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: S0142-1123(13)00236-3
DOI: http://dx.doi.org/10.1016/j.ijfatigue.2013.08.021
Reference: JIJF 3198
To appear in: International Journal of Fatigue
Received Date: 7 December 2012
Revised Date: 16 August 2013
Accepted Date: 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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1
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 E-mail: [email protected] +60-3-89466373/7847 (+60)123396917
2
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.
3
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
4
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
5
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
6
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
7
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.
<Insert Figure 5 about here>
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
8
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
9
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
10
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.
11
< 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 ( and the ratio of number of cycles to cause one millimeter of
crack length ( were determined for different load cycle intervals as illustrated in Table 4 and
Figure 14.
<Insert Table 4 about here>
<Insert Figure 14 about here>
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
number of cycles to increase one unit of strain ( in both ITFT and CM methods. For this analysis
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
12
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
13
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.
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[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.Santamarı ́a, Garcı ́a-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.
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Figure 1: Modulus variation during a fatigue test
Figure 2: Cellulose Oil Palm Fiber Figure 3: Ethylene Vinyl Acetate
PHASE IIPHASE I PHASE III
Mod
ulus
Number of Cycles
16
Figure 4: A 150 mm diameter specimen under the crack meander mapping jig
Figure 5: MMCM schematic surface plan of a cracked specimen
17
Figure 6: The output from MMCM software for the control sample after 19000 of load cycles
18
Figure 7: Example of crack comparison among various number of load cycles for the control sample
19
Figure 8: Slab roller compactor (Turamesin) and 150 mm coring plan
150 mm
150 mm 150 mm
150 mm
750 mm60
0 m
m
20
(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
21
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
22
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
23
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
24
Table 1: Cylindrical cored samples for fatigue performance test
Table 2: Aggregate gradation for SMA 14, JKR specification
Table 3: Test parameters for the repeated load indirect tensile fatigue test
SMA mixtures
No. of cored samples
OAC (%)
Desired air void content (%)
Asphalt binder grade
Control 6 5.50 4±0.3 80/100 COPFPO.6 6 5.86 4±0.3 80/100 EVAP6.0 6 5.78 4±0.3 80/100
Test parameters Value Seating force 100 N Cyclic loading force 2500 N Cycle width 200 ms Loading frequency 2 Hz Temperature 20°C Estimated Poisson’s ratio 0.35
Sieve size (mm) Percentage passing Desired (% retained) 19.0 100 0 12.5 100 0 9.5 72-83 22.5 4.75 25-38 46 2.36 16-24 11.5 0.6 12-16 6 0.3 12-15 0.5
0.075 8-10 4.5 filler 9
25
Table 4: Comparison between ∆N/∆ɛ ITFT and ∆N/∆CL from CM approach
Interval (No. of Cycles, N)
Center Point ∆N/∆ɛ
Interval (No. of Cycles, N)
Center Point ∆N/∆CL
Control Sample 200-5000 2600 4.04E+06 2000-5000 4000 64.79
5000-10000 7500 8.52E+06 5000-10000 7500 67.49 10000-15000 12500 7.68E+06 10000-15000 12500 56.80 15000-20000 17500 4.68E+06 15000-20000 17500 62.12 20000-21000 20500 3.18E+06 20000-21000 20500 155.38 COPF P0.6 500-1000 750 6.86E+05 500-1000 750 12.27 1000-1500 1250 6.06E+05 1000-1500 1250 6.97 1500-1900 1700 4.23E+05 1500-1900 1700 5.17 EVA P6.0
15000-20000 17500 2.68E+07 15000-20000 17500 924.47 20000-25000 22500 1.96E+07 20000-25000 22500 1153.14 25000-30000 27500 1.09E+07 25000-30000 27500 391.54 30000-34000 32000 3.01E+06 30000-34000 32000 131.75
Table 5: Fatigue evaluation for ITFT and CM analyses
ITFT CM ∆Nf ∆Nf/∆ɛ ∆Nf ∆Nf / ∆ɛ Control Sample 5.55E+03 4.93E+06 1.70E+04 6.47E+06 COPF P0.6 3.55E+02 3.73E+05 1.33E+03 5.84E+05 EVA P6.0 1.36E+04 9.03E+06 2.58E+04 1.09E+07
26
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.
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