Linear viscoelastic properties of warm-mix recycled asphalt binder, mastic, and fine aggregate matrix under different aging levels

Construction and Building Materials 192 (2018) 99–109

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Linear viscoelastic properties of warm-mix recycled asphalt binder, mastic, and fine aggregate matrix under different aging levels Qiang Li a,⇑, Guofen Li a, Xiang Ma a, Shuai Zhang b a b

School of Civil Engineering, Nanjing Forestry University, Nanjing 210037, China Department of Research and Development, Jiangsu Daorun Engineering Technology Limited, Nantong 226010, China

h i g h l i g h t s
The LVE properties of warm-mix recycled asphalt binder, mastic, and fine aggregate matrix were measured.
Effects of aging levels and recycling plans on the LVE properties and pavement performance were evaluated.
The critical material characteristic scales for evaluating different pavement performance were determined.

a r t i c l e

i n f o

Article history: Received 6 August 2017 Received in revised form 2 July 2018 Accepted 14 October 2018

Keywords: Warm-mix recycling Aging Dynamic shear rheometer Linear viscoelasticity Multiscale

a b s t r a c t The warm recycling technique has been increasingly used due to its advantages of environmental protection and high reclaimed asphalt pavement (RAP) utilization ratio. In this study, the linear viscoelastic (LVE) properties of warm-mix recycled asphalt binder, mastic, and fine aggregate matrix were measured by the dynamic shear rheometer (DSR) temperature and frequency sweep test. Effects of aging levels and recycling plans on the master curves of complex shear modulus |G⁄| and phase angle d as well as corresponding pavement performance parameters were evaluated by statistical methods. Pavement performance correlations among different material scales were investigated. It is found that magnitudes and master curve shapes of the |G⁄| and d vary with material length scales. The secondary aging behavior causes the improvement of the rutting resistance property and the reduction of the fatigue and low temperature cracking resistance property. Unlike the aging effect, using the WMA technique leads to opposite results. By comparison, using the SBR latex can improve all aspects of the pavement performance. The potential critical material characteristic scales for evaluating different pavement performance are finally determined. Ó 2018 Elsevier Ltd. All rights reserved.

1. Introduction The hot recycling technique of asphalt pavements is widely accepted because it has advantages of short construction period, early traffic opening, good performance, high economy benefit, and convenient use [1]. However, the heating temperature is an important factor limiting its application. For the in-plant recycling, the reclaimed asphalt pavement (RAP) from milling is not easy to be sufficiently heated due to the device limitation. It leads to a low RAP utilization ratio, generally <30% [2]. For the in-place recycling, the pavement surface is sometimes heated to over 220 °C to satisfy the construction temperature requirement. It causes a severe short-term aging for RAP and has a negative effect on the pavement performance for recycled asphalt mixtures [3]. ⇑ Corresponding author. E-mail address: [email protected] (Q. Li). https://doi.org/10.1016/j.conbuildmat.2018.10.085 0950-0618/Ó 2018 Elsevier Ltd. All rights reserved.

Moreover, a lot of smoke, toxic gases, and other harmful substances generated from the hot recycling construction violate the national policy of environmental protection and reducing emission [4]. The warm recycling technique by adding appropriate warm mix asphalt (WMA) agent during the hot recycling process can well solve this problem. It can effectively reduce the construction temperature over 30 °C, resulting in increasing the RAP utilization ratio and delaying the short-term aging process [3,5]. The warm recycling technique with the high RAP content (over 45%) has been increasingly since 2006 [6,7]. The main distresses of asphalt pavements, such as fatigue cracking, low-temperature cracking, and permanent deformation are strongly influenced by the viscoelastic properties of asphalt materials [8]. A series of exploring researches have been carried out aiming at the LVE properties of warm-mix recycled asphalt mixtures [9–12]. Most researches found that WMA mixtures with the high RAP content had similar or insignificantly lower |E*| values

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than hot mix asphalt (HMA) mixtures with the same RAP content [9,10]. However, there were still other researches reporting that using the WMA technique greatly reduced the mixture stiffness regardless of the RAP content, especially at low and intermediate temperatures [11,12]. Different or even contradictory conclusions proposed indicate the complexity in the coupling effect of the WMA, RAP, other additives, and new asphalt mixture on the LVE properties of warm-mix recycled asphalt mixtures. Traditionally, the LVE properties of asphalt materials are studied through a single material length scale experiment, mainly the mixture or binder scale. Its major drawback is either the homogeneity assumption or neglecting the complex interaction among binders, fillers, and aggregates [13]. Therefore, the multiscale experiment method has become popular. Safaei et al. [14] conducted the DSR linear amplitude sweep test and the dynamic modulus test on WMA and HMA materials to measure the |G*| for binders and |E*| for mixtures. A good agreement between the binder and mixture results was observed. Félix et al. [15] evaluated the complex modulus of the aged asphalt binder, mastic, and mixture using the Ensayo de BArrido de DEformaciones (EBADE) test. A good linear relationship between the binder and mastic stiffness was found and the correlation between the binder and mixture stiffness was fairly good. Underwood and Kim [16] performed the dynamic shear modulus test on asphalt binder, mastic, fine aggregate matrix (FAM), and mixture to identify the sensitivity to changes in the material composition. Materials at different characteristic scales showed differing levels of stiffness sensitivity. All above researches confirm the potential application prospect of the multiscale experimental method to evaluate the LVE properties of asphalt materials. The main objective of this study is to investigate the LVE properties evolution of warm-mix recycled asphalt materials during the service period. With this purpose, the DSR temperature and frequency sweep test was respectively performed on warm-mix recycled asphalt binders, mastics, and FAMs with the high RAP content under different aging levels. The master curves of complex shear modulus and phase angle were constructed based on the timetemperature superposition principle (TTSP). Effects of aging levels

and recycling plans on the rutting, fatigue cracking, and low temperature cracking parameters characterized by the LVE properties were evaluated by statistical methods. The correlations of different pavement performance parameters among asphalt binder, mastic, and FAM were finally developed.

2. Experimental plan 2.1. Materials and specimen fabrication The Lianxu Highway located in Jiangsu of China was open to traffic on November 30th, 2001. The total length of this highway was 237 km and the design speed was 120 km/h. In 2013, three different warm recycling plans were applied to the inplace recycling maintenance project for more than 40 km (single lane). For the selected pavement sections, the recycled mixture with a high RAP content of 85% was used. An experimental design as shown in Fig. 1 was developed based on this field project. The styrene butadiene styrene (SBS) modified asphalt binder (PG 7022) with similar properties as that used in the field during the construction period was selected as the virgin binder for the laboratory aging simulation besides being the new binder. A liquid rejuvenator agent that is rich in aromatics (4% of the RAP binder weight) was used in all plans. It can adjust the proportion of different constituents to partly recover the ductility and flexibility of the RAP binder. The WMA agent (5% of the total weight of the new and RAP binders) was added in plan 1 and 3 to help reduce the pavement construction temperature from 170 °C to 130 °C. The low-viscosity liquid surfactant-based WMA additive EvothermÒ DAT was selected. It is a chemical package of emulsification agent and anti-stripping agent. It can ensure the volumetric properties of the recycled mixture at a relatively low temperature by the lubrication action of the water film in the asphalt binder. In plan 1 and 2, the anionic styrene-butadiene rubber (SBR) latex (4% of the RAP binder weight) produced by the copolymerization of the SBR and emulsion was included to improve the RAP binder performance, including the resistance to the rutting, lowtemperature cracking, and moisture. Properties of three types of additives are shown in Table 1. As shown in Fig. 1, the warm-mix recycled asphalt binder under different aging levels corresponding to different service periods are obtained by a two-stage laboratory simulation method based on the rolling thin film oven test (RTFOT) and the pressure aging vessel (PAV). At the initial stage, the virgin SBS modified asphalt binder was aged 85 min at 163 °C by the RTFOT, followed by the PAV at 2.1 MPa and 100 °C for 74 h. It could simulate the binder aging level corresponding to approximate 12 years’ service before recycling. Then, the RAP binder was recycled by adding the virgin binder, rejuvenator agent, WMA agent, and/or SBR latex to the binder according to different recycling plans. The recycled binder was composed of the 85% RAP binder and 15% virgin binder. At the secondary stage, the recycled binder was aged again by the RTFOT and PAV following the same temperature and pressure

Virgin SBS modified asphalt binder Initial stage 1st RTFOT aged binder 163

/85 minutes

1st PAV aged binder 2.1 MPa/100

Recycling plan 1

85% 1st aged binder+15% new binder +rejuvenator+WMA+SBR

/74 hours

Recycling plan 2

85% 1st aged binder+15% new binder +rejuvenator+SBR

Recycling plan 3

85% 1st aged binder+15% new binder +rejuvenator+WMA

Secondary stage New limestone filler

Warm-mix recycled asphalt mastic 50% 2nd aged binder+50% filler

2nd RTFOT aged binder 163

2nd PAV aged binder 2.1 MPa/100

New limestone filler

New limestone fine aggregate

/85 minutes

/0, 6, 16, 28, 42 hours

DSR temperature and frequency sweep test Fig. 1. Experimental design.

Warm-mix recycled asphalt FAM the part (smaller than 4.75 mm) of the dense graded asphalt mixture with the nominal maximum aggregate size of 13.2 mm; the optimum binder content of 8.2%

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Q. Li et al. / Construction and Building Materials 192 (2018) 99–109 Table 1 Properties of different additives.

Table 3 Engineering properties of the limestone filler.

Property

Rejuvenator

Physical state 3

Density (g/cm ) PH Solid content (%) Amine value (mg/g) Kinetic viscosity at 60 °C (cSt) Dynamic viscosity at 60 °C (mPas) Surface tension at 25 °C (mN/m)

WMA

SBR

Brown liquid 0.935 / / / 320 /

Brown liquid 1.006 11.5 9.9 550 / /

White liquid 0.950 8 47 / / 50

52.2

/

/

Property

Result 3

Apparent density (g/cm ) Water content (%) Appearance Plasticity index (%) Passing percent < 0.6 mm (%) Passing percent < 0.3 mm (%) Passing percent < 0.15 mm (%) Passing percent < 0.075 mm (%)

2.721 0.2 No granule and caking 3.6 100.0 100.0 98.5 85.3

3. Experimental results and analysis conditions. Unlike the initial stage, the PAV aging durations at the secondary stage were 0, 6, 16, 28, 42 h to simulate the binder aging levels corresponding to different pavement service periods (re-count 0 year, 1 year, 2 years, 3 years, and 4 years), respectively [17]. Conventional physical properties of asphalt binders measured at each aging stage are provided in Table 2. The deterioration of aggregate properties during the pavement service period was not considered in this study. Artificial RAP mastic and FAM were produced by mixing the aged warm-mix recycled binder, new limestone filler, and new limestone fine aggregates. Main engineering properties of the filler and fine aggregates are shown in Tables 3 and 4, respectively. The colloid mill was used to produce asphalt mastic at 170 °C. The mass ratio of asphalt binder and limestone filler was 1:1. The filler could be more uniformly distributed in asphalt binder at a longer mixing time and a higher rotational speed. However, the electric motor of colloid mill may be burned out due to excessive heating after a too long time working or a too fast rotation. Therefore, the optimum mixing conditions were 35 min and 500–1000 rpm after several trials. The FAM gradation was designed based on the dense graded asphalt mixture with the nominal maximum aggregate size of 13.2 mm used in the field. The FAM gradation was the same as the part of the asphalt mixture gradation smaller than 4.75 mm. The specific surface area method was used to calculate the optimum binder content of FAM. It was assumed that each aggregate particle was homogeneously coated by the asphalt film with the thickness of 8 lm. The binder content was linearly correlated to the specific surface area [18]. In this study, the optimum binder content of 8.2% was finally determined. The cylindrical FAM specimen with 100 mm in diameter and 70 mm in height was firstly fabricated by the Superpave gyratory compactor. Then, each side of the specimen was sawed 10 mm due to the high air void. Finally, the high precision double-side saw was used to obtain the target beam specimen (air void of 4 ± 0.5%) with 50 mm in height, 10 mm in width, and 10 mm in length, as shown in Fig. 2.

2.2. Temperature and frequency sweep test The temperature and frequency sweep test was performed on warm-mix recycled asphalt binder, mastic, and FAM to measure the LVE properties (mainly the complex shear modulus |G*| and phase angle d) by a DSR AR 2000 instrument. In the case of asphalt binder and mastic, parallel plates of 8 mm in diameter with a 2 mm gap were used. As shown in Fig. 2, the beam specimen placed between two fixtures with the effective distance of 38.1 mm is used for FAM testing. Testing conditions are listed in Table 5. The LVE strain limits were determined by the strain sweep test [17].

3.1. Complex shear modulus |G*| The complex shear modulus |G*| and phase angle d values measured at different temperatures and frequencies were directly illustrated in the form of the master curve based on TTSP. A series of individual curves obtained at each temperature were horizontally shifted along the logarithmic frequency axis to form a single smooth master curve at a reference temperature. In the master curve, |G*| or d is only a function of the reduced frequency. The amount of the temperature dependent horizontal shift for constructing a master curve is the time-temperature shift factor. The Christensen-Anderson-Marasteanu (CAM) model [19] was used to fit the |G*| master curve for asphalt binder and mastic. For FAM the logarithm sigmoidal model [20] was used.

CAM model : jGj ¼  1þ

Gg  k mke

ð1Þ

fc fr

Logarithm sigmoidal model : lgðjGjÞ ¼ l þ

a

1 þ expbþcðlgf r Þ

ð2Þ

where |G*| is the complex shear modulus (MPa), Gg is the glassy modulus (MPa), fr is the reduced frequency at a reference temperature (Hz), fc, me, k, a, b, c, and l are model coefficients. For asphalt materials in each scale, fr can be expressed as follows:

lg f r ¼ lg f þ lg aT

ð3Þ

where f is the actual frequency at a given temperature T (Hz) and aT is the time-temperature shift factor. Based on the temperature and frequency sweep test results, the |G*| and d master curves at the reference temperature of 50 °C were

Table 2 Physical properties of asphalt binders at different aging stages. Aging condition

Penetration at 25 °C (dmm)

Softening point (°C)

Ductility at 10 °C (cm)

Brookfield viscosity at 135 °C (Pa
s)

Virgin The end of the initial stage Secondary stage (plan 1-PAV Secondary stage (plan 1-PAV Secondary stage (plan 1-PAV Secondary stage (plan 1-PAV Secondary stage (plan 1-PAV Secondary stage (plan 2-PAV Secondary stage (plan 2-PAV Secondary stage (plan 2-PAV Secondary stage (plan 2-PAV Secondary stage (plan 2-PAV Secondary stage (plan 3-PAV Secondary stage (plan 3-PAV Secondary stage (plan 3-PAV Secondary stage (plan 3-PAV Secondary stage (plan 3-PAV

61 24 54 40 34 30 28 48 38 30 27 26 50 38 30 28 25

68 76 70 76 80 84 85 70 75 80 85 86 66 73 75 82 86

70 13 37 26 24 18 13 33 24 20 16 13 30 25 22 20 15

2.0 4.4 1.8 2.7 3.6 4.3 4.7 2.3 3.4 3.9 4.6 4.9 1.4 2.3 3.4 4.2 4.5

0 h) 6 h) 16 h) 28 h) 42 h) 0 h) 6 h) 16 h) 28 h) 42 h) 0 h) 6 h) 16 h) 28 h) 42 h)

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ficient of determination R2 values for all cases are greater than 0.98. As shown in Fig. 3, master curves of plan 1 are provided to illustrate the effect of aging levels. Similar results could be obtained from plans 2 and 3. It is found that all asphalt materials show sim-

constructed for warm-mix recycled asphalt binder, mastic, and FAM with different recycling plans and aging levels. Each curve represents an average of two replicate specimens. Coefficients of the CAM model and the logarithm sigmoidal model are obtained by the nonlinear regression and listed in Tables 6 and 7. The coef-

Table 4 Engineering properties of the limestone fine aggregate. Property

Apparent density (g/cm3)

Bulk volume density (g/cm3)

Sand equivalent (%)

Water absorption (%)

Flow time (angularity) (s)

Result

2.748

2.677

64

1.1

34.0

Fig. 2. FAM specimen.

Table 5 Test conditions. Material

Shear strain limit

Frequency (Hz)

Temperature (°C)

Balance time (min)

Binder Mastic FAM

1% 0.5% 0.01%

0.01～100 0.01～100 0.01～100

30～70 30～70 30～70

15 15 60

Table 6 CAM model coefficients. Material

Recycling plan

Secondary PAV aging time (hour)

Gg (MPa)

fc (Hz)

me

k

Binder Binder Binder Binder Binder Binder Binder Binder Binder Binder Binder Binder Binder Binder Binder Mastic Mastic Mastic Mastic Mastic Mastic Mastic Mastic Mastic Mastic Mastic Mastic Mastic Mastic Mastic

1 1 1 1 1 2 2 2 2 2 3 3 3 3 3 1 1 1 1 1 2 2 2 2 2 3 3 3 3 3

0 6 16 28 42 0 6 16 28 42 0 6 16 28 42 0 6 16 28 42 0 6 16 28 42 0 6 16 28 42

6.55 7.21 8.01 9.71 10.32 6.51 7.11 8.60 9.61 10.35 6.65 7.71 9.91 10.11 11.23 7.92 8.37 9.57 13.40 15.30 8.12 8.40 9.67 13.73 15.73 8.32 8.97 9.97 14.43 16.20

4998 4651 3832 3071 2681 6261 5474 4475 3521 3031 5123 4673 3902 3091 2631 45,861 44,123 35,954 26,932 20,341 46,551 36,524 26,512 16,241 12,789 44,834 43,132 34,921 25,941 20,312

0.991 0.931 0.891 0.860 0.913 0.337 0.521 0.681 0.737 0.871 0.701 0.827 0.812 0.884 0.981 4.452 4.563 3.286 3.281 4.572 4.621 4.526 4.624 1.501 2.055 4.459 4.566 3.286 3.280 4.573

0.0037 0.0069 0.0083 0.0081 0.0097 0.0069 0.0072 0.0082 0.0890 0.0092 0.0073 0.0057 0.0082 0.0088 0.0093 0.6193 0.6600 0.6422 0.6248 0.6280 0.6642 0.6746 0.6146 0.6161 0.5851 0.6195 0.6697 0.6430 0.6246 0.6284

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Q. Li et al. / Construction and Building Materials 192 (2018) 99–109 Table 7 Logarithm sigmoidal model coefficients.

1.E+02

Secondary PAV aging time (hour)

l

a

b

c

1.E+01

1 1 1 1 1 2 2 2 2 2 3 3 3 3 3

0 6 16 28 42 0 6 16 28 42 0 6 16 28 42

3.156 3.288 3.311 3.298 3.245 3.195 3.482 3.557 3.622 3.695 3.081 3.346 3.485 3.480 3.518

3.220 2.840 2.794 2.891 2.840 3.078 2.908 2.901 2.910 2.904 3.216 3.198 3.134 3.102 3.106

0.308 0.300 0.298 0.311 0.304 0.304 0.311 0.320 0.309 0.327 0.204 0.208 0.201 0.205 0.209

0.386 0.382 0.381 0.371 0.373 0.381 0.385 0.387 0.387 0.381 0.424 0.409 0.388 0.384 0.384

1.E+00 |G*| (MPa)

Recycling plan

PAV-0 hour PAV-6 hours PAV-16 hours PAV-28 hours PAV-42 hours

1.E-01 1.E-02

1.E-03 1.E-04 1.E-04 1.E-03 1.E-02 1.E-01 1.E+00 1.E+01 1.E+02 1.E+03 1.E+04 fr (Hz)

(a) Binder 1.E+02

3.2. Phase angle d Using the same shift factors from the |G*| master curves, the d master curves are constructed and illustrated in Figs. 5 and 6. Similarly, different shapes of the curve are obtained in the semilogarithm scale coordinate system for asphalt materials in different scales. The binder d value varying from 20° to 90° continuously decreases with the reduced frequency due to its thermorheological nature. Unlike the stiffness, mastic shows a different viscoelasticity and time dependence from binder. Its rheological behavior is more close to that of FAM. The master curves of d from both mastic and FAM have similar bell-shapes commonly found from the mixture. At lower reduced frequencies, the effect of the viscoelastic asphalt binder on the mechanical behavior of mastic and FAM gradually increases with the reduced frequency although the elastic fillers and fine aggregates are still the dominant contributors. Conse-

1.E+01

|G*| (MPa)

1.E+00

PAV-0 hour PAV-6 hours PAV-16 hours PAV-28 hours PAV-42 hours

1.E-01 1.E-02 1.E-03 1.E-04 1.E-04 1.E-03 1.E-02 1.E-01 1.E+00 1.E+01 1.E+02 1.E+03 1.E+04 fr (Hz)

(b) Mastic 1.E+03

1.E+02 |G*| (MPa)

ilar simple thermorheological behavior regardless of material scales and aging levels. The complex shear modulus increases with the reduced frequency as expected. In the double-logarithm scale coordinate system the binder and mastic master curves show linear shapes, however, the S-shape master curves are constructed for FAM. That’s why different mathematical models are selected for data fitting. Moreover, the mastic stiffness does not visibly differ from the binder one. Both are on the same order of magnitude. However, the FAM stiffness is at least one order of magnitude larger than the binder and mastic ones, indicating that the FAM fine aggregate skeleton makes much greater contribution to the material stiffness than the internal structure formed in the mastic with the blend ratio of 0.5. The aging level also has a significant effect due to the stiffening effect. There are always large gaps among master curves before and after the long-term aging of asphalt binder, mastic or FAM. The material under a longer secondary PAV aging time exhibits a higher stiffness within the whole timetemperature domain. As shown in Fig. 4, master curves under two aging levels (secondary PAV aging time of 0 h and 42 h) are taken as examples to illustrate the effect of recycling plans. It is observed that asphalt materials using plan 2 (without the WMA agent) always have a little larger shear modulus within the whole time-temperature domain compared with those using plan 1. Asphalt materials using plan 3 (without the SBR latex) generally show a little larger modulus at higher reduced frequencies (higher frequencies or lower temperatures) and a little smaller modulus at lower reduced frequencies (lower frequencies or higher temperatures). The above findings are valid for asphalt binder, mastic, and FAM under each aging level.

PAV-0 hour PAV-6 hours PAV-16 hours PAV-28 hours PAV-42 hours

1.E+01

1.E+00 1.E-06

1.E-04

1.E-02

1.E+00

1.E+02

1.E+04

1.E+06

fr (Hz)

(c) FAM Fig. 3. Comparison of |G*| master curves under different aging levels.

quently, the d values of mastic and FAM also increase. At higher reduced frequencies, different components show similar elastic behavior, resulting in the decrease of the d values [21]. The d value generally reduces by 20–30° from mastic to FAM, demonstrating the change from liquid like to solid like. It is shown in Fig. 5 that the aging level also has an evident effect on the d value for all asphalt materials. The increase in the aging time aggravates the stiffening effect and causes a reduction in the phase angle within the whole time-temperature domain. The reduction magnitude varies with aging levels, material scales,

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Fig. 5. Comparison of d master curves under different aging levels.

cases by comparison of plans 1 and 3. The discrimination is more visible at higher reduced frequencies. 3.3. Rutting parameter |G*|/sind *

Fig. 4. Comparison of |G | master curves using different recycling plans.

temperatures, and loading frequencies. The reduced frequency corresponding to the peak value of the bell-shape curve slightly decreases with the aging time for mastic, however, the opposite phenomenon is observed for FAM. It is seen in Fig. 6 that under each aging level and material scale adding the WMA agent produces larger phase angles by comparison of plans 1 and 2. Adding the SBR latex causes the decrease of phase angle at lower reduced frequencies and increase at higher reduced frequencies for most

As shown in Fig. 7, the Superpave rutting parameter |G*|/sind (70 °C and 1.6 Hz) calculated from the LVE properties master curves is selected to evaluate the rutting potential of warm-mix recycled asphalt materials at high temperatures [22,23]. A larger |G*|/sind value means a better rutting resistance. It is found that the |G*|/sind value greatly increases with the PAV aging time regardless of material scales and recycling plans. Among asphalt materials the increase ratios from high to low are binder, mastic, and FAM. Taking plan 1 as an example, the increases of the |G*|/sind value after 42 h PAV aging finally reach 23.4, 7.2, and 6.3 times for asphalt binder, mastic, and FAM, respectively. It confirms that the

Q. Li et al. / Construction and Building Materials 192 (2018) 99–109

90

Plan 1(PAV 0 hour) Plan 2(PAV 0 hour) Plan 3(PAV 0 hour) Plan 1(PAV 42 hours) Plan 2(PAV 42 hours) Plan 3(PAV 42 hours)

PAV 0 hour

80 70 δ (DŽ)

105

60 50 40

PAV 42 hours

30 20 1.E-06

1.E-04

1.E-02

1.E+00 fr (Hz)

1.E+02

1.E+04

1.E+06 Fig. 7. Rutting parameter |G*|/sind values of asphalt materials.

(a) Binder 80

Plan 1(PAV 0 hour) Plan 2(PAV 0 hour) Plan 3(PAV 0 hour) Plan 1(PAV 42 hours) Plan 2(PAV 42 hours) Plan 3(PAV 42 hours)

δ (DŽ)

70 60

3.4. Fatigue parameter |G*|sind

PAV 0 hour

50 40

PAV 42 hours

30 1.E-06

1.E-04

1.E-02

1.E+00 fr (Hz)

1.E+02

1.E+04

1.E+06

(b) Mastic 60

Plan 1(PAV 0 hour) Plan 3(PAV 0 hour) Plan 2(PAV 42 hours)

50

δ (DŽ)

40

Plan 2(PAV 0 hour) Plan 1(PAV 42 hours) Plan 3(PAV 42 hours)

PAV 0 hour

30 20

PAV 42 hours

10 0 1.E-06

1.E-04

1.E-02

1.E+00 fr (Hz)

1.E+02

1.E+04

1.E+06

(c) FAM

As shown in Fig. 8, the Superpave fatigue parameter |G*|sind (20 °C and 10 Hz) calculated from the LVE properties master curves is selected to evaluate the fatigue performance of warm-mix recycled asphalt materials at intermediate temperatures [22,26]. The material with a smaller |G*|sind value has a better fatigue resistance. It could be observed that the aged asphalt materials are more susceptible to fatigue cracking. The |G*|sind value increases with the PAV aging time. However, the increasing trend varies with material scales and recycling plans, which is due to the coupling effect of the varying |G*| increment and d decrement during the aging process for each case. Binder and mastic have similar increase ratios, however, FAM generally shows a lower value. As for the plan 1 example, when the PAV aging time lasts from 0 to 42 h, the |G*|sind values increase by 1.9, 1.7, and 0.9 times for binder, mastic, and FAM, respectively. The material using plan 1 always exhibit the smallest |G*|sind value, indicating that adding appropriate amount of any additive can improve the fatigue resistance and their effectiveness in tandem is even better. The binder using plan 2 has a larger |G*|sind value before the aging (0 h) and smaller values after the aging (6 h, 16 h, 28 h, and 42 h) than that using plan 3. However, the opposite phenomenon is found from the mastic test results. The mastic using plan 2 shows smaller values under the shorter aging time (0 h and 6 h) and larger values under the longer aging time (16 h, 28 h, and 42 h). Smaller values are obtained under each aging level for the FAM using plan 3. It is unclear that which additive plays a more important role on the fatigue performance of warm-mix recycled asphalt materials.

Fig. 6. Comparison of d master curves using different recycling plans.

aging behavior mainly represented by the binder stiffening shows an expected positive effect on the rutting resistance of asphalt materials. Under a given aging level in each scale, the material using plan 2 always has the largest |G*|/sind value, followed by that using plan 1, and that using plan 3 shows the smallest value. Two types of additives bring opposite influences on the rutting resistance. The use of the WMA technique in the recycled materials approximately reduces the |G*|/sind values by 24.9–38.2% for binder, 20.2–41.0% for mastic, and 4.0–20.3% for FAM. It is basically consistent with the other studies [24,25]. On the contrary, after using the SBR latex the |G*|/sind values approximately enlarge by 44.8–77.3%, 6.9– 36.7%, and 29.5–58.6% for binder, mastic, and FAM, respectively, which can partially overcome the negative softening caused by the WMA agent.

Fig. 8. Fatigue parameter |G*|sind values of asphalt materials.

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Q. Li et al. / Construction and Building Materials 192 (2018) 99–109

3.5. Glass transition temperature Tg The glass transition temperature Tg characterizes the range of temperatures over which the glass transition of a material occurs, which is widely used as the indicator to the low temperature cracking. The viscoelastic material with a smaller Tg value can be transformed from a hard and relatively brittle glassy state into a viscous or rubbery state at a lower temperature, indicating a better resistance to the low temperature cracking. Based on the dynamic mechanical analysis method, the Tg value can be calculated using the following Williams-Landel-Ferry (WLF) equation.

C 1 ðT  T g Þ lg aT ¼ C 2 þ ðT  T g Þ

ð4Þ

where Tg is the glass transition temperature (°C), T is the temperature (°C), C1 and C2 are regression coefficients. Using the same shift factors for constructing the |G*| and d master curves, the Tg values of different asphalt materials with different recycling plans and aging levels are obtained and shown in Fig. 9. It is observed that the Tg value increases as the material length scale increases. FAM has a higher glass transition temperature than mastic, which has a higher value than binder. The Tg value increases almost linearly with the PAV aging time and the line slope does not strongly depend on material scales and recycling plans. It is known that the Tg values of the virgin SBS binder and mixture are 12.9 °C and 11.5 °C, respectively [27]. Therefore, the glass transition temperatures of warm-mix recycled

0

FAM

-1

Binder-plan 2

)

-2

Tg (

Binder-plan 1 Bi

Mastic

Binder-plan 3 B Mastic-plan 1

-3

Mastic-plan 2 M -4

Binder

Mastic-plan 3 M

-5

FAM-plan 1

-6

FAM-plan 2

-7

FAM-plan 3 0

10

20 30 PAV aging time (hour)

40

50

Fig. 9. Glass transition temperature Tg values of asphalt materials.

asphalt materials are much higher even before the secondary aging. After 42 h PAV aging, they are further raised by 2.2–3.2 °C, demonstrating the continuous deterioration of the low temperature performance throughout the pavement service period. Similar to the fatigue parameter results, the low temperature cracking resistance of warm-mix recycled asphalt materials can be improved by using the WMA agent and/or SBR latex. The latter is more effective than the former in each material scale and under each aging level. 3.6. Comparison of effects of aging levels and recycling plans The analysis of variance (ANOVA) at a 95% confidence level was utilized to examine the significance of variability sources in affecting the |G*|/sind, |G*|sind, and Tg values of warm-mix recycled asphalt materials, as shown in Table 8. It is found that there is the statistical significance (P < 0.05) in all indicators among warm-mix recycled asphalt materials with different aging levels and recycling plans. The statistical F value is always larger than the critical F value for each case. It confirms that both aging level and recycling plan have significant influence on all the pavement performance of warm-mix recycled asphalt materials. Additionally, the aging level generally shows a much more important effect (much larger statistical F values in most cases) than the recycling plan no matter which parameter is considered. The Tukey’s honestly significant differences (HSD) test (a singlestep multiple comparison procedure) was also used to distinguish statistical differences among test results from warm-mix recycled asphalt materials with different aging levels and recycling plans, as shown in Table 9. The smaller ranking number or the more front group grade in the alphabetical order indicates the better performance. Materials showing significantly different results in each indicator are grouped into different grades. A material marked with two group grades (e.g, A/B) means that it is not significantly different from either group. The Tukey’s HSD analysis (a = 0.05) also confirms that warm-mix recycled asphalt materials with different aging levels show statistically different performance. Asphalt materials with the longer PAV aging time generally have the larger ranking number and the latter group grade (poorer performance). It is valid for all material scales and performance indicators. However, the effect of the recycling plan on the material ranking and grouping is not as significant as that of the aging level. Asphalt materials under different aging levels exhibit much more pronounced ranking and grade differences compared with those using different additives. For some cases, there is even no statisti-

Table 8 ANOVA test results. Parameter

Material

Source

SS

DF

MS

F-value

P-value

Critical F

|G*|/sind |G*|/sind |G*|/sind |G*|/sind |G*|/sind |G*|/sind |G*|sind |G*|sind |G*|sind |G*|sind |G*|sind |G*|sind Tg Tg Tg Tg Tg Tg

Binder Binder Mastic Mastic FAM FAM Binder Binder Mastic Mastic FAM FAM Binder Binder Mastic Mastic FAM FAM

Aging level Recycling plan Aging level Recycling plan Aging level Recycling plan Aging level Recycling plan Aging level Recycling plan Aging level Recycling plan Aging level Recycling plan Aging level Recycling plan Aging level Recycling plan

0.00056 0.00022 0.00236 0.00051 6206.18 542.26 74.97 12.16 575.39 181.53 57034.41 4316.05 10.75 3.45 16.37 8.03 14.79 1.60

4 2 4 2 4 2 4 2 4 2 4 2 4 2 4 2 4 2

0.00014 0.00011 0.00059 0.00026 1551.54 271.13 18.74 6.08 143.85 90.76 14258.60 2158.03 2.67 1.72 4.09 4.01 3.70 0.80

19.39 15.12 19.28 8.34 43.74 7.64 29.57 9.59 14.23 8.98 94.79 14.35 220.82 141.75 176.66 173.27 249.33 53.98

0.00035 0.00191 0.00036 0.01102 0.00002 0.01393 0.00008 0.00750 0.00104 0.00902 8.9E07 0.00226 3.2E08 5.7E07 7.8E08 2.6E07 2.0E08 0.00003

3.84 4.46 3.84 4.46 3.84 4.46 3.84 4.46 3.84 4.46 3.84 4.46 3.84 4.46 3.84 4.46 3.84 4.46

107

Q. Li et al. / Construction and Building Materials 192 (2018) 99–109 Table 9 Statistical ranking and Tukey’s HSD grouping test results. Recycling plan

Secondary PAV aging time (hour)

|G*|/sind

|G*|sind

Binder

Mastic

FAM

Binder

Mastic

FAM

Binder

Mastic

FAM

1 1 1 1 1 2 2 2 2 2 3 3 3 3 3

0 6 16 28 42 0 6 16 28 42 0 6 16 28 42

14(G) 10(D) 6(C) 5(B/C) 4(B/C) 13(F) 7(C) 3(B) 2(A/B) 1(A) 15(H) 12(E) 11(D) 9(D) 8(C/D)

14(F) 11(D) 8(C) 6(B/C) 3(B) 13(E) 10(C) 4(B/C) 2(A/B) 1(A) 15(F) 12(D) 9(C) 7(C) 5(B/C)

14(E) 10(C/D) 8(C/D) 5(B/C) 2(A/B) 13(E) 9(C/D) 6(C) 4(B/C) 1(A) 15(E) 12(D/E) 11(D) 7(C/D) 3(B)

1(A) 4(B) 5(C) 9(D) 11(D/E) 3(B) 6(C) 8(C/D) 10(D/E) 13(E) 2(A) 7(C/D) 12(D/E) 14(E/F) 15(F)

1(A) 3(A/B) 4(B) 7(B/C) 11(C/D) 2(A/B) 6(B) 10(C/D) 14(D) 15(D) 5(B) 8(B/C) 9(C) 12(C/D) 13(D)

1(A) 2(A/B) 7(A/B) 10(B) 13(B/C) 4(A/B) 6(A/B) 9(B) 12(B/C) 15(C) 3(A/B) 5(A/B) 8(A/B) 11(B/C) 14(B/C)

1(A) 3(B) 6(B/C) 8(C/D) 11(D) 1(A) 4(B/C) 7(C) 10(C/D) 12(D) 4(B/C) 8(C/D) 13(D/E) 14(D/E) 15(E)

1(A) 3(A/B) 6(B/C) 8(B/C) 11(C/D) 2(A) 4(B) 7(B/C) 9(C) 12(C/D) 5(B/C) 10(C) 13(D) 14(D) 15(D)

1(A) 3(A/B) 6(B/C) 9(C) 12(C/D) 2(A) 5(B) 8(B/C) 11(C/D) 14(D) 3(A/B) 6(B/C) 10(C) 13(D) 15(D)

0.030

120 Binder vs. Mastic

Mastic vs. FAM

0.025

100

0.020 0.015

80 y = 0.489x + 3E-05 R² = 0.896 Binder vs. Mastic

60

0.010

40 y = 1383x - 0.928 R² = 0.783 Mastic vs. FAM

0.005 0.000 0.00

0.01

0.02 |G*|/sin

0.03

0.04

20

0.05

0 0.06

of mastic (MPa)

*

Fig. 10. Correlation of |G |/sind values in different material scales.

rutting performance could be ignored. However, the effect of fine aggregates is more significant at high temperatures. Based on multiscale modelling principles, FAM or even mixture seems to be the critical material characteristic scale to identify the rutting resistance for warm-mix recycled asphalt materials. As shown in Fig. 11, Binder shows a poor correlation to mastic in terms of the |G*|sind value, however a much better correlation exists between mastic and FAM. It confirms that the filler rather than the fine aggregate plays a more important role in affecting the fatigue performance of asphalt materials at intermediate temperatures. Asphalt mastic could be considered as the critical mate-

16

400 Binder vs. Mastic

|G*|sin of binder (MPa)

14 12

Mastic vs. FAM

350 300

y = 8.048x + 98.807 R² = 0.868 Mastic vs. FAM

10

250

8

200 y = 0.269x + 2.084 R² = 0.658 Binder vs. Mastic

6 4

150 100 50

2 0 0

5

10

15

20

|G*|sin *

25

30

35

40

0

of mastic (MPa)

Fig. 11. Correlation of |G |sind values in different material scales.

|G*|sin of FAM (MPa)

3.7. Performance correlation in different material scales Similar qualitative conclusions in terms of the LVE properties and pavement performance parameters are drawn for warm-mix recycled asphalt materials in different scales. Different datasets measured from asphalt binder, mastic, and FAM were correlated pairwise to quantitatively evaluate their relationships. The correlation is better for a larger coefficient of determination R2 value. The | G*|/sind, |G*|sind, and Tg were respectively selected for the correlation analysis of the rutting, fatigue cracking, and low temperature cracking resistance. As shown in Fig. 10, the |G*|/sind values of binder and mastic are well correlated. The correlation of mastic and FAM is obviously lower. The relative differences and similarities among the different material scales indicate that the effect of the filler properties on the

|G*|/sin of FAM (MPa)

|G*|/sin of binder (MPa)

cal difference among warm-mix recycled asphalt materials with different recycling plans. Moreover, the significant difference in the pavement performance becomes less from binder to FAM, signifying the reduction of the parameter discrimination. The reason is easily understood because the filler and/or fine aggregate whose properties are affected little by the aging and additives act more important parts in the LVE properties as well as pavement performance of mastic or FAM during the upscaling process. Based on the above analysis, it can be summarized that the secondary aging behavior after the warm-mix recycling has an extensive effect on the recycled pavement performance, such as the resistance to the rutting, fatigue cracking, and low temperature cracking. Although the rheological properties of the recycled binder are partly recovered by using the rejuvenator agent, the stiffening speed of warm-mix recycled asphalt materials becomes much faster during the secondary aging process compared with that during the initial aging process before recycling. The continuously increasing stiffness plays a significant role in the rutting resistance improvement at high temperatures, while causing the cracking resistance degradation at intermediate and low temperatures for all recycled asphalt materials. Using the WMA agent greatly reduces the pavement construction temperature and relieves the short-term aging. To a certain extent it can compensate the RAP flexibility and ensure the compaction quality, which provides a benefit to the fatigue and lower temperature cracking resistance. Inevitably, it is harmful to the rutting resistance. Adding the SBR latex can make different contributions to the stiffness of recycled asphalt materials at different temperatures. The high temperature stiffness slightly increases, however the intermediate and low temperatures stiffness decreases. Therefore, it can improve both rutting and cracking resistance.

Tg

108

Q. Li et al. / Construction and Building Materials 192 (2018) 99–109

0

0 Binder vs. Mastic

-1

Tg of binder (

y = 0.767 x + 0.842 R² = 0.875 Mastic vs. FAM

-2 -3

-2

)

)

Mastic vs. FAM

-3

-4

-4

-5

-5

y = 0.752x - 2.217 R² = 0.972 Binder vs. Mastic

-6

Tg of FAM (

-1

-6

-7

-7 -7

-6

-5

-4

-3

Tg of mastic (

-2

-1

0

)

Fig. 12. Correlation of Tg values in different material scales.

rial characteristic scale to distinguish the fatigue resistance for warm-mix recycled asphalt materials. High correlations are observed in all cases of the Tg value comparison as shown in Fig. 12, highlighting the importance of binder in capturing the low temperature performance. The low temperature cracking resistance of mastic and FAM or even mixture can be possibly predicted by the binder resistance, which is coherent with the result of previous study [27]. Asphalt binder may be the critical material characteristic scale for the low temperature cracking resistance of warm-mix recycled asphalt materials. It is should be mentioned that the effect of the filler and fine aggregate properties may be underestimated because the same type of the filler and aggregate are used. Therefore, the performance correlations among material scales obtained in this study may be relatively high for all cases. Moreover, only one set of the WMA agent, rejuvenator agent, virgin binder, and RAP binder was studied, a further research is needed to validate the proposed findings in a wide range of materials. 4. Conclusions Some important observations and conclusions made in this study are as follows: (1) There are always large gaps between the pavement performance before and after the secondary aging. The stiffening behavior with the aging time results in an increase in the shear modulus and a reduction in the phase angle within the whole time-temperature domain for warm-mix recycled asphalt materials. The aging behavior improves the rutting resistance and greatly reduces the resistance to the fatigue and low temperature cracking. (2) Recycled asphalt materials using the WMA agent always have a little lower shear modulus and larger phase angles. Using the WMA technique can partly relieve the shortterm aging and compensate the RAP flexibility. It plays a positive role in the fatigue and lower temperature cracking performance and a negative role in the rutting performance. (3) Using the SBR latex can increase the high temperature stiffness and decrease the intermediate and low temperature stiffness. Conversely, it causes the phase angle decreasing at high temperatures and increasing at low temperatures. It can improve both rutting and cracking resistance for warm-mix recycled asphalt materials. (4) By comparison, the secondary aging level shows a much more significant effect on the LVE properties and pavement performance than the recycling plan for warm-mix recycled asphalt materials.

(5) FAM (or mixture), mastic, and binder are determined as the potential critical material characteristic scales for evaluating the rutting, fatigue, and low temperature cracking performance of warm-mix recycled asphalt pavements, respectively. Conflicts of interests None. Acknowledgements The authors would like to acknowledge the financial support from the Natural Science Foundation of Jiangsu Province (Grant No. BK20181404), China, Qing Lan Project, China, Training Plan Project for Young Core Teachers by Nanjing Forestry University, China, Science and Technology Project by Ministry of Housing and Urban-Rural Development (Grant No. 2013-K4-9), China, and the Scientific Research Foundation for the Returned Overseas Chinese Scholars, State Education Ministry, China. The authors also would like to acknowledge Dr. Jiwang Jiang for the English grammar revision. References [1] 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. [2] M. Tao, R.B. Mallick, An evaluation of the effects of warm mix asphalt additives on workability and mechanical properties of reclaimed asphalt pavement (RAP) material, Transp. Res. Rec. 2126 (2009) 151–160. [3] J. Li, Study on Processing Technique of RAP and Pavement Performance of Warm-mixed Recycled Asphalt Mixture Master thesis, Chongqing Jiaotong University, Chongqing, 2013. [4] N. Guo, Z. You, Y. Zhao, Y. Tan, A. Diab, Laboratory performance of warm mix asphalt containing recycled asphalt mixtures, Constr. Build. Mater. 64 (2014) 141–149. [5] M. Lopes, T. Gabet, L. Bernucci, V. Mouillet, Durability of hot and warm asphalt mixtures containing high rates of reclaimed asphalt at laboratory scale, Mater. Struct. 48 (2015) 3937–3948. [6] A. Copeland, J. D’Angelo, R. Dongré, S. Belagutti, G. Sholar, Field evaluation of high reclaimed asphalt pavement-warm-mix asphalt project in Florida, Transp. Res. Rec. 2179 (2010) 93–101. [7] J. D’Angelo, E. Harm, J. Bartoszek, G. Baumgardner, M. Corrigan, J. Cowsert, T. Harman, M. Jamshidi, W. Jones, D. Newcomb, B. Prowell, R. Sines, B. Yeaton, Warm-mix Asphalt: European Practice, National Cooperative Highway Research Program, Federal Highway Administration, Washington, DC, 2008. [8] J. Füssl, R. Lackner, J. Eberhardsteiner, Creep response of bituminous mixturesrheological model and microstructural interpretation, Meccanica 49 (2014) 2687–2698. [9] J.R.M. Oliveira, H.M.R.D. Silva, L.P.F. Abreu, J.A. Gonzalez-Leon, The role of a surfactant based additive on the production of recycled warm mix asphaltsLess is more, Constr. Build. Mater. 35 (2012) 693–700. [10] Z. Xie, N. Tran, G. Julian, A. Taylor, L.D. Blackburn, Performance of asphalt mixtures with high recycled contents using rejuvenators and warm-mix additive: field and lab experiments, J. Mater. Civil. Eng. 29 (10) (2017) 04017190. [11] W.S. Mogawer, A.J. Austerman, R. Dongré, R. Kluttz, M. Roussel, Highperformance thin-lift overlays with high reclaimed asphalt pavement content and warm-mix asphalt technology: performance and workability characteristics, Transp. Res. Rec. 2293 (2012) 18–28. [12] M.H. Rashwan, R.C. Williams, An evaluation of warm mix asphalt additives and reclaimed asphalt pavement on performance properties of asphalt mixtures, in Proceeding of the Transportation Research Board 91st Annual Meeting, the National Academies of Sciences, Washington, DC, 2012. [13] B.S. Underwood, Y.R. Kim, Microstructural investigation of asphalt concrete for performing multiscale experimental studies, Int. J. Pavement Eng. 14 (5) (2013) 498–516. [14] F. Safaei, J.S. Lee, L.A.H. Nascimento, C. Hintz, Y.R. Kim, Implications of warmmix asphalt on long-term oxidative ageing and fatigue performance of asphalt binders and mixtures, Road. Mater. Pavement 15 (S1) (2014) 45–61. [15] F. Pérez-Jiménez, R. Botella, R. Miró, A. Paez-Dueñas , F.J. Barceló-Martínez, C. Virginia, Binder, mastic and mixture fatigue characterization using a cyclic uniaxial strain sweep test, in Proceeding of the Transportation Research Board 93rd Annual Meeting, the National Academies of Sciences, Washington, DC, 2014. [16] B.S. Underwood, Y.R. Kim, Experimental investigation into the multiscale behaviour of asphalt concrete, Int. J. Pavement Eng. 12 (4) (2011) 357–370.

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