Effects of different polymers on mechanical properties of bituminous binders and hot mixtures

Construction and Building Materials 42 (2013) 161–167

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Effects of different polymers on mechanical properties of bituminous binders and hot mixtures Taner Alatasß ⇑, Mesude Yilmaz Fırat University, Faculty of Engineering, Department of Civil Engineering, 23119 Elazıg˘, Turkey

h i g h l i g h t s " Two types of SBS and a type of EVA were used for bitumen modification. " 4 wt.% Modifier was used to obtain PG 70-22. " All polymers increased the Marshall stability and stiffness of mixtures. " Resistance to moisture damage and fatigue cracks were increased with polymer usage.

a r t i c l e

i n f o

Article history: Received 13 December 2012 Received in revised form 21 January 2013 Accepted 25 January 2013 Available online 27 February 2013 Keywords: Modification Hot mix asphalt SBS EVA Superpave

a b s t r a c t In this study, rheological and mechanical properties of bituminous binders and hot mixtures modified by different polymeric additives, Kraton D1101, Kraton MD243 and EvataneÒ2805, were examined. In all samples, the amount of the polymeric additive was kept constant at 4 wt.% of the bituminous binder. The experiments showed that with the addition of the polymer to binder, Marshall stability, retained Marshall stability, indirect tensile strength, tensile strength ratio, stiffness and fatigue life values of the bituminous hot mixtures increased. The effect of the EVA on stiffness modulus and fatigue life was found to be notable. When toughness index values were compared, it was detected that mixtures with SBS- Kraton MD243 demonstrated the highest elasticity, while those with EVA-EvataneÒ2805 showed the least. The rheological experiments on the binders figured out that by the use of MD243, a new type of styrene–butadiene–styrene additive, low viscosity values could be obtained. This implies that if MD243 is utilized to bituminous mixtures, an effect on bituminous mixtures similar to that created by D1101 addition could be obtained by consuming less amount of energy. Ó 2013 Elsevier Ltd. All rights reserved.

1. Introduction In hot mix asphalts (HMAs), deformations like permanent deformation at high temperatures and cracking at low temperatures may occur. Apart from these, deformations originating from moisture resent in the environment and fatigue cracks formed as a result of the heavy traffic are other deformation types frequently observed in the HMAs. Scientific studies focusing on the improvement of the rheological properties of the bituminous hot mixtures and their degradation resistance by decreasing their temperature sensitivity through utilization of additives were initiated in 1843 [1]. Within this scope, additives were utilized as binder modifier in asphalt cement (AC) or used together with aggregate in mixture [2]. In recent years, for modification of bitumen, polymeric materials are frequently used as additive in flexible pavements [3,4].

⇑ Corresponding author. Tel.: +90 4242370000. E-mail address: talatas@firat.edu.tr (T. Alatasß). 0950-0618/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.conbuildmat.2013.01.027

Polymeric materials are basically composed of three groups: thermoplastics, thermosets and elastomers, both naturel and synthetic, excluding natural polymers [5]. These macromolecules can be in the form of plastomers, elastomers, fibers and additives/coatings. For improved performance, asphalt binders are modified by using different types of polymers [6]. Among them, SBS (styrene–butadiene–styrene) and EVA (ethylene–vinyl-acetate) are the mostly used elastomer and plastomer, respectively [7]. Plastomers increase the viscosity and stiffness of the bitumen by forming rigid network structure resisting deformation, while elastomers improve the elastic behavior of the bitumen since elastomers resist permanent deformation under tensile forces and recover their original shape after loading [8]. EVA is a copolymer of ethylene and vinyl acetate (VA). Due to the presence of acetate groups, EVA shows lower crystallinity than LDPE. The weight percent of VA, which changes generally between 5 and 50, determines the flexibility of the resin. Upon the increase in VA content, the copolymer becomes softer parallel to the decrease in crystallinity. Expectedly, lower crystallinity EVA

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T. Alatasß, M. Yilmaz / Construction and Building Materials 42 (2013) 161–167 DSR and bending beam rheometer (BBR) test results of pure and modified bitumens, namely, 4 wt.% SBS D1101 (MBSBS-D), SBS MD243 (MBSBS-M) and EvataneÒ2805 (MBEVA) are given in Table 2. The performance grades of MBSBS-D and MBSBS-M are the same, i.e., PG 70-34. Low temperature performance grade of MBEVA, which is PG 70-28, is one grade higher than that of other modified binders. According to the test results, SBS modified bitumens showed better low temperature performances than EVA modified ones. In order to determine the mixing and compaction temperatures of HMAs, rotational viscosimeter tests were conducted on unaged pure and modified binders at 135 °C and 165 °C, respectively. It is desired that the bitumen binder exhibits viscosities of 170 ± 20 cP for mixing and 280 ± 30 cP for compaction [15]. In the study, a temperature–viscosity plot was drawn and the temperatures for the corresponding viscosity values were taken to be the mixing and compaction temperatures, see Table 3. Results are consistent with the requirement that the viscosity value at 135 °C should not exceed 3000 cP (3 Pa s) to maintain workability [16]. It is evident that addition of modifiers increased the viscosity of binders more than the required for the mixing and compaction temperatures. Crushed limestone aggregate was used in the study, whose physical properties are summarized in Table 4 and used gradation is presented in Fig. 1. In the preparation stage of the HMAs, bitumen and aggregate were heated at the mixing temperature and mixed in a special mixer. Uncompacted samples were put on a tray provided that a load of 21–22 kg is placed per square meter. Then, they were subjected to short-term aging in a pre-heated oven at 135 °C for 4 h. Next, the samples were compacted by using a gyratory compactor with an angle of gyration of 1.25° at a gyration rate of 30 rpm under 600 kPa at 100 gyrations. Design binder contents (DBCs) of the compacted samples were determined from their volumetric properties and they were found to be increasing with modification. Table 5 shows the volumetric properties and Superpave specification limits of the bitumen and modified bitumen mixtures prepared at the design binder contents. Note that, all studied mixtures met the Superpave specification criteria, see Table 5.

copolymer exhibits low melting points and heat seal temperatures, along with reduced stiffness, tensile strength and hardness [9]. SBS is a block copolymer of styrene and butadiene. Polystyrene (PS) blocks tend to clump with each other and clumped PS blocks are held together by polybutadiene (PB) blocks, leading to a rubbery structure. While, PS blocks from the hard segment and impart strength to the resin, PB blocks from the soft segment and increase the elasticity of the copolymer [10]. The structure of the PB block of the SBS copolymer can be changed by using special catalysts. By this way, the double bonds on the PB are partly transferred to the side chains on the backbone. This modification improves the performance of the bitumen. Then, PMB shows lower viscosity, better compatibility at equivalent molecular weight and better resistance to oxidation, hence better thermal stability [11,12]. While there are many studies on the modification of the bitumen by SBS and EVA individually, there is no study on comparison of the newly developed SBS additive with SBS or EVA modified binders and mixtures. In this study, modified binders were prepared by using two types of SBS (SBS D1101 and newly developed SBS MD243) and EVA (EvataneÒ2805). Binder tests were conducted on pure and modified binders so as to investigate the effects of additives. Moreover, the effects of additives on performance of the HMAs were examined by performing Marshall stability, resistance to moisture-induced damage, fatigue, indirect tensile and stiffness modulus tests on pure and mixtures prepared by using modified binders.

2.2. Marshall stability and flow test The samples were subjected to Marshall stability and flow tests using the method given EN 12697-34 [17]. For this purpose, first Superpave gyratory compactor (SGC) was used to obtain compacts with 4 ± 1 vol.% void. Then, they were divided into two groups and samples in each group were conditioned separately. In order to observe the effect of conditioning duration, samples in one group was short-term conditioned (immersed in water at 60 °C for 40 min and designated as S), and those in the other one was long-term conditioned (immersed in water at 60 °C for 24 h and designated as L). Special attention was paid such that the mean specific gravities of the specimens in each group were equal. The compressive load was applied at a constant rate of 50.8 mm/min until the failure of the specimens. For this purpose, curved steel loading plates were used along the diameter of the specimens. In order to calculate the Marshall correction coefficients (c) of the specimens by using their mean thickness values (h), given in mm, the following equation was used:

2. Experimental studies 2.1. Materials and sample preparation The asphalt cement, PG 58-34, was supplied from Batman Refinery of TUPRAS. Asphalt modifiers of SBS (Kraton D 1101 and Kraton MD 243) and EVA (EvataneÒ2805) were purchased from Shell Chemical Co. and Arkema, respectively. According to the literature, 3–7 wt.% SBS and 2–6 wt.% EVA are used to modify bitumen binders [13,14]. In this study, initial amount of additive loading was kept between 2 and 5 wt.%. Modified bitumens were prepared by using propeller mixer. The mixing process of bitumen and modifiers was carried out for 60 min with a rotating rate of 1000 rpm at 180 °C. In this study, binder and hot mix asphalt design were performed according to Superpave method. Malatya, a province of Turkey, was selected as the application area. By considering the traffic and climate conditions in the city, PG 70-22 was chosen to be the appropriate binder performance grade. Table 1 shows the results of dynamic shear rheometer (DSR) tests performed on unaged binders to determine the high temperature value of performance grades. It is evident from Table 1 that, in order to obtain PG 70-Y, minimum 4 wt.% modifier should be added to bitumen. To be able to determine the effects of that much additive loading on HMAs properties, loading of 4 wt.% from each additive was decided.

c ¼ 5:24  eð0:0258hÞ

ð1Þ

In order to calculate the corrected stability values, stability and correction coefficient values were multiplied with each other. Meanwhile, the Marshall quotient (MQ) of the mixtures was also determined by dividing the stability value, in kN, to the flow, in mm. By this way, a numerical value representing the stiffness of the mixtures was obtained such that high MQ values represents a mixture amenable to distribute the applied load to a larger area giving high stiffness and high

Table 1 DSR test results of original binders. Modifier type

Modifier content (%)

G/sin d (Pa)

PG

Test temperature (°C) 58

64

70

–

0

1258

574

SBS Kraton D 1101

2 3 4 5

2456 3817 4890 7844

1232 1863 2539 3971

638 941 1326 2348

2 3 4 5

1816 2817 4204 5823

937 1412 2245 3144

488 729 1183 1681

2 3 4 5

2306 3684 4534 5511

1153 1826 3012 3647

602 889 1512 2302

SBS MD 243

EVA

76

82 58-Y

735 1189

583

64-Y 64-Y 70-Y 76-Y

633 909

58-Y 64-Y 70-Y 70-Y

739 1260

64-Y 64-Y 70-Y 76-Y

624

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T. Alatasß, M. Yilmaz / Construction and Building Materials 42 (2013) 161–167 Table 2 DSR and BBR test results. Temp. (°C)

PG 58-34

MBSBS-D

DSR test results G/sin d (Pa) (specification limit min. 1000 Pa) 58 1258 4890 70 – 1326

MBSBS-MD

MBEVA

4204 1183

4534 1512

G/sin d (Pa) RTFOT residue (specification limit min. 2200 Pa) 58 7862 – – 70 – 5599 5171

– 6862

G/sin d (Pa  106) 16 22 25

– – 1.34

PAV residue (specification limit max. 5  106 Pa) 1.83 – – – 1.69 1.52 – – –

BBR test results m-Value (specification limit min. 0.300) 18 – – 24 0.309 0.314 30 0.266 0.221

– 0.325 0.291

0.306 0.277 –

Creep stiffness (MPa) (specification limit max. 300 MPa) 18 – – – 24 108.3 144.7 98.5 30 140.9 242.6 121.9

131.3 160.6 –

Performance grades (PG) 58–34

70–28

70–34

70–34

Fig. 1. Used aggregate gradation.

Table 5 Volumetric properties of pure and polymer modified mixtures.

Table 3 Rotational viscosity test results. Properties

Standard PG 58-34 MBSBS-D

MBSBS-MD MBEVA

Viscosity (cP) (135 °C)

ASTM D4402 ASTM D4402 –

Viscosity (cP) (165 °C)

Mixing temperature range (°C) Compaction temperature – range (°C)

275.0

1125.0

825.0

1250.0

112.5

350.0

262.5

375.0

Mixture properties

Specification Binder type limits PG 58-34 MBSBS-D MBSBS-MD MBEVA

Optimum binder content (%) Volume of air voids (Va) (%) Voids in the mineral aggregate (VMA) (%) Voids filled with asphalt (VFA) (%) Dust proportion (DP) %Gmm@Nini. = 8 (%) %Gmm@Ndes. = 100 (%) %Gmm@Ndes. = 160 (%)

–

4.88

5.27

5.35

5.07

4.0

4.04

4.09

4.09

3.99

Min. 14.0

14.61

15.39

15.50

14.86

65–75

72.37

73.42

73.63

73.13

0.8–1.6 Max. 89 96 Max. 98

1.07 85.71 95.96 97.78

0.98 85.62 95.91 96.76

0.97 85.52 95.91 97.34

1.02 85.09 96.01 97.75

151–158 171–173 169–171 171–173 Table 6 Marshall stability and flow test results.

129–140 167–169 163–166 167–169

Conditioning

Table 4 Physical properties of the aggregate.

MBSBS-D

MBSBS-MD

MBEVA

Stability (kN) S L

12.58 10.73

14.55 12.93

13.28 12.44

13.22 12.38

Flow (mm) S L

4.63 5.82

4.26 5.26

4.20 5.14

3.93 4.74

2.72 1.84

3.42 2.46

3.16 2.42

3.36 2.61

85.3

88.9

93.6

93.6

Properties

Standard

Specification limits

Coarse

Fine

Filler

Abrasion loss (%) (Los Angeles) Abrasion loss (%) (Micro deval) Frost action (%) (with Na2SO4) Flat and elongated particles (%) Specific gravity (g/cm3) Specific gravity (g/cm3) Specific gravity (g/cm3)

ASTM 131 ASTM 6928 ASTM 88 ASTM 4791 ASTM C127 ASTM C128 ASTM D854

D

Max 30

27.8

–

–

D

Max 15

13.6

–

–

MQ (kN/mm) S L

C

Max 10

5.8

–

–

RMS (%) –

D

Max 10

3 2.544

–

–

–

2.571

–

–

–

2.675

resistance to the permanent deformation [18]. Additionally, by using mean corrected Marshall stability for long-term conditioned specimens (MSL in kN) and mean corrected Marshall stability for short-term conditioned specimens (MSS in kN), percent retained Marshall stability (RMS) was also calculated by using the following equation

RMS ¼ 100  ðMSL =MSS Þ

ð2Þ

Table 6 demonstrates the results obtained from the Marshall stability and flow tests. Here each value represents the mean value obtained from three samples of the same type.

Binder type PG 58-34

As seen in Table 6, out of short- and long-term conditioned mixtures, those with MBSBS-D had the highest stability values. In contrast to that, the lowest stability value was obtained in mixtures with pure bitumen. It is considered that the stability values decreased due to conditioning. When the stability values of the short-term conditioned mixtures were examined, it was identified that the stabilities of mixtures with MBSBS-D, MBSBS-M and MBEVA bitumen were 15.7%, 5.6% and 5.2% higher than those with pure bitumen, respectively. For long-term conditioned mixtures, the stabilities of mixtures with MBSBS-D, MBSBS-M and MBEVA bitumen were found to be 20.5%, 15.9% and 15.4% higher than those with pure bitumen, respectively. It was determined that the effects of the modified bitumen increased as a result of the conditioning. Meanwhile, the results gathered from mixtures prepared by using MBSBS-D and MBEVA modified bitumen demonstrated similarities with the results obtained by S ß engöz and Isßıkyakar [14]. The experiments showed that mixtures with pure binder had the highest flow values while those with MBEVA had the lowest. As found in the experiments, flow values increased, while the stability values decreased due to long-term conditioning. Out of all short-term conditioned mixtures, it was identified that those with

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MBSBS-D modified bitumen had the highest MQ value. For long-term conditioned mixtures, those with MBEVA had the highest MQ value. It was considered that the highest MQ value of the long-term conditioned mixtures with MBEVA was originated from their lowest flow values. It was detected that control mixtures (prepared with pure bitumen) had the lowest MQ value before and after conditioning process as they had the lowest stability and highest flow values. Here, MQ values of the mixtures decreased due to conditioning. The examination of retained Marshal stability (RMS) values showed that control mixtures had the lowest RMS value and those with MBSBS-M and MBEVA had the highest ones. RMS values of mixtures with MBSBS-D, MBSBS-M and MBEVA bitumen were found to be 4.2%, 9.8% and 9.8% higher than RMS of the mixture with pure bitumen, respectively. This suggests that additives which promoted the resistance against moisture damage in the highest extent were SBS-M and EVA. 2.3. Resistance to moisture-induced damage test The resistances of mixtures against moisture-induced damage were determined in accordance with AASHTO T 283 standard test procedure by compacting specimens to an air void content of 7 ± 0.5% [19]. Specimens were sorted into two groups such that each group has the same mean specific gravity. The first group was unconditioned, i.e., the specimens were immersed in water for 2 h at 25 °C. The second group was conditioned, i.e., the specimens were firstly kept in freezer for 16 h at 18 °C. Following to immersing in water for 24 h at 60 °C, they were immersed again in water for 2 h at 25 °C. Before conditioning, the internal voids were 70– 80% filled with water by vacuum saturation. Cylindrical specimens were compressively loaded along the vertical axis of the specimens at a loading rate of 50.8 mm/ min by using the Marshall loading equipment. Indirect tensile strength (ITS) in kPa was determined from the equation given below:

ITS ¼ 2  F=p  L  D

ð3Þ

where F denotes peak value of the applied vertical load (kN); L is the mean thickness of the test specimen (m); and finally D is the diameter of the specimen (m). The indirect tensile strength ratio (TSR) was calculated in accordance with the equation below:

TSR ¼ 100  ðITScond =ITSuncond Þ

ð4Þ

where ITScond denotes the indirect tensile strength of the conditioned specimens and ITSuncond stands for the indirect tensile strength of the unconditioned specimens. By using the ITS results, toughness index describing the toughening characteristics in the post-peak stress region was also calculated [20]. As seen in Fig. 2, vertical and horizontal deformations were recorded via two pairs of LVDTs (Linear Variable Displacement Transducers) A dimensionless indirect tensile toughness index (TI), is defined as follows:

TI ¼ ðAe  Ap Þ=ðe  ep Þ

ð5Þ

where Ae is area under the normalized stress–strain curve up to strain e, Ap is area under the normalized stress–strain curve up to strain ep, e is strain at the point of interest, ep is strain at the peak stress. TI compares the elastic performances of a specimen and a perfectly elastic reference material which has a TI value of 1.0. However, TI is zero for an ideal brittle material with no post-peak load carrying capacity [20]. In this study, TI values were calculated up to a tensile strain of 3%. Only, for the unconditioned samples subjected to experimental testing at 25 °C, TI values were determined. ITS test was also applied to the unconditioned samples at 0 °C, after keeping the samples at 0 °C for 6 h. Fig. 3 shows the test results representing the mean value of three specimens, before and after conditioning. As seen in Fig. 3, the highest ITS value was attained by mixtures with MBEVA binder while the lowest value was obtained by those with pure binder. The experiments conducted on conditioned samples at 25 °C and on unconditioned samples

Fig. 3. Indirect tensile strength test results.

at 0 °C demonstrated that tensile strength values of mixtures with MBSBS-D and MBSBS-M binders were close to each other. When the experiments were performed on unconditioned samples at 25 °C, it was found that tensile strength values of mixtures with MBSBS-D and MBEVA binders were close to each other. The experiments conducted on unconditioned samples at 0 °C showed that ITS values of mixtures with MBSBS-D, MBSBS-M and MBEVA bitumen were found to be 13.4%, 10.7% and 21.3% higher than ITS of the control mixture, respectively. At 25 °C, for the same type of samples, ITS values of mixtures with MBSBS-D, MBSBS-M and MBEVA bitumen were found to be 13.4%, 10.7% and 21.6% higher than ITS of the mixture with pure bitumen, respectively. These results pointed out that additives were more effective on ITS values after the conditioning, while before conditioning their effects were limited, especially at low temperatures. TSR values of mixtures are given in Fig. 4. As seen from Fig. 4, the highest TSR value was attained by mixture with MBEVA bitumen, while the lowest value was obtained in mixture with pure bitumen. Meanwhile, evaluation of TSR results demonstrated that all mixtures, except for control mixture, satisfy the limit given in the Superpave specification, i.e. 80%. Additionally, TSR values of mixtures with MBSBS-D, MBSBS-M and MBEVA bitumen were found to be 5.8%, 10.7% and 12.7% higher than TSR of the control mixture, respectively. TSR values showed similarities with RMS values. As a result of this, it can be stated that the mixture with highest resistance against moisture damage would be the one with MBEVA bitumen. Fig. 5 shows the toughness index (TI) values of the mixtures examined in the study. As seen in Fig. 5, the highest TI value was attained by mixtures with MBSBS-M, while the lowest value was obtained by those with MBEVA binder. Meanwhile, TI values of mixtures with pure and MBSBS-D binders were close to each other. Additionally, TI values of mixtures with pure bitumen, MBSBS-D and MBSBS-M bitumen were found to be 13.77%, 18.44% and 41.10% higher than TI value of the mixture with MBEVA, respectively. All these results point out that mixture with MBSBS-M demonstrates the highest elasticity, while that with MBEVA shows the lowest.

2.4. Indirect tensile stiffness modulus test The indirect tensile stiffness modulus (ITSM) test is used non-destructively to evaluate the relative quality of materials and study the effects of temperature and loading rate. The repeated-load ITSM can be calculated according to the expression defined by BS DD 213 [21]. The ITSM Sm in MPa is defined by the following equation:

Fig. 2. Toughness index test configuration.

T. Alatasß, M. Yilmaz / Construction and Building Materials 42 (2013) 161–167

165

10, 20 and 30 °C, respectively. In mixtures with MBSBS-M, the value was 13.6%, 10.4% and 8.6% higher than control mixture for the same respective temperatures. It should be noted that, compared to control mixture, the difference in ITSM value was more significant when MBEVA was used as additive, i.e., 29.6%, 22.8% and 15.0%. All these results point out that with the increasing temperature the effectiveness of the additives diminishes and ITSM values get closer to each other. It is notable that, with decreasing the temperature from 30 °C to 10 °C, ITSM values of mixtures with pure bitumen, MBSBS-D, MBSBS-M and MBEVA increased 4.4, 4.7, 4.6 and 5.0 times, respectively. This states that the highest increase in the stiffness value with the decreasing temperature would be observed in mixtures with MBEVA, whereas the least increase would be those with pure bitumen. 2.5. Indirect tensile fatigue test The fatigue tests were carried out in controlled stress mode as described by the method given in BS DD ABF [22]. The typical stages observed in the fatigue behavior of a material are divided into three. Firstly, void formation causes high amount of deformation and then a reduction in the axial deformation occurs. Constant deformation and an approximate linear change are observed in the secondary stage. Finally, in the tertiary stage, crack propagation initiates and the amount of deformation increases [23]. Fatigue of a material can be described by using some definitions. Fatigue life, Nf, is the number of cycles that a specimen sustains before failure and in other words, it is the intersection value of tangents drawn to the secondary and tertiary stages [24]. Crack propagation rate, rp, is defined as the load repetition rate to form a deformation of 1 mm from the initiated crack until the end of the fatigue life [25]. It is formulated by the following equation:

Fig. 4. Tensile strength ratio values of mixtures.

rp ¼ N p =ðdf  di Þ

where rp is crack propagation rate (cycle number/mm), Np is load cycle number for crack propagation, df is total deformation at failure (mm) and di is total deformation at crack initiation (mm). Another term, the crack propagation ratio is described to be inversely related to the crack propagation rate, stating that the higher the rp, the lower the crack propagation ratio and vice versa. The number of cycles to failure is related to the tensile stress. This is governed by Wohler fatigue prediction model. In order to develop an equation for fatigue life of a material, the linear plot of the stress vs. number of cycles is obtained in logarithmic scale. For Wohler’s fatigue prediction model, the equation yielding fatigue life is given by;

Fig. 5. Variation of toughness index values with modified binder usage.

Sm ¼ F  ðR þ 0:27Þ=ðL  HÞ

ð7Þ

ð6Þ

where F is the peak value of the applied vertical load (repeated load, N), H is the mean amplitude of the horizontal deformation (mm), L is the mean thickness of the test specimen (mm) and R is the Poisson’s ratio (assumed as 0.35). Testing was performed in deformation-controlled mode by using a universal testing machine (UTM). The target peak transient diametral deformation was achieved by regulating the amount of force through the system during the first five conditioning pulses. In order to obtain consistent and accurate results, a proper value, 5 lm for this case, was chosen in a way that high signal amplitudes would be obtained from the transducers. The rise time, which shows duration of applied load between zero to the maximum level, and the load pulse application were adjusted to 124 ms and 3.0 s, respectively. Fig. 6 shows the results, mean values of three samples, of ITSM tests performed at 10, 20 and 30 °C. As seen in Fig. 6, ITSM values of mixtures increased with the utilization of the polymer at all temperatures. The highest value of ITSM was obtained when MBEVA was used as additive and the lowest value was obtained when pure binder was used. It should be noted that the level of increase in the ITSM value diminished with increasing temperature. For example, for mixtures with MBSBS-D, the ITSM value was 16.3%, 14.2% and 8.9% higher than the ITSM value of the control mixture at

Fig. 6. Variation of ITSM values of mixtures with temperature and additive type.

Nf ¼ k1  ðrÞk2

ð8Þ

where Nf represents the fatigue life, r is the applied stress in kPa, and both k1 and k2 are the sample specific coefficients [26]. In many-component systems, such as HMA with additive, coefficients k1 and k2 are obtained from the equation of fatigue life. The values of k1 and k2 can be used to assess the fatigue properties of the HMA mixtures with additives. It is known that higher k2 means less inclined slope of the fatigue line and longer fatigue life, when two mixtures with the same k1 are compared. Similarly, low value of k1 is obtained when a mixture has shorter fatigue life when two mixtures of the same k2 value are compared [27]. Pure and modified mixtures were subjected to the indirect tensile fatigue test at 25 °C. Within this scope, cyclic tests at different stress levels (300 kPa, 350 kPa and 400 kPa) were performed where the loading period and load rise time were adjusted to 1.5 s and 0.124 s, respectively. The graphs giving the accumulated deformation vs. number of cycle for pure and modified mixtures at the stress level of 300 kPa are given in Fig. 7. Based on these graphs, values of Nf, Nmax, df, and dmax are shown in Table 7, where coefficients of k1 and k2 as well as rp are also indicated.

Fig. 7. The variation of deformation with load cycle number at the stress level of 300 kPa.

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T. Alatasß, M. Yilmaz / Construction and Building Materials 42 (2013) 161–167 Table 7 Indirect tensile fatigue test results. Parameter

Stress (kPa)

PG 58-34

MBSBS-D

MBSBS-MD

MBEVA

Nf (cycle)

300 350 400

2357 763 409

8875 2012 554

6750 1277 756

19334 4560 1547

df (mm)

300 350 400

3.240 3.728 3.428

3.467 2.841 2.362

3.053 3.151 2.670

1.831 1.864 1.853

Nmax (cycle)

300 350 400

2517 801 435

9284 2145 586

7092 1353 804

20376 4822 1625

dmax (mm)

300 350 400

4.448 4.567 4.474

4.308 3.682 3.174

3.936 4.395 3.694

2.468 2.598 2.734

rp (cycles/mm)

300 350 400

550 151 89

1846 535 168

1669 298 208

7232 1822 523

1.01E+03 0.157 0.9651

7.66E+02 0.103 0.9868

8.50E+02 0.119 0.9146

9.08E+02 0.112 0.9901

k1 k2 R2

Binder type

As given in Table 7, with the use of additives fatigue life (Nf) increases. In contrast to that fatigue life decreases with increasing stress level. At stress value of 300 kPa, mixtures with MBSBS-D, MBSBS-M and MBEVA had 3.77, 2.86 and 8.20 times higher Nf values respectively, compared to the control mixtures. When the stress level was increased to 400 kPa, the difference in Nf value decreased to 1.35, 1.85 and 3.78 times for the same mixtures. These results showed the additive with highest impact on the Nf value was EVA, while the least effective one was SBS-M at 300 and 350 kPa, SBS-D at 400 kPa. The effect of the additive on fatigue properties is notable especially at the stress level of 300 kPa. This suggests that, in traffics where heavy vehicles are rare, the use of modified mixtures with SBS-D, SBS-M or EVA, mixtures would have higher fatigue lives. Nmax values showed similar variation with Nf values. When the deformation values at Nf and Nmax (df and dmax) were examined, it was seen that deformation values decreased with the utilization of the additives. However, the variation in the deformation values with the level of the stress was irregular. At the stress level of 300 kPa, the highest df value was obtained for mixtures with MBSBS-D. On the other hand, at 350 and 400 kPa, the highest value of df was observed in control mixtures. Among all samples, for all stress levels, the smallest value of df was obtained in mixtures with MBEVA. Based on the values of df and dmax, deformation values are expected to decrease at high stress levels (400 kPa) which points out that more brittle fracture would occur. It was found that rp value increased with the use of additive, while it decreased with increasing stress level. At the level of 300 kPa stress level, rp value of the mixtures with MBSBS-D was 3.55 times higher. Similarly, compared to control mixture, the value was 3.03 and 13.15 times higher for MBSBS-M and MBEVA, respectively. The results gathered in the study demonstrate that the most effective additive was EVA. The study showed that SBS-D and SBS-M had similar effects on the rp value of the mixture. Assessment of the rp values, which represents the number of loads for each 1 mm of crack growth, showed that mixtures with EVA modified bitumen had high resistance for crack growth. When the stress level was increased from 300 kPa to 450 kPa, rp values decreased 6.16, 10.97, 8.04 and 13.83 times for mixtures with pure binder, MBSBS-D, MBSBS-M and MBEVA, respectively. The values of rp showed that the mixture with MBEVA was the mostly influenced one from the variation of the stress level while control mixtures were influenced the least. Based on the k1 and k2 values, it was detected that control mixture had the shortest fatigue life while mixture with MBEVA had the longest. The results apparently showed that the utilization of the additives increased the fatigue life of the mixtures compared to pure one. Fatigue lives mixture with MBSBS-D and MBSBS-M were found to be very close to each other. For mixtures, the number of loading was detected at high coherency and the coefficient of determination value (R2) was calculated as higher than 0.9. Meanwhile, the values of k1 and k2 decreased with the utilization of the additives. It is already known that high value of k2, which is the slope of the fatigue line, demonstrates that the mixture of which fatigue life is tested has a brittle characteristic. In contrast to that, low values of k2 means the mixture possesses a resilient behavior [28]. Thus, it is consistent that mixtures with elastomeric type additives, i.e., SBS-D and SBS-M, have lower k2 values than pure mixture. However, it is inconsistent that mixture with plastomeric type EVA modified bitumen has lower k2 value compared to control mixture.

3. Conclusions In this study, rheological and mechanical properties of bituminous binders and hot mixtures modified by different polymeric additives, Kraton D1101, Kraton MD243 and EvataneÒ2805, were examined. In all samples, the amount of the polymeric additive was kept constant at 4 wt.% of the bituminous binder so that the effect of each additive can be compared with each other. By using this amount of additive, all modified bitumen attained the performance level of the application grade (PG 70-22). In the Marshall stability and flow tests, the highest stability value was reached by mixtures with MBSBS-D, while the lowest flow value was obtained in mixtures with MBEVA. The highest retained Marshall stability value was obtained in mixtures with MBSBS-M and MBEVA. The experiments also demonstrated that mixtures with polymer modified binders had higher ITS and TSR values than those with pure binder. According to the toughness index values, mixtures with MBSBS-M demonstrated the highest elasticity while those with MBEVA showed the least. The results of the study point out that ITSM values and fatigue lives of the mixtures increase with the utilization of the additives. The highest ITSM value and longest fatigue life were obtained in mixtures with MBEVA. In contrast to that, lowest ITSM value and shortest fatigue life were observed in control mixtures. It is considered that with the use of MBEVA, ultimate deformation values decreased and thus these mixtures demonstrated more brittle behavior. By overall evaluation of the results, it can be stated that the utilization of additives enhances the resistance of mixtures against moisture damage and fatigue failure. Meanwhile, with the use of MD243, a new type of styrene–butadiene–styrene additive, mixtures with low viscosity values could be obtained and an effect on bituminous mixtures similar to that created by D1101 addition could be obtained by consuming less amount of energy.

Acknowledgements This study was supported by Fırat University Scientific Research Projects Unit (FUBAP) under project number MF.12.01. The financial contribution of FUBAP is gratefully acknowledged.

T. Alatasß, M. Yilmaz / Construction and Building Materials 42 (2013) 161–167

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