Characterization of agglomeration of reclaimed asphalt pavement for cold recycling

Construction and Building Materials 240 (2020) 117912

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Characterization of agglomeration of reclaimed asphalt pavement for cold recycling Junqing Zhu, Tao Ma ⇑, Zhanyong Fang School of Transportation, Southeast University, 2 Sipailou, Nanjing, Jiangsu 210096, China

h i g h l i g h t s
Agglomeration property of RAP could be effectively evaluated using modified LA abrasion test.
A general indicator was proposed for the tests to describe the agglomeration degree of RAP and was found to be effective.
A classification method of RAP particles was proposed and weak type RAP has significantly higher agglomeration degree.

a r t i c l e

i n f o

Article history: Received 15 October 2019 Received in revised form 27 November 2019 Accepted 19 December 2019

Keywords: Reclaimed asphalt pavement Agglomeration Cold recycling Asphalt extraction test Modified Los Angeles abrasion test

a b s t r a c t Agglomeration of reclaimed asphalt pavement (RAP) is one of the most important factors affecting performance of cold recycled asphalt mixture. This research is conducted to evaluate the agglomeration of RAP collected from various sources including both raw milled-off and plant-crushed RAP. Three different test methods were used to examine the breaking of agglomerates of RAP, including asphalt extraction test, modified LA abrasion test and mixing test. LA abrasion revolution of RAP samples was performed at various rotations of 50r, 100r, 200r and 300r, and mixing test was performed at different mixing time of 0.5 min, 1 min, 2 min and 3 min. Effects of the testing conditions and plant-crushing on RAP deagglomeration were evaluated. The obtained results showed that all three tests could effectively reflect the agglomeration property of RAP materials. Good correlations were found among results of the three tests, while abrasion test and mixer test typically have lower loss% than asphalt extraction test. A general indicator of agglomeration degree was proposed for the tests to describe the agglomeration property of RAP and a classification method of RAP particles was proposed based on the results and findings in the tests. Weak structure of RAP has significantly higher agglomeration degree, while old aggregate has very low agglomeration degree. It is suggested to reduce content of weak RAP in the cold recycling process due to its negative impact on the performance of regenerated mixture. Ó 2019 Elsevier Ltd. All rights reserved.

1. Introduction Reclaimed asphalt pavement (RAP) is produced from milled or ripped off old asphalt pavement. It is commonly collected in loose granular form as a byproduct of pavement rehabilitation or reconstruction and has been widely used in new asphalt pavement as granular base/subbase course when pulverized or as additional aggregate in hot recycling or cold recycling [1]. Hot recycling of RAP currently is the most widely used asphalt recycling method in the world. Performance of hot-mix asphalt mixture containing RAP is evidently as well or even better than mixtures made with all new material [2]. Many researches have been conducted on ⇑ Corresponding author. E-mail address: [email protected] (T. Ma). https://doi.org/10.1016/j.conbuildmat.2019.117912 0950-0618/Ó 2019 Elsevier Ltd. All rights reserved.

effect of RAP on the performance of regenerated hot mixed asphalt mixture [3–8], and micromechanical properties of RAP [9–12]. Cold recycling of RAP is the process of recycling asphalt pavement without application of heat during the recycling process. Asphalt emulsions or emulsified recycling agents are typically used as the recycling additive [13]. For the Cold In-place Recycling (CIR), generally 100% of the RAP generated during the milling process is used. For the Cold Central-Plant Recycling (CCPR), content of RAP varies depending on RAP properties, such as gradation of RAP, extracted aggregates and properties of recovered asphalt binder [14]. Advantages of cold recycling include conservation of nonrenewable resources and energy, improved pavement performance and economic savings etc. [15]. The agglomeration of RAP particles is one of the most important factors affecting the performance of cold-regenerated asphalt mixtures [16]. However, minimal

J. Zhu et al. / Construction and Building Materials 240 (2020) 117912

information is available on the RAP agglomeration property to facilitate the structural design of cold recycled mixture design [17]. RAP is typically composed by bonding of old aggregate, filler and aged asphalt, showing variant physical and mechanical properties. It’s relatively easy to fracture or deform under loading. Due to the effects of the oxidized RAP binder and the potential for increased cracking at high RAP contents, the utilization rate of RAP is limited. A few studies have been carried out to study the agglomeration property of RAP. Xu et al. examined particle composition, clustering degree, crushing value and stability of RAP using extraction test, cantabro-crushing test and aggregate imaging measure system (AIMS), and it was suggested weak RAP should be avoided in the recycling process [16]. Guo analyzed breakage phenomenon of RAP in the compaction process which results in gradation changes of cold recycled mixture [18]. A discrete element model of RAP using PFC2D software was created to simulate the compaction process. It was found that with the increase of rolling times, the number of damaged RAP particles increased, which led to the change of mixtures gradation. Yang evaluated clustering property of RAP and variance of gradation, asphalt binder content, penetration of recycled asphalt binder, and the effects to the penetration of asphalt binder in the regenerated mixture [19]. Evaluation indicators of RAP were established. In the cold recycling process, the gradation of the RAP and extracted mineral aggregate have an effect on the selection of the amount of recycling additive and on final mixture performance, in light of coarse angular particles of conglomerated fines can be manufactured by cold milling that are not broken down by traffic [13]. Characterization of agglomeration of RAP particles and categorizing RAP for reuse in cold in-plant recycling more efficiently and effectively, remains an unsolved problem. The objective of this study is to investigate the agglomeration of RAP using three different tests and establish an evaluation method to quantify the agglomeration degree of RAP. A tentative categorizing method based on the evaluation method is also proposed in this study.

100 RAP1 RAP2 RAP3 RAP1 (extracted) RAP2 (extracted) RAP3 (extracted)

90 80

Percent Passing (%)

2

70 60 50 40 30 20 10 0 0.075

0.15

0.3

0.6

1.18

2.36

4.75

9.513.216 19

Sieve Size (mm) Fig. 1. Gradation of RAP materials.

Moreover, contents of fine materials smaller than 0.075 mm in the extracted RAP are significantly higher than original RAP. Due to the breaking of agglomerates of RAP particles during asphalt extraction and crushing, larger size RAP was broken down into smaller RAP particles. To accurately evaluate loss percentage after asphalt extraction or crushing, the RAP samples were first graded with sieve size 4.75 mm, 9.5 mm, 13.2 mm, 16 mm and 19 mm. RAP samples retained on each sieve size were collected and prepared for the tests. Standard test T0303-2005 in Test Methods of Aggregate for Highway Engineering (JTG E42-2005) was followed for sieve analysis [20]. 3. Methods 3.1. Asphalt extraction test

2. Materials RAP material was collected from stockpiles at three different sources. For each RAP source, both raw milled-off RAP and plantcrushed RAP were collected. Plant crushing was done by using horizontal impact crushers. RAP is crushed as a result of impact with the breaking bars and a striker plate. In consequence, there are three types of RAP materials and each RAP material were divided into crushed and unprocessed. Table 1 below presents the material properties of the collected raw RAP samples. Original compositions of them are dense-graded asphalt concrete (AC), stone matrix asphalt (SMA) and open-graded friction course (OGFC), and were labeled RAP1, RAP2 and RAP3, respectively. Nominal maximum aggregate size of RAP1, RAP2 and RAP3 are 20 mm, 13 mm and 13 mm, and asphalt binder content are 5.16%, 4.87% and 4.45%, respectively. Fig. 1 presents gradation of the RAP materials before and after asphalt extraction. Gradation of each RAP changed significantly with larger amount of finer material separated from the cluster.

To characterize the agglomeration phenomenon of RAP, centrifugal asphalt extraction test was first conducted on each size of RAP material and standard test T0722-1993 in Standard Test Method of Bitumen and Bituminous Mixtures for Highway Engineering (JTG E20-2011) was followed [21]. Chemical solvent trichloroethylene was used to remove the asphalt binder from the aggregate and a centrifuge extractor was then used to separate asphalt binder/solvent and aggregate. The initial and final weights of samples were obtained, and asphalt binder content was calculated. Fig. 2 below illustrates the RAP sample before and after the asphalt extraction test. Sieve analysis was then conducted on the extracted samples to determine the amount of aggregate retained on the original size sieve. Three parallel tests were conducted for each test and the results were averaged to obtain the final values. The loss percentage was then calculated using the following equation for each size. The loss percentage reflects the agglomeration degree of RAP. The higher the loss% is, the higher degree of agglomeration of the RAP is.

Loss%extraction ¼ ð1  wretained =wÞ  100% where, w is the weight of the RAP sample before extraction; wretained is the weight of RAP retained on the original sieve size.

Table 1 Material properties of RAP samples. Name

RAP1

RAP2

RAP3

Mixture Type Moisture Content Crushing Value (coarse agg.) Nominal Max. size (mm) Asphalt Binder Content

AC 1.21% 10.11% 20 5.16%

SMA 1.19% 11.29% 13 4.87%

OGFC 1.94% 10.71% 13 4.45%

3.2. Modified Los Angeles abrasion test A modified Los Angeles Abrasion test was conducted to evaluate the resistance to crushing and de-agglomeration of RAP. Standard test T0317-2005 in Test Methods of Aggregate for Highway

J. Zhu et al. / Construction and Building Materials 240 (2020) 117912

3

Fig. 2. RAP material before and after asphalt extraction test.

Fig. 3. (a) LA Abrasion tester; (b) asphalt concrete mixer.

Engineering (JTG E42-2005) was generally followed. RAP sample of each size was subjected to the rotating drum without steel balls and rotations of the drum was set at 50, 100, 200 and 300 to determine the effect of #rotations. Mass of RAP sample is 2000 g. Three replicate tests were conducted at each rotation and the results were averaged to obtain the final values. RAP sample was weighted before the test and RAP sample retained on the original size sieve was weighted after the test. The loss percentage was calculated using the following equation. The higher the loss% is, the lower resistance to degradation the RAP is. Fig. 3(a) shows the LA abrasion tester.

Loss%LA abrasion ¼ ð1  wretained =wÞ  100% where, w is the weight of the RAP sample before abrasion test; wretained is the weight of RAP retained on the original sieve size after abrasion test. 3.3. Mixer test To simulate the cold mixing process and evaluate the deagglomeration of RAP material during mixing, a mixer test was proposed and conducted. This test is significant for cold recycling of RAP. The prepared dry RAP sample was weighted to 1500 g and added into a mixing bowl and placed in the mixer for mixing at room temperature. Mixing duration was set at 0.5 min, 1 min, 2 min and 3 min to determine effects of mixing time. Three replicate tests were conducted for each test and the results were averaged to obtain the final values. After mixing, sieve analysis was then conducted on the mixed RAP samples. Mass of RAP samples retained on the original size sieve was weighted. The loss% of the RAP was then calculated using the following equation, similarly

to the previous equations. Fig. 3(b) shows the asphalt concrete mixer.

Loss%mixing ¼ ð1  wretained =wÞ  100% where, w is the weight of the RAP sample before mixing; wretained is the weight of RAP retained on the original sieve size after mixing. 4. Results and discussion 4.1. Test results 4.1.1. Asphalt extraction Figs. 4(a)–6(a) below present the asphalt binder content of RAP1, RAP2 and RAP3 of each individual size, and Figs. 4(a)–6(a) present the loss% of both raw milled off and plant crushed RAP1, RAP2 and RAP3 of each individual size after asphalt extraction test, respectively. Nominal size of RAP2 and RAP3 are 13 mm, maximum size of 13.2 mm was tested consequently. Figs. 4(a)–6(a) shows that asphalt binder content decreases with RAP size. This can be explained by the fact that the specific surface area (surface area per unit weight of the material) of aggregate particle increases with the reduction of size. As a result, finer aggregates of given weight absorb more binder than coarse aggregates. Figs. 4(b)–6(b) shows that agglomeration exists on all RAP samples reflected by the loss percentage after asphalt extraction. The agglomeration degree increases with RAP size and is relatively small and stable below size 4.75 mm. This shows coarse RAP particles are comprised of smaller size RAP particles and are prone to break down when subject to external forces. Comparing the three types of RAP samples, unprocessed RAP1 and RAP2 have significantly higher loss% than RAP3. This can be explained by the fact

J. Zhu et al. / Construction and Building Materials 240 (2020) 117912

8 7 6 5 4 3 2 1 0

100 80

RAP1

Loss %

Binder content (%)

4

60 40 RAP1 RAP1 (crushed)

20

RAP1 (crushed)

0

0.3 0.6 1.18 2.36 4.75 9.513.21619

Particle Size (mm)

2.36 4.75

9.5

13.2 16

19

Particle Size (mm)

8 7 6 5 4 3 2 1 0

100 80

RAP2

Loss %

Binder content (%)

Fig. 4. (a) Asphalt binder content of RAP1 and RAP1 (crushed); (b) Loss% of RAP1 and RAP1 (crushed) after asphalt extraction.

60 40 RAP2 RAP2 (crushed)

20

RAP2 (crushed)

0

0.3 0.6 1.18 2.36 4.75 9.513.21619

Particle Size (mm)

2.36 4.75

9.5

13.2 16

19

Particle Size (mm)

8 7 6 5 4 3 2 1 0

100 80

RAP3 RAP3 (crushed) 0.3 0.6 1.18 2.36 4.75 9.513.21619

Particle Size (mm)

Loss %

Binder content (%)

Fig. 5. (a) Asphalt binder content of RAP2 and RAP2 (crushed); (b) Loss% of RAP2 and RAP2 (crushed) after asphalt extraction.

RAP3 RAP3 (crushed)

60 40 20 0

2.36 4.75

9.5

13.2 16

19

Particle Size (mm)

Fig. 6. (a) Asphalt binder content of RAP3 and RAP3 (crushed); (b) Loss% of RAP3 and RAP3 (crushed) after asphalt extraction.

that RAP3 is open graded, which contains less amount of fine aggregates, and is therefore less likely to conglomerate. Comparing unprocessed and plant-crushed RAP samples, loss% of crushed samples are significantly lower, indicating that crushing is conducive to reduce agglomeration of RAP and produce more stable and uniform RAP aggregates. It is suggested to crush RAP particles before using it to produce consistent material. 4.1.2. Modified LA abrasion Figs. 7(a)–9(a) present the loss% of RAP1, RAP2 and RAP3 of each individual size after abrasion test with different #rotations of the test drum, and Figs. 7(b)–9(b) present the loss% of both raw milled off and plant-crushed RAP1, RAP2 and RAP3 of each individual size with 300 rotations of the test drum, respectively. As can be seen from Figs. 7(a)–9(a), loss% increase with more rotations of drum as expected. Figs. 7(b)–9(b) shows loss% increases with RAP particle size, similar to the asphalt extraction test. It proves existence of large RAP agglomerates comprised of fine RAP particles and are prone to break down when subject to external forces. The value of the loss% is obviously lower than

loss% of asphalt extraction test, however. Comparing unprocessed and plant-crushed samples, plant-crushed RAP samples have lower loss% than uncrushed ones. This is because agglomerates were downsized during the plant crushing process and again it shows that it is crushing contributes to produce consistent RAP particles. Comparing the three types of RAP samples, RAP1 has much higher loss% than RAP2 and RAP3. This is because RAP 1 has larger nominal size and is more prone to conglomeration. Original aggregates of RAP3 contain less fine materials and is therefore have lower loss % in the test. 4.1.3. Mixer test Figs. 10(a)–12(a) present the loss% of RAP1, RAP2 and RAP3 of each individual size after mixer test with different mixing durations, and Figs. 10(b)–12(b) present the loss% of both raw milled off and plant-crushed RAP1, RAP2 and RAP3 of each individual size at 3-min mixing time, respectively. As can be seen from above figures, overall trend of the loss% with respect to particle size is close to that in the asphalt extraction test and LA abrasion test. Figs. 10(a)–12(a) show that loss%

5

J. Zhu et al. / Construction and Building Materials 240 (2020) 117912

100

100

60 40

80

Loss%

Loss %

80

50r 100r 200r 300r

60 40 20

20 0

RAP1 RAP1 (crushed)

0 4.75

9.5

13.2 16

2.36 4.75

19

Particle Size (mm)

9.5

13.2 16

19

Particle Size (mm)

Fig. 7. (a) Effect of #rotations on the loss% of RAP1; (b) Loss% of RAP1 after LA abrasion test at 300 r.

100

100

60 40

80

Loss%

Loss %

80

50r 100r 200r 300r

60 40 20

20 0

RAP2 RAP2 (crushed)

0 4.75

9.5

13.2 16

2.36 4.75

19

9.5

13.2 16

19

Particle Size (mm)

Particle Size (mm)

Fig. 8. (a) Effect of #rotations on the loss% of RAP2; (b) Loss% of RAP2 after LA abrasion test at 300 r.

100

100

60 40

80

Loss%

Loss %

80

50r 100r 200r 300r

60 40

20

20

0

0 4.75

9.5

RAP3 RAP3 (crushed)

2.36 4.75

13.2 16

9.5

13.2 16

19

Particle Size (mm)

Particle Size (mm)

Fig. 9. (a) Effect of #rotations on the loss% of RAP3; (b) Loss% of RAP3 after LA abrasion test at 300 r.

100

100

60 40

0.5 min 1 min 2 min 3 min

60 40 20

20 0

RAP1 RAP1 (crushed)

80

Loss%

Loss %

80

0 2.36 4.75

9.5

13.2 16

19

Particle Size (mm)

2.36 4.75

9.5

13.2 16

19

Particle Size (mm)

Fig. 10. (a) Effect of mixing time on the loss% of RAP1; (b) Loss% of RAP1 after mixing test at 3 min.

of each RAP group increase with mixing duration as expected. The loss% is significantly lower, however. This is because less mixing force and therefore less abrasion and grinding are involved in the mixing process, compared with LA abrasion test. Figs. 10(b)–12

(b) show that plant-crushed RAP samples have lower loss% than uncrushed ones, similarly. Comparing the three types of RAP samples, RAP1 has higher loss% than RAP2 and RAP3 due to its larger nominal size. RAP3 has the lowest loss% because it’s open graded.

6

J. Zhu et al. / Construction and Building Materials 240 (2020) 117912

100 0.5 min 1 min 2 min 3 min

30 20

RAP2 RAP2 (crushed)

80

Loss%

Loss %

40

60 40

10

20 0

0

2.36 4.75

9.5

13.2 16

2.36 4.75

19

Particle Size (mm)

9.5

13.2 16

19

Particle Size (mm)

Fig. 11. (a) Effect of mixing time on the loss% of RAP2; (b) Loss% of RAP2 after mixing test at 3 min.

100

40 0.5 min 1 min 2 min 3 min

20

RAP3 RAP3 (crushed)

80

Loss%

Loss %

30

10

60 40 20 0

0

2.36 4.75

9.5

13.2 16

2.36 4.75

19

9.5

13.2 16

19

Particle Size (mm)

Particle Size (mm)

Fig. 12. (a) Effect of mixing time on the loss% of RAP3; (b) Loss% of RAP3 after mixing test at 3 min.

4.2. Analysis 4.2.1. Correlation analysis Figs. 7 and 13 (a) shows the correlation between loss% in the LA abrasion test at 300 rotations and loss% in the extraction test, and Figs. 7 and 13 (b) shows the correlation between loss% in the mixer test at 3 min mixing time and extraction test. Both alternative methods showed good linear correlation with the extraction test, with R2 value of 0.8894 and 0.8291. It suggests that LA abrasion test and mixer test could effectively reflect the agglomeration of RAP materials. However, neither crushing methods could completely break agglomeration of RAP aggregates. Loss% are both lower than asphalt extraction test, therefore. LA abrasion test is more effective in terms of breaking the agglomerates since more breaking force and grinding is involved during the process. The mixer test, on the other hand, was not designed for downsizing of RAP materials and could only break down weak RAP agglomerates.

4.2.2. Agglomeration degree indicator To quantify the agglomeration degree of RAP in each test, a agglomeration degree indicator w was defined as combined loss

LA Abrasion Loss%

y = 0.8715x - 13.51 R² = 0.8894

80 60

w¼

40 20 0

 n  1X wi1  wi2 % n i¼1 wi1

where, n is the number of sieve size; wi1 is weight of the ith particle size before test; wi2 is the weight of the ith particle size after test. In this study, only sieve size above 4.75 mm was used. Table 2 below presents the agglomeration degree using three types of tests. Crushed RAP has clearly lower agglomeration degree. Agglomeration degree in the asphalt extraction test is significantly higher than the other two tests, as expected. The mixer test has the lowest agglomeration degree because of less mixing force and therefore less abrasion and grinding are involved in the mixing process. Among the three types of RAP material, RAP1 has the highest agglomeration degree. RAP2 has the lowest agglomeration degree. The effect of crushing is more significant on RAP3. The asphalt extraction test reflects the actual agglomeration degree of RAP and wextraction is the ideal indicator for agglomeration degree of RAP. However, for the cold recycled mixture, the RAP is

Mixing vs. Extraction

100

Mixing Loss%

LA Abrasion vs. Extraction

100

percentages of each size sieve. The equation is shown as below. Higher w indicates higher loss percentage of RAP during the test and therefore higher agglomeration degree of the RAP.

80 60

y = 0.4569x - 9.033 R² = 0.8291

40 20 0

0

20

40

60

80

Extraction Loss%

100

0

20

40

60

80

Extraction Loss%

Fig. 13. Correlation analysis (a) LA abrasion vs. extraction; (b) mixing vs. extraction.

100

7

J. Zhu et al. / Construction and Building Materials 240 (2020) 117912 Table 2 Agglomeration degree indicators of three tests. Test Type wextraction wLA Abrasion wmixer

RAP1 79.33 58.87 31.26

RAP1 (crushed)

RAP2

70.28 43.47 21.37

46.21 32.47 14.95

Table 3 Proportions and agglomeration degrees of different RAP particle types. RAP2 (crushed)

RAP3

36.90 28.79 8.72

72.09 41.00 16.87

RAP3 (crushed) 44.36 19.34 10.61

RAP Particle Type

Proportion (%)

wextraction

wLA

Weak Strong Agg.

35.58 44.27 20.15

100 74.21 4.70

93.58 72.18 16.68

abrasion

5. Conclusions not completely broken in the blending process. What is crucial to the performance of the mixture is the loss% during the blending process. LA abrasion test and mixer test simulate the blending process of RAP and are closer to the actual loss percentage of RAP. Therefore, retained% in the LA abrasion test and mixer test is more practical in terms of characterizing the agglomeration degree of RAP.

4.2.3. Implementation of RAP classification method Based on the results and findings in the above tests, RAP particles were empirically classified into strong RAP, weak RAP and aggregate. Strong RAP is defined as large RAP particle conglomerated by fines. Weak RAP is defined as RAP particle composed of small particles wrapped with asphalt binder. Aggregate is mainly the original complete aggregate particles. The classification method contributes to improve consistency of RAP in mix design for cold recycled mixture. Fig. 14 presents the illustration of the three RAP types. Based on the above classification, RAP2 aggregates of size above 16 mm were manually classified and weighed in the lab. Five replicate specimens of 2 kg each were prepared and hand-picked individually. The reason for using size of 16 mm and above is for the practicability cause for manual classification. Table 3 presents the average proportions of three RAP types among all 16-mm RAP2 particles and agglomeration degrees for extraction test and LA abrasion test. Strong RAP is the main type with 44% and aggregate is the least type with 20%. Weak RAP has highest wextraction and wLA abrasion, indicating high agglomeration degree and weak resistance to de-agglomeration. Aggregate has the lowest loss% in both tests, indicating minimum agglomeration degree and strong resistance to degradation. Strong RAP has slightly lower loss% than weak RAP but is still prone to de-agglomeration.

RAP material possesses variable and unpredictable performance due to its huge difference of structure and composition among different RAP particles. Some RAP particles are composed of coarse and fine aggregates coated with asphalt binder, and some are composed of a single coarse aggregate bonded by fine aggregates. And some are individual aggregate particles wrapped by aged asphalt. The structural characteristic of RAP material makes it prone to degradation during cold recycling process which significantly affects performance of the regenerated asphalt mixture. This study presents results of a tentative study on agglomeration of three types of RAP materials using three different tests, which are asphalt extraction test, modified LA abrasion test and mixer test. Findings in this study contributes to improve the consistency of RAP in mix design procedures and practices of cold recycling. It is also suggested to further investigate the effect of agglomeration degree on mix design and performance of the cold mixture. Main conclusions in this study are summarized as below. (1) Agglomeration exists on all RAP samples indicated by the loss of original size of RAP in all three tests. The agglomeration degree typically increases with RAP particle size. Among the three types of RAP samples, RAP1 has the higher agglomeration degree. (2) The asphalt extraction test reflects the actual agglomeration degree of RAP. Correlation analysis indicates that modified LA abrasion test and mixing test could also reflect the agglomeration degree of RAP. A general indicator is defined to describe the agglomeration degree of RAP for the three tests. (3) RAP particles were classified into strong RAP, weak RAP and aggregate. Weak structure of RAP has significantly higher agglomeration degree, while old aggregate has very low

Fig. 14. RAP types: (a) Weak RAP; (b) Strong RAP; (c) Aggregate.

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J. Zhu et al. / Construction and Building Materials 240 (2020) 117912

agglomeration degree. It is suggested to reduce content of weak RAP in the cold recycling process due to its negative impact on the performance of the regenerated mixture. CRediT authorship contribution statement Junqing Zhu: Methodology, Formal analysis, Writing - original draft, Writing - review & editing. Tao Ma: Conceptualization, Funding acquisition, Methodology, Supervision. Zhanyong Fang: Investigation, Data curation, Formal analysis. 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. Acknowledgements The study is financially supported by the National Natural Science Foundation of China (No. 51878164), Natural Science Foundation of Jiangsu Province, China (Grant No. BK20161421, BK20180149). References [1] A. Copeland, Reclaimed Asphalt Pavement in the Asphalt Mixtures: State of the Practice, Federal Highway Administration, McLean, VA, USA, 2011. [2] R. McDaniel, R.M. Anderson, NCHRP Report 452 Recommended Use of Reclaimed Asphalt Pavement in the Superpave Mix Design Method: Technician’s Manual, National Academy Press, Washington D.C., 2001. [3] S. Abraham, G.D. Ransinchung R.N, Effects of reclaimed asphalt pavement aggregates and mineral admixtures on pore structure, mechanical and durability properties of cement motar, Constr. Build. Mater. 216 (2019) (2019) 202–213. [4] X. Ding, L. Chen, T. Ma, et al., Laboratory investigation of the recycled asphalt concrete with stable crumb rubber asphalt binder, Constr. Build. Mater. 203 (2019) (2019) 552–557.

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