Valdés, Pérez-Jiménez, Miró and Martínez 1

Valdés, Pérez-Jiménez, Miró and Martínez

1

EXPERIMENTAL STUDY OF RECYCLED ASPHALT MIXTURES WITH HIGH 1 PERCENTAGES OF RECLAIMED ASPHALT PAVEMENT (RAP) 2

3

By 4

5 Valdés Vidal, Gonzalo 6 Researcher, Technical University of Catalonia 7 Associate Professor, Universidad de La Frontera 8 Francisco Salazar 01145, Temuco, Chile 9 Phone 005645325680, Fax 005645592812 10 [email protected] 11 12 Pérez Jiménez, Félix 13 Professor, Technical University of Catalonia 14 Jordi Girona 1–3, Módulo B1, 08034 Barcelona, Spain 15 Phone 0034934017085, Fax 0034934017264 16 [email protected] 17 18 Miró Recasens, Rodrigo 19 Associate Professor, Technical University of Catalonia 20 Jordi Girona 1–3, Módulo B1, 08034 Barcelona, Spain 21 Phone 0034934017085, Fax 0034934017264 22 [email protected] 23 24 Martínez, Adriana 25 Associate Professor, Technical University of Catalonia 26 Jordi Girona 1–3, Módulo B1, 08034 Barcelona, Spain 27 Phone 0034934017273, Fax 0034934017264 28 [email protected] 29 30 31 32 33 Submitted for Presentation and Publication at the 2010 Annual Meeting of the Transportation 34 Research Board 35 Submission date: November 13, 2009 36 Word count: 3765+3000+1250=8015 37

TRB 2010 Annual Meeting CD-ROM Paper revised from original submittal.

mailto:[email protected]�





2

ABSTRACT 1 2 This paper presents an experimental study to characterize the mechanical behaviour of 3 bituminous mixtures containing high rates of RAP. Two semi-dense mixtures of 12 and 20 mm 4 maximum aggregate size and containing 40 and 60% RAP, respectively (S-12 and S-20, in 5 accordance with Spanish specifications), which were used for rehabilitation of a Spanish 6 highway section, were evaluated. First, the effect of RAP variability on the recycled mixtures 7 was analyzed. Their mechanical properties were then studied by determining the stiffness 8 modulus and indirect tensile strength and applying a new direct tensile test, i.e. Fénix test, and 9 the three-point bending beam test. Results show that high rates of recycled material can generally 10 be incorporated into bituminous mixes by proper characterization and handling of RAP 11 stockpiles. 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46



3

INTRODUCTION 1 2 RAP rates between 10 and 30% are commonly used in bituminous mixes. According to several 3 studies, with these rates bituminous mixtures perform similarly to conventional mixtures (1, 2, 3, 4 4, 5, 6, 7, 8). However, environmental restrictions are causing an increase in RAP content added 5 to recycled mixtures used in bituminous pavement construction and rehabilitation. This has a 6 beneficial effect from the economic point of view and makes pavement construction sustainable 7 over time due to lower energy and natural resource consumption (9,10). 8

Laboratory and experimental field studies on mixtures containing large amounts of RAP 9 show the feasibility of this technique (11, 12, 13). However, as its use in road construction and 10 rehabilitation projects becomes more widespread, further research is necessary due to the 11 damaging effect of traffic and climatic conditions on mixtures. 12

The FENIX Project (“Strategic Research on Safer and More Sustainable Roads”) is 13 currently being undertaken in Spain. The FENIX Project is the greatest effort in research & 14 development of road paving made in Europe. It is structured around the following main research 15 lines: warm mixtures, perpetual pavements, recycling (cold and hot), by-products, safety and 16 comfort, nanomaterials, low energy consumption plants and fluidized bed (14). Its main purpose 17 is to create technical knowledge in order to develop construction technologies for safer, 18 sustainable, environmentally-friendly road infrastructure. The following experimental study, 19 which evaluates RAP variability and mechanically characterizes the properties of mixtures 20 containing high rates of RAP, has been performed in the area of recycled asphalt mixtures within 21 the FENIX project framework. 22

The aim of this work is to analyze the behaviour of mixtures with large RAP contents 23 (specifically, 40 and 60%) and compare it with that of conventional mixtures. 24 25 EXPERIMENTAL PROGRAM 26 27 Four tasks were carried out in cooperation with companies involved in the development area of 28 recycled asphalt mixtures within the framework of the Fénix project: 29

- Proper selection of a rehabilitation project where mixtures containing high rates of RAP 30 could be used. 31

- Determination of RAP characteristics (aggregate grading and binder content and 32 characteristics). 33

- Design of job mix formulas for the recycled mixtures and the standard conventional mix. 34 - Evaluation of the effect of RAP variability on higher RAP mixes and their mechanical 35

properties, and comparison of these properties with those of a conventional S-20 mixture 36 containing 60/70 penetration binder. 37

38 Project selection 39 40 The selected project consisted in rehabilitating the pavement of a highway section located in 41 Huesca, Spain, Figure 1. The top 80 mm of the asphalt mix was milled from the damaged 42 pavement, and an 80 mm asphalt layer of S-20 recycled mixture containing 60% RAP (S20R60) 43 was then laid. On top of this course, a 50 mm intermediate course of S-12 recycled mixture 44 containing 40% RAP (S12R40) was placed, and finally a wearing course of gap-graded mixture 45 prepared with a polymer-modified binder was laid. 46



4

1

2 (a) (b) 3 4

FIGURE 1 Spanish province where the selected project was conducted: (a) map of Spain 5 and (b) A-140 highway. 6

7 In order to reduce the heterogeneity of the recycled mixtures, they were fabricated with 8

two fractions of RAP, as recommended for recycled mixture preparation with higher RAP 9 percentages (15). The RAP proportions and fractions used in S20R60 mixture were 15% and 0/8 10 mm RAP and 45% and 8/25mm RAP, and for S12R40 mixture, 20% and 0/8 mm RAP and 20% 11 and 8/25mm RAP. Table 1 shows the RAP grading and the bitumen content for both RAP 12 fractions. Mixtures were made in a Double Barrel® drum mixer. 13

14 TABLE 1 RAP Grading and Bitumen Content (after extraction) 15

16 RAP Fraction (mm) 0/8 8/25 Bitumen content (% by weight of mix) 5.7 3.2 Sieve size (mm) Gradation (% Passing) 25 100 100 20 100 96 12.5 100 77 8 99 59 4 91 35 2 67 24 0.5 33 14 0.25 21 9 0.125 15 8 0.063 8.8 4.6

17 The binder recovered from the RAP had the following characteristics: 18 - Penetration grade of binder extracted at 25ºC (dmm) 5 19 - Softening point of aged binder (ºC) 87 20 - Asphaltenes (%) 44.62 21



5

Binders used in S20R60 and S12R40 mixtures had rejuvenating agents and their 1 penetrations grades were 250 and 200 (dmm), respectively. 2

An S-20 mixture incorporating 60/70 penetration bitumen and without RAP was used as 3 the control mixture. 4

5 Job Mix Formula 6

7 Mixtures were designed by the Marshall method, Tables 2 and 3. 8

9 TABLE 2 Gradations of Tested Mixtures 10

11 Sieve Size (mm)

Gradation for each Mix Type (% Passing) S 20R60 S 12R40 S 20

25 100 100 100 20 88 99 100 12.5 66 85 87.5 8 53 67 67.5 4 37 41 42.5 2 26 29 31 0.5 14 15 16 0.25 9 10 11 0.125 7 7.4 7.5 0.063 4.5 4.8 5

12 TABLE 3 Marshall Characteristics for Design of Tested Mixtures 13

14 Mix Type S 20R60 S 12R40 S 20

New bitumen penetration (dmm) 250 200 60/70 New bitumen content (% by weight of mix) 2.11 2.72 4.5 Total bitumen content (% by weight of mix) 4.4 4.5 4.5 Density (g/cm3) 2.449 2.418 2.426 Air voids (%) 3.8 4.4 3.4 Stability (kN) 17.5 15.6 15.1 Displacement (mm) 2.41 2.47 2.30 Marshall quotient (kN/mm) 7.26 6.31 6.57

15 Experimental Test 16 17 Stiffness Test 18 19 The stiffness modulus was determined in accordance with UNE-EN 12697-26:2006 Annex C at 20 a temperature of 15 ºC by the following expression: 21

22

hzFSm ⋅

+=

)27.0(ν (1) 23

24



6

where Sm = stiffness modulus (MPa); F = maximum value of applied vertical load (N); ν = 1 Poisson coefficient; h = specimen thickness (mm); z = horizontal displacement (mm). 2 3 Indirect Tensile Test 4 5 In order to evaluate indirect tensile resistance of the mixtures, the European standard UNE-EN 6 12697-23:2004 test was used where temperature was 15ºC and velocity was 50 mm/min. The 7 indirect tensile test consists in breaking cylindrical specimens by applying a compressive load 8 along the vertical diameter. Assuming a virtually constant distribution of stress across the load 9 application plane, indirect tensile resistance can be determined by the following expression: 10

11

hDPITS⋅⋅

⋅=π

2 12

(2) 13 14

where ITS = indirect tensile strength (MPa); P = applied load (N); D = specimen diameter (mm); 15 h = specimen thickness (mm). 16 17 Fénix Test 18 19 A new direct tensile test, the Fénix test, has recently been developed by the Road Research 20 Laboratory of the Technical University of Catalonia to determine the cracking resistance of 21 bituminous mixes by mainly evaluating the dissipated energy during the cracking process, GD, 22 together with stiffness and displacement parameters, IRT and ∆mdp, respectively (16). 23

The Fénix test consists in subjecting one half of a cylindrical specimen prepared by 24 Marshall or gyratory compaction to a tensile stress at a constant displacement velocity (1 25 mm/min) and specific temperature. A 6 mm-deep notch is made in the middle of its flat side 26 where two steel plates are fixed. Each plate is attached to a loading platen so that they can rotate 27 about fixing points, as illustrated in Figure 2. 28

29

30 (a) (b) 31

32 FIGURE 2 Fénix test: (a) test photo and (b) typical load vs. displacement output curve. 33

Loading platen

Fixing point

Notch

Steel plate



7

1 Load and displacement data are recorded throughout the test to calculate the parameters 2

involved in the cracking process. 3 Dissipated energy during cracking, GD, is determined by Equations 3 and 4: 4

5

lhW

G DD ⋅= (3) 6

7 where GD = dissipated energy during test application, J/m2; WD= dissipated work during test 8 application, area under load-displacement curve, kN-mm; h= specimen thickness, m; l= initial 9 ligament length, m. 10

11

∫∆

⋅=R

D duFW0

(4) 12

13 where F= Load, kN; u= displacement, mm; ∆R= displacement at F = 0.1 kN post- peak curve, 14 mm. 15

16 The tensile stiffness index, IRT, is calculated by Equation 5. Displacement at 50% of 17

post-peak load, ∆mdp, is also determined to evaluate the mixture ability to deform: 18 19

m

FIRT

∆

⋅=

max21

(5) 20

21 where IRT = tensile stiffness index, kN/mm; Fmax= peak load, kN; ∆m= displacement before peak 22 load at ½ Fmax, mm. 23

24 Fatigue Test 25 26 Fatigue laws of the analyzed mixtures were found by a three-point bending beam test under 27 controlled displacement, Figure 3. This test consists in subjecting a prismatic specimen to a time-28 varying displacement, according to a sinusoidal function described in European Standard UNE-29 EN 12697-24:2006. 30

The dynamic modulus at a specified cycle is defined as the quotient between the cyclic 31 amplitude of the stress function and the cyclic amplitude of the strain function: 32

33 c

c

TMDε

= (6) 34

35 where MD = dynamic modulus; Tc = cyclic amplitude of the stress function; εc = cyclic amplitude 36 of the strain function. 37 38



8

1 2 3

FIGURE 3: Anchoring devices for specimen testing: (a) scheme and (b) photo. 4 5

The fatigue law under controlled displacement is obtained from the following pairs of 6 values: half of the cyclic amplitude of the strain function at cycle 200 and the total number of 7 cycles applied to reduce the applied load to 50%. The fatigue law is expressed by the following 8 kind of equation: 9

10 bNa −⋅=ε (7) 11

12 where ε = half of the cyclic amplitude of the strain function at cycle 200; N = total number of 13 cycles; a and b = coefficients of the strain fatigue law. 14 15 DATA ANALYSIS AND RESULTS 16 17 RAP Variability Analysis 18 19 Some test results of the extraction of bitumen from RAP show greater dispersion for the coarser 20 RAP fraction. However, in general RAP binder contents were found to be approximately the 21 same as those in the job mix formula, Figure 4. 22

Deviations in RAP gradation are illustrated in Table 4 and represented in Figures 5 and 6. 23 Table 4 shows that the largest standard deviations from the job mix formula occur for 2, 4, 8 and 24 12.5 mm sieves, namely, the coarser RAP fraction, i.e. 8/25 mm. Furthermore, for this coarser 25 RAP fraction, a finer gradation on average was observed, Figure 5, as found by Solaimanian and 26 Tahmoressi in one single RAP fraction (17). On the other hand, the 0/8 mm fraction met on 27 average the job mix formula as reflected by the lower variation of its gradation, Figure 6. 28 Therefore, this analysis shows that variability of asphalt content and particle size is higher in the 29 coarser RAP fraction. 30



9

0.00

1.00

2.00

3.00

4.00

5.00

6.00

7.00

0 2 4 6 8 10 12 14 16 18 20

Extraction Number

% B

itum

en C

onte

nt (%

by

wei

ght o

f mix

) .

RAP 0/8 RAP 8/25 Target RAP 0/8 Target RAP 8/25

1 FIGURE 4: Control chart for RAP asphalt content. 2

3 4

TABLE 4 Standard Deviation From Job Mix Formula RAP Gradation for S 20R60 and 5 S12R40 mixtures 6

7 Sieve Size (mm)

RAP 0/8 RAP 8/25 Target Gradation

(%) Standard Deviation

Target Gradation (%)

Standard Deviation

25 100 - 100 0.51 20 100 - 96 1.70 12.5 100 - 77 6.36 8 99 0.61 59 7.90 4 91 3.12 35 6.51 2 67 3.61 24 5.04 0.5 33 1.82 14 2.48 0.25 21 2.15 9 1.88 0.125 15 1.38 8 1.23 0.063 8.8 0.67 4.6 0.91

8



10

Sieve Size Raised to 0.45 Power

Perc

ent P

assi

ng (%

)

RAP 8/25 Target GradationsAverage% Min% Máx.

70

40

50

60

80

90

100

0

10

20

30

0.50

0 2 4

12.5 20 25 40

0.06

30.

125

0.25

0 8 1

FIGURE 5 Control gradations from 8/25 RAP extraction. 2 3

Sieve Size Raised to 0.45 Power

Perc

ent P

assi

ng (%

)

RAP 0/8 Target GradationsAverage% Min% Máx.

70

40

50

60

80

90

100

0

10

20

30

0.50

0 2 4

12.5 20 25 40

0.06

30.

125

0.25

0 8

4 FIGURE 6 Control gradations from 0/8 RAP extraction. 5

6 Effect of RAP on Recycled Mixtures Variability 7 8 Recycled mixtures variability was determined from the mean deviations from mean values and 9 mean deviation from job mix formula values. These parameters were calculated by the following 10 equations: 11

12



11

∑=

−=n

ii XX

nD

1

1 (8) 1

∑=

−=n

iTFiTF XX

nD

1

1 (9) 2

3 where D = mean deviation (%); DTF =mean deviation from target formula; Xi = individual value; 4 X = mean value; XTF = target formula value 5 6

Figures 7 and 8 show the results obtained of the parameters indicated in previous 7 equations for the mixture bitumen content and gradation, respectively. Values of the mean 8 deviations of mixtures without RAP, as summarized in these figures, were obtained from 9 Solaimanian and Tahmoressi’s work because of the large number of samples used (17). 10

Results in Figure 7 show a greater mean deviation of bitumen content for the mixtures 11 with the largest RAP proportion, i.e. S20R60, and the largest coarse fraction percentage, i.e. 8/25 12 mm (45%). The mean deviations of S12R40 mixture are lower than those of S20R60 and similar 13 to the mean deviation from the job mix formula obtained in mixtures without RAP. 14

Figure 8a shows a greater mean deviation from the job mix formula for the 8 mm sieve of 15 recycled mixtures than for the 10 mm sieve used for mixtures without RAP. However, for the 16 0.063 mm sieve, the statistic values calculated reveal variability similar to that observed for 17 mixtures without RAP, Figure 8b. 18

This analysis shows that the increase in RAP content and the use of a coarser RAP 19 fraction, as the case of S20R60, have an influence on the variability of mixture grading and 20 bitumen content. This confirms the recommendations of Don Brock (15), namely that variability 21 of bitumen content and gradation is reduced by preparing mixtures with RAP separated and 22 stockpiled into different material fractions. 23 24

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

S20 R60 S12 R40 Without RAP

Types of Mixtures

Mea

n D

evia

tion

(%)

. Mean Deviation Mean Deviation from Target Value

25 FIGURE 7 Mean deviations from job mix formula target gradation for bitumen content. 26



12

0

2

4

6

8

10

12

S20 R60 S12 R40 Without RAP Sieve Nº 10

Types of Mixtures

Mea

n D

evia

tion

(%)

Mean Deviation Mean Deviation from Target Value

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

S20 R60 S12 R40 Without RAP

Types of Mixtures

Mea

n D

evia

tion

(%)

Mean Desviation Mean Desviation from Target Value

1 (a) (b) 2 FIGURE 8 Mean deviations from job mix formula target gradation: (a) 8 mm sieve and (b) 3

0.063 mm sieve. 4 5

Experimental Test Result Analysis 6 7 Figures 9 and 10 present the mean values of stiffness modulus and indirect tensile resistance 8 obtained for specimens and cores of the recycled mixtures used in the rehabilitation of A-140 9 highway. 10

Specimens of the mixture with the largest RAP content, i.e. S20R60, have a higher 11 stiffness modulus than that of the standard mixture containing 60/70 penetration binder. The 12 average modulus of S12R40 mixtures is slightly lower than that of S20R60 mixture. All 13 specimens have similar density levels. 14

The results for the cores extracted after 6-month service time show slightly lower average 15 density levels than those observed for laboratory specimens. The stiffness modulus values for all 16 recycled mixtures were very similar but slightly lower than those for specimens. 17

Stiffness moduli of S12R40 and S20R60 mixtures obtained from the cores after 12 and 18 24-month service times are slightly higher than those from the 6-month core, while density levels 19 were similar. 20

The indirect tensile test yielded very similar values for specimens of both recycled 21 mixtures but higher than those found for S20 mixture containing 60/70 binder. The ITS values 22 for 6-month cores are considerably lower than those obtained for the recycled mixtures but very 23 similar to those for 12-month cores. 24

The results of the above test show that there may be some factors of the construction 25 phase affecting the strength and density values obtained during the design of recycled mixtures, 26 such as laying temperature, compaction energy, etc. 27 28



13

2.000

2.050

2.100

2.150

2.200

2.250

2.300

2.350

2.400

2.450

2.500

S12R40

S20R60

S20B60/70

S12R40

S20R60

S12R40

S20R60

S12R40

S20R60

Den

sity

(gr/c

m3)

0

2000

4000

6000

8000

10000

12000

14000

Sm (M

Pa)

Density(gr/cm3) Sm (MPa)

Field Cores6 monthsSpecimens

Field Cores12 months

Field Cores24 months

1 FIGURE 9 Stiffness moduli and densities, specimens and field cores. 2

3 4

5

2.000

2.050

2.100

2.150

2.200

2.250

2.300

2.350

2.400

2.450

S12 R40 S20 R60 S20B60/70

S12 R40 S20 R60 S12 R40 S20 R60

Den

sity

(gr/c

m3)

0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

4.00

4.50

5.00

ITS

(MPa

)

Density(gr/cm3) ITS (MPa)

Field Cores6 monthsSpecimens Field Cores

12 months

6 FIGURE 10 Indirect tensile strength and densities, specimens and field cores. 7

8 9



14

The results of Fénix test on specimens of conventional and recycled mixtures are shown 1 in Figure 11. It can be observed a more fragile behaviour in recycled mixtures as RAP content 2 increases, showing higher loads, Fmax, and stiffness, IRT, values with regard to conventional 3 mixtures. Furthermore, values of displacement at 50% post-peak load, ∆mdp, are lower with 4 increasing RAP content. 5

6

00.20.40.60.8

11.21.41.61.8

22.22.42.62.8

3

0 0.5 1 1.5 2 2.5 3 3.5 4Displacement (mm)

Load

(KN

)

S20 R60S12 R40S20 B60/70

Fmax(KN)

IRT(KN/mm)

GD(J/m2) (mm)

∆mpd(mm)

∆Fmax

0.54 0.25 6.00 248 1.071.24 0.27 8.05 520 0.841.61 0.21 9.88 459 0.54

7 FIGURE 11 Fénix test results on specimens at 20 ºC. 8

9 The average values of the parameters obtained from specimens and cores by the Fénix 10

test for the standard and recycled mixtures are listed in Table 5. This table shows that Fmax and 11 IRT values for 6 and 12-month cores of recycled mixtures are very similar and lower than those 12 of the specimens, just like the results obtained for stiffness and ITS tests. 13

Values of dissipated energy during cracking, GD, are higher for the recycled mixture with 14 40% RAP content. Both recycled mixtures have higher GD values than the standard mixture 15 containing 60/70 binder. In the case of cores, values are slightly lower than those obtained for 16 specimens. 17

Under the Fenix test conditions, the results confirm that cracking propagation in the 18 recycled mixtures studied requires more dissipated energy than in the conventional mixture. 19 20 21 22 23 24 25 26 27 28



15

TABLE 5 Fenix Test Results at 20 ºC 1

Mixtures

Peak Load

Displacement Peak Load

Tensile Stiffness

Index

Dissipated Energy

Displacement 50% Post Peak

Load Fmax ∆Fmax IRT GD ∆mdp (kN) (mm) (kN/mm) (J/m2) (mm)

Specimens S 20 R60 1.61 0.21 9.88 459 0.54 S 12R40 1.24 0.27 8.05 520 0.84

S20 B 60/70 0.54 0.25 6.00 248 1.07 Cores 6 months

S 20 R60 0.91 0.27 6.20 446 0.95 S 12R40 0.87 0.20 6.36 510 0.82

Cores 12 months

S 20 R60 0.90 0.28 5.54 402 0.97 S 12R40 0.74 0.18 6.54 477 0.79

2 Figure 12 illustrates the fatigue laws of standard and recycled mixtures. The latter have 3

very similar deformation values for the same number of cycles, although the mixture with 60% 4 RAP content shows a higher dynamic modulus. The standard mixture has a lower dynamic 5 modulus and a greater ability to deform. 6 7

S20R60 y = 0.0008x-0.1458

R2 = 0.6576

S12R40 y = 0.0011x-0.1751

R2 = 0.9585

S12R40 y = 0.0031x-0.1903

R2 = 0.7696

0.00001

0.00010

0.00100

0.01000

10000 100000 1000000

Number of Cycles

Def

orm

atio

n (m

m/m

m)

.

S20 R60 S12 R40 S20 B60/70MD = 5584 MPaMD = 11282 MD = 9671 MPa

8 FIGURE 12 Fatigue Laws. 9

10 CONCLUSIONS 11 12

The analysis performed on RAP samples reveals a certain degree of variability in RAP 13 binder content and gradation, being higher in the coarse RAP fraction. As a consequence, 14



16

dividing RAP into several fractions and using higher percentages of fine RAP fraction results in 1 greater control over bitumen content and gradation of recycled mixtures. 2

Stiffness modulus and ITS values for specimens of the recycled mixtures are higher than 3 those for the standard mixture. Cores have lower values than specimens, but differences between 4 cores extracted after different service times are not significant. 5

Fénix test allows distinguishing between more fragile or more ductile mixture behaviour 6 through the analysis of stiffness and displacement parameters, IRT and ∆mdp, respectively. 7 Results obtained indicate that recycled mixtures showed higher IRT, as well as higher stiffness, 8 Sm, and dynamic modulus, MD. Besides, it was also observed that recycled mixtures presented 9 lower displacement at 50% post-peak load (∆mdp), just like the deformation level of fatigue laws 10 regarding to the same parameters of the standard mixture. 11

No significant differences are found between the fatigue laws of the two recycled 12 mixtures. Nevertheless, their ability to deform at the same number of cycles is lower than that of 13 the standard mixture, and their dynamic moduli are higher, particularly that of the mixture with 14 the highest RAP content. 15

The evaluation of properties of the recycled mixtures analyzed in this study shows that it 16 is possible to use up to 60% RAP content in mix preparation. However, proper characterization 17 and handling of RAP stockpiles is crucial to avoid excessive mix heterogeneity. 18 19 ACKNOWLEDGMENTS 20 21 The authors thank the Spanish Centre for the Development of Industrial Technology (CDTI) for 22 its support in the development of the FENIX Project (www.proyectofenix.es). 23 24 REFERENCES 25 26 1. Kandhal, P. S., S. S Rao., D. E. Watson, and B. Young. Performance of recycled hot mix 27

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http://www.proyectofenix.es/�


17

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Valdés, Pérez-Jiménez, Miró and Martínez 1