Construction and Building Materials xxx (2013) xxx–xxx

Contents lists available at ScienceDirect

Construction and Building Materials

journal homepage: www.elsevier .com/locate /conbui ldmat

Effect of LDHs on the aging resistance of crumb rubber modifiedasphalt

0950-0618/$ - see front matter � 2013 Elsevier Ltd. All rights reserved.http://dx.doi.org/10.1016/j.conbuildmat.2013.10.040

⇑ Corresponding author. Tel./fax: +86 27 87162595.E-mail address: wusp@whut.edu.cn (S. Wu).

Please cite this article in press as: Pang L et al. Effect of LDHs on the aging resistance of crumb rubber modified asphalt. Constr Build Mater (2013),dx.doi.org/10.1016/j.conbuildmat.2013.10.040

Ling Pang a,b, Kuangyi Liu a, Shaopeng Wu a,⇑, Min Lei b, Zongwu Chen a

a State Key Laboratory of Silicate Materials for Architectures, Wuhan University of Technology, Wuhan 430070, Chinab School of Sciences, Wuhan University of Technology, Wuhan 430070, China

h i g h l i g h t s

� LDHs improved the ageing resistance of crumb rubber modified asphalt (CRMA).� LDHs present significant influences on properties of CRMA after UV aging.� Less carbonyl groups appeared in the aged LDHs/CRMA than in the aged CRMA.� LDHs modified CRMA has a better performance at both low and high temperatures.

a r t i c l e i n f o

Article history:Available online xxxx

Keywords:Crumb rubber modified asphaltAging resistanceUltraviolet radiation agingLDHs

a b s t r a c t

Layer double hydroxides (LDHs), a kind of ultraviolet light resistant material, was added into the CrumbRubber Modified Asphalt (CRMA) and its effects on the aging resistance of the CRMA were investigated inthis paper. The short-term and long-term aging processes of asphalt were simulated by Thin Film OvenTest (TFOT) and ultraviolet (UV) radiation test, respectively. With Fourier Transform Infrared Spectros-copy (FTIR) measurements, it was found that LDHs can slow down the formation of carbonyl groups dur-ing the aging process. The conventional physical properties test and Dynamic Shear Rheometer (DSR) testwere used to evaluate the properties of the asphalt. The results showed that the softening point increasesand G* ratios of CRMA decreases significantly, the ductility and the penetration retention rate increaseafter ultraviolet aging due to the introduction of LDHs. Besides, the results of both creep and relaxationtest implied that the LDHs modified CRMA binder has a better UV aging resistance.

� 2013 Elsevier Ltd. All rights reserved.

1. Introduction

With the development of motor transportation industry, theamount of discarded tires nearly reaches 10 million every year inthe world [1]. A great number of waste rubber tires have causedserious environmental problems. Therefore, the utilization ofwaste rubber tires has attracted great interests of researchers in re-cent decades [2–4]. A lot of researches show that crumb rubber,made from waste rubber tires, can improve the temperature sensi-tivity, deformation resistance at high temperatures, crack resis-tance at low temperatures and fatigue resistance of asphalt asasphalt modifier. Therefore, the service life of crumb rubber mod-ified asphalt (CRMA) pavement will be longer than unmodifiedones [5–7]. In addition, CRMA can also reduce the traffic noiseand improve the driving comfort [8]. So the utilization of wastecrumb rubber as asphalt modifier is one of the most promising

ways to solve the problems caused by waste rubber tires consider-ing the benefits of economy and environment [9].

Some researches on interaction mechanism of crumb rubberand base asphalt indicated that crumb rubber swells in asphaltby adsorbing the light components of asphalt [10–12]. However,just like other asphalt materials, the aging of CRMA during activetime can induce the change of proportion of the components inthe asphalt, the light components of asphalt volatilize, and micro-molecules convert into large molecular size fractions by oxidationand polymerization [13–15]. The components of asphalt determineits properties, and the properties of CRMA binder are degradedwith the decrease of light components and the structure destruc-tion of asphalt [16], as a result, the CRMA pavement diseases takeplace. Therefore, it is important to improve the aging resistance ofCRMA binder.

LDHs have attracted a considerable attention as the UV lightresistant materials to improve the properties of rubber, plastics,coating material in recent years. These layered materials are multinestification layered structure. The inorganic layer sheets have thephysical shield effect against UV light, and some metal elements of

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2 L. Pang et al. / Construction and Building Materials xxx (2013) xxx–xxx

layer sheets and negative ions between layer sheets will chemi-cally absorb UV light. This kind of multi chemical absorbabilityand physical shield effect of LDHs result in excellent UV agingresistance in the organic material [17–19]. Wu et al. studied the ef-fect of LDHs on the aging property of the asphalt and found that theLDHs can enhance the aging resistance of asphalt [20]. So, LDHs, asa kind of UV aging resistant materials, has the potential to improvethe aging resistance of CRMA. In this paper, LDHs, were added intothe CRMA at 0, 3, 5 wt% mass ratio, and the impact of the LDHs onthe aging resistance of CRMA was investigated. Thin film oven(TFOT) test and UV light accelerated aging process were used tosimulate the short-term aging and long-term field aging of asphalt,respectively. The rheological properties of asphalt before and afterartificial UV aging were investigated by using Dynamic Shear Rhe-ometer (DSR) through temperature sweep, creep tests and relaxa-tion test. FTIR test result, conventional physical properties,complex modulus ratio, creep and relaxation curve of asphalt wereused to evaluate the chemical and physical characteristics of as-phalt before and after artificial UV aging.

2. Materials and experimental

2.1. Materials

The CRMA used in this paper was provided by Hubei Guochuang Hi-tech Mate-rial Co., Ltd. The diameter of crumb rubber power modifier was smaller than0.3 mm and the content was 15% by weight. The basic properties of CRMA areexhibited in Table 1.

Mg–Al layered double hydroxides complex metallic material was used to mod-ify the CRMA. The LDHs was produced by Rui Fa Chemical Company Limited, JiangSu, China. The density of the LDHs was 1.7 g/cm3 and the moisture content was lessthan 0.3%.

2.2. Preparation of LDHs modified asphalt

Many researchers suggested the blending temperature of crumb rubber andbase asphalt should be more than 160 �C and less than 200 �C [21]. In China, themost commonly used blending temperature for CRMA is 175–185 �C. Although thistemperature range may lead to the degradation of base asphalt, it is good for theswelling process of crumb rubber. Therefore, LDHs was blended into CRMA binderusing a shear blender at 180 �C in this research. The rotation speed of the blenderwas 5000 r/min and 60 min of blending was used to ensure a good distribution ofLDHs. The CRMA without LDHs was also processed under the same conditions asthe reference group.

2.3. Aging procedures

TFOT was employed to simulate the short-term oxidation that occurs during thehot-mix process according to Chinese standard test methods of bitumen and bitu-minous mixtures for highway engineering JTG E20-2011(T0609-2011) [22]. AfterTFOT aging, the asphalt samples with film thickness of 1 mm were prepared for fur-ther UV aging to simulate the photodegradation that occurs during the service life.The UV aging performed on the asphalt samples lasted for 10 days in a UV lightaccelerated aging oven, the radiation strength of the UV light was set at 26.5 W/m2 with the wavelength of 360 nm, and the test temperature was controlled at60 �C.

Table 1Properties of base asphalt and CRMA.

Index Baseasphalt

CRMA Specification

Penetration at 25 �C (0.1 mm) 72 51 T0604-2011Ductility of base asphalt at before

TFOT65 12 T0605-2011

15 �C, CRMA at 5 �C (cm) after TFOT 19 8.5 T0605-2011Softening point (�C) 44.5 68 T0606-2011Education, softening point difference

(�C)– 2 T0661-2011

Elasticity resume at 25 �C (%) – 79 T0662-2000

Please cite this article in press as: Pang L et al. Effect of LDHs on the aging resisdx.doi.org/10.1016/j.conbuildmat.2013.10.040

2.4. Characterization methods

2.4.1. FTIRA Thermo Nicolet Model Nexus FTIR–Raman spectrophotometer was used to re-

cord FTIR spectra of rubber asphalt. A sample was prepared by casting an asphaltfilm onto a KBr thin plate from 5 wt% solution in carbon disulfide, then the solventwas dried for the FTIR analysis.

2.4.2. Conventional physical properties testThe conventional physical properties tests including penetration, ductility, soft-

ening points and some other property indexes. They were conducted according toChinese standard test methods of bitumen and bituminous mixtures for highwayengineering JTG E20-2011.

2.4.3. DSRA MCR101 Dynamic Shear Rheometer (DSR) produced by Anton Paar Company

was adopted to measure the rheological property of CRMA and LDHs/CRMA. DSRtemperature sweep test was performed under the strain-controlled mode at a con-stant frequency of 10 rad/s. The tests were performed within the linear viscoelasticrange of the tested asphalts. When the test temperature is higher than 30 �C, 25 mmdiameter plates with 1 mm gap were used. When the test temperature is lower than30 �C, 8 mm diameter plates with 2 mm gap were used. Furthermore, creep testingand relaxation testing were also used to evaluate the aging resistance of CRMA andLDHs/CRMA.

3. Results and discussion

3.1. FTIR characterization analysis

FTIR was applied to study the effect of LDHs on the aging resis-tance of the CRMA. The aging of asphalt includes thermal oxygenand light oxygen aging. The occurrence of carbonyl groups is theresult of the oxidation aging of base asphalt. According to the pre-cious research, the carbonyl (C@O) index can be used as an indica-tor to evaluate the aging extent of asphalt [23,24]. It was computedas the following formula [25]:

IC@O ¼Area of the carbonyle band centered around 1700 cm�1P

Area of the spectral bands between 2000 and 600 cm�1

The FTIR spectrums of asphalts without aging and asphalts withUV aging were shown in Fig. 1. As an indicator of the aging extent,the corresponding functional groups indices were listed in Table 2.Fig. 1 shows no obvious absorbance peak can be observed for as-phalts without aging, while carbonyl clearly appeared after UVaging for 10 days. The intensity of carbonyl absorption peaks ofLDHs/CRMA were lesser than that of CRMA. Table 2 shows moredetails about these changes discussed above. The carbonyl indexof CRMA is 0.013, larger than that of LDHs/CRMA after UV agingfor 10 days, which means less carbonyl groups formation afterthe introduction of LDHs, indicating that LDHs modified asphaltshad better resistant to the formation of carbonyl and hence mightgetting more stable. Therefore, the LDHs can improve the agingresistance of CRMA binder.

3.2. Conventional physical properties

Figs. 2–4 showed the conventional properties test results ofCRMA and LDHs/CRMA before and after aging. It is obvious thatLDHs provide increased soft points and decreased penetration ofCRMA before UV aging, therefore LDHs is good for deformationresistance of asphalt at high temperatures although it degradesthe ductility of CRMA slightly. After subjected to UV aging, therewould be a great difference in conventional properties, the soften-ing points decreased, the penetration and ductility increased withthe addition of LDHs, especially when 5 wt% of LDHs was added.

Table 3 lists the softening point increment, ductility retentionrate and penetration retention rate after UV aging using originalvalues as references. The softening point increment, ductilityretention rate and penetration retention rate can be used to evalu-

tance of crumb rubber modified asphalt. Constr Build Mater (2013), http://

0

0.1

0.2

0.3

0.4

600 800 1000 1200 1400 1600 1800 2000

Wavenumber (cm-1)

Abs

orba

nce

CRMA CRMA-UV

3%LDHS/CRMA 3%LDHS/CRMA-UV

5%LDHS/CRMA 5%LDHS/CRMA-UV

1700cm-1

Fig. 1. FTIR analysis of asphalts before and after aging.

Table 2FTIR absorbance indices of asphalts after UV aging for 10 days.

Asphalt CRMA–UV 3% LDHs/CRMA–UV 5% LDHs/CRMA–UV

Carboyl index 0.013 0.009 0.008

0

10

20

30

40

50

60

CRMA 3%LDHs/CRMA 5%LDHs/CRMA

Pene

trat

ion

(0.1

mm

)

Fresh UV

Fig. 2. Penetration of asphalts at 25 �C.

0

10

20

30

40

50

60

70

80

90

100

CRMA 3%LDHs/CRMA 5%LDHs/CRMA

Soft

enin

g po

int (° C

)

Fresh UV

Fig. 3. Softening points of asphalts.

0

2

4

6

8

10

12

14

CRMA 3%LDHs/CRMA 5%LDHs/CRMA

Duc

tility

(cm

)

Fresh UV

Fig. 4. Ductility of asphalts at 5 �C.

Table 3The softening point increment, ductility and penetration retention rate after UV agingfor 10 days.

Asphalt CRMA 3% LDHs/CRMA 5% LDHs/CRMA

Softening point increment (�C) 11.0 8.5 7.0Ductility retention rate (%) 41.7 46.4 55.6Penetration retention rate (%) 64.7 72.9 76.6

L. Pang et al. / Construction and Building Materials xxx (2013) xxx–xxx 3

ate the aging resistance [26]. According to Table 3, the 3% and 5%LDHs/CRMA exhibited lower softening point increment, higher

Please cite this article in press as: Pang L et al. Effect of LDHs on the aging resisdx.doi.org/10.1016/j.conbuildmat.2013.10.040

ductility retention rate and penetration retention rate comparedto the CRMA, indicating LDHs can significantly improve the agingresistance of CRMA. Compared with CRMA, properties of CRMA/LDHs was much retained after UV aging, which indicated theLDHs/CRMA had better UV aging resistance than CRMA.

3.3. Temperature sweep test

The temperature sweep conducted by DSR can characterize thevariation of complex modulus and phase angle of asphalt in a widerange of temperature. Figs. 5 and 6 respectively showed the com-plex modulus and phase angle of CRMA and LDHs/CRMA beforeand after aging, and also showed the effect of LDHs on the agingresistance. The complex modulus (G*) of LDHs/CRMA was higherand phase angle was smaller than that of CRMA at all test temper-atures before aging. It means that the addition of LDHs increasedthe G* and reduced the phase angle. The increase of G* and the de-crease of phase angle caused by aging, which induced more solid-like and hardening [23]. However, after UV aging for 10 days, the G*

and phase angle curve of all asphalts tended to get closer with thedeepened aging of asphalts, but the G* of LDHs/CRMA was lowerand phase angle was higher than that of CRMA. This means thatthe LDHs/CRMA binder suffered less hardening and it was moreviscous than CRMA.

Table 4 displays the G* ratios at different temperatures usingoriginal modulus as reference value. From Table 4, it can be seenthat the G* ratios of 3% and 5% LDHs modified asphalts were lowerthan that of CRMA after UV 10 days. The more the G* value of as-phalt increase, the more aging the asphalts suffer. So, the aging de-gree of the LDHs modified asphalt was not as serious as CRMA. Itimplied that the addition of LDHs improved the aging resistanceof CRMA.

3.4. Creep and relaxation test

The effect of LDHs modifier on the aging properties of CRMAbinder was also studied by shear creep test. Fig. 7 gave the creepstrain response curve of CRMA and LDHs/CRMA. The creep testingwas conducted at 60 �C by DSR. A constant shear stress of 5 Pa was

tance of crumb rubber modified asphalt. Constr Build Mater (2013), http://

0

40

80

120

160

-10 -5 0 5 10 15 20 25 30

Com

plex

mod

ulus

(M

Pa)

CRMA 3%LDHs/CRMA

5%LDHs/CRMA CRMA-UV

3%LDHs/CRMA-UV 5%LDHs/CRMA-UV

Temperature (°C)

Fig. 5. Complex modulus curves of asphalts before and after aging.

20

30

40

50

60

-10 -5 0 5 10 15 20 25 30

Temperature (°C)

Phas

e an

gle

(°)

CRMA 3%LDHs/CRMA

5%LDHs/CRMA CRMA-UV3%LDHs/CRMA-UV 5%LDHs/CRMA-UV

Fig. 6. Phase angle curves of asphalts before and after aging.

0

2

4

6

8

10

0 100 200 300 400 500

Time (s)

Cre

ep s

trai

n (%

)

CRMA CRMA-UV 3%LDHs/CRMA

5%LDHs/CRMA 3%LDHs/CRMA-UV 5%LDHs/CRMA-UV

Fig. 7. Creep strain curve at 60 �C.

2.E+04

4.E+04

6.E+04

8.E+04

1.E+05

1.E+05

0 50 100 150 200 250 300

Time (s)

Shea

r st

ress

(Pa

)

CRMA 3%LDHs/CRMA

5%LDHs/CRMA CRMA-UV

3%LDHs/CRMA-UV 5%LDHs/CRMA-UV

Fig. 8. Stress relaxation curves at �5 �C.

4 L. Pang et al. / Construction and Building Materials xxx (2013) xxx–xxx

applied and the creep strain of asphalts was recorded during 100 sof the loading stage and 400 s of the unloading stage. As indicatedin Fig. 7, the total creep strain of LDHs/CRMA was lower than thatof CRMA binder before aging, which indicates that the introductionof LDHs increases the resistance to creep of CRMA at high temper-atures. After UV aging for 10 days, the total creep strains of as-phalts were lower than that of asphalts without UV aging,however among asphalts of having suffered UV aging, the totalcreep strains increased with the addition of LDHs, which indicatesthat LDHs can lower hardening of CRMA when subjected to UVaging, therefore the aging resistance of LDHs/CRMA is superior toCRMA.

The shrinkage stress of asphalts with aging is higher than that ofones without aging, because the aging process has hardenedasphalts. It is well known that the pavement will crack when theshrinkage stress is higher than the tensile strength. The shearrelaxation testing was used to evaluate the low temperature per-formance of asphalt with the application of DSR instrument understrain-controlled model. The applied shear strain level was kept to5%. Fig. 8 presented the relaxation test results of CRMA and LDHs/CRMA before and after aging at �5 �C. It indicated that the

Table 4G* ratio of asphalts after UV aging for 10 days.

Asphalts G* ratio

�10 �C 0 �C 10 �C 20 �C 30 �C

CRMA 1.36 1.43 1.58 1.69 1.603% LDHs/CRMA 1.17 1.18 1.27 1.40 1.485% LDHs/CRMA 1.05 1.05 1.12 1.20 1.26

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inclusion of LDHs into CRMA resulted in a higher shear stress,mainly because LDHs enhanced the elasticity of CRMA. Comparedto CRMA, the shear stress of the LDHs/CRMA was lower after UVaging, especially 5% LDHs/CRMA had the lowest shear stress. Theresults implied that LDHs can lower hardening of CRMA with theaddition of LDHs during aging process. Therefore LDHs can im-prove the UV aging resistance of CRMA. The reason why agedLDHs/CRMA had a lower shear stress is that LDHs could retardthe oxidation of asphalt through the multi chemical absorbabilityand physical shield effect, slowing down the reduction of viscouscomponent during the aging process. The more the viscous compo-nent, the better the low temperature property is.

4. Conclusions

In this research, LDHs was added into the CRMA binder and theeffects of LDHs on the UV aging resistance of the CRMA were inves-tigated by means of FTIR analysis, conventional physical propertiestest and DSR test. Based on these test results, the following conclu-sions can be drawn:

(1) The carbonyl groups, occurred after UV aging, was used as anaging index to evaluate the effect of LDHs on the aging resis-tance of CRMA. It was found that less carbonyl groupsappeared in the aged LDHs/CRMA than in the aged CRMA,indicating that the CRMA binder would get less sensitiveto UV aging when LDHs was introduced.

(2) LDHs stiffened CRMA by increasing its softening points anddecreasing its penetration. However, the softening pointincrement of LDHs/CRMA decreased and the penetrationand ductility retention rate increased after UV aging, which

tance of crumb rubber modified asphalt. Constr Build Mater (2013), http://

L. Pang et al. / Construction and Building Materials xxx (2013) xxx–xxx 5

implied that LDHs can lower hardening speed of CRMA whensubjected to UV aging. Therefore LDHs can improve the UVaging resistance of CRMA.

(3) The G* ratio of LDHs/CRMA was lower and phase angle washigher than that of CRMA after aging. It means that theLDHs/CRMA binder suffered less hardening and it was moreviscous than CRMA after UV aging.

(4) The results of creep and relaxation test also supported theconclusions that LDHs can slow down the hardening speedof CRMA when subjected to UV aging. Therefore LDHs canimprove UV aging resistance of CRMA and it can slow downthe degradation of CRMA when LDHs/CRMA was subjectedto UV aging.

Acknowledgements

This work is supported by the Ministry of Science and Technol-ogy of China (2011BAE28B03) and the National InstrumentationProgram (2013YQ160501). The authors gratefully acknowledgetheir support.

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