Laboratory Fatigue Evaluation of Modified and Unmodified Asphalt binders in
Stone Mastic Asphalt Mixtures using a newly Developed Crack Meander Tech
Ratnasamy Muniandy, Nor Azurah Binti Che Md Akhir, Salihudin Hassim,
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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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, firstname.lastname@example.org Department of Civil Engineering, University Putra Malaysia, email@example.com Department of Civil Engineering, University Putra Malaysia, firstname.lastname@example.org
Department of Civil Engineering, University Putra Malaysia, email@example.com
Corresponding Author E-mail: firstname.lastname@example.org +60-3-89466373/7847 (+60)123396917
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.
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 . However, Lundstrom et al.  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 .
Therefore, in order to portray the nature of cracks, studying the fatigue crack network and its pattern
seems necessary. Braz et al.  used computed tomography technique to detect crack evolution in
asphaltic mixtures submitted to fatigue test. Birgisson et al.  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
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 . Because of the high
similarity with site conditions, controlled stress mode is widely used . 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
Dynamic reactions are responsible in evaluation of fatigue resistance in bituminous mixtures .
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 
according to Figure 1 . 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
. Although SMA is rut resistance, due to high proportions of coarse aggregates, it shows poor
performance in fatigue resistance due to the reduced amount of fine aggregates . 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 .
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  as well as fatigue of asphalt mixtures . 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 .
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  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
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
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
Sample information and test control parameters in MMCM software were designed based on ITFT
format. This software was developed at UPM  based on 2004 original concept .
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
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...