties and microstructure of SBS and EVA polymer modified bitumen. Construction and Building Materials 2008;22(9):1897-1905. [23] British Standards Institution–BS EN 12697-24. Bituminous mixtures - Test methods for hot mix asphalt. In: Part 24: Resistance to fatigue London 2004. [24] Radkeya S. Development of crack meander protocol for the fatigue resistance of stone mastic asphalt mixture using cellulose fibers In: Civil Engineering: Ph.D.dissertation, University Putra Malaysia, 2010. [25] Muniandy R, Selim AA, R.Schaefer V. Effect of the Newly Developed Cellulose Oil Palm Fiber in the Fatigue Cracking of Stone Mastic Asphalt. Transportation Research Board Washington, D.C., 2004. [26] Muniandy R, Hassim S, Jakarni FM, Selim A. Determination of SMA Slab Properties Using a Newly Developed Roller Compactor (Turamesin). In: Transportation and Development, 2008, pp. 505-510. [27] Huang Y. Pavement Design and Analysis. Pearson/Prentice Hall, 2004. [28] Airey GD. Rheological evaluation of ethylene vinyl acetate polymer modified bitumens. Construction and Building Materials 2002;16(8):473-487.
14
PHASE I
PHASE III
PHASE II
Modulus
Number of Cycles
Figure 1: Modulus variation during a fatigue test
Figure 2: Cellulose Oil Palm Fiber
Figure 3: Ethylene Vinyl Acetate
15
Figure 4: A 150 mm diameter specimen under the crack meander mapping jig
Figure 5: MMCM schematic surface plan of a cracked specimen
16
Figure 6: The output from MMCM software for the control sample after 19000 of load cycles
17
Figure 7: Example of crack comparison among various number of load cycles for the control sample
18
150 mm
150 mm
150 mm
600 mm
150 mm
750 mm Figure 8: Slab roller compactor (Turamesin) and 150 mm coring plan
19
(a) Control Sample
(b) COPF P0.6
(c) EVA P6.0
Figure 9: Tensile strain and dynamic modulus versus number of load cycles for various samples
20
Figure 10: Comparison of crack length among control, COPF P0.6 and EVA P6.0 samples
Figure 11: Comparison of crack area among control, COPF P0.6 and EVA P6.0 samples
Figure 12: Comparison of crack density among control, COPF P0.6 and EVA P6.0 samples
21
Figure 13: Comparison of tensile strain plots among control, COPF P0.6 and EVA P6.0 samples
Figure 14: Comparison of trend lines between ∆N/∆ɛ and ∆N/∆CL for all tested samples
22
Figure15: Example of difference between two points in tensile strain graph for ITFT
Figure 16: Comparison of fatigue strength power curves for the Crack Meander and ITFT approaches
23
Table 1: Cylindrical cored samples for fatigue performance test
SMA mixtures Control COPFPO.6 EVAP6.0
No. of cored samples 6 6 6
OAC (%) 5.50 5.86 5.78
Desired air void content (%) 4±0.3 4±0.3 4±0.3
Asphalt binder grade 80/100 80/100 80/100
Table 2: Aggregate gradation for SMA 14, JKR specification
Sieve size (mm) 19.0 12.5 9.5 4.75 2.36 0.6 0.3 0.075 filler
Percentage passing 100 100 72-83 25-38 16-24 12-16 12-15 8-10
Desired (% retained) 0 0 22.5 46 11.5 6 0.5 4.5 9
Table 3: Test parameters for the repeated load indirect tensile fatigue test
Test parameters
Value
Seating force Cyclic loading force Cycle width Loading frequency Temperature Estimated Poisson’s ratio
24
100 N 2500 N 200 ms 2 Hz 20°C 0.35
Table 4: Comparison between ∆N/∆ɛ ITFT and ∆N/∆CL from CM approach Interval (No. of Cycles, N) Control Sample 200-5000 5000-10000 10000-15000 15000-20000 20000-21000 COPF P0.6 500-1000 1000-1500 1500-1900 EVA P6.0 15000-20000 20000-25000 25000-30000 30000-34000
Center Point
∆N/∆ɛ
Interval (No. of Cycles, N)
Center Point
∆N/∆CL
2600 7500 12500 17500 20500
4.04E+06 8.52E+06 7.68E+06 4.68E+06 3.18E+06
2000-5000 5000-10000 10000-15000 15000-20000 20000-21000
4000 7500 12500 17500 20500
64.79 67.49 56.80 62.12 155.38
750 1250 1700
6.86E+05 6.06E+05 4.23E+05
500-1000 1000-1500 1500-1900
750 1250 1700
12.27 6.97 5.17
17500 22500 27500 32000
2.68E+07 1.96E+07 1.09E+07 3.01E+06
15000-20000 20000-25000 25000-30000 30000-34000
17500 22500 27500 32000
924.47 1153.14 391.54 131.75
Table 5: Fatigue evaluation for ITFT and CM analyses
ITFT
∆Nf Control Sample COPF P0.6 EVA P6.0
CM
5.55E+03
1.70E+04
∆Nf / ∆ɛ 6.47E+06
3.55E+02 1.36E+04
3.73E+05 9.03E+06
1.33E+03 2.58E+04
5.84E+05 1.09E+07
25
∆Nf
∆Nf/∆ɛ 4.93E+06
Fatigue evaluation of SMA mixtures using crack meander technique was introduced. ‘Measurement and Mapping of crack Meander’ (MMCM) Software was developed. Crack initiation, propagation and failure were analyzed by MMCM tool. Control sample indicated the maximum crack length, crack area and crack density. Same results were followed by COPF P0.6 and EVA P6.0, respectively.
26