Evaluation of Crack Potency in the Bituminous Concrete using Fracture Mechanics Parameters
Suman SK* and Shrikant
Department of Civil Engineering, NIT Patna, Patna, Bihar, India
Submission: September 04, 2020; Published: September 21, 2020
*Corresponding Author:Suman SK, Department of Civil Engineering, NIT Patna, Patna, Bihar, India
How to cite this article: Suman S, Shrikant. Evaluation of Crack Potency in the Bituminous Concrete using Fracture Mechanics Parameters. Civil Eng
Res J. 2020; 10(5): 555796.DOI: 10.19080/CERJ.2020.10.555796
Fatigue cracking is very critical among all types of distresses in pavements once the fatigue crack start in pavement it led to fast pavement deterioration and thus reduced the life of pavement and quality of riding on pavement. Thus, to control such distress it is necessary to understand the mechanics behind such crack initiation and propagation and to find the fracture parameters to choose best mixture to resist the failure. There are various methods to understand the fracture properties of the bituminous concrete (BC) mix. This paper describes the semi-circular bending test for BC mix, which was designed to be very effective, and user friendly. This method is adopted because it simulates the field conditions and its availability. Semi-circular samples of forty-eight were prepared out of which half was made of unmodified bitumen and the rest were made of plastic modified bitumen. These all samples were then tested at different loading rates and value of load at each deflection is measured. Two fracture parameters like fracture energy and stress intensity factor are evaluated. The plastic modified bituminous concrete shows that the value of energy is increased 2 to 3 times than the unmodified bituminous concrete at intermediate temperature. Hence, plastic modified bituminous concrete has the greater cracking resistance potential.
Crack in the pavement influences the long-term durability of the bituminous concrete. The highways maintenance and management could not be done without considering the characteristics and fracture resistance of the bituminous mix during the life of the pavement. The life of the pavement depends upon the fracture resistance and the characteristics of bituminous mix, which is indirectly, affect the pavement maintenance and the management. Crack in the pavement may occur due to the low temperature, fatigue and moisture . Thus, it is very necessary to analyses the cracking behaviour of bituminous concrete. The cracking behaviour of bituminous mix were studied by the various researchers at the low temperature using linear elastic fracture mechanics. But in India, the temperature in the most of the area found to be moderate and on the other hand continues use of plastic in the construction of road; require a complete study on these two aspects. The aim of this paper is to estimate fracture parameters of bituminous concrete at the moderate temperature and at different loading rates with or without modification of plastic.
Ozer Hasan (2009) studied about the use of recycles materials in the construction of bituminous concrete (BC) pavement that
improves the sustainability of BC pavement because it reduces the initial of cost of construction . The fracture resistance of BC mix was obtained by conducting the semi-circular bending test and flexibility index. It was calculated from load-displacement profile obtained during the test. The result shows that flexibility index is the best parameter to understand the fatigue failure of BC pavement in the field. Zegeye (2011) carried out studies on four SCB samples which was prepared with different diameters such as 76.4 mm, 101 mm, 147 mm, and 296 mm. Every diameter size sample was notched to obtain notch to radius ratio 0, 0.05, 0.2. The test result shows that less specimen crack start from far end in larger diameter notch. Strength was decreased as the diameter of samples increased thus sample having diameter above 150 mm is not of any practical use. Krishna Saha Gourab (2016) investigated fracture behavior of DBM, open-graded and gap graded using SCB test. Fracture parameters were obtained from load-displacement profile and these parameters were used to evaluate the fracture damage. The damage model was also developed based on energy and material behavior. The results show that energy dissipation was nearly 2 times more than conventional mix. Pirmohammad S. (2012) studied the effects of temperature and loading mode on fracture resistance of BC mix under constant loading. The result shows that under different loading mode and temperature
fracture resistance first increase and then start decreasing
below fix temperature i.e. 20 °C. The minimum value of fracture
resistance under mixed mode is said to be the fracture index. The
fracture index was used further for crack growth analysis in the
BC mix. The test result also shows that at the low temperature
modified mix shows more fracture resistance than normal mix.
Krishna Saha Gourab (2017) investigated fracture behavior of
DBM for open-graded and gap graded using SCB test. Fracture
parameters were obtained from load-displacement profile and
these parameters were used to evaluate the fracture damage
. The damage model was also developed based on energy and
There are various fracture test configurations, which were
used by many researchers to determine the fracture parameters.
Testing methods are single notch beam, semi-circular bending,
indirect tensile strength and disk shaped tension compact test.
These all test configurations have their own advantages and
disadvantages. Semi-circular bending test is used to analyse
mixed mode failure. In the linear elastic fracture mechanics
approach stress intensity factor is considered as the main factor
for describing the fracture behaviour of the elastic material. While
in the viscos-elastic material such as bituminous concrete fracture
energy better represents the resistance to the crack instead of
stress intensity factor.
One crucial parameter when addressing cracking resistance is
the fracture energy, which is the energy required to produce a unit
surface area crack. In asphalt specimen, the load initially creates
an elastic strain that may trigger a fracture. If this happens,
the energy is then used to propagate the cracking and deform
the specimen [4-5]. It is very difficult to measure the fracture
parameters of the bituminous concrete because of viscos-elastic
nature. Normalized fracture energy was calculated by area of
load-deflection diagram. The load-deflection curve was formed
from the values of load and deflection noted down from machine
during testing. Fracture energy was normalized by dividing the
area of load-deflection by area of ligament of specimen which is
equal to (w-a) t. Normalization of energy decrease the effect of
notch length and size of specimen.
Thus, fracture energy represents the fracture work and in
other words energy dissipated in resisting the fracture in the
bituminous concrete. In this work this concept will be used to
determine the fracture properties of bituminous concrete at
different loading rates and bitumen contents with or without
During the testing of specimens, load and deflection values are
obtained and these values are plotted and thus, a load-deflection
curve is obtained. ASTM also presented the standard loaddeflection
curve as mentioned in the Figure 1. Load-deflection
curve indicates that value of load is increased linearly with
deflection. Thus, the value of the stress intensity factor increases
as the load increase and as the load reaches to the maximum
value crack is initiated and value of stress intensity factor become
Since 1970 concept of fracture energy and stress intensity
factor is used for the evaluation of fracture properties of bitumen
mix. M. Fakhria et. al. studied the effect of moderate temperature
and void ratio on the fracture energy. Ozer Hasan studied that
the use of recycle materials in the construction of bituminous
concrete pavement improves the sustainability of pavement [6-7].
However, literature study shows that mixed mode failure of plastic
modified bituminous concrete at intermediate temperature rarely
Mainly three types of crushed aggregates was taken in this
work namely coarse aggregate 20mm passing (CA1), coarse
aggregate 10mm passing (CA2) and fine aggregate (sand -zone III).
Cement (PPC) is used as the filler. Properties of coarse aggregates
indicated in the Table 1. Grading system for bituminous concrete
(BC) is presented in the Table 2 as per Ministry of road transport
and highways (MORTH) specifications.
The plastic waste shredded to the size varying between
2.36mm and 4.75mm is used to coat the aggregate surface by dry
process. This shredded plastic waste is added over hot aggregate
(170 °C) with constant mixing to give a uniform distribution.
Bituminous concrete mix is prepared with and without
plastic modified. A specimen of size 150mm diameter and
50mm thickness is prepared in modified Marshal Mould. The
graded materials are heated to temperature of 170 to 190°C. The
bitumen binder is heated to temperature 120 - 165°C. The mixing
temperature for VG 30 is 160°C and compacting temperature is
149°C. Mix was poured in the mould and compacted by hammer
at recommended temperature, by applying 75 blows on each side
of specimen. After compaction, the specimen was allowed to cool
down to the room temperature. In order to prepare the plastic
modified specimens same procedure was followed but 8 % (by
the weight of bitumen) shredding plastic was added to the heated
aggregate. Prepared specimens were drilled concentrically with
the diamond drill of 16 mm diameter. In order to obtain the semicircular
specimen, the drilled specimens were used to cut along
diametrically. A notch of 10 mm length was also cut in each semicircular
specimen Figure 2 & Figure 3.
Initially, the two supports made of concrete were placed 120
mm apart on the circular plate of machine. Then after, specimen
was placed on these two supports, the marked points on the
specimen were exactly meeting with the inner face of supports
thus, clear span of 120 mm were obtained. A strip of small width
was placed exactly in the same line of notch (so as to obtain the
predefined crack path) on top of specimen in order to convert load
into point load. Thereafter, load plunger (50 mm) were placed
on the top of the strip. The strain gauge was calibrated and set
on the circular plate of machine because plate move with same
amount as deflection Thereafter, machine was started and set the
initial reading of load and deflection zero. The load rate was first
set at the 1.25 mm/min, value of load and corresponding value of
deflection were depicted on the display. As the load was increased
the specimen start store the energy, after reaching the load up to
maximum value at which specimen start cracking, the machine
was stop [8-10]. In order to understand the effect of loading
rate on the energy stored in the specimen, second specimen of
same bitumen content was tested at different loading rate i.e.
1.5 mm/min and same procedure as above was followed. Testing
arrangement is shown in Figure 5 and crack shown in Figure 6.
Semi-circular bending test is performed on the bituminous
mix samples. Samples consists of bitumen content from 4.5% to
6% with increment of 0.5% in the mix and tested at two rate of
loading 1.25mm/min and 1.5mm/min. Observed load - deflections
data are applied to plot graphs for determination of area to be
used in fracture energy. Load-deflection graphs for unmodified
bituminous concrete (UMBC) are shown in Figures 7-14. Fracture
energy is determined using Eqn.1 is tabulated in the Table 4.
The value of fracture energy increases with increase of bitumen
content up to bitumen content 5 % then after decreases for both
the rate of loading. Similar trend has been also found by the
Rodrigo et. al. The value of fracture energy is increased by about
two times as the loading rate increases from the 1.25 mm/min to
the 1.5 mm/min.
Likewise, load-deflection graph for plastic modified
bituminous concrete are drawn at both the rate of loadings.
Afterwards, fracture energy is computed and tabulated in the Table
5. The value of fracture energy increases with increase of bitumen
content upto 5% at both rate of loading then after decreases. It
has been observed that fracture energy at 1.5mm/min rate of
loading is approximately 1.12 times more than 1.25mm/min
rate of loading. However, plastic modified bituminous concrete
has more ability to absorb mechanical energy in the mix than the
unmodified bituminous concrete.
The value of stress intensity factor increases as the bitumen
content increases; the same result also presented by the Rodrigo
et. al.  The result shows that fracture resistance increases with
the bitumen content means chance of crack grow in bituminous
concrete get decreases Table 6. Values mentioned in the Table 7
show that as the bituminous concrete is modified with the plastic
value of stress intensity factor is increased by 2 to 3 times with
respect to the unmodified bituminous concrete [12-13]. The effect
of loading is remained same as in the unmodified bituminous
concrete means the value of stress intensity factor is increased as
the loading rate increases from the 1.25 mm/min to the 1.5 mm/
min. Thus, the results obtained from the fracture energy concept
are supported by another approach i.e. stress intensity factor.
Total 48 semi-circular specimens were tested at different
bitumen contents and loading rates. The 24 specimens were
tested with the unmodified bituminous concrete. In order to
check the effect of plastic modification in the bituminous concrete,
the remaining specimens were prepared with plastic modified
bituminous concrete. The value of fracture energy and stress
intensity factor were then compared and found.
i. Value of fracture energy increases as the bitumen
content increases but only up to 5 %, after this bitumen content
the value of fracture energy start decreasing. Thus, this result
shows that at intermediate temperature, the value of fracture
energy is maximum at nearly optimum bitumen content in the
ii. Effect of loading rates were also checked in both
unmodified and plastic modified bituminous concrete at
intermediate temperature. The result shows that as the loading
rate increases from 1.25 to 1.5 mm/min the value of energy is
also increased, it means that at high loading rate more energy
dissipation is required to grow the crack in the bituminous
concrete. The high loading represents the high speed of load
iii. The modification of plastic in bituminous concrete shows
that at intermediate temperature, the value of energy is increased
2 to 3 times with respect to the unmodified bituminous concrete.
The result shows that modification of bituminous concrete with
the plastic enhance the fracture properties of bituminous concrete
i.e. fracture resistance.
iv. The fracture energy is the best fracture parameters for
viscos-elastic material but in order to check the validation of
the results, the value of stress intensity factor also checked. The
value of stress intensity factor increases as the bitumen content
increases. The value of stress intensity factor increases as the
loading rate is increased from 1.25 to 1.5 mm/min.
The values stress intensity factor increases as the bituminous
concrete is modified with the plastic. This result shows that more
stress requires growing the crack for plastic modified bituminous
concrete. The stress intensity factor supports the results
obtained from energy concept.