Propagation Mechanisms for Surface Initiated Cracking in Composite Pavements


  Al-Khwarizmi 

Engineering   

Journal Al-Khwarizmi Engineering Journal,  Vol. 5, No. 3, PP 51  - 59  

(2009) 

 

 

Propagation Mechanisms for Surface Initiated Cracking  

in Composite Pavements 
 

 Zainab Ahmed Alkaissi*       Duraid Ali Al Khafagy** 
Department of Civil Engineering/ University of Al-Mustansiriya 

  * Email: Zainabalkaisi77@yahoo.com 
** Email: djeeran2005@yahoo.com 

 
(Received 3 February 2009; accepted 2 June 2009) 

 

 

Abstract: 

 
 The primary objective of this study was to identify the mechanisms for the development and propagation of 
longitudinal cracks that initiate at the surface of composite pavement. In this study the finite element program ANSYS 

version (5.4) was used and the model worked out using this program has the ability to analyze a composite pavement 

structure of different layer properties. Also, the aim of this study was modeling and analyzing of the composite 

pavement structure with the physical presence of crack induced in concrete underlying layer. The results obtained 

indicates that increasing the thickness of the asphalt layer tends to decrease the stress intensity factor, which may be 

attributed to the rapidly decrease of horizontal tensile stress in the asphalt layer. The cracks initiate at the surface due to 

high vertical stress and shear stress from wheel loads tends to propagate downward due tensile stress generated at the 

bottom of the asphalt layer or near crack tip, and the whole process occur at the same location of the existing cracks in 

underlying concrete layer rather than travel up from existing crack. As the load position varies from the crack zone, this 
result in tensile stresses or tension at the crack tip, leading to increase the stress intensity factor and intern result in 

crack propagation further into the depth of the pavement. 

 

Key Words: Finite element; pavement model; crack propagation; composite pavement; stress intensity factor; stress 

distribution; crack initiation; horizontal tensile stress. 
 

 

1.  Introduction 

 
 Cracking of road pavements is one of a major 

source of distress in roadways. A model that is 
able to simulate the initiation and propagation of 

cracks in asphalt layer is highly desirable. It will 

provide an insight into these distress mechanisms 
and help improve mechanistic design procedure 

for cracks.  

 The primary objective of this study was to 
identify the mechanisms for the development and 

propagation of longitudinal cracks that initiate at 

the surface of bituminous pavements. Also 

investigate the stress state (horizontal tensile 
stress and vertical stress within composite 

pavement structure), and how affect on the 

direction of crack propagation. Moreover, the aim 
of this study was modeling and analyzing of 

composite pavement structure with the physical 

presence of crack induced in concrete base layer, 

which result in the critical condition for top-down 
crack propagation. 

 

 

2.  Literature Review 
 
 For cracking problems, a natural solution 
would be to use fracture mechanics (Anderson, 
1995). The single parameter could be either stress 

intensity factor K ( or equivalency energy release 

G) or j integral, depending on the size scale of the 
yielding of the material: the basis for the use of 

this approach is that the stress and strain field in 

the small zone ahead of the crack tip (called 

fracture zone , or FPZ) in which fracture occurs is 
controlled by a signal parameter, the stress 

intensity factor (Canga et. al.,2001). 

mailto:Zainabalkaisi77@yahoo.com
mailto:djeeran2005@yahoo.com


Zainab Ahmed Alkaissi                        Al-Khwarizmi Engineering Journal, Vol. 5, No. 3, PP 51 -59  (2009) 
 

52 

 The traditional fatigue approach and the 
distortion energy approach both implement 

analysis of a homogeneous continuum pavement.  

 The distortion energy approach is being used 
by some researchers (Kim et.al., 1997). The 

fatigue life of asphalt mixtures under cyclic 

loading conditions was found from relationship 

between pseudo-stiffness and number of loading 
cycles. The damage mechanics model can then 

predict damage growth for local load conditions 

with different loading rates and rest periods; 
however, in reality, it attempts to simulate the 

conditions for a cracked pavement. The physical 

presence of the crack is omitted, and the stress 

redistributions that result from crack growth are 
not captured.  

 Definition of the traditional fatigue approach 

to pavement evaluation has been cited in some 
publications (Huang, 1993; Yoder and Witzak, 

1975). The existing approach to performance 

prediction is broad and classifies pavement failure 
types that have been studied several times. The 

theories reviewed included the traditional fatigue 

approach, distortion energy approach, damage 

mechanics and fracture mechanics. Although it 
would possible to use any of the methods 

examined for predicting failure, it was determined 

that the combination of using finite element 
modeling and fracture mechanics was most 

appropriate for best analysis the behavior of crack 

growth and critical conditions at crack tip (Collop 
and Cebon,1995). 

 Analysis of cracked asphalt pavement has been 
studied using the ABAQUS finite element 

computer program and show that the mechanism 

of crack failure was tension. Also the load 
position and base stiffness for flexible pavement 

affect on crack propagation and confirmed 

observation of crack growth in the field (Leslie et. 

al., 2001). 
 

 

3. Description of Finite Element Model for 

Composite Pavement Structure 

 
 The finite element numerical analysis allows 

for physical representation of cracks and 

discontinuities in pavement structure. In this study 
the finite element program ANSYS version (5.4) 

was used. The model worked out using this 

program has the ability to analyze a composite 
pavement structure of different layer properties. A 

typical schematic of composite pavement 

structure is shown in Figure (1) was analyzed to 

investigate the possible mechanisms of cracking 
initiation and propagation. The entire composite 

pavement system (i.e., asphalt layer, old concrete 

layer, base and subgrade) was modeled, loaded 
with measured contact stresses and analyzed for 

pavement response. The input material properties 

for composite pavement layers are shown in 
Table(1). 

 

 

  

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

                 

 

 

 

 

 

 

 
Fig. 1. Schematic Representation of Composite Pavement Structure. 

Subgrade 

Subbase 

Concrete Base 

   Asphalt                                     Reflection Crack (2.54-15.24) cm 

 15-25 cm 

20 cm  

30 cm 



Zainab Ahmed Alkaissi                        Al-Khwarizmi Engineering Journal, Vol. 5, No. 3, PP 51 -59  (2009) 
 

53 

Table 1,  

Input Material Parameters for Composite Pavement Layers. 

PARAMETERS 

LAYERS 

Asphalt layer Concrete layer Base Layer Subgrade Layer 

  0.35 0.2 0.35 0.4 

C(kPa) 158 16.8 9.2 5.7 

1
 (degree) 26.3 10 30 25 

 

 
 The analysis procedure was repeated for each 

time of different loading position, asphalt layer 

thickness and crack length. Also, to represent the 

reflective cracking in composite pavement a crack 
have been induced by applying a space gap in 

concrete in the underlying concrete layer equal to 

crack length to investigate the effect of reflection 
crack that appears at top pavement surface. 

 A plane 42, 2-D structural solid has been 

adopted in this research. The element can be used 
as a plane element (plane strain or plane stress) or 

as an axisymmetric element. The element is 

defined by four nodes having two degrees of 

freedom at each node, translations and the nodal x 
and y directions. The element has plasticity, and 

large strain capability. 

 

  

4.  Results and Discussions 
 
 The structural model and the finite element 

mesh of composite pavement is described in 
Figure (6) to investigate the possible mechanisms 

of cracking in asphalt layer taking into 

consideration the effect of pavement structure and 
load spectra.  

 Generation of finite element mesh and defining 

load ,boundary conditions as shown in Figure (6). 
It preferable to use finite element in places were 

high stress or strain gradients are expected, 

therefore the mesh consists of fine mesh close 

loaded area and at the layers interface, the left and 
right vertical boundary are constrained to move 

only in vertical direction whereas those on bottom 

boundary are all fixed, the rest of the nodal point 
including those on surface are unconstrained as 

shown in Figure (6). 

 The load case studied is a rectangular domain 

representation with uniform distribution within 

the rectangular. For uniform stress distribution 

analysis, a contact radius of .136 m (5.35 inch) is 

assumed for a single tire. The radius is based on 

80 kN (18 kip) single axle load with a contact 
pressure of 690 kPa (100 psi). 

         Computing strains, stresses displacement 

and stress intensity factor and finally converted 
the obtained results into graphical outputs for ease 

understanding and discussions as shown in next 

section. 
 A comprehensive parametric study was 

conducted to determine the effects of load spectra 

(magnitude and position) and pavement structure 

on crack propagation. Different thickness values 
for the asphalt layer are considered, ranging from 

lightly trafficked to heavily trafficked pavement 

(1-6) inch (2.54-15.24) cm. The results of stress 
and stress intensity factor are obtained using the 

ANSYS Version (5.4) finite element computer 

program. 
 Figure (2) shows the variation of stress 

intensity factor with the thickness of asphalt layer 

for top and bottom of asphalt layer. The shape of 

curve for top is similar to that at bottom of asphalt 
layer, and the only difference is that the stress 

intensity factor for bottom crack is less than the 

surface crack. Increasing the thickness of asphalt 
layer tend to decrease the stress intensity factor. 

This can be attributed to the rapidly decrease of 

horizontal tensile stress in the asphalt layer as 

shown in Figure (3). And the initiation of cracks 
is due to high vertical stress applied due to wheel 

traffic loading at the asphalt surface layer. This is 

confirmed with results obtained for vertical and 
horizontal stress distribution in the whole 

structure of pavement as shown in Figure (4) and 

(5) respectively. 
 

 



Zainab Ahmed Alkaissi                        Al-Khwarizmi Engineering Journal, Vol. 5, No. 3, PP 51 -59  (2009) 
 

54 

0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18

Thickness of Asphalt Layer (m)

0.0

0.5

1.0

1.5

2.0

S
t
r
e
s
s
 I

n
t
e
n

s
it

y
 F

a
c
t
o

r
 (

M
p

a
) Bottom of asphalt layer

Top Asphalt Layer

 
 
Fig. 2. Variation of Stress Intensity Factor with 

Thickness of the Asphalt Layer. 

 

 

0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16

Thickness of Asphalt Layer (m)

40

50

60

70

80

90

100

110

  
H

o
r
iz

o
n

t
a

l 
T

e
n

s
il

e
 S

t
r
e
s
s
 a

t

 B
o

t
t
o

m
 o

f
 A

s
p

h
a

lt
 L

a
y

e
r
 (

k
P

a
)

 
 
Fig. 3. Effect of Thickness on Horizontal Tensile 

Stress at Bottom of the Asphalt Layer. 

 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Fig. 4. Vertical Stress Distribution within Pavement Structure. 

 

 
 

 Finite element analysis of the cracked 

pavement was conducted to define the critical 

design conditions at which crack growth will 
occur. A finite element mesh of the cracked 

pavement was modeled by induced a gap spacing 

for crack length at the concrete base layer to 
simulate the composite pavement structure as 

shown in Figure (6). 

 Figure (7) shows the stress intensity factor at 

pavement surface as a function of crack length 

already exist in the concrete base layer of the 
composite pavement. It can be noticed that the 

increase in crack length result in higher stress 

intensity factor at the surface of pavement which 
result in a reflection cracks that appears and 

exhibit on most composite pavement. Also this 

can be seen in Figure (8) which shows the stress 



Zainab Ahmed Alkaissi                        Al-Khwarizmi Engineering Journal, Vol. 5, No. 3, PP 51 -59  (2009) 
 

55 

intensity factor for whole pavement structure. 
This confirmed the generation of cracks at surface 

and propagates downward. It may concluded that 

cracks are initiated at surface due to high vertical 

and shear wheel stress applied then tend to 
propagate downward due tensile stress generated 

at the bottom of asphalt layer.  

 
 

 

 

 
 

 

 
 

 

 

 
 

 

 
 

 

 
 

 

 

 
 

Fig. 5. Horizontal Stress Distribution within Pavement Structure. 

 

 
 

 

 
 

 

 

 
 

 

 
 

 

 
 

 

 

 
 

 

 
 

 

 
Fig. 6. Finite Element Mesh Induced Crack in the underlying Concrete Layer. 

 

 

 



Zainab Ahmed Alkaissi                        Al-Khwarizmi Engineering Journal, Vol. 5, No. 3, PP 51 -59  (2009) 
 

56 

 
 

 

 
 

 

 

 
 

 

 
 

 

 

 
 

 

 
Fig. 7. Variation of Stress Intensity Factor at Pavement Surface with Crack Length. 

 

 

 
 

 

 
 

 

 

 
 

 

 
 

 

 

 
 

 

 
 

 

 
 

Fig. 8. Variation of Stress Intensity Factor within Pavement Structure. 

 

 
 Also it can be concluded that reflection cracks 

initiate and propagate at the same location of the 

existing cracks in underlying concrete layer since 

its represent the weak zone in pavement structure 
rather than travel up from down crack.  

 To study the effect of load spectra, different 

load positions are considered in this study, which 
they are important factors to induce critical stress 

and strain. The finite element model was analyzed 

at four different loading positions as shown in 

Figure (9), relative to crack location (tire’s widest 

rib over crack, 25, 40, 50, and 70) cm and the 

obtained results for stress intensity factor are 

shown in Figure (10). It can be seen from figure 
that intensity factor increases with radial distance 

from load positions, which can be attributed to the 

horizontal tensile stresses that generated near the 
crack zone as shown in Figure (11). As the load 

position varies from the crack, this results in 

tensile stresses or tension at the crack tip, leading 

4 6 8 10 12 14 16 18 20 22

Crack Length (cm)

0.50

1.00

1.50

2.00

S
tr

e
ss

 I
n

te
n

si
ty

 F
a

c
to

r
 (

M
P

a
)



Zainab Ahmed Alkaissi                        Al-Khwarizmi Engineering Journal, Vol. 5, No. 3, PP 51 -59  (2009) 
 

57 

to increase the stress intensity factor and intern 
result in crack propagation further into the depth 

of pavement. And throughout the asphalt layer 

depth, the crack propagate straight down into the 

pavement by tension then after the direction or 
crack propagation change due to stress state 

change with depth. 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 
Fig. 9. Finite Element Mesh Induced Crack in the underlying Concrete Layer for Different Loading 

Positions. 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 
Fig. 10. Variation of Stress Intensity Factor with Loading Position. 

 

 

 

 

0 10 20 30 40 50 60 70 80

Local Positioning from Center

 Line of Wheel Loading (cm)

0.80

0.85

0.90

0.95

1.00

1.05

S
tr

e
ss

 I
n

te
n

si
ty

 F
a

c
to

r
 (

M
P

a
)



Zainab Ahmed Alkaissi                        Al-Khwarizmi Engineering Journal, Vol. 5, No. 3, PP 51 -59  (2009) 
 

58 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 
Fig. 11. Horizontal Stress Distribution within Pavement Structure (Local Positioning From Center of 

Loading 50 cm). 

 

 

5. Conclusions 

 
 The main concluding remarks can be 
summarized as follows: 
 

1. Increasing the thickness of the asphalt layer 
tends to decrease the stress intensity factor. 

Which may be attributed to the rapidly 

decrease of horizontal tensile stress in the 
asphalt layer. And the stress intensity factor 

for bottom crack is less than the surface crack. 

2. The generation of cracks at the surface and 
propagate downward. It’s initiate at surface 

due to high vertical and shear wheel stress 

applied then tend to propagate downward due 
tensile stress generated at the bottom of 

asphalt layer or near crack tip. Also the crack 

initiate and propagate at the same location of 

the existing cracks in underlying concrete 
layer rather than travel up from down crack.  

3. As the load position varies from the crack 
zone, this result in tensile stresses or tension 
at the crack tip, leading to increase the stress 

intensity factor and intern result in crack 

propagation further into the depth of the 
pavemen 

 

6. References 

 
[1] Anderson, T. (1995): “Fracture Mechanics”, 

CRC Press, and 2nd Edition. 

[2] ."ANSYS Manual", Version (5.4), USA, 
1996. 

[3] Canga, M. , Becker, E., and Ozupek, S. 
(2001): “Constitutive Modeling of 
Viscoelastic Materials with Damage 

Computational Aspects”. Computer Methods 

in Applied Mechanics and Engineering, 

Vol.190, PP: 15-17. 
[4] Collop, A and Cebon, D. (1995): “A 

Theoretical Analysis of Fatigue Cracking in 

Flexible Pavements”. Proceedings, Institution 
of Mechanical Engineers, Vol. 209, pp. 345-

361. 

[5] Huang, H.Y. (1993): “ Pavement Analysis 
and Design ”. Prentice-HALL, Englewood 
Cliffs, New Jersey. 

[6] Yoder, E. and Witczak, M.  (1975): 
“Principles of Pavement Design ”. John Wiley 
and Sons, New York. 

[7] Kim, Y. R., Lee, H., and Little, D.  (1997): 
“Fatigue characterization of Asphalt Concrete 
using Viscoelasticity and Continuum Damage 

Theory”. Journal of the Association of 

Asphalt Paving Technologists, Vol.66, 

pp.520-569. 
[8] Leslie, A., Reynaldo, R. and Bjorn, B. (2001): 

“Propagation Mechanisms for Surface- 

Initiated Longitudinal Wheel Path Cracks ”. 
Paper Presented at the 80

th
 Annual Meeting, 

TRB, Washington, D.C, USA, January 2001, 

01-0433. 



 59 - 51، صفحة 3، العذد 5مجلة الخوارزمي الهنذسية المجلذ                                                            زينب احمذ القيسي
(200 9) 

 

59 

 

ميكانيكية انتشار الشقوق في التبليط المركب 
 

    دريذ علي الخفاجي    * زينب احمذ القيسي
 انجايعح انًسرُظزٚح/ كهٛح انُٓذسح / لسى انُٓذسح انًذَٛح * 

 

 

 

الخالصة 

فٙ ْذِ انذراسح ذى .  اٌ انٓذف االساسٙ يٍ ْذِ انذراسح ْٕ نرعٍٛٛ انًٛكاَٛكٛح نرٕنذ ٔاَرشار انشمٕق انطٕنٛح انرٙ ذُشا فٙ سطح انرثهٛظ انًزكة

انٓذف يٍ ْذِ انذراسح كاٌ عًم .  انذ٘ نّ انماتهٛح عهٗ ذحهٛم ذزكٛة انرثهٛظ انًزكة تاخرالف خٕاص طثماذANSYSّاسرخذاو تزَاج انعُاطز انًحذدج 

اٌ انُرائج انرٙ ذى انحظٕل عهٛٓا ذضًُد اٌ سٚادج سًك طثمح . يٕدٚم ذحهٛهٙ نرزكٛة انرثهٛظ انًزكة يع ٔجٕد أ اَشاء شك فٙ طثمح انكَٕكزٚد انرحرٛح

اٌ انشمٕق ذُشا فٙ سطح انرثهٛظ َرٛجح االجٓاداخ . االسفهد ٕٚد٘ انٗ َمظاٌ يعايم شذج االجٓاد  ٔانذ٘ ٚعشٖ انٗ َمظاٌ اجٓاداخ انشذ فٙ طثمح االسفهد

انعًٕدٚح ٔاجٓاداخ انمض انكثٛزج انًرٕنذج يٍ احًال انعجهح انًسهطح ثى ذسرًز اسفم تسثة اجٓاداخ انشذ انًرٕنذج اسفم طثمح االسفهد أ تمزب حاف انشك 

اٚضا . ٔاٌ ْذِ انعًهٛح ذحذز تُفس يكاٌ انشك انمذٚى انًٕجٕد فٙ انطثمح انكَٕكزٚرح انرحرٛح تعكس يا ْٕ يعزٔف تاٌ انشمٕق ذسرًز يٍ االسفم انٗ االعهٗ

اخرالف يٕلع انحًم يع يُطمح انشمٕق ٚسثة اجٓاداخ شذ فٙ حافح انشك ٔٚؤد٘ انٗ سٚادج يعايم شذج االجٓاد ٔتذٔرِ ٚسثة اسرًزار ذٕنذ انشمٕق فٗ عًك 

 .انرثهٛظ