Effect of temperature and air void on mixed mode fracture toughness of modified asphalt mixtures

Construction and Building Materials 95 (2015) 545–555

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Effect of temperature and air void on mixed mode fracture toughness of modified asphalt mixtures M.R.M. Aliha a,⇑, H. Fazaeli b, S. Aghajani b, F. Moghadas Nejad c a

Welding and Joining Research Center, School of Industrial Engineering, Iran University of Science and Technology (IUST), Narmak, 16846-13114, Tehran, Iran Department of Civil Engineering, Iran University of Science and Technology (IUST), Narmak, 16846-13114, Tehran, Iran c Department of Civil Engineering, Amirkabir University of Technology, Tehran, Iran b

h i g h l i g h t s  Mixed mode fracture toughness of different modified asphalt mixtures was determined.  Effects of temperature changes and air-void were studied on fracture toughness values.  The mixtures modified with CR and SBS additives had the most KIc and KIIc values.  Critical mode of fracture was not noticeably sensitive to the type of modifier.

a r t i c l e

i n f o

Article history: Received 14 January 2015 Received in revised form 14 July 2015 Accepted 16 July 2015

Keywords: Modified asphalt mixtures Mixed mode I/II loading Fracture toughness Temperature effect Air void effect Critical fracture mode

a b s t r a c t The use of modified asphalt mixtures is a suitable solution for preventing low temperature cracking of pavements in cold regions. In this paper, mixed mode I/II fracture toughness of five modified asphalt mixtures containing poly phosphoric acid (PPA), Styrene Butadiene Styrene (SBS), anti-stripping agent, crumb rubber (CR) and F-T paraffin wax (Sasobit) and an unmodified one (with no additive) is investigated experimentally using a large number of cracked semi-circular bend (SCB) specimens. The effects of four different mode mixities from pure mode I to pure mode II, temperature changes, and air void percentage are also studied on fracture toughness values of modified asphalt mixtures. The obtained result showed that the fracture toughness of tested mixtures depends noticeably on the modifier type, air void content and the test temperature. It is shown that the performance grade (PG) of the tested binders has significant effect on the low temperature fracture resistance of the investigated modified asphalt mixtures. Also, according to the test results, mixed mode loading cases were more critical than the pure modes I and II situations. Ó 2015 Elsevier Ltd. All rights reserved.

1. Introduction Visco-elastic behavior of bitumen may lead to different performances for asphalt mixtures as the temperature is changed. At higher temperatures, the bitumen behaves as viscous material and failure mode such as rutting, is more pronounced to occur at these conditions. Conversely, at low temperatures, brittle fracture is the major failure mode of asphalt pavements due to the elastic and brittle nature of the binder. Because of the huge amount of costs that are spent annually for the maintenance and rehabilitation of cracked roads and pavements, it is necessary to study the affecting parameters on cracking behavior of asphalt mixtures at low temperatures. The use of linear elastic fracture mechanics ⇑ Corresponding author. E-mail address: [email protected] (M.R.M. Aliha). http://dx.doi.org/10.1016/j.conbuildmat.2015.07.165 0950-0618/Ó 2015 Elsevier Ltd. All rights reserved.

(LEFM) is a suitable discipline for evaluating the fracture toughness of asphalt pavements based on the crack tip stress field [1–7]. In this framework, the stress intensity factor (SIF) is known as the main parameter for describing the crack growth resistance. Since 1970, a large number of research works have been performed to study the fracture resistance of different asphalt mixtures using the concept of fracture energy or the stress intensity factor by employing numerical analyses, simulation techniques and experimental methods [1–18]. The influence of asphalt characteristic specifications including the binder type, aggregate type, size of aggregates, air void contents, temperature, and loading condition have been investigated in the past for different asphalt mixtures. Most of the previous research studies have focused on mode I fracture, but in practice a real crack initiated in an overlay can be subjected to mixed mode tensile–shear deformations [2,3,19,20]. However, the fracture behavior of modified asphalt mixtures under

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mixed mode tensile–shear deformations has been rarely investigated in the past. The use of modifiers is one of the important techniques for improving the performance of asphalt mixtures at high and low temperatures. Lee and Marasteanu [16] showed that the Styrene Butadiene Styrene (SBS) modifier can increase the fracture resistance of asphalt mixtures. Using semi-circular bend specimen, Liu [21] studied the fracture energy of three asphalt mixtures (one unmodified and two modified mixtures with crumb rubber (CR) and showed that the modification of the binder can increase the fracture energy of asphalt mixtures and provides better performance for the hot mix asphalt mixture. Zegeye and co-workers [22] studied the fracture resistance of modified asphalt mixtures at low temperatures using indirect tensile test (IDT), three-point semi-circular bend test and disc shape compact tension (DCT) test. They used different modifiers such as SBS, Polyphosphoric Acid (PPA), SBS + PPA, and PPA + Elvaloy in their experimental program and showed that the SBS provides the best performance for asphalt mixtures at low temperatures. Recently, Pirmohammad and Ayatollahi [23] have reported a positive influence of using the SBS modifier on mixed mode fracture toughness of asphalt mixtures. However, as mentioned earlier, most of the previous research works have only focused on mode I fracture behavior of modified asphalt mixtures. But recent papers published by the authors and coworkers [2,3,19,20,23] have demonstrated the importance of mode II component in fracture process of asphalt pavements in addition to the mode I loading as well. On the other hand, due to different effects of modifiers on visco-elastic behavior of bitumen, investigating the performance of modified asphalt mixtures against cracking and comparing them in similar manufacturing and testing conditions is an important issue for understanding the advantages/disadvantages of each modifier. Hence, the aim of this research is to investigate the effects of adding some commonly used modifiers in the composition of asphalt mixtures on pure mode I, pure mode II and mixed mode I/II fracture toughness of asphalt mixtures. Moreover, the influence of change in the air void content and the test temperature is also investigated on the fracture behavior of modified asphalt mixtures. Modifiers such as SBS, PPA, crumb rubber (CR), Sasobit and anti-stripping agent are some of the most frequently used materials for modifying the hot and warm mix asphalt mixtures which was used for the asphalt mixture preparation in this paper. SBS copolymers with a combination of blocks with thermoplastics characteristics (Polystyrene terminal blocks) and blocks with rubber properties (poly-Butadiene middle blocks), have elastic and thermoplastic characteristics simultaneously. Butadiene elastomers have the glass transition temperature of 75 °C while, the glass transition temperature of Styrene division is 100 °C. Hence, SBS has both thermoplastic and elastomeric properties. This will improve the performance of SBS modified asphalts against permanent deformation, as well as, rutting at high temperatures, and thermal cracks at low temperatures [24–27]. According to several studies, the proper consumption rate of the additive in the asphalt mixture of roads has been proposed to be 5–6 weight percentage of binder [24–27]. PPA breaks the asphaltene agglomerates and creates the possibility for better distribution of asphaltene in the molten phase [28,29]. PPA is a mineral polymer in liquid form which is used in order to improve the rheological properties of the bitumen and the asphalt mixtures. Previous researches show that PPA can be used to improve the lower and upper limits of performance grade (PG) of bitumen. Thus, it will improve the performance of the asphalt mixture against cracking at low temperatures and against rutting under high temperature conditions. However, this influence significantly depends on the structure of the base bitumen and the used aggregates [28–31]. PPA consumption rate varies between 0.5 and 1 wt.% of bitumen [28–31].

CR has been known as one of the oldest additives used in the composition of modified asphalt mixtures. This can improve the performance of bitumen depending on the type of CR. Increasing the resistance against rutting, reducing thermal sensitivity, improving the performance grade of bitumen, and enhancing the fatigue and thermal cracking resistance of asphalt are the main advantages of using this additive [32–35]. However, operational issues like difficult blending with bitumen, lack of adequate stability in bitumen for long term, and a high density energy requirement have limited the usage of this additive. Various studies show that application of CR (about 15–20 wt.% of bitumen) can considerably improve the rheological performance of both asphalt and bitumen [32–35]. Fischer-Tropsch paraffin wax (Sasobit) is an aliphatic hydrocarbon derived from coal gasification which is known as the most widely used additives in producing warm mix asphalts. It can be easily dissolved in bitumen due to its low melting point (about 100 °C) and can form a stable compound. After the compaction process and cooling of the asphalt, it will form a crystalline structure in bitumen and will enhance the strength and resistance against deformation [36,37]. Reducing the viscosity, improving the compaction and blending processes, increasing the upper limit of PG, enhancing the performance of asphalt against the permanent deformations, and decreasing the amount of bitumen aging are the main characteristics of this additive [34,36–39]. However, increasing the lower limit PG of bitumen can elevate the risk of cracking at low temperatures. Researchers have suggested the amount of 1–3 wt.% of bitumen for consumption of this additive [36–39]. Stripping is one of the most major failure modes of asphalt mixtures in cold or rainy regions. Thus, the use of lime, Portland cement, and anti-stripping agent is a possible solution for preventing this failure mode. Since lime and cement are brittle at low temperature, the use of anti-stripping agent provides better performance for the asphalt mixture. Moreover, reducing the bitumen viscosity and improving the mixing and compacting condition of asphalt mixtures are some other advantages of the anti-stripping agent modifier [40,41]. The optimum percentage of anti-stripping agent has been reported in the range of 0.3–0.5% weight of bitumen [41]. Since the performance of asphalt mixtures may be dependent significantly on the temperature, in this research the fracture resistance of different modified asphalt mixtures will be studied experimentally at three subzero temperatures of 30, 22 and 15 °C. Also, the effect of air void content in the composition of modified mixtures is investigated under different mode I/II mixities. In the next section the experimental program of this research is described and presented. 2. Materials and methods Employing a suitable test specimen and method for conducting fracture toughness experiments under different mode I/II mixities is a primary issue that should be selected for asphalt mixtures. Hence, in the following, previously used samples for fracture toughness determination of asphalt materials are introduced and then the selected test configuration for the experimental study of this research is described in more detail. 2.1. Fracture test specimen geometry In the past decades, several test specimens have been used for determining the fracture resistance of asphalt mixtures. The single edge notched bend beam (SENB) subjected to three or four-point bend loading [1,12,15,42,43], the modified indirect tension (IDT) specimen [11], the disc shape compact tension (DCT) specimen [13,14,18,44], the center cracked diametral compression disc (Brazilian disc) specimen [45] and the semi-circular bend (SCB) specimen subjected to three-point bend loading [3,6,10,16,19,23,46–54] are some of the previously used test configurations for investigating the crack growth behavior of asphalt mixtures. It should be noted that many of the mentioned specimen, cannot provide pure or dominantly mode II

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M.R.M. Aliha et al. / Construction and Building Materials 95 (2015) 545–555 loading cases. However in recent years, the use of SCB specimen has been widely increased by researchers who work on asphalt cracking due to simple geometry and loading condition of this specimen and also its ability to introduce the full mode mixities ranging from pure mode I to pure mode II. The state of mode mixity can be changed in the SCB specimen in three different manners: (i) changing the loading support distance relative to the fixed crack location, (ii) changing the edge vertical crack location from the center of specimen, and (iii) changing the crack inclination angle relative to the vertical direction [3]. In this research, the SCB specimen (shown in Fig. 1) with the vertical edge crack at the middle of the specimen and subjected to asymmetric three-point bending was used for fracture toughness testing of asphalt mixtures. Convince of introducing a fixed crack at the middle of bottom edge and ease of changing the bottom loading supports for controlling the modes I and II contributions, are some of the advantages of the SCB configuration. The critical modes I and II stress intensity factors (KIf, KIIf) at the onset of fracture for this specimen can be determined from Eqs. (1) and (2) as [3,20,55]:

K If ¼

P f pffiffiffiffiffiffiffi p aY I ða=R; S1=R; S2=RÞ 2R t

ð1Þ

K IIf ¼

Pf pffiffiffiffiffiffiffi p aY II ða=R; S1=R; S2=RÞ; 2R t

ð2Þ

where YI and YII are the geometry factors of mode I and mode II (i.e. opening and shearing modes, respectively) which are functions of the crack length (a), the semi-disc radius (R), and the loading support distances (S1 and S2). t is the specimen thickness and Pf refers to the fracture load of the SCB specimen. Ayatollahi and co-workers [55], determined YI and YII for this specimen using extensive finite element numerical analysis under different mixed mode loading by means of J-integral method. The contribution of modes I and II in the crack tip deformation can be expressed in terms of the parameter Me , which is a mixity parameter defined as:

Me ¼

2

p

tan1



KI K II

 ð3Þ

Me varies between 0 and 1 for different mode mixities such that pure mode I occurs at Me = 1 and Me = 0 corresponds to pure mode II. Furthermore, the effective mixed mode I/II fracture toughness (Keff) is defined as:

K eff ¼

qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi K 2I þ K 2II

ð4Þ

Table 1 Geometry factors and the loading support parameters of the tested SCB specimens. Unit Pure mode I Mixed mode I/II Mixed mode I/II Pure mode II (S1, S2) Me YI [3] YII [3]

(50,22) 0.8 1.766 0.578

(50,15) 0.38 0.802 1.179

(50,9) 0 0 1.772

a

Test

Standard test

Unit

Test results

Specific gravity (25 °C) Flash point (Cleveland) Penetration (25 °C) Ductility (25 °C) Softening point Kinematic viscosity @ 120 °C Kinematic viscosity @ 135 °C Kinematic viscosity @ 150 °C Penetration index (PI)a Performance grade (PG)

ASTM ASTM ASTM ASTM ASTM ASTM ASTM ASTM – –

g/cm3 °C °C cm °C mm2/s mm2/s mm2/s – –

1.03 308 62 100 49 810 420 232 –1.12 64–22

D70 D92 D5 D113 D36 D2170 D2170 D2170

PI = [1952–500 log (Pen25)  20SP]/[50 log (Pen25)  SP  120].

Table 3 Physical properties of limestone aggregate. Test

Unit

Test method

Limestone aggregate

Specific gravity L.A. Abrasion Absorption (coarse aggregate) Absorption (fine aggregate) Percent fracture (one face) Percent fracture (two face)

g/cm3 % % % % %

ASTM C-127 AASHTO T-96 AASHTO T-85 AASHTO T-84 ASTM D5821 ASTM D5821

2.61 4.6 2.2 2.4 100 98

100 90 80

Percent Passing (%)

The base bitumen used for preparation of asphalt mixtures was binder 60/70 with performance grade of PG 64-22 obtained from Tehran oil refinery. The limestone aggregates with grading NO. 4 (according to Iranian paving code 234), with the nominal maximum aggregate size (NMAS) of 19 mm was also chosen for manufacturing the asphalt mixtures. The characteristic specifications of the base binder and limestone aggregate are presented in Tables 2 and 3 and Fig. 2, respectively. The curves presented in Fig. 2, correspond to the upper limit, average limit, and lower limit of the gradation and in this research, the aggregates were prepared according to the average curve (i.e. the middle one in Fig. 2).

(50,50) 1 3.734 0

Table 2 Physical properties of the base bitumen.

Accordingly, several modified and unmodified asphalt mixtures were tested in this research under four different loading situations (i.e. pure mode I (Me = 1), mixed mode I/II with higher fraction of mode I (Me = 0.8), mixed mode I/II with higher fraction of mode II (Me = 0.38), and pure mode II (Me = 0)). The loading support distances (S1 and S2), and the corresponding geometry factors for any of the testing cases have been presented in Table 1.

2.2. Base bitumen and aggregates

mm – – –

70 60 50 40 30 20 10 0 0.01

0.1

1

10

100

Sieve Size (mm) Fig. 2. Asphalt mixture aggregates gradation.

P 2.3. Mixing procedure of additives

R

a S1

S2

Fig. 1. Geometry of the semi-circular bending test specimen used for mixed mode I/ II asphalt fracture toughness testing.

As mentioned earlier, five additives namely PPA, CR, SBS, Sasobit, and anti-stripping agent were chosen to use in the composition of asphalt mixtures of this study. The optimum percentages of each additive and its mixing temperature with binder have already been obtained and proposed in previous research studies [24–41]. The main specifications of each modifier are briefly outlined in the following. PPA used in this study is ‘‘STARPHOS 04’’ from STAR ASPHALT co., Italy (see Table 4 for its properties). To ensure the appropriate mixing of the PPA with bitumen, PPA was mixed with 1 wt.% (i.e. weight percentage) of bitumen at 160 °C for 30 min.

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Table 4 Characteristics of PPA used in this study.

Table 6 Characteristics of SBS used in this study.

Characteristics

Unit

Description

Quantity

Test method

Unit

Test

Appearance @ 25 °C Melting point Color Viscosity @ 25 °C Density @ 25 °C Boiling point

– °C – cP g/cm3 °C

Viscous liquid 20–30 Clear 840 2.02 275>

5 <0.1 <0.35

MA 04-3-064 MA 04-3-018 ASTM D-5669

Pa.s (%) (%)

Toluene soluble viscosity Toluene insoluble materials Ash content

The mixing process of CR and bitumen was implemented at 175 °C for 120 minutes with 6000 rpm high shear mixer following by 60 extra minutes at 1000 rpm at 150 °C. CR was applied in amount of 15 wt.% of the base bitumen. The properties of CR are listed in Table 5. The SBS used in this study was produced by Dynasol co. (Spain). The properties of this polymer have been summarized in Table 6. The mixing of the SBS with bitumen is similar to the procedure described for the CR. The SBS content of the mix was about 5 wt.% of the bitumen. Sasobit was added to base bitumen in the amount of 2.5 wt.% of base bitumen at 130 °C. The mixing was carried out for 10 minutes with low shear mixer at a frequency of 300 rpm. Table 7 presents the properties of Sasobit used in this research. The anti-stripping agent used in this study was ‘‘STARDOP 130 P’’ provided from STAR ASPHALT co., Italy. STARDOP 130 P is a liquid cationic adhesion promoter for pure bitumen and polymer modified bitumen based on inorganic esters and vegetable oils. The properties of STARDOP 130 P can be seen in Table 8. In this research, the anti–stripping agent was added to the base bitumen in amount of 0.4 wt.% of base bitumen at 145 °C and mixing was carried out for 30 minutes with low shear mixer at a frequency of 1000 rpm. Physical properties of the modified bitumen materials have also been compared with the base binder in Table 9, where in Table 9, B, BA, BP, BSa, BSb and BCR, refer to Base bitumen, anti-stripping modified bitumen, Polyphosphoric modified bitumen, Sosobit modified bitumen, SBS modified bitumen and crumb rubber modified bitumen, respectively.

Table 7 Characteristics of Sasobit used in this study. Characteristics

Standard

Unit

Description

Congealing point Penetration @ 25 °C Penetration @ 65 °C Appearance

ASTM D938 ASTM D1321 ASTM D1321 –

°C dmm dmm –

106 <1 6 Prills (diameter = 1 mm)

Table 8 Characteristics of anti–stripping agent used in this study. Characteristics

Unit

Description

Appearance @ 25 °C Color Flammability PH Viscosity @ 50 °C Density @ 15 °C Boiling point

– – °C – °E kg/L °C

Dark liquid Brown >140 N.A. 6.4 0.975 275<

Table 9 Physical propitious of base and modified bitumen materials.

3. Samples preparation and experimental set up In order to produce the same condition for the test samples and for investigating only the effect of compaction energy (air void percentage) on the behavior of modified asphalt mixtures, a fixed optimum percentage of bitumen (i.e. 4.5 wt.%) of the asphalt mixtures was used for manufacturing the whole mixtures. This optimum bitumen percentage was obtained from the Marshall mix design of unmodified asphalt mixture. The air void contents of 3% and 7% were considered for investigating the influence of air void percentage on the fracture resistance of modified and unmodified asphalt mixtures. A gyratory compactor machine (GCM) with different compaction energies was used for creating the mentioned air void contents. The required air void percentages (i.e. 3% and 7%) were obtained with a tolerance of ±0.5% by 90 and 35 gyratory rotations, respectively. The mixing process of the bitumen with aggregates was performed at different temperatures depending on the type of modifier and using the viscosity results obtained for modified binders. Accordingly, several cylindrical asphalt samples with diameter of 150 mm and height of 130 mm were manufactured using different modifiers and two gyratory rotations of 35 and 90. Each cylinder was then sliced into three discs of 32 mm thickness using a high speed rotary diamond saw water-cooled masonry machine. The discs were then split into two halves to produce two semi-circles. A very narrow notch with a length of 20 mm and width of 0.4 mm was then introduced at the middle of the flat edge by a very thin rotary high-speed diamond saw blade. Accordingly, Table 5 Characteristics of CR modifier used in this study. Characteristics

Unit

Description

Moisture content Maximum grain size Unit weight Ash content

% mm g/cm3 %

0.1 0.4 0.31 10

Test

B

BA

BP

BSa

BSb

BCR

Penetration (at 25 °C) Ductility (25 °C) (cm) Softening point (°C) Performance grade

62 >100 49 64–22

56 >100 53 64–22

48 >100 61 70–22

45 >100 63 70–22

43 >100 66 70–28

44 >100 67 70–28

using the procedure described above, several edge-cracked semi-circular specimens were manufactured with different binder types. Fig. 3 shows some steps of specimen preparation for fracture testing of this research. The fracture toughness experiments were conducted at four loading modes of Me = 1, 0.8, 0.38, and 0 at three temperatures of 30, 22 and 15 °C. The cracked SCB samples were kept inside a freezer for 8 hours and then were placed inside the three-point bend fixture in which the locations of right bottom loading roller were variable to introduce the required mode mixities. The samples were then loaded using 15 kN SANTAM compression test machine with the cross head speed of 3 mm/min until the final fracture. Fig. 4 shows the schematic of loading setup for testing of the considered mode mixtures (i.e. the bottom loading support locations relative to the crack line). While the left loading support distance (S1) was equal to 50 mm for the whole tests, the distance of right variable support (S2) was changed from 50 mm (for pure mode I) to 9 mm (for pure mode II). The fracture toughness (or critical values of stress intensity factor at the onset of fracture, KIf and KIIf) of the tested samples were determined from Eqs. (5) and (6) using the critical fracture loads (Pcr) obtained from each experiment and the geometry factors (YI and YII) presented in Table 1 (extracted from [3] for each mode mixity).

K If ¼

Pf pffiffiffiffiffiffiffi p aY I 2R t

ð5Þ

K IIf ¼

P f pffiffiffiffiffiffiffi p aY II 2R t

ð6Þ

M.R.M. Aliha et al. / Construction and Building Materials 95 (2015) 545–555

549

Fig. 3. Some of the steps for preparing the SCB test specimens.

Fig. 4. (a) loading support locations (dimensions in mm) for introducing different mode mixities, (b) a typical loading set up for testing the SCB samples.

For conducting the fracture toughness experiments, a total number of 288 modified and unmodified asphalt mixtures in the shape of SCB specimen were manufactured and then tested. For each asphalt mixture and mode mixity, three fracture tests were conducted to obtain an average value for fracture toughness. The summary of conducted experimental program is presented in the flowchart of Fig. 5. 4. Results and discussions In this section, the influence of modifier type, air void percentage and the temperature change is investigated on the fracture

toughness of asphalt mixtures. The critical fracture mode of each mixture is also obtained experimentally. 4.1. Effect of additive type on mixed mode fracture toughness of modified asphalt mixtures The average values of critical stress intensity factors are shown in Fig. 6 for the tested modified and unmodified asphalt mixtures under different mode mixities. These tests were performed at 15 °C and the compaction energy level was equal to 90 gyratory rotations (i.e. air void percentage of about 3%) for all investigated mixtures. As seen from this Figure the modified asphalt mixtures

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Fracture test specimens

Pure mode I

Mixed mode I/II

Mixed mode I/II

e

Pure mode II

e

(M =0.38)

-15 C

(M =0. 8)

-22 C

3

B, BA, BP, BSa, BSb, BCR

7

B, BA, BP, BSa, BSb, BCR

-30 C

Effect of air void

Fig. 5. Flowchart of experimental program of this research.

Fig. 6. Fracture toughness values of modified and unmodified asphalt mixtures at gyratory rotation of 90 and for different mode mixities.

show higher fracture toughness in comparison with the unmodified asphalt mixtures for all mode mixities. Among the investigated modified asphalt mixtures, the mixture containing CR (BCR) provided the highest resistance against cracking for the whole modes I and II mixities. The most enhancements in the value of fracture toughness were observed for BCR subjected to pure mode II loading. Swell of binder, due to reaction of CR particles with bitumen through absorption of aromatic particles of bitumen, results in improving the rheological behavior of bitumen [29,32,34]. Thus, this can decrease the lower limit of PG and also at the same time can conversely increase the higher limit of PG as presented in Table 9. From the other hand, the high ability of energy absorbing and the improved resilient behavior of bitumen modified with the CR can increase the fracture resistance for this

type of asphalt mixture against low temperature cracking. This conclusion is in agreement with other similar research studies that have been conducted only for pure mode I [21,56,57]. The binder modified with the SBS had both elastic and thermoplastic behaviors due to having poly-styrene blocks and butadiene middle blocks. Thus similar to the BCR, reduction in the lower PG limit and increase of higher PG limit is also seen in the BSb. Existence of butadiene blocks with glass transition temperature of 75 °C [24,25], can improve the resistance of binder against low temperature cracking. Accordingly as shown in Fig. 6, the BSb asphalt mixtures showed the highest fracture resistance value after the BCR mixtures for the entire tensile–shear mode mixities. While for pure modes I and II cases, both BSb and BSa mixtures had approximately similar fracture toughness values but their behavior

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were different under mixed mode loading conditions. Furthermore, in contrast with the BCR mixtures, the highest fracture toughness values of the BSb mixtures were observed at pure mode I condition. Sasobit can increase the stiffness of binder due to creation of a crystalline structure [36–38]. This can increase the risk of cracking at lower temperatures, but since the test temperature (15 °C) was higher than the lower PG limit of the binder modified with the Sasobit, a small increase still is seen in the value of fracture toughness of BSa mixture in comparison with the unmodified asphalt mixture. This can be attributed to the higher stiffness of the BSa relative to the unmodified binder which can increase the required peak load for initiation of fracture from the tip of pre-existing crack. However, this enhancement was more pronounced only for pure mode I loading case. For the asphalt mixtures containing PPA (BP) and anti-stripping agent (BA), the fracture toughness results demonstrated that the influence of these two modifiers is not significant on mixed mode fracture behavior of asphalt mixtures. For example, the use of PPA can even decrease the mixed mode fracture resistance of mixture in comparison with the unmodified mixture. Performance of asphalt mixture modified with PPA, is noticeably affected by the characteristics of the base bitumen [22]. A small improvement of fracture resistance in the samples containing anti-stripping modifier was due to the higher tensile strength and greater binding between the binder and aggregates. Since at low temperature test conditions, the tensile stresses between the binder and aggregate become more due to contractile stress and hence the higher cohesion between the bitumen and aggregate would increase the resistance of material against cracking. Consequently, according to this section, the fracture toughness of modified asphalt mixtures strongly depends on the type of additive used in the composition of mixture. 4.2. Effect of air void on mixed mode fracture toughness of modified asphalt mixtures In order to study the influence of compaction energy and air void percentage on the fracture toughness of modified asphalt mixtures, a number of SCB specimens made of asphalt mixtures with 35 gyratory rotations (GR) and the air void percentage of about 7% were also manufactured and tested at 15 °C and their corresponding fracture toughness results were compared with the results of pervious section (i.e. GR = 90 rotation and air void percentage of 3%). Fig. 7 shows the fracture toughness results of specimen prepared with 35 gyratory rotations. The fracture toughness ratio (Keff @ GR=90/Keff @ GR=35) has been presented in Fig. 8. Comparison of Figs. 6 and 7 demonstrates that the trends of fracture toughness results for mixtures compacted with 90 gyratory rotations are similar to those previously observed for the mixtures with 35 gyratory rotations. For example, similar to Fig. 6, the data shown in Fig. 7 indicates that the greatest fracture toughness values for the whole mode mixities were related to the BCR mixtures and again pure mode II fracture toughness of the BCR mixture is the greatest KIIc value among the investigated mixtures. However the difference between the fracture toughness values of the BSa and BSb mixtures manufactured with 35 GR were reduced in comparison with the specimen manufactured with 90 GR. This can be possibly attributed to the lower viscosity of binder modified with Sasobit such that can result on better compaction of the BSa mixtures in comparison with the BSb mixtures at smaller compaction energy of 35 gyratory rotation. Indeed, the BSb mixture was more sensitive to the compaction level or the air void content. Although the effect of compaction energy on pure mode II or pure shear loading of mixtures containing the BSb and BSa modifiers becomes smaller, but both mixtures showed higher fracture toughness values in comparison with the unmodified asphalt mixtures.

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The variation of fracture toughness for the BP and BA at GR = 35 and GR = 90 were similar. It should be noted that, for the whole modified and unmodified mixtures, the fracture toughness values decrease when the air void percentage was increased (i.e. by reducing the compaction energy) as shown in Fig. 8. The effect of compaction energy on mixed mode fracture resistance of modified asphalt mixtures investigated in this research was different. For mixed mode tensile–shear loading conditions, the influence of increasing air void on the reduction of Keff was more pronounced for those mixtures containing CR additive. While for pure mode II loading case this phenomenon (i.e. the most reduction in the fracture toughness) was observed for mixture containing BP additive when the air void content was increased from 3% to 7%. Therefore, it can be concluded that the reduction of fracture toughness depends on the type of additive and the loading mode as well. 4.3. Effect of loading mode on mixed mode fracture resistance of modified asphalt mixtures Figs. 9 and 10 show the variations of fracture toughness for the modified and unmodified asphalt mixtures manufactured at two gyratory rotations of 35 and 90 and tested at different mode mixities ranging from pure mode I (Me = 1) to pure mode II (Me = 0). As seen from these figures, for both compaction energy levels, by increasing the contribution of shear deformation (i.e. moving from Me = 1 to Me = 0) the fracture toughness value is decreased for both tested mixed mode I/II conditions (i.e. Me = 0.8 and 0.38) relative to the pure mode I case and then its value is increased for pure mode II loading condition. Accordingly, the most reduction in the value of fracture toughness of the modified and unmodified asphalt mixtures is observed at Me = 0.38. This reduction is more pronounced for the mixture having greater values of air void content. The value of fracture toughness was dependent on the additive type for each mode mixity. As stated earlier, the modified asphalt mixture made of CR additive had the greatest fracture toughness value for all mode mixities, which demonstrates the better performance of this type of mixture against cold thermal cracking. Under the mixed mode tensile–shear loading condition, the lowest fracture toughness values was related to the BP, BA, B, BSa, BSb mixtures, respectively. The BP mixture showed even somewhat a lesser mixed mode I/II fracture toughness than the mixture made of base bitumen. Moreover, except for the BCR mixture, the greatest value of fracture toughness was obtained at pure mode I loading conditions. Recently, some research studies have been performed to figure out the critical mode of fracture in the asphalt mixtures. For example, Ayatollahi and Pirmohammad [20,23], Ameri et al. [19], and Artamendi and Khalid [58] investigated the influence of temperature on fracture resistance of different asphalt mixtures and found that the smallest value of fracture toughness (i.e. the critical mode of fracture) is occurred at different mode mixities of Me = 0.8, 0.57 and 0.3, respectively. But, Aliha et al. [3] showed experimentally that the critical mode of fracture for unmodified asphalt mixtures, depends noticeably on the characteristic specifications of asphalt mixture including the size and type of aggregates, binder type, and air void percentage. Moreover, the type of loading setup for testing the SCB specimens in the work of Ayatollahi and Pirmohammad [20,23], Ameri et al. [19] and Artamendi and Khalid [58] was different with the employed configuration by Aliha et al. [3]. While in Refs. [19,20,23] the state of mode mixity was controlled by changing both crack location and loading supports of the SCB specimen, Artamendi and Khalid [58] used an inclined edge cracked SCB specimen for conducting their mixed mode fracture toughness experiments. This issue (i.e. the type of SCB configuration) can be considered as another possible affecting parameter on the critical mode of fracture. However, the result of

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Fig. 7. Fracture toughness values of modified and unmodified asphalt mixtures at gyratory rotation of 35 and for different mode mixities.

4.4. Effect of temperature on mixed mode fracture toughness of modified asphalt mixtures In order to study the effect of temperature on the fracture resistance of investigated asphalt materials, several fracture toughness experiments were performed on asphalt mixtures compacted with 90 gyratory rotation and at three subzero temperatures. According to the superpave tests and the performance grade (PG) values determined for each modified asphalt mixture, the test temperatures were chosen as: (i) 15 °C (i.e. temperature greater than the lower limit of PG for the base binder used for manufacturing the modified asphalt mixtures), (ii) 22 °C (i.e. the lower limit of PG of B, BA, BP, and BSa), and (iii) 30 °C (i.e. the temperature lower than the lower PG limit of the whole used modified binders). For better understanding the behavior of modified binder at low 90 Gyratory Rotaon

@ 90 GR/

all and the present research work, reveal that the critical fracture mode is occurred at combined tensile–shear loading conditions and not at pure mode opening or shearing cases. However, most of the previous research papers have focused on the pure mode I fracture toughness of asphalt mixtures. Based on the finding of this research the critical mode (i.e. the lowest fracture toughness) was observed at Me = 0.38 for the whole six investigated mixtures. Hence, it can be concluded that although modification of asphalt mixtures with commonly used modifiers can increase in general the crack growth resistance of different types of modified asphalt mixtures, but the critical mode of fracture is controlled mainly by other affecting parameters such as binder and aggregate type, gradation of aggregate, and etc. [3].

1.60

Stress Intensity Factor (MPa.m 0 .5 )

Fig. 8. Fracture toughness ratio at two gyratory rotations of 90 and 35 (Keff Keff @ 35 GR) for the tested mixtures.

B

1.40

BA 1.20

BP BSa

1.00

BSb 0.80

BCr

0.60 0.00

0.20

0.40

0.60

0.80

1.00

Me Fig. 9. Variations of mixed mode stress intensity factors for mixtures prepared with gyratory rotation of 90 GR.

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1.30

Stress Intensity Factor (MPa.m 0.5 )

1.20

B

1.10

BA

1.00

BP

0.90

BSa

0.80

BSb BCr

0.70 0.60 0.00

0.20

0.40

0.60

0.80

Keff Rao (Keff (-22°C) /Keff(-15°C) )

35 Gyratory Rotaon 1.30

1.25

B

BA

BP

BSa

BSb

BCr

1.20 1.15 1.10 1.05 1.00 0.95

1.00

0.00

Me

0.20

0.40

0.60

0.80

1.00

1.20

Me

Fig. 10. Variations of mixed mode stress intensity factors for mixtures prepared with gyratory rotation of 35 GR.

Fig. 12. Fracture toughness ratio at two test temperatures (Keff for different mode mixities.

@ (22 °C)/Keff

@ (15 °C))

Sffness (MPa)

1000

100

B

BA

BP

BSa

BSb

BCr

10 -24

-18

-12

-6

Temperature (°C) Fig. 11. Variations of stiffness for modified binders with temperature obtained from BBR test.

1.20

Keff Rao (Keff(-30 °C) /Keff (-22°C))

temperatures, the variations of stiffness versus temperature have been shown in Fig. 11 based on the results of Bending Beam Rheometre (BBR) test of the modified and unmodified binders. It is seen from this Figure that the binders that were modified with the CR and SBS additives provide lower stiffness values in comparison with the other modified binders. Accordingly, the lower PG limit of these binders was determined about 28 °C. Moreover the modified binders with anti-stripping agent and Sasobit showed higher stiffness than the base bitumen at low temperature (i.e. about 22 °C). The lower PG limit for preparing the B, BA, BP and BSa specimens was therefore 22 °C. Figs. 12 and 13 show the fracture toughness ratio (Keff @ (22 °C)/Keff @ (15 °C)) and (Keff @ (30 °C)/Keff @ (22 °C)) for different mode mixities of the tested modified asphalt mixtures. Accordingly, the variation of stress intensity factor at each reference temperature can be compared with the corresponding fracture toughness value obtained at a higher temperature. As seen from Fig. 12, up to 22 °C an enhancement in the value of fracture toughness is seen for the tested mixtures in comparison with the fracture toughness results obtained at 15 °C. Indeed, the decrease in the test temperature up to 22 °C can increase the stiffness of mixture and hence can increase the required load for initiation of fracture in the tested specimens. The mentioned enhancement in fracture toughness ratio is more pronounced for mixed mode loading condition of the modified mixtures examined in this research. In other words, it can be concluded that by decreasing the test temperature, the difference between the fracture toughness of pure modes I and II and mixed mode I/II becomes smaller. The maximum increase in the ratio of fracture toughness at two temperatures of (22 and 15 °C) was related to the BCR and BSb mixtures. Conversely, the minimum increase in the ratio

1.15 1.10

B

BA

BP

BSa

BSb

BCr

1.05 1.00 0.95 0.90 0.85 0.80 0.75 0.00

0.20

0.40

0.60

0.80

1.00

1.20

Me Fig. 13. Fracture toughness ratio at two test temperatures (Keff for different mode mixities.

@ (830 °C)/Keff @

(22 °C))

of Keff @ (22 °C)/Keff @ (15 °C) was observed for the BA and BSa mixtures. This observation can be attributed to the higher stiffness of binder containing Sasobit and anti-stripping agent at low temperatures (as shown in Fig. 11). The fracture toughness ratio (Keff @ (30 °C)/Keff @ (22 °C)) for different mode mixities have been presented in Fig. 13 for the six tested asphalt mixtures. It is seen that except for the BCR mixture, the fracture toughness has been decreased at -30 °C in comparison with the greater temperature of -22 °C. This reduction was more pronounced for the B, BA, and BSa mixtures which their binder had the lower PG limit of 22 °C. The most reduction in the value of fracture toughness was related to the mixtures containing Sasobit and anti-stripping agent modifiers. However, the fracture behavior of BSb and BCR mixtures was not noticeably sensitive to the temperature when the test temperature was varied from 22 to 30 °C. This is mainly because of the lower PG limit of 28 °C for these two modified binders containing CR and SBS additives. Indeed by decreasing the test temperature up to the lower PG limit range, the stiffness of binder becomes more, and hence the required critical fracture load for initiation stage of crack growth in the asphalt mixtures also becomes greater. However, when the temperature becomes lesser than the lower PG limit of binder, this condition may result in nucleation of micro cracks inside the binder that leads to more brittleness of bitumen and reduction in the bounding between the binder and aggregates. Therefore, a reduction in the crack growth resistance of asphalt mixture is expected to occur in such low temperature conditions. As a conclusion, the trend of changes in fracture toughness ratio with the test temperature depends on the mode mixity and the type of additive used.

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5. Conclusions In this study, the influence of some affecting parameters including the type of additives that are frequently used for modifying the bitumen (such as SBS, PPA, CR, Sasobit, Anti stripping agent), the air void content (i.e. 3% and 7%), temperature change (30, 22 and 15 °C) and tensile–shear mode mixities, were investigated on the crack growth resistance of different asphalt mixtures. The main concluding remarks of this research are: – The modified asphalt mixtures showed higher fracture toughness values in comparison with the unmodified one for both air void contents of manufactured samples. The mixtures containing CR and SBS had the most enhancements on the fracture toughness value of modified asphalt materials. But the use of PPA modifier had no significant influence on the performance of asphalt mixture against cracking. – The behavior of modified asphalt mixtures was dependent on the mode mixity. The maximum values of the fracture toughness for BCR was obtained at pure mode II (pure shear) loading condition, but for other modified asphalt mixtures, the maximum fracture toughness value was obtained at pure tensile or pure mode I loading. – By increasing the air void percentage from 3% to 7%, the fracture toughness of all mixtures was decreased. This reduction was more pronounced at Me = 0.38. – Different trends were observed for the variations of fracture toughness by decreasing the test temperature. Such that up to the lower PG limit range of binders, the fracture toughness of tested mixtures was increased. However, when the test temperature became lesser than the lower PG limit of each binder, the fracture toughness was decreased. The increase in the fracture toughness with decreasing the test temperature was more pronounced for the mixed mode loading with higher fraction of shear deformation (i.e. Me = 0.38). – The critical mode of fracture (i.e. the lowest fracture toughness value) was not noticeably sensitive to the type of modifier and for the whole modified and unmodified asphalt mixtures was obtained under mode mixity of Me = 0.38. In other words, the critical mode of fracture was affected mainly by the characteristic parameters such as the base bitumen type, air void percentage, aggregate type and the test specimen configuration and its loading setup.

References [1] A. Braham, W. Buttlar, F. Ni, Laboratory mixed-mode cracking of asphalt concrete using the single-edge notch beam, Road Mater. Pave. Des. 11 (2010) 947–968. [2] M. Ameri, A. Mansourian, M. Heidary Khavas, M.R.M. Aliha, M.R. Ayatollahi, Cracked asphalt pavement under traffic loading – a 3D finite element analysis, Eng. Fract. Mech. 78 (2011) 1817–1826. [3] M.R.M. Aliha, H. Behbahani, H. Fazaeli, M.H. Rezaifar, Study of characteristic specification on mixed mode fracture toughness of asphalt mixtures, Constr. Build. Mater. 54 (2014) 623–635. [4] H. Akbulut, K. Aslantas, Finite element analysis of stress distribution on bituminous pavement and failure mechanism, Mater. Des. 26 (2004) 383–387. [5] X.J. Li, M.O. Marasteanu, The fracture process zone in asphalt mixture at low temperature, Eng. Fract. Mech. 77 (2010) 1185–1190. [6] H. Behbahani, M.R.M. Aliha, H. Fazaeli, S. Aghajani, Experimental fracture toughness study for some modified asphalt mixtures, Adv. Mater. Res. 723 (2013) 337–344. [7] M. Novak, B. Birgisson, R. Roque, Near-surface stress states in flexible pavements using measured radial tire contact stresses and ADINA, Comput. Struct. 81 (2003) 859–870. [8] K. Majidzadeh, Application of fracture mechanics for improve design of bituminous concrete. Rep, FHWA-RD-76-91. 1976; 1 & 2, Federal Highway administration, Washington, D.C. [9] A.A.A. Molenaar, Fatigue and reflection cracking due to traffic loads, J. Assoc. Asphalt Technol. 53 (1984) 440–474. [10] A.A. Molenaar, A.A. Scarpas, X. Liu, G. Erkens, Semi-circular bending test; simple but useful, J. Assoc. Asphalt Technol. 71 (2002) 794–815.

[11] R. Roque, Z. Zhang, B. Sankar, Determination of crack growth rate parameters of asphalt mixtures using the Superpave IDT, J. Assoc. Asphalt Technol. 68 (1999) 404–433. [12] M.P. Wagoner, W.G. Buttlar, G.H. Paulino, Development of a single-edge notched beam test for asphalt concrete mixtures, J. Test. Eval. 33 (2005). Paper ID JTE12579. [13] M.P. Wagoner, W.G. Buttlar, G.H. Paulino, P. Blankenship, Investigation of the fracture resistance of hot-mix asphalt concrete using a disk-shaped compact tension test, Transp. Res. Rec. 1929 (2005) 183–192. [14] H. Kim, M.P. Wagoner, W.G. Buttlar, Numerical fracture analysis on the specimen size dependency of asphalt concrete using a cohesive softening model, Constr. Build. Mater. 23 (2009) 2112–2120. [15] H. Kim, M.P. Wagoner, W.G. Buttlar, Micromechanical fracture modeling of asphalt concrete using a single-edge notched beam test, Mater. Struct. 42 (2009) 677–689. [16] X.J. Li, M.O. Marasteanu, Using semi circular bending test to evaluate low temperature fracture resistance for asphalt concrete, Exp. Mech. 50 (2010) 867–876. [17] S.A. Tekalur, A. Shukla, M. Sadd, W. Lee, Mechanical characterization of a bituminous mix under quasi-static and high strain rate loading, Constr. Build. Mater. 23 (2009) 1795–1802. [18] B.E. Behnia, V. Dave, S. Ahmed, W.G. Buttlar, H. Reis, Effects of recycled asphalt pavement amounts on low-temperature cracking performance of asphalt mixtures using acoustic emissions, Transp. Res. Rec. 2208 (2011) 64–71. [19] M. Ameri, A. Mansourian, S. Pirmohammad, M.R.M. Aliha, M.R. Ayatollahi, Mixed mode fracture resistance of asphalt concrete mixtures, Eng. Fract. Mech. 93 (2012) 153–167. [20] M.R. Ayatollahi, S. Pirmohammad, Temperature effects on brittle fracture in cracked asphalt concretes, Struct. Eng. Mech. 45 (2013) 19–32. [21] J. Liu, Low temperature cracking evaluation of asphalt rubber mixtures using semi-circular bending test, Adv. Mater. Res. 243–249 (2011) 4201–4206. [22] E. Zegeye, K. Moon, M. Turos, T. Clyne, M.O. Marasteanu, Low temperature fracture properties of polyphosphoric acid modified asphalt mixtures, J. Mater. Civ. Eng. 24 (2012) 1089–1096. [23] S. Pirmohammad, M.R. Ayatollahi, Fracture resistance of asphalt concrete under different loading modes and temperature conditions, Constr. Build. Mater. 53 (2014) 235–242. [24] S. Tayfur, H. Ozen, A. Aksoy, Investigation of rut ting performance of asphalt mixtures containing poly mer modifiers, Constr. Build. Mater. 21 (2007) 328– 337. [25] G.D. Airey, Rheological properties of styrene butadiene styrene polymer modified road bitumens, Fuel 82 (2003) 1709–1719. [26] F. Dong, W. Zhao, Y. Zhang, J. Wei, W. Fan, Y. Yu, Influence of SBS and asphalt on SBS dispersion and the performance of modified asphalt, Constr. Build. Mater. 62 (2014) 1–7. [27] M. Singha, P. Kumara, M.R. Maurya, Strength characteristics of SBS modified asphalt mixes with various aggregates, Constr. Build. Mater. 41 (2013) 815– 823. [28] S.C. Haung, T.F. Turner, F.P. Miknis, K.P. Thomas, Long-term aging characteristic of polyphosphoric acid modified asphalt, J. Trans. Res. Rec. 2051 (2008) 1–7. [29] G. Yadollahi, M.H. Sabbagh, Improving the performance of crumb rubber bitumen by means of poly phosphoric acid (PPA) and vestenamer additives, Constr. Build. Mater. 25 (2011) 3108–3116. [30] Y. Edwards, Y. Tasdemir, U. Isacsson, Rheological effects of commercial waxes and polyphosphoric acid in bitumen 160/220 – high and medium temperature performance, Constr. Build. Mater. 21 (2007) 1899–1908. [31] Y. Edwards, Y. Tasdemir, U. Isacsson, Rheological effects of commercial waxes and polyphosphoric acid in bitumen 160/220 – low temperature performance, Fuel 85 (2006) 989–997. [32] P. Cong, P. Xun, M. Xing, S. Chen, Investigation of asphalt binder containing various crumb rubbers and asphalts, Constr. Build. Mater. 40 (2013) 632–641. [33] V. Gonzalez, F.J. Martinez, F.J. Navarro, C. Gallegos, A. Perez-Lepe, A. Paez, Thermomechanical properties of bitumen modified with crumb tire rubber and polymeric additives, Fuel Process. Technol. 91 (2010) 1033–1039. [34] A.M. Rodríguez-Alloza, J. Gallego, I. Pérez, A. Bonati, F. Giuliani, High and low temperature properties of crumb rubber modified binders containing warm mix asphalt additives, Constr. Build. Mater. 53 (2014) 460–466. [35] H. Wang, Z. Dang, L. Li, Z.O. You, Analysis on fatigue crack growth laws for crumb rubber modified (CRM) asphalt mixture, Constr. Build. Mater. 47 (2013) 1342–1349. [36] H. Fazaeli, H. Behbahan, A.A. Amini, J. Rahmani, G. Yadol Lahi, High and low temperature properties of FT paraffin modified bitumen, Adv. Mater. Sci. Eng. 2012 (2012) 7. [37] G. Hurley, B. Prowell, Evaluation of SasobitÒ for use in warm mix asphalt, National Center for Asphalt Technology (2005) report 05–06, Auburn, Alabama. [38] E. Sanchez-Alonso, A. Vega-Zamanillo, D. Castro-Fresno, M. DelRio-Prat, Evaluation of compatibility and mechanical properties of bituminous mixes with warm additives, Constr. Build. Mater. 25 (2011) 2304–2311. [39] S.J. Lee, S.N. Amirkhanian, N.W. Park, K.W. Kim, Characterization of warm mix asphalt binders containing artificially long-term aged binders, Constr. Build. Mater. 23 (2008) 2173–2179. [40] Y.R. Kim, I. Pinto, S.W. Park, Experimental evaluation of anti-stripping additives in bituminous mixtures through multiple scale laboratory test results, Constr. Build. Mater. 29 (2012) 386–393.

M.R.M. Aliha et al. / Construction and Building Materials 95 (2015) 545–555 [41] M. Ameri, S. Kouchaki, H. Roshani, Laboratory evaluation of the effect of nanoorganosilane anti-stripping additive on the moisture susceptibility of HMA mixtures under freeze–thaw cycles, Constr. Build. Mater. 48 (2013) 1009–1016. [42] S.H. Baek, J.P. Hong, S.U. Kim, J.S. Choi, K.W. Kim, Evaluation of fracture toughness of semirigid asphalt concretes at low temperatures, Transp. Res. Rec. 2210 (2011) 30–36. [43] M.Y. Yoo, S.H. Jeong, J.Y. Park, N.H. Kim, K.W. Kim, Low-temperature fracture characteristics of selected warm-mix asphalt concretes, Transp. Res. Rec. 2208 (2011) 40–47. [44] M.A. Edwards, S.A.M. Hesp, Compact tension testing of asphalt binders at low temperatures, Transp. Res. Rec. 1962 (2006) 36–43. [45] M.A. Mubaraki, A.A. Abd-Elhady, H.E.M. Sallam, Mixed mode fracture toughness of recycled tire rubber-filled concrete for airfield rigid pavements, Int. J. Pave Res. Technol. 6 (2013) 8–14. [46] J.H. Liu, Fatigue life evaluation of asphalt rubber mixtures using semi-circular bending test, Adv. Mater. Res. 255 (2011) 3444–3449. [47] L.N. Mohammad, M. Kim, M. Elseifi, Characterization of asphalt mixture’s fracture resistance using the semi-circular bending (SCB) test 7th RILEM International Conference on Cracking in Pavements, RILEM Book series 4, 2012, pp. 1–10. [48] M.M. Hassan, H.A. Khalid, Fracture characteristics of asphalt mixtures containing incinerator bottom ash aggregate, Transp. Res. Rec. 2180 (2010) 1–8. [49] H. Hakimelahi, S. Saadeh, J. Harvey, Investigation of fracture properties of California asphalt mixtures using semicircular bending and beam fatigue tests, Road Mater. Pave Des. 14 (2013) 252–265.

555

[50] M.A. Elseifi, L.N. Mohammad, H. Ying, S. Cooper, Modeling and evaluation of the cracking resistance of asphalt mixtures using the semi-circular bending test at intermediate temperatures, Road Mater. Pave Des. 13 (2012) 124–139. [51] B. Huang, X. Shu, G. Zuo, Using notched semi circular bending fatigue test to characterize fracture resistance of asphalt mixtures, Eng. Fract. Mech. 109 (2013) 78–88. [52] F.P. Jiménez, R. Botella, K.H. Moon, M. Marasteanu, Effect of load application rate and temperature on the fracture energy of asphalt mixtures, Constr. Build. Mater. 48 (2013) 1067–1071. [53] I.M. Lancaster, H.A. Khalid, I.A. Kougioumtzoglou, Extended FEM modelling of crack propagation using the semi-circular bending test, Constr. Build. Mater. 48 (2013) 270–277. [54] M.R.M. Aliha, H. Behbahan, H. Fazaeli, M.H. Rezaifar, Experimental study on mode I fracture toughness of different asphalt mixtures, Scientia Iranica. Trans. A Civil Eng. 22 (2015) 120–130. [55] M.R. Ayatollahi, M.R.M. Aliha, H. Saghafi, An improved semi-circular bend specimen for investigating mixed mode brittle fracture, Eng. Fract. Mech. 78 (2011) 110–123. [56] M.A. Mull, K. Stuart, A. Yehia, Fracture resistance characterization of chemically modified crumb rubber asphalt pavement, J. Mater. Sci. 37 (2002) 557–566. [57] A.M. Othman, Fracture resistance of rubber-modified asphaltic mixtures exposed to high-temperature cyclic aging, J. Elastomer Plastics 38 (2006) 19–30. [58] I. Artamendi, H.A. Khalid, A comparison between beam and semi-circular bending fracture tests for asphalt, Road Mater. Pave Des. 7 (2006) 163–180.