Evaluation of temperature and loading rate effect on fracture toughness of fiber reinforced asphalt mixture using edge notched disc bend (ENDB) specimen

Construction and Building Materials 234 (2020) 117365

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Evaluation of temperature and loading rate effect on fracture toughness of fiber reinforced asphalt mixture using edge notched disc bend (ENDB) specimen Hamed Motamedi a, Hassan Fazaeli b,⇑, M.R.M. Aliha c, Hamid Reza Amiri a a b c

Department of Civil Engineering, Yazd Branch, Islamic Azad University, Yazd, Iran Islamic Azad University-North Tehran Branch, Vafadar Blvd., Shahid Sadoughi St., Hakimiyeh Exit, Shahid Babaee Highway, Tehran, Iran Welding and Joining Research Center, School of Industrial Engineering, Iran University of Science and Technology (IUST), Narmak, 16846-13114, Tehran, Iran

h i g h l i g h t s
The mode I and III fracture resistances were increased by increase the fiber content.
Influence of fiber was more pronounced for mode III case.
Both KIc and KIIIc became more by decreasing the test temperature and increasing the loading rate.
The temperature had more significant effect on mode III fracture toughness value.

a r t i c l e

i n f o

Article history: Received 1 December 2018 Received in revised form 8 October 2019 Accepted 23 October 2019

Keywords: Fracture toughness Edge notched disc bend specimen Fiber reinforced asphalt mixture

a b s t r a c t A number of specimen configuration and testing method have been developed till now for determining the fracture toughness of asphalt concrete. The Edge Notch Disc Bend (ENDB) specimen is among the suitable test specimens in this regard due to its some primary advantages such as simple geometry and testing procedure and also covering different combination of mode I and III fracture case. In this paper the influence of fiber, temperature and loading rate is investigated experimentally on mode I and III fracture toughness of asphalt mixtures tested with the ENDB specimen. The fracture toughness experiments were conducted on three different low temperature value, three loading rates and different fiber percentages. Ó 2019 Published by Elsevier Ltd.

1. Introduction The viscoelastic behavior of asphalt mixtures as composite materials made of bitumen and aggregate, results in different response under variable temperature and loading rate. For high or intermediate temperature and lower loading rates, degradation of asphalt concrete takes place due to rutting, bleeding or slippagecracking mechanism. In contrary, by decreasing the temperature which results in dominantly elastic and brittle behavior of binder, crack growth and brittle fracture is common mode of failure in asphalt pavements. Such thermal top-down cracks can gradually grow and extend downward by passing the vehicles and traffic loading.

⇑ Corresponding author. E-mail addresses: [email protected] (H. Motamedi), [email protected] (H. Fazaeli), [email protected] (M.R.M. Aliha), [email protected] (H. Reza Amiri). https://doi.org/10.1016/j.conbuildmat.2019.117365 0950-0618/Ó 2019 Published by Elsevier Ltd.

High temperature distresses in asphalt pavement can be controlled easier than the thermal crack initiated in the surface of road. Therefore, investigation of strength and performance of asphalt mixtures and increasing the resistance of pavement against cracking or other distresses is an important issue for designer, manufactures and constructor of roads and highways. The use of binder modifiers such as Polyphosphoric Acid (PPA), Styrene Butadiene Styrene (SBS), Ethyl Vinyl Acetate (EVA), FT-Paraffin Wax (Sasobit), and Crumb Rubber are known as suitable solution for enhancing the performance of asphalt mixtures at moderate and high temperatures conditions by modifying the rheological characteristics of the binder [1–10]. In addition, the use of fiber with high tensile strength provides positive influence on the strength and integrity of asphalt pavement both under high and low temperature conditions. Different researchers have investigated the effect of glass, polyester, carbon, cellulose and aramid fibers on the mechanical properties such as rutting, fatigue life, tensile strength and cracking resistance of asphalt concretes and showed that the mentioned fibers can

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increase in general the performance and durability of pavements [11–15]. For example, recently Fazaeli et al. [16] enhanced the low temperature performance of Warm Mix Asphalt mixtures (WMA) by adding aramid fibers in the composition of WMA mixtures. Since pavement cracking at low temperature is a major failure mode in such constructional materials, several methods and techniques have been employed by the researcher to investigate the fracture behavior of asphalt mixtures. Among these methods, the concepts and principals of fracture mechanics has received much attention. Accordingly, a large number of numerical, experimental and theoretical studies are available in the literature for explaining the fracture behavior of asphalt mixture using some parameters like Stress Intensity Factor (SIF) or fracture energy [17–31]. Ameri and coworkers [17] analyzed a 3D pavement containing a semicircular top-down crack in the surface of road and by performing several finite element analyses, they demonstrated that depending on the location of moving traffic load relative to the crack, different combinations of mode I, II and III crack deformation are introduced in the crack. Base on this research work, the mode III (either under pure or mixed mode tension-tear) can contribute in the process of pavement cracking. Other researcher has focused on the fracture mechanism of asphalt mixture under the influence of pure shear (i.e. mode II) or mixed mode I + II conditions. For example, Aliha and coworkers [28–31], studied the fracture mechanism of asphalt mixtures made of base binder and different modified polymeric bitumen under mode I, mode II and mixed mode I/II loading conditions. Base on their results, pure tensile type (i.e. mode I) is not necessarily dominate and critical mode of cracking in asphalt concrete pavements. In their research, they used the SCB samples as one of the most widely used specimen for testing the fracture toughness of asphalt mixtures. The fast and easy fabrication and coring of samples, easy molding and the possibility of simulating a failure test in different modes, such as displacement of the support, change in position and angle of crack are the most important advantages of this test geometry. However, the fracture behavior of asphalt mixture under the influence of mode III (i.e. out–of plane sliding) deformation has rarely been investigated in the past. The works performed by Avci et al [32] using the inclined edge cracked three-point bend beam specimen is one of the very limited research works in this regard that was conducted to investigate mixed mode I + III fracture toughness of a polymeric concrete. But the mentioned test specimen was not able to produce pure or dominantly mode III loading condition. Other test specimens like Compact – Tension Specimen employed by Edward and Hesp [33] and Wagoner et al., [23] and also rod shape specimen containing a circumferential crack and subjected to tension – torsion load used by Berto et al. [34], Ayatollahi and saboori [35], Liu et al. [36] are some other test specimens for investigating the out of plane fracture problem in cracked materials. However, introducing pure or dominantly mode III case is not possible for the described specimens. Recently, Aliha and his coworkers [37–44] introduced a new and simple test configuration called Edge notched Disc Bend - ENDB that can be used easily for obtaining the fracture toughness of brittle and quasi-brittle materials like asphalt concretes. They showed that full combination of mode I and mode III mixities including pure mode III case can be achieved by this specimen. They also demonstrated the practical ability of ENDB specimen for obtaining the fracture toughness of a typical hot mix asphalt (HMA) mixture under different mode I/III mixities. The obtained results showed that asphalt specimen had higher potential for crack propagation under mode III loading conditions. The present study was carried out in line with the previous studies to investigate the fracture behavior of control and fiber reinforced asphalt mixtures under pure tensile (mode I) and pure tear (mode III) using the ENDB sample. In addition, the effects

of Temperature and loading rate (as two important parameters) on the performance of asphalt pavement have been investigated experimentally in this study. 2. Fracture test specimen geometry and numerical analysis As shown in Fig. 1, the ENDB specimen is a circular disk with the radius ‘‘R” and thickness ‘‘t” in which a crack with the depth ‘‘a” in the center and along with the diameter of disk has been created. This sample provides the possibility to perform fracture test as with a 3-point bending loading. The distance between the two supports and the angle between the loading direction and crack direction are shown by 2S and h, respectively. It is possible to simulate any of the pure modes I, III, or mixed mode of I/III by changing the value of h. Mode I is performed at h = 0 and a combination of modes I and III is created by increasing the value of h. In a given ratio of a/ t, S/R and h, the sample would produce pure-mode III loading condition. The highest values of SIFs regardless of h are always being obtained at the center of the disk (mid-section of ENDB) [37]. Eqs. (1) and (2) Indicate the general form of mode I and III stress intensity factors in the ENDB sample [37,38].

pffiffiffiffiffiffi KIðENDBÞ ¼ ð6PS paYIðENDBÞÞ =Rt2; YIðENDBÞ hða=t; S=RÞ

ð1Þ

pffiffiffiffiffiffi KIIIðENDBÞ ¼ ð6PS paYIIIðENDBÞÞ =Rt2; YIIIðENDBÞ hða=t; S=R; hÞ

ð2Þ

In this regard, Y is the geometry factor and is calculated by finite element analysis. Fig. 2 shows the finite element model of ENDB samples in this research. The modeling was carried out by ABAQUS software using 65,000 elements for meshing the cracked sample and considering mechanical properties as E = 4GPa and m = 0.35 for asphalt mixture and applying P = 150 N reference load. Thus, the geometric parameter of Y was determined in both pure opening and tearing modes by keeping ‘‘R”, ‘‘t”, ‘‘a”, ‘‘S”, at constant values of 75 mm, 40 mm, 20 mm and 67.5 mm, respectively and changing h within the range of 0–67.5°. Table 1 shows the calculated values of YI, YIII for the Analyzed ENDB of this research 3. Materials As composite material, an asphalt mixture is composed of coarse and fine aggregates, filler materials, bitumen and also 4– 7% total volume percentage air voids. In order to achieve the best mechanical performance for such composite mixture, the fraction of three main ingredients (i.e. aggregate, bitumen and air void) should be optimized. To do that, first, a standard aggregate size is chosen and then a number of asphalt test samples are manufactured using different bitumen percentages and the optimum percentage of bitumen is determined in which the corresponding asphalt mixture would have the highest strength, maximum density, and the most suitable volumetric parameters (such as void percentage, void percentage between aggregate (VMA) and the voids filled with asphalt (VFA)). Fig. 3 present schematically different parts of an asphalt mixture in terms of weight and volume of composition. Since determination of optimum binder percentage is influenced by the other ingredient, hence in the following the specifications of aggregate and binder utilized for manufacturing the asphalt mixture is described. 3.1. Aggregate The aggregate involves approximately 95% weight of most asphalt concrete. Hence physical and chemical specifications of aggregates can affect significantly the mix design and performance of asphalt mixture. In this research, limestone aggregates obtained from Farsh-Rah Asphalt factory in Yazd province of Iran was uti-

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Fig. 1. Geometry specification and loading setup in ENDB samples.

Fig. 2. Finite element model in the ABAQUS code.

lized for preparing the asphalt concrete. The maximum aggregate size (MAS) of 19 mm (that is in accordance with the grading No. 4 of Iranian paving code 234) was used. The specifications of aggregate type and aggregate gradation have been illustrated in Table 2 and Fig. 4.

aramid fiber reinforced asphalt concretes is expected. In order to investigate the influence of fiber amount on the fracture toughness and cracking resistance of asphalt mixtures different percentage of fiber (i.e. 0%, 0.025%, 0.05% and 0.1%) were added to the composition of mixture. The fibers were mixed directly with the aggregate at 170 °C and after mixing these two ingredients, the bitumen was added at 135 °C for 3 min. Fig. 5 and Table 4, presents the properties of polyolefin – aramid fibers used for manufacturing the asphalt mixtures of this study. In this paper the optimum content of bitumen was obtained using the Marshall mix design method. Accordingly, different asphalt mixtures containing (0, 0.025, 0.05 and 0.1%) fibers and (3,3.5,4,4.5,5,5.5 and 6%) bitumen was manufactured and the corresponding values of optimum binder content was determined experimentally. All the control and fiber reinforced concrete specimens were prepared with an optimum percentage of bitumen. Table 5 summarizes the results obtained from mixing scheme and the resulting value.

3.2. Bitumen

4. Sample preparation and testing procedure

Although the binder used in the composition of asphalt mixtures only consist 5% of total weight of mixture, but physical and chemical characteristic of bitumen can affect noticeably the performance of asphalt pavement due to viscoelastic behavior of bitumen. The binder used in this research was semi hard bitumen with penetration grade 60/70 and performance grade (PG 64-22) that was supplied from Tehran oil- Refinery Company. This kind of binder is the most popular bitumen in paving Iran’s road and its main characteristics properties are listed in Table 3.

The asphalt mixtures were manufactured using gyratory compactor machine and by adding different percentages of fibers. Accordingly, some cylindrical asphalt mixtures with diameter and height of 15 and 14 cm respectively were manufactured and then each cylinder was sliced to obtain three discs with thickness of 4 cm. A very narrow diamond saw blade with thickness of 0.3 mm was also utilized for creating the crack in the surface of ENDB specimen along the diameter. The depth of crack was constant and equal to a = 20 mm in the manufactured samples. Fig. 6 shows the manufacturing and cutting process of ENDB specimens made of fiber reinforced asphalt concretes. The fracture test was carried out using a GALDABINI tension/compression loading machine. The ENDB samples were kept inside a freezer for 12 h at three different temperatures of 5, 15 and 25 °C and then were tested under both pure modes I and III loading conditions. The loading rates were also considered as variable and equal to 0.5, 1 and 5 mm/min. Three replicates were conducted for each case and hence a total number of 216 ENDB specimens were tested in this research. The load –displacement curves of tested ENDB specimens were recorded for different loading and environmental condition and it was found that the whole samples were behaved as a brittle and linear material at the onset of failure

3.3. Polyolefin – aramid fiber The fiber used for manufacturing asphalt mixtures of this research was composed of polyolefin (75% weight) and aramid Kevlar 29 (25% weight). The polyolefin fibers are dissolved in the binder due to lower melting temperature of this fiber than the asphalt mixing temperature. This results in enhancing the bitumen performance especially at higher temperature conditions. In contrary the aramid fibers, that are distributed randomly in the mixture of asphalt concrete, can reinforced the pavement along three –dimensional axis. Due to very good tensile resistance of these fibers, a noticeable enhancement in the tensile type strength of

Table 1 Calculated geometric parameter (Y) in mode I (YI) and mode III (YIII) by ABAQUS. Parameters

Thickness (t) mm

Length of crack (a) mm

Support (S) mm

h degree

Y

Mode I (YI) Mode III (YIII)

40 40

20 20

67.5 67.5

0 64

0.3715 0.0631

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Fig. 3. Schematically different part of Asphalt mixtures.

Table 2 Physical specifications of fine and coarse aggregates used for manufacturing asphalt mixtures of this research. Specification

Unit

Limestone aggregate

Specific gravity (coarse aggregate) Specific gravity (fine aggregate) Loss angles abrasion Solubility of sodium sulfate Water absorption (coarse aggregate) Water absorption (fine aggregate) Percent fracture (one face) Percent fracture (two face)

g/cm3 g/cm3 % % % % % %

2.638 2.619 22 0.7 0.7 1.3 100 100

and under the investigated temperatures and loading rates. Fig. 7 shows the ENDB test set-up for both modes I and III fracture toughness testing and typical load–displacement curves obtained for different environmental and loading conditions. The values of stress intensity factor in different temperature and load conditions for each asphalt sample was calculated according to the data obtained from the experiments and by calculating the mean value of the critical fracture load using the Eqs. (1) and (2). Fig. 8 shows the schematic of research procedure. 5. Results and discussions 5.1. Experimental results After fracture tests and recording the critical fracture load data, the corresponding values of modes I and III stress intensity factors were calculated. In this part the effects of characteristic parameters such as loading mode, loading rate, temperature, and content of fibers on the fracture strength of asphalt mixtures are investigated and discussed.

Fig. 4. Gradation of lime stone aggregate.

Table 3 Physical specification of binder used for manufacturing asphalt mixtures of this research. Specification

Unit

Standard method

Result

Specific gravity Penetration at 25 °C Softening point of bitumen Elasticity at 25 °C The flash point of bitumen Solubility in trichloroethylene Kinematics viscosity in 135 °C Bitumen performance grade

g/cm3 0.1 mm °C cm °C % mm2/s –

ASTM ASTM ASTM ASTM ASTM ASTM ASTM –

1/013 63 58 >100 304 99.5 344 64–22

D70 D5 D36 D113 D92 D2042 D2170

5.1.1. Effect of loading rate on fracture toughness of asphalt mixture Variations in stress intensity factors (as indicator of the asphalt mixtures strength) under the influence of loading rates at different temperatures are shown in Fig. 9. According to Fig. 9 (a), in mode I loading the stress coefficient of the asphalt mixtures in a specific loading rate at 5° C increases with increasing the percentage of fiber consumed for manufacturing of the samples. This can also be seen at all tested loading rates which means that fiber reinforced asphalt specimens can provide a better performance in improving the fracture strength of asphalt mixtures at low temperatures. The presence of aramid fiber with a high tensile strength and a 3-D distribution in the asphalt mix has resulted in arming the asphalt mixture against the forces in all directions. Therefore, after the load and occurrence of micro-cracks at the initial moments of loading and engagement of the fiber in tolerance of the tensions, higher force will be needed to propagate the cracks which subsequently resulted in enhancement of stress intensity factor. On the other hand, the presence of polyolefin fibers in the compounds and dissolving them in bitumen during consumption will increase the elastic behavior of bitumen. In fact, in the load- displacement, the peak load shifted to higher values by increasing elastic behavior of the material. However, this may reduce the area

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Fig. 5. Picture of polyolefin – aramid fibers (a) and fiber reinforced asphalt mixture (b).

Table 4 Physical properties of polyolefin – aramid fibers. Specification

Polyolefin

Aramid

Shape

Twisted strings and single-stranded 0.91 70,000 19 Black Ineffective 100

single-stranded

Specific gravity (g/cm3) Tensile strength (psi) Length (mm) Color Resistance Acid/Base Melting Point °C

1.44 400,000 19 Yellow Ineffective 427

Table 5 Specification of asphalt mixture samples manufactured by Marshall mix design method. Specification

Unit

Result

Asphalt content Stability Specific gravity Air void Void in mineral aggregate (VMA) Void filled by asphalt (VFA)

% Kgf g/cm3 % % %

4.2 1260 2.36 4.5 14 65

below the graph due to the possible increase in the toughness of mixture, and thus reduce in the fracture energy. A closer look at Fig. 9(a) revealed the effect of loading rate on the asphalt mixture fracture toughness. The fracture toughness values in all asphalt specimens have enhanced significantly by increasing loading rate. This suggests that the elastic behavior of the asphalt mixture becomes more obvious at higher rates of loading. In all three loading rates, modified asphalt specimens with higher content of fiber exhibited higher strength. By comparing Fig. 9(a) with Fig. 9(b) and Fig. 9(c), similar trend in the variations of fracture toughness of asphalt mixtures is observable by changes in the fiber content and loading rates. However, an enhancement in the stress intensity factor of asphalt mixtures in all of the control samples and modified with different percentages of the fibers can be seen as with the test temperature drop from 5 to 25 °C. Due to the viscoelastic behavior of bitumen at lower temperatures, the elastic behavior of bitumen increases which will increase stiffness of bitumen and subsequently asphalt mixture. Enhancement in the stiffness of the asphalt mixture at low temperatures will lead to an increase in the critical fracture load and subsequently improvement in the fracture toughness of the mixture. Fig. 9 (a’, b’, c’) show the variation of the stress intensity factor under the mode III loading at various loading rates. Accordingly, the variations of the stress intensity factor were similar to that of observed in pure mode I so that in pure mode III loading condition,

Fig. 6. Manufacturing and cutting process of ENDB samples.

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a: setup

a:loading

a: fractured section

b: setup

b:loading

b: fractured se

n

Fig. 7. An overview of performing the fracture test in pure tensile mode (a) and pure tear mode (b).

Fig. 8. Flowchart of experimental program.

samples modified with higher fiber content could possessed higher fracture strength. This increase in toughness varies depending on the loading rate and the fiber percent, so that an increase between 8 and 35% in fracture strength was observed when 0.1 wt% fibers was incorporated into the asphalt mixture. The trend of variation in the impact of the loading rate was similar to the trend observed in Mode I loading conditions so that the fracture toughness of asphalt mixture enhanced by increasing the loading rate in mode III loading conditions. Noteworthy that the difference between

fracture toughness in mode I and III is significant so that at similar experimental conditions (i.e. similar temperature and loading rate), the fracture toughness of asphalt mixtures in mode III were 0.5 to 0.7 times of the values calculated for mode I. It can be concluded that the risk of crack initiation and propagation in a pavement under pure mode III loading is higher than the traffic type loading. Although using fibers has resulted in a significant increase in fracture toughness of asphalt mixtures under mode III loading, the fracture toughness of modified asphalt with the highest fiber

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Fig. 9. Effect of loading rate on fracture toughness of asphalt mixture: mode I at test temperature 5 °C (a), 15 °C (b), and 25 °C (c), mode III and test temperature 5 °C (aˊ), 15 °C (bˊ) and 25 °C (cˊ).

content (0.1% of the weight of the mixture) at the highest loading rate in mode III were barely equal to the fracture toughness of nonmodified asphalt mixture at the lowest loading rate so that in these conditions 5 °C, the improvement in fracture toughness of the specimens under mode III was around 11% compared to mode I. Besides, at 15 and 25 °C, the ratio of KIII to KI was 0.87 and 0.77, respectively. This suggests that although the use of fibers is

effective in increasing resistance to crack propagation, the method of applying load and mode of loading will have a more significant impact on the strength of the asphalt mixture against cracking. The lower fracture toughness of the asphalt mixtures in mode III means that the occurrence and propagation of cracks in this loading mode provide more critical conditions than pure mode I. Yet, the majority of the laboratory and numerical studies were con-

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Fig. 10. Effect of test temperature on fracture toughness of asphalt mixture: mode I at loading rate 0.5 mm/min (a), 1 mm/min (b) and 5 mm/min (c), mode III and loading rate 0.5 mm/min (aˊ), 1 mm/min (bˊ) and 5 mm/min (cˊ).

ducted to investigate the fracture strength of asphalt mixtures in pure tensile loading or pure sliding modes or a mixture of these two modes [21–31]. 5.1.2. Effect of test temperature on fracture toughness of asphalt mixture Fig. 10 presents the influence of test temperature on mode I and III fracture toughness of asphalt mixtures that have been obtained for the same loading rates. Based on this figure for a constant load-

ing rate of 0.5 mm/min the mode I fracture toughness of asphalt mixtures is increased about 25% and 26% for control and 0.1% fiber reinforced mixtures respectively, when the test temperature decrease from 5 °C to 25 °C. However, such enhancement in fracture toughness value reduces by increasing the loading rate, such that for loading rate of 5 mm/min, only 19 and 8% increase is seen in the KIc value of control and 0.1% fiber reinforced mixture, respectively. Generally, by decreasing the temperature and increasing the loading rate simultaneously the response of all

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Fig. 11. The fracture propagation trajectory of tested asphalt mixture for (a) mode I and (b) mode III fracture.

tested mixtures tend to elastic behavior and hence their fracture behaviors become nearly identical. For example, at a constant temperature of 5 °C, while the KIc value can increase up to 25% when the loading rate increase from 0.5 to 1 mm/min, but fracture increase in the loading rate (i.e. 1 to 5 mm/min) can only enhance further the fracture toughness value about 4%. According to Fig. 10, increase in the content of fiber led to improve in performance of asphalt mixture against cracking at all temperatures and loading rates. Depending on the test temperatures and loading rates, this increase was fallen into the range of 7–29% as the content of fibers increased from 0 to 0.1 wt%. Similar trend and behavior observed for mode I loading can be seen for fracture behavior of mode III case. Indeed, mode III fracture toughness value of investigated asphalt mixtures was increased between 16 and 34% by increasing the fiber content depending on the loading rate and test temperature. This demonstrates that, the influence of fiber on mode III fracture toughness is more pronounced than the mode I fracturing. A possible reason for such improvement can be due to a wider area of propagation path for mode III fracture relative to mode I fracture path. Therefore, due to 3D distribution of fibers in the texture of asphalt concrete, higher amount of fiber can resist against cracking and propagation of crack under mode III loading condition in the tested ENDB specimen. Fig. 11 shows the fracture propagation trajectory of tested asphalt mixture for mode I and III fracture. By comparing Fig. 10 (a, b, c) and Fig. 10 (aˊ, bˊ, cˊ) it can be seen that for any given constant loading rate, the influence of test temperature on the fracture resistance of mode I samples was greater than the mode III case. Meanwhile for a constant temperature both KIc and KIIIc becomes more by increasing the loading rate. In all tests carried out at different temperatures and loading rates, in to minimize the errors, three samples were made under the same conditions and subjected to fracture test. The average values of fracture toughness obtained from the tests were reported as the fracture toughness of the asphalt mixtures. The results showed that depending on the different test conditions, such as loading mode, temperature and rate of loading, the fracture toughness varies from 0.45 to 0.85 in mode I and 0.3 to 0.5 in the mode II loadings. These values are consistent with the obtained fracture toughness values for asphalt mixtures using ENDBs sample by other researchers [38,39]. Obviously, the differences observed in the results are due to the effect of temperature, loading rate and the amount of fiber in each mixture 6. Conclusions In this research the cracking response of asphalt mixtures were studied experimentally using a suitable test configuration under

both pure mode I and pure mode III loading condition and the influence of some affecting parameters like temperature loading rate and fiber content on KIc and KIIIc values were investigated. - The fracture resistances of both modes were increased by increase the fiber content; demonstrating the positive influence of fiber reinforcement on the load bearing capacity of asphalt mixtures. However, the influence of fiber was more pronounced for mode III case. - The mode I and mode III fracture toughness value became more by decreasing the test temperature and increasing the loading rate, due to dominantly elastic behavior of asphalt mixtures at such condition. The temperature had more significant effect on mode III fracture toughness value.

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