Laboratory evaluation of the composition of nano-clay, nano-lime and SBS modifiers on rutting resistance of asphalt binder

Construction and Building Materials 238 (2020) 117592

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Laboratory evaluation of the composition of nano-clay, nano-lime and SBS modifiers on rutting resistance of asphalt binder Seyed Alireza Ghanoon a, Javad Tanzadeh b,⇑, Mehrnaz Mirsepahi c a

Department of Civil Engineering, South Tehran Branch, Islamic Azad University, Tehran, P.O. Box: 11365-4435, Iran Department of Civil Engineering, Bandar Anzali Branch, Islamic Azad University, Bandar Anzali, P.O. Box: 43111, Iran c Department of Road and Transportation, Science and Research Branch Islamic Azad University, Tehran, Iran b

h i g h l i g h t s
The effect of nano-lime is greater than of nano clay in composite combination.
Temperature increase in both high and low stresses increased the values of the non-recoverable creep compliance.
The combination of this additives can increase the bitumen yield results dramatically.
Nano-clay can improve the storage stability and temperature susceptibility of polymer modified bitumen.
Nano-clay increases rutting resistance and reduces its stress sensitivity at tolerance temperature.

a r t i c l e

i n f o

Article history: Received 5 August 2019 Received in revised form 1 November 2019 Accepted 11 November 2019

Keywords: Bitumen Nano-clay Nano-lime SBS MSCR Rutting Asphalt binder Non-recoverable creep compliance Recovered creep Stress sensitivity Compound modifiers

a b s t r a c t The physical and rheological properties of asphalt mixtures affect pavement performance at high and low ambient temperatures, and thus can affect the final performance of the mixture. Adding modifiers such as polymers and nano additives to improve asphalt mixture performance has become popular in recent years. The purpose of this study is to modify the bitumen with nano-clay, nano-lime and StyreneButadiene-Styrene (SBS). PG 64-22 bitumen was modified using 2, 4 and 6 wt% of nano-clay and the results showed that increasing the nano-clay to the base bitumen improved the rheological properties and rutting resistance of asphalt binder. Also, it was examined the effect of adding 3% SBS to the bitumen sample, and the results indicated a positive effect of this additive, especially at lower temperatures. In the next step, bitumen was modified using 4 and 6 wt% of nano-lime and 3% SBS with 4 and 6 wt% of nanoclay in combination with the base bitumen and tested to evaluate the combined effect of these three materials. The effect of this modifier on reducing rutting failure was evaluated compared to the control sample. To this end, we evaluated the effect of these materials on the rheological properties of bitumen by performing multiple stress creep recovery (MSCR) test by Dynamic Shear Rheometer (DSR). Results showed that increasing the nano-clay to the base bitumen improved the rheological properties and rutting resistance of asphalt binder and best improvement is achieved with 6%. The effect of 3% SBS although did not produce results similar to nano-clay, but the results showed significant improvement in bitumen properties. Finally, the best combination in this study was a combination of 3% SBS, 4% nano-clay, and 6% nano-lime, which yielded good results. Ó 2019 Elsevier Ltd. All rights reserved.

1. Introduction One of the most important forms of failure in asphalt pavement is stretching or permanent rutting. Permanent deformation along the horizontal track of the wheel appears at the longitudinal surface, which results in reduced pavement efficiency and makes ⇑ Corresponding author. E-mail addresses: [email protected] (S.A. Ghanoon), Tanzadeh@iaubanz. ac.ir (J. Tanzadeh). https://doi.org/10.1016/j.conbuildmat.2019.117592 0950-0618/Ó 2019 Elsevier Ltd. All rights reserved.

the vehicles rough and dangerous [1]. The main reason for the asphalt pavement track is the known ‘‘accumulated strain” that results from traffic loading [2]. Although the rutting observed in the flexible pavements can be calculated by aggregating the total of the tensile accumulated in single or multilayer, but the accumulation of stable tensile stress in the surface layer of the asphalt mixture is considered as the main source of rutting [3]. The aptitude of rutting in a pavement is largely influenced by its grading and mixing properties. However, bitumen properties are also important,

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especially for modified bitumen, which is claimed to be used to improve asphalt rutting resistance. Bitumen because of its two properties of adhesion and impermeability used in the road construction industry for coating and gluing stone materials in asphalt mixtures. Therefore, in recent years various methods and researches and a wide range of additives have been investigated to improve the properties and behavior of bitumen. These materials include Rubber, Gilsonite, Styrene– Butadiene–Styrene (SBS), Ethylene–Vinyl–Acetate (EVA) [4] and nano materials. Among the disadvantages of using these additives is their inability to improve all the weaknesses in asphalt mixtures such as rutting, moisture sensitivity, fatigue cracks and etc. However, laboratory results indicate that these additives can have a significant impact on the performance of asphalt mixtures [5]. This weakness in improving all the properties of bitumen led the researchers to use different modifiers in combination. Yoo et al. in a study, used a combination of polypropylene and glass fiber additives simultaneously in asphalt [6]. The results showed improved asphalt performance as well as increased rutting resistance. Liangcai et al. performed a research under the title ’Laboratory evaluation of composed modified asphalt binder and mixture containing nano-silica/rock asphalt/SBS’ [7]. Comparing these tests results with the properties of unmodified asphalt mixture, indicated that nano-silica and rock asphalt cause an improvement in pavement performance. Nano-silica/rock asphalt/SBS modified asphalt mixture had higher temperature stability, lowtemperature cracking resistance, moisture susceptibility and durability than 5% SBS modified asphalt except the similar fatigue life. In this respect Lili Han et al. performed another research about effect of nano-silica and pretreated rubber on the properties of terminal blend crumb rubber modified asphalt [8]. The results showed a significant improvement in bitumen properties. Tanzadeh et al. in a research investigated the effect of nanosilica, hybrid synthetic fiber, glass fiber, SBS and polypropylene fiber in combination on porous asphalts [9]. Like other similar studies, they could to achieve the desired results by combining these materials together and simultaneously improve the different properties of asphalt mixture. In 1970, Europeans sought to reduce maintenance and operating costs in the guarantee period, were more inclined to use polymer bitumen than Americans. That’s why in the early 1980s, they succeeded in producing new polymers and exporting their technology. In the same years, the US Department of Roads issued reports on the effectiveness of these materials by expanding economic analysis over the life cycle of polymer asphalts. Since then, studies in the 90s have yielded similar results, and these days, studies of the effects of polymers and the production of different composites to improve the properties of asphalt mixtures continue. In recent years, SBS has been one of the polymers widely used in modifying bitumen and asphalt properties. Feipeng et al. carried out experimental investigations and used SBS and Crumb Rubber (CR) as additives [10]. They used the effects of these substances separately, and the results indicated a positive effect of SBS on bitumen performance and properties. Awanti [11], Huang [12], Al Hadidy [13], Khodaii [14] and et al, also Peng et al. [15] conducted some research on the effects of SBS polymer on the performance of bitumen. The results showed that adding SBS polymer would improve the performance of bitumen. In general, it can be concluded that the use of SBS as a single or composite additive can has very positive effects on the rheological properties of bitumen [16–22]. Nanotechnology is a term that applies to all advanced nanoscale technologies. The major difference between nanotechnology and other technologies is the scale of materials and structures used in this technology. This difference is due to the change in the inher-

ent properties of the material at this scale [23]. As the particle size decreases, a larger percentage of atoms and molecules appear on the surface. Accordingly, their surface properties become more important and dominant, and thus have a greater impact on the physical and chemical properties of the materials. Therefore, the application of these materials in various branches of civil engineering has received much attention. Today, these materials are also used in bitumen and asphalt modification. Erol [24], Farias [25], Ratnasamy [26,27], Jahromi [28], Ven [29], Zhanping [30] and their colleagues conducted researches between 2009 and 2016 on the impact of nano-clay on bitumen and asphalt mixtures. The results of all the investigations showed the positive impact of single and composite usage of nano-clay. In 2019 Mousavinezhad and et al. [31] performed another research about improvement of rutting performance in asphalt mixtures containing steel slag aggregates with nano clay and SBS. The results indicated respective improvement of toughness and viscosity by an average of 25% and 101% upon addition of nano-polymer which enhanced the bitumen rheological characteristics while reducing the penetration grade. The asphalt rutting resistance and rutting depth exhibited some improvements as well. In this respect Ziari [32] and abkari [33] With their colleagues performed new research and they also saw positive results from using nano-clay in bitumen. Aditya and et al. performed a research about effects of Basalt and hydrated lime fillers on rheological and fracture cracking behavior of polymer modified asphalt (PMA) mastic [34]. In this research hydrated lime significantly improved rutting resistance of PMA mastics at high temperatures. In this respect Rasouli et al. conducted similar research with evaluating the effect of laboratory aging on fatigue behavior of asphalt mixtures containing hydrated lime [35]. Test results showed that fatigue life of asphalt mixtures is sensitive to their hydrated lime content. Addition of 1%, 1.5% and 2% of hydrated lime to mix design was found to improve the fatigue life of unaged asphalt specimens. Singh [36], Albayati [37], Aboelkasim [38], Kollaros [39] and et al. performed another similar research on modifying asphalt mixture with hydrated lime and all of them were able to achieve the desired results. However, the role of asphalt binder as an effective factor in the performance of asphalt mixtures has always been the focus of attention by researchers, particularly using of modified bitumen which improved the rheological properties of bitumen and increased its rutting resistance [40]. Various experiments are available to evaluate the performance of bitumen against rutting in high temperatures, such as the Rotational Viscometer (RV), Multi Stress Creep Recovery (MSCR), and Sweep Frequency. In recent years, the Multi Stress Creep Recovery (MSCR) test with the ASTM D7405-15 [41] and AASHTO T350-14 [42] standard was used as an alternative to estimate the rutting for various SHRP + tests. Several studies were conducted to evaluate linear and nonlinear viscoelastic behavior on modified and pure bitumen, which resulted in reduced permanent deformation and increased resistance to rutting [43–52]. In the present research, the effect of nano-clay, nano-lime and SBS additives on modification of polymer bitumen was evaluated to provide a suitable solution for increasing the capacity of asphalt pavements against dynamic loads. The materials and protocols of the tests used in the current study are presented in the following sections. In order to analyze and evaluate the creep parameters such as non-recoverable creep compliance (Jnr) and creep percentage recovery (R %) in the MSCR test, were investigated. The purpose of adding polymer to pure bitumen was to provide a polymer modified bitumen with higher quality. The percentages of added nanomaterials were obtained from previous studies.

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S.A. Ghanoon et al. / Construction and Building Materials 238 (2020) 117592 Table 2 Polymer specifications.

2. Materials, Mix design and test method 2.1. Bitumen

Specifications

The asphalt binder used in the current research was PG 64-22 produced by Pasargad oil refinery; the specifications of the bitumen are shown in Table 1.

Specific gravity Tensile strength Elongation at fracture point Module 300% Hardness Melting factor Brookfield viscosity

Unit 3

g/cm MPa % MPa Sh A g/10 min Pa.s

Standards

Value

ASTM ASTM ASTM ASTM ASTM ASTM ASTM

0.94 18 700 2.5 82 <1 20

D D D D D D D

792 412 412 412 2240 1238 1084

2.2. Polymer Polymers can increase the viscosity of asphalt binders at high temperatures or ductility of them at low temperatures. Styrene– Butadiene–Styrene (SBS) copolymers, because of their excellent engineering properties, are the most frequently used thermoplastic elastomers to modify the properties of asphalt binders [53]. SBS have a loose cross-link structure and only contribute to tensile strength when the chains are stretched to a great degree. They can stretch and recover their shape. Among the positive effects of this additive on bitumen are increasing resistance to rutting, good flow at high temperature, reducing temperature sensitivity, adhesive and cohesive failure, increasing stiffness and etc. [11–21]. The SBS polymer was used in this paper produced in Italy and specifications of it presented in Table 2.

Table 3 Specifications of montmorillonite nano-clay. Specifications

Unit

Value

SSA Density Moisture Size of particles, nm *Morphology: Cubic and hexagonal *Physical appearance: yellow powder, pale

m2/g g/mL °C nm

220–270 18 700 2.5

Table 4 Specifications of nano-lime. Specifications

2.3. Nanomaterials Two types of nanomaterials, Montmorillonite nano-clay and nano-lime (CaCO3) with high purity produced in the USA were used in the current study. Nanomaterials specifications are shown in Tables 3 And 4.

SSA Density Melting point Size of particles *Morphology: Cubic and hexagonal *Physical appearance: white powder

Unit 2

m /g g/mL °C nm

Value 220–270 0.68 825 10–45

2.5. Multiple stress creep recovery (MSCR) test 2.4. Mixing plan and aging The bitumen was mixed with nanomaterials and SBS by a highshear mixer at 3500 rpm for 60–80 min at 150–160 °C, according to ASTM C1738 [33], so that all compounds became homogeneous and uniform. Details of the bitumen mixing plan are shown in Table 5. From now on, the term BB refers to the Base bitumen and the control sample, and the terms C, L and S refer to nanoclay, nano-lime and SBS respectively. Before performing the MSCR test, the samples were placed in the aged state. The aging process was performed by RTFO machine at a temperature of 164 °C for 90 min. The aging of bitumen results from the evaporation of its light oils and oxidation (reaction with environmental oxygen). While producing hot asphalt and during its displacement, bitumen is aged due to high temperature and air flow in both mechanisms, as described in ASTM-D2872 [40]. The Rolling Thin Film Oven (RTFO) was used to simulate short term aging of bitumen and aging of the bitumen during the mixing and compaction of the hot mix asphalt at the field.

Table 1 Bitumen specifications. Specifications

Unit

Standards

Value

Density at 25 °C Penetration degree (100 g, 25 °C, 5 s) Softening point Ductility (25 °C, 5 cm/min) Flash point Solubility Penetration index The room-temperature dropKinematic viscosity at 135 °C

g/cm3 1/0 mm °C Cm °C % – % c.St

ASTM ASTM ASTM ASTM ASTM ASTM

1.045 68 53 min 100 304 99.5 0.3 0.05 357

D 70 D5 D36 D113 D92 D2042

ASTM D1754 ASTM 2170

The MSCR test was conducted in the DSR machine. 64 °C, is the highest work temperature of the control asphalt binder PG 64-22. But to investigate bitumen performance at higher and lower temperatures, this experiment was also performed at 58 °C and 70 °C. A water bath was used to control the temperature. Three replicates were used for each type of binder. The specimen diameter and thickness were 25 and 1 mm, respectively. 1 s shear creep load was applied on the sample, followed by a 9 s recovery. First 20 cycles of creep and recovery were conducted under the shear load of 0.1 kPa (the first 10 cycles are just for conditioning the binders). Then 3.2 kPa of shear load was applied on the same specimen for another 10 cycles. MSCR test was performed after the aging of samples in short term and in accordance with the ASTM D7405-15 and AASHTO T350-14 standard at three temperatures of 58 °C, 64 °C and 70 °C. The MSCR test in addition to describing the fundamental specifications of this test the stress performance will be easily available to users. DSR was used to test the samples. MSCR test characterizes the recovery and non-recovery properties of the asphalt binder under the shear creep load which are the percent recovery and non-recoverable creep compliance (Jnr). Jnr is used to evaluate the rutting potential of HMA and is determined by dividing the nonrecoverable shear strain by the shear stress. The average of values for each stress level was used in this study. Jnr is the rutting potential index in MSCR test while percent recovery reflects the elasticity of asphalt binder. Thus both Jnr and percent recovery (R%) were investigated to evaluate the effect of additive on asphalt high temperature performance. Also the percentage difference between (Jnr) for both stresses was calculated using Eqs. (1) to (3)

R% ¼

cr  100 ct

ð1Þ

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Table 5 Mixing plan of samples. Sample

Bituman

SBS (%)

Nano-Lime (%)

Nano-Clay (%)

Description

Temperature (°C(

1 2 3 4 5 6 7 8

PG PG PG PG PG PG PG PG

0 0 0 0 3 3 3 3

0 0 0 0 0 4 6 4

0 2 4 6 0 4 4 6

BB C2 C4 C6 S3 S3L4C4 S3L6C4 S3L4C6

58/64/70 58/64/70 58/64/70 58/64/70 58/64/70 58/64/70 58/64/70 58/64/70

J nr ¼

64-22 64-22 64-22 64-22 64-22 64-22 64-22 64-22

cnr  100 l

J nr diff ¼

J nr 3:2  J nr 0:1  100 J nr 0:1

ð2Þ

ð3Þ

where in Eq. (1) cr refers to the recoverable deformation and ct refers to total deformation; In Eq. (2) cnr is non-recoverable deformation and l refers to stress test (Pa). Asphalt binders can be classified based on the results of MSCR tests as acceptable for a certain traffic volume, using the value of J nr as a parameter, for which the literature presents some good correlations with mechanical tests on asphalt mixtures. 3. Results and analysis The results of the MSCR test included non-recoverable creep compliance (J nr ) and Deformation recovery percentage (R%) as well as relative differences between two stress levels (jnr diff ), were analyzed on samples. 3.1. Non-recoverable creep compliance (J nr ) This parameter may be the most important parameter obtained from MSCR test. This parameter, in addition to specifying unrecoverable creep, can also represent the delayed elasticity of bitumen. When the results of this parameter trends to zero, our results are more positive and resistance to rutting increases.

Figs. 1 and 2 show the results for this parameter. In these two figures, the decrease in J nr parameter is clearly visible in the modified samples compared to BB sample. What is that clear is the negative effect of temperature rise on all samples. When C2 as an additive was used, the J nr parameter ameliorated at stresses of 0.1 and 3.2 kPa, but this improvement was much more substantial at temperatures higher than the PG 64-22 bitumen tolerance temperature. This improvement trend increased by increasing the amount of nano-clay to C4 and C6 and was closer to zero. If we want to investigate the effect of nano-clay additive alone on bitumen, we can conclude that the increase in nano-clay content has a direct relationship with decreasing parameter J nr at all three temperatures of 58 °C, 64 °C, and 70 °C and at stresses of 0.1 and 3.2 kPa. This decrease indicates an increase in bitumen rutting resistance. Considering the values obtained from the effect of S3 on bitumen at stresses of 0.1 kPa, it can be concluded that at 58 °C and 64 °C, S3 had better results than C2 and C4, but upon further investigation, we can see the greater impact of C6 compared to 3S. This trend was changed at 70 °C and the effect of S3 was only better than C2 and had less positive effect on this parameter than C4 and C6. This procedure is repeated at high stresses, however, at 70 °C the effect of C2, C4, and C6 is greater than that of S3. The highest and lowest impacts are clearly identified by examining Tables 6 and 7, as well as Figs. 3 and 4. After investigating the effect of nano-clay as well as SBS on the improvement of J nr parameter, the composite effect of these two materials with nano-lime was investigated. For this purpose, three different composite types have been used to combine these

Fig. 1. Non-recoverable creep compliance values (J nr Þ at 0.1 kPa.

S.A. Ghanoon et al. / Construction and Building Materials 238 (2020) 117592

5

Fig. 2. Non-recoverable creep compliance values (J nr Þ at 3.2 kPa.

Table 6 Non-recoverable creep compliance (J nr ) values at 0.1 kPa. Sample

BB C2 C4 C6 S3 S3L4C4 S3L6C4 S3L4C6

Temperature (°C) 58

64

70

0/013 0/01211 0/00544 0/00301 0/00317 0/0025 0/00202 0/00179

0/034 0/0176 0/00891 0/00554 0/00653 0/00651 0/0046 0/00497

0/081 0/02012 0/0147 0/01056 0/0198 0/0185 0/0144 0/015

Table 7 Non-recoverable creep compliance (J nr Þ values at 3.2 kPa. Sample

BB C2 C4 C6 S3 S3L4C4 S3L6C4 S3L4C6

Temperature (°C) 58

64

70

0/014 0/0136 0/00887 0/00417 0/00365 0/00287 0/00255 0/0023

0/041 0/01919 0/01003 0/00677 0/00851 0/00735 0/0066 0/00678

0/103 0/0235 0/01681 0/01201 0/02681 0/02382 0/01989 0/01937

materials. SBS content was constant in all three composites and was used at 3%. The first composite used 4% nano-clay with 4% nano-lime (S3L4C4), the second composite used 4% nano-clay with 6% nano-lime (S3L6C4) and the third composite used 6% nano-clay with 4% nano-lime (S3L4C6). What is clearly visible at both high and low stresses is that at the PG 64-22 bitumen tolerance temperatures, the composites of these three materials together in all three states have a more positive effect on the bitumen than nano-clay and SBS. But at 70 °C, the impact of C6 on bitumen is far more favorable than the composite state of these three materials. Overall, in composite conditions, it can be concluded that at 58 °C, at both high (3.2 kPa) and low (0.1 kPa) stresses, the greatest improvement was achieved with the S3L4C6 composition. At 64 °C, the greatest improvement was achieved with the combina-

tion of S3L6C4 too. But this procedure is different at high and low stresses at 70 °C. At this temperature and at low stresses (0.1 kPa), S3L6C4 is most affected and S3L4C6 at high stresses (3.2 kPa). This is also clearly evident in Tables 6 and 7, as well as Figs. 3 and 4. Another parameter calculated is the jnr diff which can determine the amount of bitumen stress sensitivity. By observing Fig. 5 and the calculated values, we can understand the stress sensitivity of the samples, although this parameter may not clearly represent the stress sensitivity of the bitumen, but it may be somewhat indicative. The performance of the materials is clearly recognizable. In the composite state the best additive was S3L6C4 and S3L4C4.also C6 and C2 showed acceptable performance in this parameter.

3.2. Deformation recovery percentage (R %) As this parameter name implies, this parameter shows the percentage of deformation returned during bitumen loading, so it can be said that the higher this parameter, the better the results. In fact, the values obtained from the R% parameter complement the results of J nr parameter, and along with the J nr parameter can provide more complete results about the bitumen viscoelastic behavior. Figs. 6 and 7 show the results of this parameter at stresses of 0.1 and 3.2 kPa. After comparing these results with temperature differences, as in J nr , it is obvious that at 58 °C we will see the best performance of bitumen, but the purpose of this study is to investigate the effect of different modifiers on bitumen. We study the types of samples at low stresses first and then at high stresses. Results according to Tables 8 and 9, as well as Figs. 8 and 9, show that C2 had a negative effect on R% parameter of bitumen at low stresses and BB samples showed better results. But increasing the percentage of nano-clay to C4 and C6 changed the effect of this additive and improved bitumen performance, and this improvement was more significant with C6. Evaluation of bitumen behavior with S3 modifier also showed the positive effect of this additive on nano-clay. But this positive effect, at 70 °C, was less than effect of the C6 and could be related to the change in bitumen behavior at temperatures higher than the PG 64-22 bitumen tolerance temperature.

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0.09 0.08 0.07

BB

Jnr % (0/1 kPa)

0.06

C2

0.05

C4

0.04

C6 S3

0.03

S3L4C4

0.02

S3L6C4

0.01 0

S3L4C6 58

64

70

Temp (°C) Fig. 3. Increasing trend of Non-recoverable creep compliance (J nr ) values at 0.1 kPa.

0.12 0.1 BB

Jnr % (3/2 kPa)

0.08

C2 C4

0.06

C6 S3

0.04

S3L4C4 S3L6C4

0.02

S3L4C6 0

58

64

70

Temp (°C) Fig. 4. Increasing trend of Non-recoverable creep compliance (J nr ) values at 3.2 kPa.

The results obtained in the composite mode in all three samples indicated the positive effect of the composite of the three additives, except that the most improvement in all three temperatures was related to the S3L6C4 composite, which resulted in the highest R %. Next up is the S3L4C6 composite which has a more effective recovery than the S3L4C4 bitumen. At high stresses, the results were significantly different from those at low stresses, and these differences were very pronounced at 64 °C and 70 °C. Comparison of the results of BB and modified nano-clay samples at the three temperatures was similar to low stresses with two minor differences. First, C2 also improved bitumen behavior, and secondly, at 64 °C and 70 °C, R% values of BB samples were negative. At high stresses, SBS at 64 °C and 70 °C did not meet expectations like J nr , even at 70 °C made R% results worse than BB samples. Although the S3L4C4 composite performed better than SBS at

64 °C, the results were negative at 70 °C. The best performance in composite mode was again related to S3L6C4, which had the most positive effect on bitumen performance at high temperatures. However, at 70 °C, this effect was less than C6. Next up is the S3L4C6 composite. 4. Summary The best and worst additives for improving bitumen properties are summarized in Table 10, as shown in Tables 6–9. According to Table 10, it can be concluded that among the modified samples, the worst performance was related to C2 and S3. Also, it can be concluded that the greatest improvement was achieved with the S3L6C4 composition. The C6 caused the highest decrease in the J nr parameter and the highest increase in the R% parameter. The S3 additive at 58 °C showed better performance than all

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S.A. Ghanoon et al. / Construction and Building Materials 238 (2020) 117592

Fig. 5. jnr diff values and stress sensitivity.

50 45 40

-5

58

64

Temp (°C) Fig. 6. Deformation recovery percentage (R%) values at 0.1 kPa.

S3 S3L4C4 S3L6C4 S3L4C6

C4

0

C2

5

C4

10

BB C2

C6

15

C4 C6

20

BB C2

25

C6 S3 S3L4C4 S3L6C4 S3L4C6

S3 S3L4C4 S3L6C4 S3L4C6

30

BB

R % (0/1 KPa)

35

70

8

S.A. Ghanoon et al. / Construction and Building Materials 238 (2020) 117592

35

S3L4C4 64

S3

C6

S3

58

-5

BB C2 C4

0

C4

5

C6

10

BB C2

R % (3/2 KPa)

15

BB C2 C4 C6 S3 S3L4C4 S3L6C4 S3L4C6

20

S3L4C4 S3L6C4 S3L6C4

25

S3L4C4 S3L6C4

30

70

-10 -15

Temp (°C) Fig. 7. Deformation recovery percentage (R%) values at 3.2 kPa.

Table 8 Deformation recovery percentage (R%) values at 0.1 kPa. Sample

BB C2 C4 C6 S3 S3L4C4 S3L6C4 S3L4C6

5. Conclusions

Temperature (°C) 58

64

70

5/81587 3/58891 9/00156 16/94156 24/9497 28/37691 38/03018 35/6301

4/51003 2/69501 6/0569 12/98808 18/29622 20/51063 28/88284 24/76384

1/1589 0/00267 4/1289 10/02687 8/58551 13/63272 20/47367 15/15399

Table 9 Deformation recovery percentage (R%) values at 3.2 kPa. Sample

BB C2 C4 C6 S3 S3L4C4 S3L6C4 S3L4C6

Temperature (°C) 58

64

70

1/06782 2/51706 6/00478 10/45879 15/05548 20/08455 25/79356 24/49159

1/00236 0/98557 3/26987 8/70089 3/40406 6/2268 12/43461 9/8082

2/20896 0/00089 1/54236 3/98745 2/70062 1/68937 1/66253 0/43534

nano-clay modified samples. At 64 °C and 70 °C, although it was able to improve bitumen rutting resistance to a large extent, but C4 and C6 produced better results. Evaluation of bitumen performance at temperatures higher than the bitumen tolerance temperature showed that C6 could perform best at this temperature. The results obtained from the performance of samples modified with S3L6C4 and S3L4C6 show that the effect of L6 is greater than of C6. Regardless of the bitumen performance in the samples tested, the lowest stress sensitivity at 58 °C, 64 °C and 70 °C was related to C2, C2 and C6, respectively.

After thoroughly examining the results of the experiments, the following results were obtained: - The results of the MSCR test indicate improvement of elastic properties of modified asphalt binders at a high temperature in all specimens. They also show that nano-clay (C) not only increases rutting resistance in modified asphalt but also reduces its stress sensitivity at PG 64-22 tolerance temperature (64 °C). Moreover, the nano-clay modifier alone had a significant improvement in bitumen performance. This improvement increased with the increase of nano-clay. It can be deduced that the binder modified by nano-clay contributes to resistance of the asphalt mixture against permanent deformations. Overall using nano-clay can improve the storage stability and temperature susceptibility of polymer modified bitumen. - Comparison of the results obtained in this study with previous studies, confirmed the positive effect of nano-clay on rutting resistance again and also showed that it can perform better in the composite state. - The results of the MSCR test for SBS modified bitumen, indicated positive effect of this additive on improving the rutting parameters. This improvement was greater at 58 °C than other temperatures. Moreover, this material in addition to increase resistance to rutting can reduce temperature sensitivity and increase stiffness. At high stresses and at temperatures higher than the PG 64-22 tolerance temperature, it did not show good stress sensitivity. - Examination of the composite states shows that the combination of this additives (nano-clay and SBS with nano-lime) can increase the bitumen yield results dramatically. In the composite state, these materials decreased the Non-recoverable creep compliance (J nr ) and increased the deformation recovery percentage (R %), which appeared as resistance to rutting. The composites of these materials showed high stress sensitivity. - The results obtained from the performance of samples modified show that the effect of nano-lime is greater than of nano clay in composite combination.

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50 45 40

R % (0/1 KPa)

35 30 25

58

20

64

15

70

10 5 0

BB

-5

C2

C4

C6

S3

S3L4C4

S3L6C4

S3L4C6

(Additive) Fig. 8. Graphical comparison of the effect of additives at 0.1 kPa.

35 30 25

R % (3/2 KPa)

20 15

58

10

64 70

5 0 -5

BB

C2

C4

C6

-10

S3

S3L4C4

S3L6C4

S3L4C6

(Additive) Fig. 9. Graphical comparison of the effect of additives at 3.2 kPa.

Table 10 Summary of best results. Stress

Temperature (°C)

0.1 kPa

58 64 70 58 64 70

3.2 kPa

Jnr

R%

Best

Worst

Best

Worst

S3L4C6 S3L6C4 S3L6C4 S3L4C6 S3L6C4 C6

C2 C2 C2 C2 C2 S3

S3L6C4 S3L6C4 S3L6C4 S3L6C4 S3L6C4 C6

C2 C2 C2 C2 C2 S3

- Temperature increase in both high and low stresses increased the values of the non-recoverable creep compliance (Jnr) and decreased deformation recovery percentage (R %) both in the base bitumen and modified bitumen samples, but addition of nano-clay, nano-lime and SBS largely neutralized this effects.

Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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