Experimental study of recycled asphalt concrete modified by high-modulus agent

Construction and Building Materials 128 (2016) 128–135

Contents lists available at ScienceDirect

Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat

Experimental study of recycled asphalt concrete modified by high-modulus agent Tao Ma a,⇑, Xunhao Ding a, Deyu Zhang b, Xiaoming Huang a, Jun Chen c a

School of Transportation, Southeast University, 2 Sipailou, Nanjing, Jiangsu 210096, China Department of Civil Engineering and Architecture, Nanjing Institute of Technology, 1 Hongjin Road, Nanjing, Jiangsu 211167, China c College of Civil and Transportation Engineering, Hohai University, Nanjing, Jiangsu 210098, China b

h i g h l i g h t s  High modulus recycled asphalt concrete with high modulus agents was deigned.  High modulus recycled asphalt concrete shows satisfied engineering properties.  Increasing asphalt content is helpful to reduce negative property effects of RAP.  High percentage of RAP can be used in high modulus recycled asphalt concrete.

a r t i c l e

i n f o

Article history: Received 14 September 2016 Received in revised form 10 October 2016 Accepted 14 October 2016

Keywords: Recycled asphalt concrete Rutting stability Moisture susceptibility Thermal cracking resistance Fatigue cracking resistance

a b s t r a c t Property characterization of high modulus recycled asphalt concretes modified by high modulus agents based on experimental evaluation and comparison with normal recycled asphalt concretes was performed in this paper. Both normal recycled asphalt concretes and high modulus recycled asphalt concretes with percentages of reclaimed asphalt pavement (RAP) varying from 20% to 60% were prepared for property evaluation including dynamic modulus by simple performance tester (SPT), rutting stability by wheel loading test, moisture susceptibility by Marshall test and indirect tensile test, thermal cracking resistance by three-point beam bending test, and fatigue cracking resistance by four-point beam bending test. It is found that, both RAP and high modulus agents can improve the dynamic modulus and rutting stability of asphalt concrete but jeopardize the thermal cracking resistance and fatigue cracking resistance of recycled asphalt concrete. However, the high modulus agents can enhance the moisture susceptibility of recycled asphalt concrete while the RAP could harm the moisture susceptibility of recycled asphalt concrete. It is also noticed that the high modulus agents can reduce the harmful effects by RAP on the properties of recycled asphalt concrete. Meanwhile, increasing the asphalt content of high modulus recycled asphalt concrete can further improve its moisture susceptibility, thermal cracking resistance and fatigue cracking resistance while keep its dynamic modulus and rutting stability still much better than the normal recycled asphalt concrete. The evaluation results show that the high modulus asphalt concrete have more tolerance than the normal asphalt concrete for negative effects of RAP on the engineering properties. It is more promising to use large percentage of RAP in the high modulus recycled asphalt concrete than in the normal recycled asphalt concrete. Ó 2016 Elsevier Ltd. All rights reserved.

1. Introduction It is proved that the long-term field service of asphalt pavement could lead to serious property degradation of asphalt and aggregates which are the basic raw materials for asphalt concrete, however, it doesn’t change the intrinsic characters of the two materials ⇑ Corresponding author. E-mail address: [email protected] (T. Ma). http://dx.doi.org/10.1016/j.conbuildmat.2016.10.078 0950-0618/Ó 2016 Elsevier Ltd. All rights reserved.

which make them still valuable for recycling [1–4]. Therefore, the recycling of reclaimed asphalt pavement (RAP) has been widely performed in asphalt paving industry for decades and it appears to cause more and more attentions across the world nowadays since it can help to offset the increased engineering costs, conserve energy and natural resources, solve waste disposal problems and protect environment [5–9]. Although the recycled asphalt concrete containing RAP can perform as well as virgin asphalt concrete, there are still many

129

T. Ma et al. / Construction and Building Materials 128 (2016) 128–135

technical barriers and concerns to prevent recycled asphalt concrete to be commonly used like virgin asphalt concrete, especially for recycled asphalt concrete with high percentage of RAP. One of the most concerns is that the RAP materials are often seriously aged which can cause mixing difficulties between RAP materials and virgin materials as well as property degradation of recycled asphalt concrete [10–14]. It is also one of the most important reasons for that the RAP percentage is usually controlled in the recycled asphalt concrete, commonly under 30%. To improve the property of RAP materials and minimize its potential compromise to the property of recycled asphalt concrete, soft asphalt and/or rejuvenators are usually taken into consideration during production of recycled asphalt concrete [15–18]. However, it is difficult to balance the cracking resistance and rutting stability for recycled asphalt concrete by using soft asphalt and rejuvenators. Although the soften asphalt and rejuvenators can improve the cracking resistance of recycled asphalt concrete, they can also jeopardize the rutting resistance of recycled asphalt concrete. More importantly, the property improvement is highly depended on the mixing and diffusion of soft asphalt and rejuvenators into RAP materials which is a very complex process hasn’t been clearly figured out by current studies [19–22]. It is one of the import reasons why recycled asphalt concrete usually has higher property variation and lower durability than virgin asphalt concrete. To avoid the problems with soft asphalt and rejuvenators, another technical approach by combining crumb rubber asphalt into the recycled asphalt concrete has been recently studied. Based on laboratory investigation, it is found that the crumb rubber asphalt can well improve the engineering properties and durability of recycled asphalt concrete [23–27]. However, the high viscosity of crumb rubber asphalt causes serious barrier to the merge of crumb rubber asphalt and RAP asphalt during field production and high percentage of RAP asphalt can cause sharp property degradation to crumb rubber asphalt. Therefore, as a promising technical approach, the combination of crumb rubber and RAP is still in practice and needs to be further studied. With the continuously increased traffic volume and heavy traffic loading, high modulus asphalt concrete keeps receiving attentions from worldwide pavement research communities. Due to its high dynamic modulus which is normally required to be higher than 14,000 MPa at testing temperature of 15 °C and loading frequency of 10 Hz, using of high modulus asphalt concrete is helpful to efficiently reduce the thickness of asphalt pavement and remarkably promote the rutting resistance of asphalt pavement [28–30]. According to previous studies, stiff asphalt, which can be obtained from refinery produced hard-grade asphalt, neat asphalt blended with natural asphaltite, and/or polyolefin modified asphalt, are usually used to prepare high modulus asphalt concrete [31–33]. Due to the hardness similarity between the stiff asphalt used for high modulus asphalt concrete and aged asphalt in RAP, the high modulus asphalt concrete is expected to have good potentiality for incorporating high percentages of RAP materials. Accordingly, the goal of this paper is to gain an improved understanding of the incorporating feasibility of high modulus asphalt concrete for RAP and the impacts by RAP on the engineering properties of high modulus asphalt concrete. Experiments were performed to evaluate the engineering properties such as dynamic modulus, rutting stability, moisture susceptibility, thermal cracking resistance and fatigue cracking resistance for high modulus asphalt concrete containing RAP named as high modulus recycled asphalt concrete in this study. And proposals were made to balance the cracking resistance and rutting resistance for high modulus recycled asphalt concrete.

2. Experimental 2.1. Materials Neat asphalt with penetration grade of 70, limestone aggregates and mineral fillers were used to produce normal asphalt concretes which are used as control asphalt concretes in this study. The basic properties of neat asphalt are shown in Table 1 while the basic properties of aggregates and fillers are shown in Table 2. According to Marshall mix design [34], normal asphalt concretes AC20 with nominal maximum aggregate size of 19 mm were produced. The designed normal AC20 with aggregate gradation presented in Fig. 1 has asphalt content of 4.3%. RAP materials, which were separated as coarse RAP and fine RAP, were obtained from the asphalt mixing plant. The original RAP was also dense-graded asphalt concrete with nominal maximum aggregate size of 19 mm. The basic properties of aged asphalt in RAP are also summarized in Table 1. It can be seen that the RAP asphalt is much aged compared to the neat asphalt. The aggregate gradations for coarse RAP and fine RAP are presented in Table 3 and the asphalt contents for coarse RAP and fine RAP are 4.1% and 5.1%, respectively. The coarse RAP and fine RAP were mixed based on weight ratio of 1:1 to get the mixed RAP materials for using in recycled asphalt concretes. The gradation of the mixed RAP is also presented in Table 3 and its asphalt content is 4.6%. A commercial high modulus agent as presented in Fig. 2 was used to produce high modulus asphalt concretes. The high modulus agents are synthetic low-molecular weight polyolefin polymers with basic properties presented in Table 4. It can be seen that the high modulus agents are in powder form and its melting point is within the normal production temperature range of asphalt concrete which are very helpful for the high modulus agents to be mixed into asphalt concrete. Based on the designed normal asphalt concrete AC20, two kinds of high modulus asphalt concretes named as high modulus AC20-A and high modulus AC20-B were prepared by adding the high modulus agents directly into the normal asphalt concretes during the production of asphalt concretes. Since the dynamic modulus of the prepared high modulus asphalt concretes at 15 °C and 10 Hz should be over 14,000 MPa according to previous studies [29,30], the content of high modulus agents were determined to be 0.3% by the weight of aggregates in the high modulus asphalt concretes based on trial tests. For the high modulus AC20-A, while the gradation and asphalt content were kept the same with the normal AC20, 0.3% of high modulus agents were used to produce high modulus asphalt concretes. Previous studies [17,19] indicate the both RAP and hard agents may influence the low-temperature and fatigue cracking resistance of asphalt mixture, therefore, a solution by increasing the asphalt content was evaluated in this study. Based on trial tests, while keeping the dynamic modulus at 15 °C and 10 Hz over 14,000 MPa, for the high modulus AC20B, the gradation and content of high modulus agents are the same with high modulus AC20-A, but the asphalt content was increased from 4.3% to 4.5%. Based on the designed normal asphalt concretes and high modulus asphalt concretes, while the gradations and asphalt contents kept constant, normal recycled asphalt concretes and high modu-

Table 1 Basic properties of neat asphalt and RAP asphalt. Test properties

25 °C penetration/ 0.1 mm

15 °C ductility/ cm

Softening point/ °C

Neat asphalt RAP asphalt

72 33

>100 13

47 57

130

T. Ma et al. / Construction and Building Materials 128 (2016) 128–135

Table 2 Basic properties of aggregates and fillers. Aggregates and fillers Apparent specific gravity Bulk specific gravity Absorption/%

9.5–16 mm 2.719 2.691 0.33

4.75–9.5 mm 2.733 2.694 0.42

2.36–4.75 mm 2.725 2.671 0.45

0–2.36 mm 2.681 2.548 1.44

Filler 2.722 / /

100 AC20 Upper limit Lower limit

Passing ratio/%

80 60 40 20 0

26.5

19

16

13.2 9.5 4.75 2.36 1.18 0.6

0.3 0.15 0.075

Sieving size/mm Fig. 1. Aggregate gradation for normal AC20.

lus recycled asphalt concretes were prepared based on different weight percentages (i.e., 20%, 30%, 40%, 50% and 60%) of RAP in the recycled asphalt concretes.

Fig. 2. Illustration of high modulus agents.

Table 4 Basic properties of high modulus agents.

2.2. Laboratory tests Based on the Chinese standard specification [35], to use the high modulus recycled asphalt mixture in the pavement structure, its engineering properties including dynamic modulus, rutting stability, moisture susceptibility, thermal cracking resistance, and fatigue cracking resistance should be evaluated and meet the requirements. Thus, to meet the standard requirements and to reveal the property characteristics of high modulus recycled asphalt mixture, the engineering properties of different asphalt concretes including dynamic modulus, rutting stability, moisture susceptibility, thermal cracking resistance, and fatigue cracking resistance were evaluated by SPT test (T0719-2011), wheel loading test (T0719-2011), three-point beam bending test (T0715-2011), Marshall test (T0709-2011) and indirect tensile test (T07162011), and four-point beam bending test, following the standard protocols in Chinese test specification and previous studies [23,26]. During the SPT test, the dynamic modulus, which is an important structural parameter for pavement design, is defined as the ratio of the axial stress to the recoverable axial strain measured from the test specimen. Since the most important design parameter for high modulus asphalt concrete is the dynamic modulus at temperature of 15 °C and loading frequency of 10 Hz, thus, SPT tests were conducted at temperature of 15 °C and loading frequency of 10 Hz for the different high modulus asphalt concretes in this study. For the wheel loading test, the dynamic stability, which is defined as the wheel loading cycles to cause 1 mm rutting depth on the testing specimen at 60 °C, is used to describe the

Test items

Test results

Test methods

Melting point/°C Viscosity at 140 °C/cps

120–130 400–600

ASTM D-3954 ASTM D-4402

high-temperature rutting stability of asphalt concretes, and higher dynamic stability represents better rutting stability. During the Marshall test, the Marshall strength ratio tested at 25 °C is defined as the ratio of the Marshall strength of specimens after specific immersion conditioning to the Marshall strength of the dry specimens. During the indirect tensile test, the indirect tensile strength ratio tested at 25 °C is defined as the average tensile strength of specimens after specific freeze-thaw conditioning to the average tensile strength of dry specimens. Both the Marshall strength ratio and tensile strength ratio are used to describe the moisture susceptibility of asphalt concrete, and higher Marshall strength ratio and tensile strength ratio indicate better moisture susceptibility. During the three-point beam bending test, the bending fracture strain, which is obtained when the testing beam is bending fractured at 10 °C, is used to characterize the thermal cracking resistance of asphalt concrete, and higher fracture strain means better thermal cracking resistance. During the four-point beam bending test, the fatigue life, which is defined as the loading cycles to cause the stiffness of the test specimen reduced by 50% at temperature of 15 °C and loading frequency of 10 Hz, is used to describe the fatigue cracking resistance of asphalt concrete, and higher fatigue life means better fatigue cracking resistance of asphalt concrete.

Table 3 Aggregate gradations for RAP materials. Sieving size/mm Passing ratio/%

Coarse RAP Fine RAP Mixed RAP

26.5

19

16

13.2

9.5

4.75

2.36

1.18

0.6

0.3

0.15

0.075

100 100 100

95.8 100 97.9

89.6 100 94.8

80.3 100 90.2

51.1 100 75.5

23.1 87.6 55.3

14.3 63.9 39.1

9.9 49.3 29.6

6.5 34.8 20.6

4.5 25.2 14.8

3.6 20.1 11.9

2.8 15.0 8.9

131

T. Ma et al. / Construction and Building Materials 128 (2016) 128–135

stiffer leading to higher dynamic modulus. The RAP addition is helpful to promote modulus of asphalt concrete.

3. Results and discussions 3.1. Dynamic modulus evaluation

3.2. Rutting stability evaluation The SPT tests were performed for different asphalt concretes and the test results are presented in Fig. 3. Fig. 3(a) illustrates the dynamic modulus for the normal asphalt concrete AC20 and the normal recycled asphalt concretes AC20 with different percentages of RAP. Fig. 3(b) illustrates the dynamic modulus for the high modulus asphalt concrete AC20 and the high modulus recycled asphalt concretes AC20 with different percentages of RAP. It is clearly noticed that, the dynamic modulus of high modulus asphalt concretes with no RAP is much higher than the normal asphalt concretes with no RAP. The dynamic modulus of high modulus AC20-B with no RAP is lower than that of high modulus AC20A with no RAP due to its higher asphalt content. However, it is still much higher than the dynamic modulus of normal asphalt concrete and can meet the modulus requirement of 14,000 MPa for high modulus asphalt concrete. Therefore, the high modulus agents can well promote the dynamic modulus of asphalt concretes. Meanwhile, for both normal AC20 and high modulus AC20, the recycled asphalt concretes have higher dynamic modulus than the asphalt concretes without RAP, and the dynamic modulus of recycled asphalt concretes gets bigger when the RAP percentage gets higher. It is indicated that the RAP addition raises the dynamic modulus of asphalt concretes. It is known that the stiffness of asphalt binder has important impacts on the dynamic properties of asphalt mixture and aged asphalt of RAP is stiffer than the neat asphalt [36–38]. Therefore, with the neat asphalt continuously replaced by the aged asphalt, the recycled asphalt concretes get

According to the planned wheel loading tests, the dynamic stability for different asphalt concretes are presented in Fig. 4. Fig. 4 (a) illustrates the test results for normal recycled asphalt concretes with different percentages of RAP. Fig. 4(b) gives the test results for high modulus recycled asphalt concretes with different percentages of RAP. And the dash lines in the figures represent the commonly accepted limit value for the dynamic stability [34]. It clearly illustrates that, the dynamic stability of high modulus asphalt concretes with and without RAP are much higher than that of the normal asphalt concretes with and without RAP. Although the dynamic stability of high modulus AC20-B is lower than the dynamic stability of high modulus AC20-A due to the increased asphalt content, they are still much higher than the dynamic stability of normal AC20. It proves that the high modulus asphalt concretes with and without RAP have much better high-temperature rutting stability than the normal asphalt concretes with and without RAP. The reasons are similar to the previous dynamic modulus evaluation. The high modulus agents can well enhance the stiffness and hardness of asphalt leading to good improvement on the hightemperature rutting stability of asphalt concretes. Based on further observation from the testing results, for both normal recycled asphalt concretes and high modulus recycled asphalt concretes, the dynamic stability grows while the RAP percentage grows, which means the high-temperature rutting stability gets better with the bigger RAP percentage. It is known that

1800

Dynamic stability /(cycles/mm)

9500

Dynamic modulus /MPa

9000 8500 8000 7500 7000 6500 6000 5500 5000

1600 1400 1200 1000 800 600 400 200 0

0

20

30

40

50

0

20

60

30

40

50

60

50

60

RAP Percentange /%

RAP Percentage /%

(a)

(a) 10000

Dynamic stability /(cycles/mm)

Dynamic modulus /MPa

24000 22000 20000 18000 16000 14000

High modulus AC20-A

12000 10000

High modulus AC20-B 0

20

30

40

50

60

RAP Percentage /%

(b) Fig. 3. Dynamic modulus for different asphalt concretes: (a) normal asphalt concretes with different percentages of RAP; (b) high modulus asphalt concretes with different percentages of RAP.

9000 8000

High modulus AC20-A High modulus AC20-B

7000 6000 5000 4000 3000 2000 1000 0

0

20

30

40

RAP Percentage /%

(b) Fig. 4. Test results from wheel loading tests: (a) for normal asphalt concretes with different percentages of RAP; (b) for high modulus asphalt concretes with different percentages of RAP.

132

T. Ma et al. / Construction and Building Materials 128 (2016) 128–135

the hardness of asphalt has important impact on the rutting stability of asphalt concrete [39–41]. Since the aged asphalt in RAP is harder than the neat asphalt, similar to the high modulus agents, the aged asphalt of RAP can increase the hardness of asphalt concrete which leads to better rutting stability. Therefore, the addition of RAP can further improve the rutting stability of high modulus asphalt concretes. The rutting stability evaluation confirms well with the previous dynamic modulus evaluation.

3.3. Moisture susceptibility evaluation The testing results from Marshall test and indirect tensile test for different asphalt concretes are presented in Fig. 5. Fig. 5 (a) and (b) illustrates the Marshall strength ratio vs RAP percentage and tensile strength ratio vs RAP percentage for normal asphalt concretes and high modulus asphalt concretes, respectively. And

RAP percentage /%

60 50

normal AC20

40

High modulus AC20-A High modulus AC20-B

30 20 0 60

65

70

75

80

85

90

95

100

Marshall strength ratio /%

(a)

RAP percentage /%

60

the dash lines in the figures represent the commonly accepted values [34] for the Marshall strength ratio and tensile strength ratio, respectively. Since the aging of asphalt damages its adhesion, the RAP addition could decay the asphalt adhesion which is critical for the moisture susceptibility of asphalt concrete [42,43]. Therefore, it is clearly presented that, for both normal recycled asphalt concretes and high modulus recycled asphalt concretes, the Marshall strength ratio and tensile strength ratio decrease with the RAP percentage increasing, which means that the moisture susceptibility for both normal recycled asphalt concretes and high modulus recycled asphalt concretes degrade with the RAP percentage increasing. It is also noticed that, with the same RAP percentage, the high modulus recycled asphalt concretes have better moisture susceptibility than the normal recycled asphalt concretes presented as higher Marshall strength ratio and tensile strength ratio. It is mainly due to the strong improvement by high modulus agents on the adhesion of asphalt. Meanwhile, the high modulus recycled asphalt concretes with higher asphalt content (represented by the high modulus AC20-B) show better moisture susceptibility than the high modulus recycled asphalt concretes with lower asphalt content (represented by the high modulus AC20-A). It is mainly because that, the higher asphalt content can reduce the air voids within asphalt concretes to reduce water infiltration and more neat asphalt can decline the negative effects by aged asphalt on the asphalt adhesion within recycled asphalt concretes. It can be further seen that, both the Marshall strength ratio and tensile strength ratio for the normal recycled asphalt concrete, high modulus recycled AC20-A and high modulus recycled AC20-B decay close to the commonly accepted values when the RAP content increases to be 30%, 50% and 60%, respectively. Therefore, both the addition of high modulus agents and the increasing of asphalt content can decrease the negative impacts of RAP and improve the moisture susceptibility of recycled asphalt concretes.

50 normal AC20

40

High modulus AC20-A

30

High modulus AC20-B

20 0 60

65

70

75

80

85

90

95

Tensile stregnth ratio /%

(b) Fig. 5. Test results for moisture susceptibility evaluation: (a) Marshal strength ratio by Marshall test; (b) tensile strength ratio by indirect tensile test.

3.4. Thermal cracking resistance evaluation Based on the low-temperature three-point beam bending tests for different asphalt concretes, Fig. 6 illustrates the fracture strain for normal recycled asphalt concretes and high modulus recycled asphalt concretes with different percentages of RAP. And the dash line in the figure illustrates the commonly accepted limit value [34]. It can be seen that, for both normal recycled asphalt concretes and high modulus recycled asphalt concretes, the higher the RAP percentage is, the lower the low-temperature fracture strain gets. It means that the thermal cracking resistance of recycled asphalt concretes decline with RAP percentage raises. It is proved that

2800

Fracture strain /

2600 2400

RAP content 0%

2200

RAP content 20% RAP content 30%

2000

RAP content 40%

1800

RAP content 50%

1600

RAP content 60%

1400 1200 1000

normal AC20

High modulus AC20-AHigh modulus AC20-B

Fig. 6. Test results for thermal cracking resistance evaluation.

133

T. Ma et al. / Construction and Building Materials 128 (2016) 128–135

the hardness of aged asphalt in RAP has negative effects on the flexibility and deformability of recycled asphalt concrete at low temperature [44,45]. From this point of view, it is easy to understand that high modulus asphalt concrete with no RAP (high modulus AC20-A) has lower fracture strain than the normal asphalt concrete with no RAP. It is also noticed that the high modulus AC20-B illustrates higher fracture strain than the high modulus AC20-A due to its higher asphalt content. Therefore, the addition of high modulus agents can improve the hardness of asphalt concrete leading to better rutting resistance but harm its flexibility leading to worse thermal cracking resistance while the increasing of asphalt content results in reverse effects. The further comparison between the normal recycled AC20 and the high modulus recycled AC20-A indicate that the high modulus agents can compromise the decay impacts by RAP on the fracture strain. It clearly illustrates that, with 40% RAP, the fracture strain of normal recycled AC20 is below the commonly accepted value while the fracture strain of high modulus AC20 is still above the commonly accepted value. Furthermore, with the asphalt content increasing, the high modulus recycled AC20-B illustrates higher fracture strain than the normal recycled asphalt concrete and high modulus recycled AC20-A at the same RAP percentage and the high modulus recycled AC20-B with 50% RAP still has higher fracture strain than the commonly accepted value. Therefore, high modulus asphalt concrete has better tolerance for RAP, especially with higher asphalt content. 3.5. Fatigue cracking resistance evaluation Based on the conduction of four-point bending beam fatigue tests at different test strains (i.e., 250 le, 350 le, 450 le, 550 le), the fatigue life for normal AC20, high modulus AC20-A and high

modulus AC20-B with different percentages of RAP are presented in Fig. 7. It can be seen that, for all of the asphalt concretes, the fatigue life decline with the RAP percentage growing. It is known that the fatigue cracking resistance of asphalt concrete highly relies on the asphalt property and aging can severely affect the fatigue properties of asphalt [46,47]. Based on the previous analysis in the moisture susceptibility evaluation and thermal cracking resistance evaluation, the addition of RAP harms the adhesion and flexibility of neat asphalt which can also lead to degradation of anti-fatigue property of recycled asphalt concretes. The reasons could also be used to explain the fatigue life comparison between the normal AC20 and the high modulus AC20-A. It is presented that, with no RAP addition, the high modulus AC20-A has lower fatigue life than the normal AC20. It is mainly due to the flexibility loss induced by the high modulus agents. However, the fatigue life difference between the normal AC20 and the high modulus AC20-A narrows with the RAP percentage growing. Especially when the RAP percentage exceeds 30%, the fatigue life of the high modulus AC20-A are close to the fatigue life of the normal AC20. It is because that the asphalt adhesion enhancement by the high modulus agents can compromise the negative effects by RAP. By looking into the comparison between the high modulus AC20-A and the high modulus AC20-B, it is clearly presented that higher asphalt content can improve the fatigue life of high modulus recycled asphalt concretes. Further observations also notice that, after the RAP content exceeds 30%, the high modulus AC20-B show better fatigue life than the high modulus AC20-A and the normal AC20. It indicates that more asphalt can further weaken the negative impacts of RAP by improving the asphalt adhesion and flexibility of asphalt concretes. The relationships between the fatigue life (presented as lgN) and test strains (presented as lgle) at different RAP percentages

90000

600000

80000

normal AC20

High modulus AC20-A

70000

High modulus AC20-A

60000

High modulus AC20-B

High modulus AC20-B

400000 300000 200000

Fatigue life /cycles

Fatigue life /cyles

500000

normal AC20

100000 0

50000 40000 30000 20000 10000

0

20

30

40

50

0

60

0

20

30

(a)

50

60

(c)

200000

45000

180000

normal AC20

40000

normal AC20

160000

High modulus AC20-A

35000

High modulus AC20-A

140000

High modulus AC20-B

30000

High modulus AC20-B

120000 100000 80000 60000

Fatigue life /cycles

Fatigue life /cycles

40

RAP percentage /%

RAP percentage /%

25000 20000 15000

40000

10000

20000

5000

0

0

20

30

40

RAP percentage /%

(b)

50

60

0

0

20

30

40

50

60

RAP percentage /%

(d)

Fig. 7. Fatigue life vs RAP percentage for different asphalt concretes at different testing strains: (a) 250 le; (b) 350 le; (c) 450 le; (d) 550 le.

134

T. Ma et al. / Construction and Building Materials 128 (2016) 128–135

3.9

6

0

5.8

20

5.6

30 40

5.2

50

5

60

4.8

normal AC20

3.7

High modulus AC20-A

3.6

High modulus AC20-B

3.5

Slope

lg N

5.4

3.8

3.4 3.3

4.6

3.2

4.4

3.1 3

4.2

2.9

4 2.3

2.4

2.5

2.6

2.7

2.8

0

lg

20

30

40

50

60

RAP percentage /%

(a)

Fig. 9. Slope vs RAP percentage for different asphalt concretes.

5.8 0

5.6

20

5.4

30

lg N

5.2

40

5

50

4.8

60

4.6 4.4 4.2 4 2.35

2.4

2.45

2.5

2.55

2.6

2.65

2.7

2.75

2.8

exceeding 30% while the slopes of high modulus AC20-A were lower than that of normal AC20 after the RAP percentage exceeding 30%. Since the higher slope means more sensitivity of fatigue life to test strain, it indicates that the enhancement by high modulus agents could intensify the sensitivity of fatigue life to test strain but weaken the impacts by RAP on the sensitivity of fatigue life to test strain. Meanwhile, by comparing the slopes of high modulus AC20-B to the high modulus AC20-A and normal AC20, it can be seen that increasing the asphalt content of high modulus recycled asphalt concretes can negative the sensitivity of fatigue life to the test strain.

lg 4. Conclusions

(b)

Laboratory property characterization of high modulus recycled asphalt concretes modified by high modulus agents were performed and compared with normal recycled asphalt concretes in this paper. The conclusion are summarized as follows:

5.8 0

5.6

20

5.4

30

lg N

5.2

40

5

50

4.8

60

4.6 4.4 4.2 4 2.35

2.4

2.45

2.5

2.55

2.6

2.65

2.7

2.75

2.8

lg

(c) Fig. 8. Relationships of fatigue life vs test strain at different RAP percentages for different asphalt concretes: (a) normal AC20; (b) high modulus AC20-A; (c) high modulus AC20-B.

for normal AC20, high modulus AC20-A and high modulus AC20-B are presented in Fig. 8. And the slopes for the regression curves in Fig. 8 are summarized in Fig. 9. From Fig. 8(a), it can be seen that, the difference between the regression curves for normal AC20 grows with the RAP percentage increasing, especially after the RAP percentage exceeding 30%. From Fig. 8(b), it is presented that, the difference between the regression curves for high modulus AC20-A increases with the RAP percentage increasing, especially after the RAP content exceeding 40%. Fig. 8(c) illustrates that the difference between the regression curves for high modulus AC20B raises with the RAP percentage increasing, especially after the RAP content exceeding 50%. The changing trends for the slopes vs RAP percentage presented in Fig. 9 proves the previous observations. It is also noticed that, the slopes of high modulus AC20-A were higher than that of normal AC20 before the RAP percentage

(1) The RAP addition cause property variations to both normal asphalt concrete and high modulus asphalt concrete. For both normal recycled asphalt concrete and high modulus recycled asphalt concrete, when the RAP content grows, the dynamic modulus and rutting stability increases while the thermal cracking resistance, moisture susceptibility and fatigue cracking resistance declines. (2) Compared to the normal asphalt concrete, high modulus asphalt concrete exhibits better dynamic modulus, rutting stability and moisture susceptibility but worse thermal cracking resistance and fatigue cracking resistance. Meanwhile, the addition of high modulus agents can reduce the negative impacts by RAP on the properties of recycled asphalt concrete. With the RAP percentage growing, the dynamic modulus, rutting stability and moisture susceptibility of high modulus recycled asphalt concrete are still much better than that of normal recycled asphalt concrete while the thermal cracking resistance and fatigue cracking resistance of high modulus recycled asphalt concrete get close to or even better than that of normal recycled asphalt concrete. (3) Increasing the asphalt content of high modulus recycled asphalt concrete illustrates negative impacts on the dynamic modulus and rutting stability but positive impacts on the moisture susceptibility, thermal cracking resistance and fatigue cracking resistance. Due to the strong improvement by the high modulus agents, the high modulus recycled asphalt concrete with higher asphalt content still has much better dynamic modulus and rutting stability than normal asphalt concrete. Due to the combining effect by high modulus

T. Ma et al. / Construction and Building Materials 128 (2016) 128–135

agents and high asphalt content, the high modulus recycled asphalt concrete can further compromise the negative impacts of RAP and get better thermal cracking resistance and fatigue cracking resistance than normal recycled asphalt concrete. (4) Compared to the normal recycled asphalt concrete, the high modulus recycled asphalt concrete have more tolerance for the negative effects of RAP on the engineering properties, and it presents a more effective way to consume large percentage of RAP. Due to property the characteristics of high modulus recycled asphalt concrete, it can be used in the pavement structure to provide satisfied rutting stability and moisture susceptibility. If the low-temperature cracking resistance and fatigue cracking resistance of pavement need to be paid attentions to, the RAP content of high modulus recycled asphalt concrete need to be controlled and the asphalt content of high modulus recycled asphalt concrete can be further increased based on the optimal asphalt content.

Acknowledgements The study is financially supported by the National Natural Science Foundation of China (Nos. 51378006 and 51378123), Huoyingdong Foundation of the Ministry of Education of China (No. 141076), Fundamental Research Funds for the Central Universities (No. 2242015R30027 and No. 2015B17014), Natural Science Foundation of Jiangsu Province (BK20161421 and BK20140109), State Key Laboratory of High Performance Civil Engineering Materials (2014CEM008) and National Engineering Laboratory for Advanced Road Materials. References [1] J. Yan, H. Zhu, Z. Zhang, L. Gao, S. Charmot, The theoretical analysis of the RAP aged asphalt influence on the performance of asphalt emulsion cold recycled mixes, Constr. Build. Mater. 71 (30) (2014) 444–450. [2] F. Gu, X. Luo, R. Luo, R.L. Lytton, E. Hajj, R.J. Siddharthan, Numerical modeling of geogrid-reinforced flexible pavement and corresponding validation using large-scale tank test, Constr. Build. Mater. 122 (2016) 214–226. [3] T. Ma, X. Huang, Y. Zhao, Aging behaviour and mechanism of SBS-modified asphalt, J. Test. Eval. 40 (7) (2012) 1186–1191. [4] T. Ma, X. Huang, Y. Zhao, Degradation behavior and mechanism of HMA aggregate, J. Test. Eval. 40 (5) (2012) 697–770. [5] T.W. Kennedy, W.O. Tam, Optimizing use of reclaimed asphalt pavement with the Superpave system, J. Asphalt Paving Technol. 67 (1998) 311–328. [6] X. Yu, Y. Li, Optimal percentage of reclaimed asphalt pavement in central plant hot recycling mixture, J. Wuhan Univ. Technol.-Mater. Sci. Ed. 25 (2010) 1070– 1076. [7] F. Hong, D.H. Chen, M.M. Mikhail, Long-term performance evaluation of recycled asphalt pavement results from Texas: pavement studies category 5 sections from the long-term pavement performance program, Transp. Res. Rec. 2180 (2010) 58–66. [8] C.T. Chiu, T.H. Hus, W.F. Yang, Life cycle assessment on using recycled materials for rehabilitating asphalt pavements, Resour. Conserv. Recycl. 52 (3) (2008) 545–556. [9] G. Thenoux, A. Gonzalez, D. Rafael, Energy consumption comparison for different asphalt pavements rehabilitation techniques used in Chile, Resour. Conserv. Recycl. 49 (4) (2007) 325–339. [10] J.P. Zhang, F.H. Yang, J.Z. Pei, S.C. Xu, F.W. An, Viscosity-temperature characteristics of warm mix asphalt binder with Sasobit, Constr. Build. Mater. 78 (2015) 34–39. [11] R. McDaniel, M. Anderson, Recommended use of reclaimed asphalt pavement in the Superpave mix design method: Technician’s Manual, National Cooperative Highway Research Program, NCHRP Report 452, 2001. [12] X. Luo, F. Gu, R.L. Lytton, Prediction of field aging gradient in asphalt pavements, J. Transp. Res. Rec. 2507 (2014) 19–28. [13] M. Tusar, E. Nielsen, F. Batista, M.L. Antunes, K. Mollenhauer, S. Vansteenkiste, I. Carswell, D. Kuttah, L. Viman, A. Waldemarson, Optimization of Reclaimed Asphalt in Asphalt Plant Mixing, Re-Road End of Life Strategies of Asphalt Pavements, European Commission DG Research, 2012. [14] T. Ma, X. Huang, Y. Zhao, Y. Zhang, H. Wang, Influences of preheating temperature of RAP on properties of hot-mix recycled asphalt mixture, J. Test. Eval. 44 (2) (2016) 762–769.

135

[15] S.P. Wu, X.M. Huang, Y.L. Zhao, The development of recycling agent for asphalt pavement, J. Wuhan Univ. Technol.-Mater. Sci. Ed. 17 (2002) 63–65. [16] J. Yan, Z. Zhang, H. Zhu, F. Li, Q. Liu, Experimental study of hot recycled asphalt mixtures with high percentages of reclaimed asphalt pavement and different recycling agents, J. Test. Eval. 42 (2014) 110–119. [17] T. Ma, X. Huang, Y. Zhao, B. Hussain, Compound rejuvenation of polymer modified asphalt binder, J. Wuhan Univ. Technol.-Mater. Sci. Ed. 25 (6) (2010) 1070–1076. [18] N.H. Tran, A. Taylor, R. Willis, Effect of rejuvenator on performance properties of HMA mixtures with high RAP and RAS contents, Final Report, NCAT Report 12-05, 2012. [19] T. Ma, X. Huang, Y. Zhao, Y. Zhang, Evaluation of the diffusion and distribution of the rejuvenator for hot asphalt recycling, Constr. Build. Mater. 98 (2015) 530–536. [20] R. Karlsson, U.L.F. Isacsson, Application of FTIR-ATR to characterization of bitumen rejuvenator diffusion, J. Mater. Civ. Eng. 15 (2003) 157–165. [21] M. Zaumanis, R. Mallick, R. Frank, Evaluation of rejuvenator’s effectiveness with conventional mix testing for 100% reclaimed asphalt pavement mixtures, Transp. Res. Rec. 2370 (2013) 17–25. [22] A. Booshehrian, W.S. Mogawer, S. Vahidi, Evaluating the effect of rejuvenators on the degree of blending and performance of high RAP, RAS, RAP/RAS mixtures, J. Assoc. Asphalt Paving Technol. 82 (2013). [23] T. Ma, H. Wang, Y. Zhao, X. Huang, S. Wang, Laboratory investigation of crumb rubber modified asphalt binder and mixtures with warm-mix additives, Int. J. Civ. Eng. (2016) (published online). [24] A. Ameli, R. Babagoli, M. Aghapour, Laboratory evaluation of the effect of reclaimed asphalt pavement on rutting performance of rubberized asphalt mixtures, Pet. Sci. Technol. 34 (5) (2016) 449–453. [25] F.P. Xiao, S.N. Amirkhanian, B.J. Putman, J. Hsein, Feasibility of Superpave gyratory compaction of rubberized asphalt concrete mixtures containing reclaimed asphalt pavement, Constr. Build. Mater. 27 (1) (2012) 432–438. [26] T. Ma, Y. Zhao, X. Huang, Y. Zhang, Characteristics of desulfurized rubber asphalt and mixture, KSCE J. Civ. Eng. 20 (4) (2016) 1347–1355. [27] F.P. Xiao, S.N. Amirkhanian, C.H. Juang, Rutting resistance of rubberized asphalt concrete pavements containing reclaimed asphalt pavement mixture, J. Mater. Civ. Eng. 19 (6) (2007) 475–483. [28] S.D. Capitao, S.L. Picado, Assessing permanent deformation resistance of high modulus asphalt mixtures, J. Transp. Eng. 5 (2006) 394–401. [29] P.J. Sanders, M. Nunn, The application of Enrobe Module Eleve in Flexible Pavements, Transport Research Laboratory, TRL Report 636, 2005. [30] W. Ban´kowski, M. Tušar, L.G. Wiman, Laboratory and Field Implementation of High Modulus Asphalt Concrete-Requirements for HMAC Mix Design and Pavement Design, European Commission DG Research, Paris, 2009. [31] J.F. Corte, Development and uses of hard-grade asphalt and of high-modulus asphalt mixes in France, Transp. Res. Rec. 503 (2003) 12–30. [32] E.F. Montanelli, I. Srl, Fiber/polymeric compound for high modulus polymer modified asphalt (PMA), Procedia – Soc. Behav. Sci. 104 (2013) 39–48. [33] H. Geng, S. Cristian, B. Clopotel, B. Hussain, Effects of high modulus asphalt binders on performance of typical asphalt pavement structures, Constr. Build. Mater. 44 (2013) 207–213. [34] Ministry of Transport of the People’s Republic of China, Standard Specification for Construction of Highway Asphalt Pavements, 2004. [35] Ministry of Transport of the People’s Republic of China, Standard Test Methods of Bitumen and Bituminous Mixtures for Highway Engineering, 2011. [36] T. Ma, X.M. Huang, U.B. Hussain, Evaluation of reclaimed asphalt pavement binder stiffness without extraction and recovery, J. Cent. South Univ. Technol. 18 (4) (2011) 1316–1320. [37] Y. Zhang, R. Luo, R.L. Lytton, Characterization of viscoplastic yielding of asphalt concrete, Constr. Build. Mater. 47 (2013) 671–679. [38] S. Wu, Q. Ye, N. Li, H. Yue, Effects of fibers on the dynamic properties of asphalt mixtures, J. Wuhan Univ. Technol.-Mater. Sci. Ed. 22 (2007) 733–736. [39] T. Xu, H. Wang, Z. Li, Y. Zhao, Evaluation of permanent deformation of asphalt mixtures using different laboratory performance tests, Constr. Build. Mater. 53 (2014) 561–567. [40] T. Xu, X. Huang, Investigation into causes of in-place rutting in asphalt pavement, Constr. Build. Mater. 28 (1) (2012) 525–530. [41] J. Zhang, J. Pei, Z. Zhang, Development and validation of viscoelastic-damage model for three-phase permanent deformation of dense asphalt mixture, J. Mater. Civ. Eng. 24 (7) (2012) 842–850. [42] T. Ma, X. Huang, E. Mahmoud, M. Garibaldy, Effect of moisture on the aging behavior of asphalt binder, Int. J. Min. Metall. Mater. 18 (4) (2011) 460–466. [43] J. Chen, H. Wang, L. Li, Virtual testing of asphalt mixture with two-dimensional and three-dimensional random aggregate structures, Int. J. Pavement Eng. (2015). [44] F. Gu, Y. Zhang, X. Luo, R. Luo, R.L. Lytton, Improved methodology to evaluate fracture properties of warm mix asphalt using overlay test, J. Transp. Res. Rec. 2506 (2014) 8–18. [45] Y. Zhang, X. Luo, R. Luo, R.L. Lytton, Crack initiation in asphalt mixtures under external compressive loads, Constr. Build. Mater. 72 (2014) 94–103. [46] H.N. Wang, Z. Dang, L. Li, Z. You, Analysis on fatigue crack growth laws for crumb rubber modified (CRM) asphalt mixture, Constr. Build. Mater. 47 (2013) 1342–1349. [47] F. Gu, X. Luo, Y. Zhang, R.L. Lytton, Using overlay test to evaluate fracture properties of field-aged asphalt concrete, Constr. Build. Mater. 101 (2015) 1059–1068.