Incorporating hollow glass microsphere to cool asphalt pavement: Preliminary evaluation of asphalt mastic

Construction and Building Materials 244 (2020) 118380

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Incorporating hollow glass microsphere to cool asphalt pavement: Preliminary evaluation of asphalt mastic Du Yinfei a, Dai Mingxin a, Deng Haibin b, Deng Deyi b, Cheng Peifeng c, Ma Cong a,⇑ a

School of Civil Engineering, Central South University, Changsha, Hunan 410075, China Highway Administration Bureau of Huzhou, Zhejiang 313000, China c School of Civil Engineering, Northeast Forestry University, Harbin, Heilongjiang 150040, China b

h i g h l i g h t s
Glass microsphere was used to prepare asphalt mastic.
The thermal conductivity of asphalt mastic reduced by 40%.
The infrared reflectance of asphalt mastic increased by 60%.
Glass microsphere had a negative effect on the rutting property of asphalt mastic.
Glass microsphere help to improve the fatigue property of asphalt mastic.

a r t i c l e

i n f o

Article history: Received 25 November 2019 Received in revised form 6 February 2020 Accepted 6 February 2020

Keywords: Asphalt mastic Hollow glass microsphere Thermal conductivity Solar reflectance Anti-rutting performance Fatigue performance

a b s t r a c t In order to cool asphalt pavement by replacing limestone mineral filler (LMF) with hollow glass microsphere (HGM) in asphalt mixture, this work preliminarily evaluated the thermal, high-temperature rheological and fatigue properties of asphalt mastic. The microstructure, particle size distribution, chemical element composition and crystal structure of LMF and HGM were tested to characterize their physical and chemical properties. A series of tests, including scanning electron microscope, Fourier transform infrared, thermal conductivity, spectral reflectance, multiple stress creep recovery (MSCR) and linear amplitude sweep (LAS) tests were performed to investigate the influence of HGM on the performances of asphalt mastic. The results show that HGM/LMF and asphalt were physically blended, and some HGM particles were broken when preparing asphalt mastic. Completely replacing LMF with HGM in asphalt mastic resulted in a decrease of thermal conductivity by 40% and an increase of infrared reflectance by 60%. The MSCR test result shows that HGM negatively affected the anti-rutting performance of asphalt mastic, while the LAS test result shows that HGM could extend the fatigue life of asphalt mastic. The findings in this study indicate that HGM is a potential material for cooling asphalt pavement. Ó 2020 Published by Elsevier Ltd.

1. Introduction As a commonly used pavement material, asphalt has a high solar absorbing ability, which leads to very high pavement temperature [1,2]. It was reported that the peak temperature of asphalt pavement was over 10 °C higher than that of cement concrete pavement in the same regions [3,4]. The asphalt pavement with high temperature can cause rutting and other thermally induced hazards, which will seriously reduce road surface roughness, affect material/structure performance and traffic safety of asphalt pavement [5]. The high-temperature asphalt pavement also releases a ⇑ Corresponding author. E-mail address: [email protected] (M. Cong). https://doi.org/10.1016/j.conbuildmat.2020.118380 0950-0618/Ó 2020 Published by Elsevier Ltd.

large amount of heat to the atmosphere, leading to an increase of ambient temperature and the aggravation of urban heat island effect. The urban heat island effect will increase the consumption of urban energy, thus inducing secondary hazards to atmospheric environment and harms to the health of residents [6]. Therefore, it is necessary to adopt a reasonable plan to reduce the temperature of asphalt pavement. At present, there are many methods to solve the high temperature problem of asphalt pavement, such as heat-reflective coating technology [7,8], thermal resistance technology [9,10], porous/ water-retaining asphalt pavement [11,12], phase change asphalt pavement [13,14] and solar collection asphalt pavement [15,16]. Among them, the asphalt mixture with low thermal conductivity was proved to be able to prevent heat from entering the pavement,

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which is beneficial to reduce the inside temperature of asphalt pavement [17,18]. Hollow glass microsphere (HGM) is a kind of lightweight filler, which has been used in various coating [19,20] and concrete [21,22] preparations. This material can also be used to prepare road marking due to its excellent retroreflective property [23,24]. Combined with heat reflectance and thermal resistance pavement technology, HGM is a potential material for cooling asphalt pavement. However, in the reference [25] the HGM was added in asphalt as a modifier, and the properties of HGM/asphalt mastic were compared with those of base asphalt. For further application of HGM in asphalt pavement, this paper tries to investigate the influence of HGM on the properties of asphalt mastic by replacing the same volume of limestone mineral filler (LMF). Asphalt mastic has a significant effect on the overall performance of asphalt mixture [26]. So this paper focuses on investigating the influence of HGM on the performances of asphalt mastic. To this end, the thermal conductivity, spectral reflectance, antirutting, and fatigue performances of asphalt mastic with four LMF-HGM ratios were analyzed. Before the above tests, the physical and chemical properties of the two fillers were first investigated using a series of micro tests, including particle size distribution, X-ray fluorescence spectroscopy (XRF), X-ray diffraction (XRD), scanning electron microscope (SEM) and Fourier transform infrared (FTIR) tests. Besides, the interactive effects between asphalt and LMF/HGM were also studied by FTIR and SEM tests. 2. Materials and test methods 2.1. Materials The HGM was provided by a purification Plant in Henan Province, China. 80/100 penetration grade base asphalt, which was produced by Liaoning Panjin Petrochemical Industry Co. Ltd., China, was used to prepare asphalt mastic by incorporating different contents of LMF and HGM. The fillers used in this study had a particle size of less than 0.075 mm. The asphalt mastics that had a filler-to-asphalt ratio of 1.2 [27] were used to characterize their micro structure, thermal conductivity, rheological and fatigue performances. HGM was added in asphalt to prepare asphalt mastic by replacing the same volume of LMF. The specific ratios of component in different asphalt mastics are shown in Table 1. It should be noted that when replacing LMF with HGM, the actual filler-toasphalt ratio will change, because the densities of LMF and FAC were 2.75 g/cm3 and 0.43 g/cm3, respectively. For example, when LMF was completely replaced by HGM, the filler-to-asphalt ratio was 0.188. Fillers were added into asphalt at the temperature of 160 °C and the adding rate of 1 g/min. Meanwhile, the composite was stirred for 30 min by a paddle agitator at a speed of 1000 rpm.

in crystal structures were characterized by XRF (S4 Pioneer, Bruker Co. Ltd., Germany) and XRD (D8 Advance, Bruker Co. Ltd., Germany), respectively. The morphologies of the two fillers were measured using SEM (JEOL JSM-7900F Instrument, Japan). The functional groups of the fillers were examined by a FTIR spectrometer (Nicolet iS50, Thermo Co., Ltd., USA). The wavenumber ranged from 650 to 4000 cm1. 2.2.2. Tests for characterizing asphalt mastic FTIR spectrometer was also used to characterize the functional groups of different asphalt mastic, which could distinguish the interaction between asphalt and LMF/HGM. SEM (Phenom Pro, Netherland) was used to present the filler distribution in asphalt. The images were magnified by 265 times. 2.2.3. Thermal conductivity test A transient plane heat source method was used to measure the thermal conductivity by a thermal conductivity tester (DRE-2C, Xiangtan Instruments and Meters, Hunan Province, China). During the test process, a measuring probe was tightly clamped between asphalt mastic slices with smooth surfaces, as shown in Fig. 1. For each kind of asphalt mastic, more than ten tests were repeated. The averaged results were referred to as the measured thermal conductivity. 2.2.4. Spectral reflectance test Ultraviolet (UV)-visible (Vis)-near infrared (NIR) spectrophotometer (Cary 5000, Agilent Technologies (Malaysia) Company) was used to measure the diffuse reflectance of asphalt mastic along the wavelength of 200–2500 nm. The spectral reflectance was calculated according to ASTM Standard G173-03 [28], as shown in Eq. (1). The standard solar spectral irradiance specified in the above standard is shown in Fig. 2. In order to avoid the contamination of integrating sphere by asphalt mastic due to its viscosity at room temperature, asphalt mastic was coated on the surface of a glass sheet, and then the glass sheet was placed to the integrating sphere. The influence of glass sheet on the reflectance was eliminated by measuring the reflectance of reference standard reflectance material (polytetrafluoroethylene plate) with glass sheet.

Operating host

2.2. Test methods 2.2.1. Tests for characterizing fillers The particle size distributions of LMF and HGM were measured by a Laser particle size analyzer (Hydro 2000MU, Malvern Instruments Ltd., America). The chemical compositions and difference

Probe Asphalt mastic

Fig. 1. Schematic diagram of thermal conductivity instrument.

Table 1 Mass ratios of component in asphalt mastic (wt. %). Mastic type

Asphalt

LMF

HGM

LMF:HGM (Volume ratio)

Control mastic Mastic-25 Mastic-50 Mastic-75 Mastic-100

100 100 100 100 100

120 90 60 30 NA

NA 4.7 9.3 14.0 18.8

100:0 75:25 50:50 25:75 0:100

D. Yinfei et al. / Construction and Building Materials 244 (2020) 118380

0.1–30 Hz. The test was used to evaluate the undamaged material properties. (2) Linear amplitude strain sweep test used oscillatory shear loading under the strain-controlled mode of 10 Hz frequency. A linearly increasing load amplitude ranging from 0.1 to 30% was used. 35% reduction in the initial G*sin d was used to represent the value of damage accumulation at failure. Finally, the fatigue life Nf was predicted using Eq. (2).

1.8

Global tilt spectral irradiance (W/(m2nm))

3

1.5

1.2

0.9

Nf ¼ A35 ðcmax ÞB

ð2Þ

where A35 and B are the viscoelastic continuum damage (VECD) coefficients. In this study, the test with 8 mm parallel spindles and 2 mm thickness gap was performed at the temperature of 25 °C.

0.6

0.3

3. Results and discussion 0.0

3.1. Surface morphology and particle size distribution of filler -0.3 0

500

1000

1500

2000

2500

Wavelength (nm) Fig. 2. Standard solar spectral irradiance specified in ASTM Standard G173-03.

Z RS ¼

k1

k2

Z

RðkÞEk ðkÞdk k1

k2

ð1Þ

Ek ðkÞdk

where R(k) represents the measured spectral data and Ek(k) represents the solar spectral irradiance. 2.2.5. Multiple stress creep recovery (MSCR) test A dynamic shear rheometer (DSR) (SmartPave302, Anton Paar Instrument, Austria) was used to perform MSCR test at the temperature of 58 °C. This test used two stress levels, which were 0.1 kPa and 3.2 kPa. At each stress level the creep stress was held constant for 1 s, and then the stress was removed. After 9 s the recovery response was measured. Each stress level included ten creep recovery cycles [29]. In order to characterize the rutting resistance of asphalt mastic, non-recovery creep compliance (Jnr) and creep recovery rate (R) were adopted as indicators [30–32]. This test used two parallel plates (diameters of 25 mm) with a gap of 1 mm. 2.2.6. Linear amplitude sweep (LAS) test It was found that the LAS results were well correlated with the long-term fatigue cracking data of asphalt pavement in the field [33]. The test procedure included two parts [34]: (1) Frequency sweep test was conducted with a strain amplitude of about 0.1%, and the frequency used in the test varied in the range of

3.1.1. Surface morphology The SEM images of LMF and HGM are shown in Fig. 3, respectively. The particle sizes of irregular shaped LMF varied in a wide range. The irregular shape provided the possibility of the high specific surface area of LMF that could have a high contacting area with asphalt. By contrast, Fig. 3(b) shows the surface morphology of HGM, which all presented spherical particles with smooth surface. The huge difference in surface morphology between these two fillers would result in different rheological and fatigue properties of asphalt mastic. 3.1.2. Particle size distribution The particle size distributions of LMF and HGM are shown in Fig. 4. On the whole, LMF had a relatively wider range of particle size distribution than HGM. In order to quantitatively characterize the particle size distribution of fillers, several parameters representing the particle size characteristic (e.g. D10 for the diameter with passing ratio of 10% and Dav for the average diameter), were calculated, as shown in Table 2. Obviously, HGM had larger particle size parameters than LMF, especially for the parameters D10 and D50. In comparison, the D90 of the two fillers was very close to each other. The information in Table 2, together with Fig. 3, illustrates that HGM was generally coarser than LMF. 3.2. Chemical composition 3.2.1. XRF results The XRF test results of LMF and HGM are summarized in Table 3. It can be seen that there were two main element compositions in the LMF: O and Ca. By contrast, the main element compositions

Fig. 3. SEM images of (a) LMF and (b) HGM.

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D. Yinfei et al. / Construction and Building Materials 244 (2020) 118380

16 14

1.calcite

LMF

2.dolomite

12 10

Intensity(Counts)

Passing ratio (%)

HGM

HGM LMF

8 6 4 2 0 0.01

0.1

1

10

100

1000

Particle diameter (μm)

5

10

15

20

25

30

35

40

45

50

55

60

65

70

2θ(°)

Fig. 4. Particle size distributions of LMF and HGM.

Fig. 5. XRD patterns of LMF and HGM.

that many spherical HGM and its fragments were deposited on the surface of asphalt.

Table 2 Diameters representing particle size characteristic (lm). Filler type

D10

D50

D90

Dav

LMF HGM

1.997 23.051

16.539 33.794

46.635 49.034

20.635 35.153

3.3.2. FTIR spectrum In order to chemically characterize the relationship between HGM and asphalt, the FTIR spectrums of LMF, HGM, asphalt and asphalt mastics were measured, as shown in Fig. 7. LMF and HGM had different functional groups, indicating that they had different constituents, which has been proved by the XRF and XRD results. Specifically, it can be found from the spectrum of LMF that there was a strong absorption peak with a large opening near the wavenumber of 1419 cm1. Two sharp absorption peaks could also be observed near the wavenumber of 877 cm1 and 717 cm1 near the wavenumber of 798 cm1 and 1390 cm1 there were weak absorption peaks with small openings, according to the FTIR spectrums of HGM. Besides, there was an absorption peak with a large opening near the wavenumber of 1026 cm1. There were four main characteristic absorption peaks near the wavenumber of 2920 cm1, 2850 cm1, 1600 cm1, 1456 cm1 and 1376 cm1 for asphalt, which all appeared in the FTIR spectrums of the three asphalt mastics. In addition, the absorption peaks of LMF could be found in the FTIR spectrums of the mastics with the addition of LMF. Compared with the spectrums of asphalt, LMF and HGM, there were no new absorption peaks in the spectrum of asphalt mastic, indicating that LMF or HGM/asphalt mastic was chemically stable.

in HGM were O, Si, Ca, and Na, respectively. It can be inferred that the oxides in the LMF and HGM might exist in the form of CaO and SiO2, respectively. In addition, there might also be CaO and Na2O in the HGM.

3.2.2. XRD results The XRD patterns of LMF and HGM are shown in Fig. 5. It can be seen that the main crystal phases of LMF were calcite (CaCO3) and dolomite (CaMg[CO3]2), respectively. This result was in consistence with the data in Table 4. The red XRD pattern shows that HGM had an amorphous structure, of which there was a broad peak at the 2h angle of 20–35°. This peak, combining with the data in Table 3, denoted that there was amorphous SiO2 in HGM [35,36]. 3.3. Characterization of asphalt mastic 3.3.1. SEM image The distribution states of LMF and HGM in asphalt were characterized by scanning the SEM images of control mastic and mastic100. The two images were both magnified by 256 times, as shown in Fig. 6, respectively. In a whole, LMF and HGM were well dispersed in asphalt. Specifically, it is difficult to observe the morphology change of LMF in control mastic. However, it can be found that many HGM fragments distributed in mastic-100, indicating that spherical HGM particles were partially broken in the process of asphalt mastic preparation due to the high-speed stirring force. Because of the larger particle size of HGM (Fig. 4), it can be obviously observed

3.4. Thermal conductivity In order to illustrate the effect of HGM on the heat conduction performance of asphalt pavement, the thermal conductivity of asphalt mastics with different HGM contents was compared, as shown in Fig. 8. Due to the high thermal resistance of asphalt, together with some pores in asphalt mastic (Fig. 6(a)), the thermal conductivity of control asphalt mastic was only 0.371 W/(mK). When using

Table 3 XRF results of LMF and HGM. Element type Chemical element content (%)

LMF HGM

O

Mg

Al

Si

Ca

Na

47.7 48.2

0.41 0.112

0.046 0.287

0.0915 37.31

39.44 6.991

— 6.881

*Note: Only the chemical elements with content of more than 0.1% were presented.

5

D. Yinfei et al. / Construction and Building Materials 244 (2020) 118380 Table 4 Calculated spectral reflectance of different asphalt mastics (%). Mastic type

Reflectance

Control mastic Mastic-25 Mastic-50 Mastic-75 Mastic-100

UV

Vis

NIR

Average

9.33 9.36 9.41 9.51 9.64

12.71 12.93 13.24 13.45 13.79

17.40 20.96 23.70 25.73 28.01

13.36 14.53 15.60 16.39 17.25

Fig. 6. SEM images of (a) control mastic and (b) mastic-100.

HGM to replace an equal volume of LMF, the thermal conductivity of asphalt mastic reduced. Specifically, the thermal conductivity of mastic-100 was 0.214 W/(mK), which was about 40% lower than that of control mastic. According to their discussion in Section 3.3.2, there was no chemical reaction between HGM and asphalt, so HGM could maintain the hollow structure to play a thermal resistance role in asphalt mastic. The result means that incorporating HGM in asphalt mixture may be potential to prevent heat conduction in asphalt pavement.

3.5. Spectral reflectance The spectral reflectance of asphalt mastics along the wavelength of 300–2500 nm was shown in Fig. 9. It should be noted that only the reflectance of three asphalt mastics were plotted in the figure, in order to identify their differences more clearly. It can be seen from the Fig. 9 that the reflectance of asphalt mastics were basically the same with each other in the UV (300–400 nm)-Vis (400–760 nm) band, while the reflectance of

4000

3500

3000

2500

Thermal conductivity (W/(m.K))

1419

877

717

717

877

0.371

789 877

1376 1376 1376 1026

Asphalt HGM Mastic-100 Mastic-50 Control mastic LMF

1026

1600 1600 1600 1600

1456 1456 1456 1456

2850 2850 2850 2850

Passing ratio (%)

2920 2920 2920 2920

0.40

0.352 0.337

0.35

0.30

0.284

0.25 0.214 0.20

2000

1500

-1

Wave number (cm ) Fig. 7. FTIR spectrums of filler, asphalt and mastic.

1000

Control mastic Mastic-25

Mastic-50

Mastic-75

Mastic-100

Mastic type Fig. 8. Thermal conductivity of different asphalt mastics.

D. Yinfei et al. / Construction and Building Materials 244 (2020) 118380

Control mastic Mastic-50 Mastic-100

Reflectance (%)

50

40

30

20

10

0 500

1000

1500

2000

2500

Wavelength (nm) Fig. 9. Reflectance of different asphalt mastics.

mastic-100 was significantly higher than that of control mastic in the NIR (760–2500 nm) band. In order to quantitatively analyze the reflectance of asphalt mastics, the spectral reflectance of the five asphalt mastics was calculated based on the ASTM Standard G173-03 [28], as shown in Table 4. The black color of asphalt has a very high covering ability, resulting in the weak influence of HGM on the Vis reflectance of asphalt mastic. However, using HGM as filler could significantly improve the NIR reflectance of asphalt mastic. The NIR reflectance of mastic-100 was about 60% higher than that of control mastic., which tells us that it is possible to improve the NIR reflectance of asphalt pavement by adding fillers with high reflectance in the NIR band, so that to cool asphalt pavement.

strain of asphalt mastic at the specified time and stress level increased with the increase of HGM content. In order to quantitatively analyze the anti-rutting performance of asphalt mastic, two indicators (i.e. non-recovery creep compliance (Jnr) and creep recovery rate (R)) were calculated. The results are shown in Fig. 11 and Fig. 12, respectively. It can be found from Fig. 11 that with the increasing replacement ratio of HGM, Jnr increased at the stress level of 0.1 kPa and 3.2 kPa. The Jnr, 0.1 and Jnr, 3.2 of mastic-100 were 50% and 80% higher than those of control mastic, respectively. This result indicates that HGM reduced the deformation resistance of asphalt. In terms of the percentage difference of non-recovery creep compliance (Jnr-diff), the results show that the stress sensitivity of asphalt mastic could be improved by replacing LMF with HGM [32]. When the stress level was 0.1 kPa, replacing LMF with HGM could increase the indicator R, indicating that HGM could improve the elastic property of asphalt mastic. However, the creep recovery abilities of asphalt mastics dramatically reduced when the stress level was 3.2 kPa. The R of the mastics was all lower than 1%. Moreover, the varying trend of R was unstable with the increasing replacing content of LMF with HGM. The main reason for this phenomenon is that the specific surface area of HGM was small and its surface was smooth, which affected its bonding ability with asphalt, resulting in a negative influence on the deformation resistance of asphalt mastic. 50

1.6

Jnr0.1 Jnr3.2 Jnrdiff

1.2

40

0.8 30

3.6. MSCR test results 0.4

The anti-rutting performance of asphalt mastic was evaluated by MSCR test. Fig. 10 illustrates the variations of shear strain with time under two stress levels. The shear strain of all the asphalt mastics presented very similar varying trends, regardless of stress level. However, the cumulative strain of control mastic under either 0.1 kPa or 3.2 kPa stress level was lower than those of asphalt mastics with HGM. The shear

Mastic-50

Control mastic Mastic-25

Mastic-75

Mastic-100

Asphalt mastic type Fig. 11. Non-recovery creep compliances of different asphalt mastics.

b

225

Control mastic Mastic-25 Mastic-50 Mastic-75 Mastic-100

200

Shear strain γ (%)

0.0

175

5000

Shear strain γ (%)

a

20

150

125

Control mastic Mastic-25 Mastic-50 Mastic-75 Mastic-100

4000

3000

2000

1000 100

0

75 0

20

40

60

80

100

100

120

Time (s) Fig. 10. Shear strain variations with time: (a) 0.1 kPa; (b) 3.2 kPa.

140

160

Time (s)

180

200

Jnr-diff /%

60

Jnr /kPa-1

6

7

D. Yinfei et al. / Construction and Building Materials 244 (2020) 118380

350

0.1kPa 3.2kPa

Control mastic Mastic-25 Mastic-50 Mastic-75 Mastic-100

R /%

Shear stress (kPa)

300 250 200 150 100 50 0

Control mastic

Mastic-25

Mastic-50

Mastic-75

Mastic-100

0

5

Fig. 12. Creep recovery rates of different asphalt mastics.

Control mastic:logG'(ω)=0.897logω-0.408 Mastic-25: logG'(ω)=0.899logω-0.448 Mastic-50: logG'(ω)=0.905logω-0.475 Mastic-75: logG'(ω)=0.896logω-0.478 Mastic-100: logG'(ω)=0.899logω-0.513

0.1

1

20

25

30

10

Frequency ω (Hz) Fig. 13. Relationship of storage modulus vs. frequency.

3.7. LAS test results The fatigue performance of asphalt mastic was evaluated, according to the LAS test method introduced in section 2.2.6. The relationship of storage modulus vs. frequency is shown in Fig. 13. The parameter B could be fitted using the data in Fig. 13, as shown in Table 5. It can be found that for different asphalt mastics, the relationship of storage modulus vs. frequency were very similar to each other, thus leading to the very small difference of parameter B between asphalt mastics. The relationship of shear stress vs. strain in the second procedure of LAS test is shown in Fig. 14. With the increase of shear strain, the shear stress first increased until it reached the peak, and then decreased. The peak shear stress of asphalt mastic decreased with increasing replacing ratio of HGM.

According to AASHTO TP-101 [34], the damage curves of asphalt mastics were plotted, as shown in Fig. 15. The damage characteristic curve was fitted to achieve the parameter A35, as shown in Table 5. With the increase of replacing ratio of HGM, the parameter A35 gradually increased. The parameters shown in Table 5 were used to predict the fatigue life of asphalt mastics at different strain levels. According to Eq. (2), pavement strain level has a significant impact on the fatigue life of asphalt mastics. The fatigue life of asphalt mastics at the strain levels of 2.5% [35–39] and 5% [38–40] were calculated and shown in Fig. 16. The fatigue life of asphalt mastics was significantly reduced when the strain level increased from 2.5% to 5%. At the specified strain level, the fatigue life of mastic-100 was slightly higher than that of control mastic. For example, the fatigue life of mastic-100 was 19.9% higher than that of control mastic when the strain level was 5%. This result indicates that replacing LMF with HGM was beneficial for the fatigue performance of asphalt mastic. As shown in Fig. 6, HGM particles were broken during the mixing process, which, together with the hollow structure of HGM, made the actual replaced volume of HGM be lower than it’s supposed to be. Thus, there was a higher volume of asphalt in the asphalt mastic containing HGM, which led to a better fatigue performance [41].

Control mastic Mastic-25 Mastic-50 Mastic-75 Mastic-100

|G*|•sinδ (MPa)

Storage modulus G' (MPa)

Control mastic Mastic-25 Mastic-50 Mastic-75 Mastic-100

0.1

15

Fig. 14. Relationship of shear stress vs. strain.

10

1

10

Shear strain (%)

Asphalt mastic type

Table 5 Fitting parameters in the LAS test. Mastic type

B

A35

Control mastic Mastic-25 Mastic-50 Mastic-75 Mastic-100

4.230 4.226 4.228 4.234 4.226

1.461E 1.626E 1.652E 1.682E 1.733E

+ + + + +

07 07 07 07 07

0

1000

2000

3000

4000

Damage Intensity (D) Fig. 15. Damage characteristic curve of asphalt mastics.

5000

8

D. Yinfei et al. / Construction and Building Materials 244 (2020) 118380

a

b 0.0195

0.37

0.36 0.0190

N f (1 million ESALs)

N f (1 million ESALs)

0.35

0.34

0.33

0.0185 0.0180 0.0175

0.32

0.0170

0.31

0.0165

0.30

0.0160

Control mastic Mastic-25

Mastic-50

Mastic-75

Mastic-100

Control mastic Mastic-25

Asphalt mastic type

Mastic-50

Mastic-75

Mastic-100

Asphalt mastic type

Fig. 16. Fatigue life at (a) strain level of 2.5% and (b) strain level of 5%.

4. Conclusions This paper studied the feasibility of using hollow glass microsphere (HGM) to replace limestone mineral filler (LMF) to prepare asphalt mastic for the purpose of cooling asphalt pavement. The properties of HGM and LMF were characterized from the microscopic perspective. The effects of filler type on the thermal conductivity, spectral reflectance, anti-rutting and fatigue performance were studied. Based on the test results, the following conclusions were obtained in this paper: (1) Compared with LMF, HGM had larger particle size, wider particle size distribution range. From the results of XRF and XRD tests, it was found that the two fillers had very different chemical element composition and crystal structure. (2) According to the FITR spectrum analysis of asphalt, HGM, LMF and asphalt mastic, it was found that HGM and LMF were physically mixed with asphalt. The SEM result shows that some HGM particles with hollow structure were broken during the preparation of asphalt mastic. (3) Replacing LMF with HGM could enhance the thermal resistance of asphalt mastic. The thermal conductivity of mastic-100 was about 40% lower than that of control mastic. In addition, HGM could increase the spectral reflectance of asphalt mastic, especially in the near – infrared band. The NIR reflectance of mastic-100 was about 60% higher, compared to control mastic. (4) The non-recovery creep compliance and creep recovery rate were measured using MSCR test. From the results it was found that the anti-rutting performance of asphalt mastic reduced with the addition of HGM. (5) The LAS test was used to analyze the fatigue characteristics of asphalt mastic. At the same strain level, the fatigue performance of asphalt mastic mixed with HGM was slightly improved. Therefore, the addition of HGM had a positive effect on the fatigue performance of asphalt mastic. In spite of the positive effects on the thermal conductivity, solar reflectance and fatigue performance of asphalt mastic due to replacing LMF with HGM, the reduced anti-rutting performance means that some further measures should be applied to deal with

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