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Comparison of high temperature performance and microstructure for foamed WMA and HMA with RAP binder
Construction and Building Materials 134 (2017) 594–601
Contents lists available at ScienceDirect
Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
Comparison of high temperature performance and microstructure for foamed WMA and HMA with RAP binder Fuqiang Dong, Xin Yu ⇑, Bo Xu, Tianyu Wang College of Civil and Transportation Engineering, Hohai University, Nanjing, Jiangsu Province 210098, PR China
h i g h l i g h t s RAP binders improve the high temperature performance and temperature sensitivity. RAP binders compromise the low temperature performance and fatigue resistance. The optimum RAP binder content of foamed WMA is more than that of HMA.
a r t i c l e
i n f o
Article history: Received 7 August 2016 Received in revised form 26 October 2016 Accepted 21 December 2016
Keywords: RAP binder Foamed warm mix recycled asphalt Hot mix recycled asphalt High temperature performance Microstructure
a b s t r a c t The foamed warm-mix recycled asphalts and hot mix recycled asphalt with different reclaimed asphalt pavement (RAP) binder contents (0wt%, 20wt%, 40wt%, 60wt%, and 80wt%) were prepared in laboratory. The influence on the viscosity-temperature performance, rheological properties, temperature sensitivity, fatigue resistance, and microstructure were investigated by conventional tests, Brookfield viscosity tests, Dynamic Shear Rheometer (DSR) tests, and Fourier Transform Infrared Spectroscopy (FTIR) tests. The results show that the RAP binder content has great effect on the performance of foamed warm mix recycled asphalt and hot mix recycled asphalt, and there is different change between foamed warm mix recycled asphalt and hot mix recycled asphalt. Compared to foamed warm-mix asphalt, foamed warm-mix recycled asphalt provides better high temperature performance and temperature sensitivity. Adding the RAP binder compromise the fatigue resistance of asphalt and with the increase of RAP binder content, the fatigue resistance of asphalt becomes worse. And the high temperature performance and temperature sensitivity of hot mix recycled asphalt is better than that of foamed warm mix recycled asphalt, while the fatigue resistance is on the contrary. By the microstructure analysis, the foaming process could slow down the aging degree of asphalt, and the aging degree of hot mix recycled asphalt is deeper than that of foamed warm mix recycled asphalt. The optimum RAP binder content of foamed warm mix recycle asphalt is more than that of hot mix recycled asphalt. Ó 2016 Elsevier Ltd. All rights reserved.
1. Introduction The use of recycled materials for road construction has been widely promoted due to environmental and economic benefits. It is reported that billions of dollars are spent annually in resurfacing and reconstruction of asphalt pavements [1] and over 500 million tons of asphalt are produced each year in the USA, which has brought considerable environmental burdens [2]. The reuse of reclaimed asphalt pavements (RAP) in asphalt layers can offer a sustainable alternative for pavement resurfacing and replacement.
⇑ Corresponding author. E-mail addresses: [email protected] (F. Dong), [email protected] (X. Yu), [email protected] (B. Xu), [email protected] (T. Wang). http://dx.doi.org/10.1016/j.conbuildmat.2016.12.106 0950-0618/Ó 2016 Elsevier Ltd. All rights reserved.
Hot-mix asphalt (HMA), which is the most widely used all over the world, is a material which can be recycled in 100% and could be totally reused to construct new asphalt layers in flexible pavements [3]. And many researches focused on the performance of hot-mix recycled asphalt and hot-mix recycled asphalt mixtures [4–6]. There are several advantages using hot recycling technology, and the performance of hot recycled asphalt mixtures are not worse than that of hot asphalt mixtures with new materials, and then the shortage of RAP materials could be covered by the different new aggregate and asphalt binder [7]. However, the higher construction temperature, the further aging of recycled and new asphalt and the more consumption of energy limit the development of hot recycling technique for asphalt pavement [8]. A low-carbon and saved energy technology, which is known as Warm Mix Asphalt (WMA), is developed to meet the increasingly
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F. Dong et al. / Construction and Building Materials 134 (2017) 594–601
stringent environmental regulations. The WMA technology could decrease the mixing and compacting temperatures by 30–50 °C, and reduce the emissions of SOx, NOx, CO2, and volatile organic compounds (VOC’s) by 15–70% [9,10]. Recently, there are three types of WMA technologies commonly used: (a) organic additives [11,12], (b) chemical additives [13], and (c) water foaming process or water containing additives [14] which reduce the mixing temperature by foaming the liquid asphalt to expand. Among the above technologies, the foaming technology involves minimal cost for the additives and is the most widely used in USA. However, when it comes to the combination of WMA and RAP, there are less research about the question that whether the blending efficiency between RAP binder and new asphalt is better or not, and how about the difference between foamed WMA and HMA with RAP binders. And few of them have focused on comparison of the high temperature performance and microstructure of the foamed warm mix recycled asphalt and hot mix recycled asphalt. Therefore, the objective of this paper is to investigate the influence of RAP binder content of viscosity-temperature performance, rheological properties, temperature sensitivity, fatigue resistance, and microstructure by Brookfield viscosity tests, DSR tests, and FTIR tests. 2. Materials and testing methods 2.1. Materials The 60/80 penetration grade of virgin asphalt produced by Ssangyong asphalt plant of South Korea was selected to prepare the foamed warm-mix asphalt, foamed warm-mix recycled asphalt and hot mix recycled asphalt, and the properties of virgin asphalt are summarized in Table 1. And the RAP materials were recycled from the asphalt road in Zhejiang province and the service life is about 5 years. Then the RAP binder was extracted from RAP materials by the rotary evaporator method using extracted liquid. The properties of RAP binder are listed in Table 1. 2.2. Preparation for foamed warm-mix recycled asphalt samples Firstly, the foamed warm-mix asphalt samples were prepared by Wirtgen foaming machine, and the conditions of foaming process as follows: the foaming water content is 1.5% (by the weight of virgin asphalt), and the temperature of virgin asphalt and the foaming water were controlled at 150 °C and 30 °C, respectively. The foamed warm-mix asphalt samples were then ready for preparing the foamed warm-mix recycled asphalt samples. Secondly, the foamed warm-mix recycled asphalt samples were prepared with foamed warm-mix asphalt and RAP binder by stirring for 30 min at 125 °C. The RAP binder contents used in this study were 20%, 40%, 60% and 80% by weight of foamed warmmix asphalt.
And then, the samples were conducted by Rolling Thin Film Oven Test (RTOFT) tests to stimulate the process of mixing and compaction of hot-mix asphalt mixtures. Also the samples were conducted by Pressure Aging Vessel (PAV) to stimulate the oxidation process of the asphalt during the first five years. 2.3. Preparation for hot-mix recycled asphalt samples The hot-mix recycled asphalt samples were prepared by a stirring mixer. Firstly, the virgin asphalt and RAP binder were heated to fluid condition at about 120–140 °C. Secondly, the RAP binder (20%, 40%, 60% and 80% by weight of virgin asphalt) was added to virgin asphalt at 150 °C and mixed for 30 min. And then the samples were conducted by RTOFT tests and PAV tests to stimulate the short-aging process and long-aging process. 2.4. Test and evaluation methods In this study, the comparison of foamed warm-mix recycled asphalt and hot-mix recycled asphalt with different RAP binder content were investigated and the high temperature performance including viscosity-temperature characteristic, failure temperature, temperature sensitivity and fatigue resistance as well as microstructure of above samples were evaluated by Dynamic Shear Rheometer (DSR) tests and Fourier Transform Infrared Spectroscopy (FTIR) tests. The flow chart of the experiment program was illustrated in Fig. 1. 2.4.1. Rotational viscosity tests The viscosity-temperature characteristic can be used to evaluate the high temperature performance of asphalt, and the workability of asphalt mixture could be obtained. And the Brookfield viscometer (Model DV-II+, Brookfield Engineering Inc., USA) was employed to determine the viscosity of foamed warm-mix recycled asphalt and hot-mix recycled asphalt at the temperatures of 90 °C, 100 °C, 110 °C, 120 °C, 130 °C, 135 °C, and 140 °C. 2.4.2. Rheological performance tests It is an effective and common method to evaluate the performance of asphalt by rheological tests. In this study, a TAAR1500EX DSR was employed to determine the rheological performance of foamed WMA and HMA with different RAP binder content. And the test conditions are 25 mm diameter plates and 1 mm gap. And the failure temperature and complex number index were calculated by the relationship between storage modulus (G0 ), loss modulus (G00 ) and rutting resistance factor (G⁄/sind) and temperature (T) obtained from the temperature sweep tests at the temperature range from 40 °C to 80 °C. The ultimate fatigue temperature was calculated by the relationship between fatigue resistance factor (G⁄sind) and temperature (T) obtained from the temperature sweep tests at the temperature range from 10 °C to 50 °C.
Table 1 Properties of the virgin asphalt and RAP binder. Property
Test Standards
Virgin asphalt
RAP binder
Penetration (25 °C)/(0.1 mm) Ductility (15 °C)/(cm) Softening point/(°C) Density (15 °C)/(g/cm3) Solubility (trichloroethylene)/(%) Components
ASTM D ASTM D ASTM D ASTM D ASTM D T0618
70 >100 48.2 1.035 99.8 27.31 41.34 26.27 5.38
11 0.4 71.7 1.062 99.6 9.25 21.39 40.84 27.61
Saturate/wt% Aromatic/wt% Resin/wt% Asphaltene/wt%
5 113 36 70 2042
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Fig. 1. The flow chart of the experiment program.
2.4.3. Microstructure characteristic In order to characterize the difference of microstructure between foamed WAM and HMA with different RAP binder content, the Fourier Transform Infrared (FTIR) Spectroscopy (Nexus, Thermo Nicolet) tests was used in wavenumbers ranging from 500 cm1 to 4000 cm1. The samples dissolved by solvent of carbon tetrachloride smeared on the KBr pellet and then the sample was measured on the FTIR. 3. Results and discussions 3.1. Viscosity-temperature performance The viscosity-temperature characteristic is an important index for evaluating the high temperature performance and workability of asphalt binders. So the influence of RAP binder content on the viscosity of foamed WMA and HMA samples and the comparison of between foamed WMA and HMA were investigated in this study. And then the viscosity of foamed WMA and HMA are presented in Fig. 2.
As shown in Fig. 2, it could be concluded that there are great difference in viscosity between foamed WMA and HMA, and the RAP binder content has significant influence on the viscosity of both foamed WMA and HMA. On the whole, the viscosity of foamed WMA and HMA decreases at various different levels as the testing temperature is increasing. When it comes to the foamed WMA, with the increase of RAP binder content the viscosity of asphalt increases, because the components of RAP binder and virgin asphalt binder have major difference and the addition of RAP binder change the components of recycled asphalt system. Meanwhile, the higher the RAP binder content is the greater changing the viscosity of asphalt is becoming. Moreover, compared to foamed WMA, the viscosities of HMA are higher than that of foamed WMA with different RAP binder content at different testing temperature. On the one hand, more RAP binder improves the hard components of system. On the other hand, the mixing and compaction temperatures of HMA are higher than those of foamed WMA by 30–50 °C, and the higher temperature could accelerate the aging levels of asphalt and increase the content of hard components. In other words, the RAP binder could improve the high
Fig. 2. The viscosity-temperature characteristic difference between foamed warm-mix recycled asphalt and hot-mix recycled asphalt.
F. Dong et al. / Construction and Building Materials 134 (2017) 594–601
temperature performance of asphalt, and the high temperature performance of HMA is better than that of foamed WMA, while the workability of foamed WMA is better than that of HMA. 3.2. Failure temperature As we all known, rheological properties are very sensitive to the changes of component of asphalt binders. Therefore, the storage modulus G0 , loss modulus G00 , and rutting resistance factor G⁄/sind were obtained from the temperature sweep tests by DSR to evaluate the high temperature performance of foamed WMA and HMA. The influence of RAP binder content on the storage modulus G0 and loss modulus G00 of foamed WMA and HMA samples are presented in Figs. 3 and 4. As shown, the temperature has a significant effect on the evolution of G0 and G00 , and G0 as well as G00 decreases dramatically with the increase of temperature. Meanwhile, loss modulus G00 is always higher than storage modulus G0 , which indicates that the rheological behavior is dominated by viscous properties and the viscous component is more than elastic component. Moreover, the gap of G0 and G00 becomes narrower with the RAP binder content increasing, which is due to the difference of component between base asphalt and RAP binder. Compared to foamed warm-mix asphalt, RAP binder could improve the value of G0 and G00 , especially the G0 , which suggests that elastic component increase after adding RAP binder. Form Figs. 3–5, it can be concluded that RAP binder content has great influence on the storage modulus G0 , loss modulus G00 , and rutting resistance factor G⁄/sind of both foamed WMA and HMA, and there are great difference in rheological properties between foamed WMA and HMA. With the increase of RAP binder content, the storage modulus G0 , loss modulus G00 , and rutting resistance factor G⁄/sind all increase dramatically. Compared to foamed WMA, the above rheological properties of HMA are higher than those of foamed WMA with different RAP binder content. Meanwhile, the difference in rheological properties between foamed WMA and HMA becomes greater when the RAP binder content is increasing. The reasons are that the more RAP binder improves the hard components in this system, and the higher mixing and compaction temperature for HMA accelerate the aging degree of asphalt binder. In order to evaluate the influence on the RAP binder on the high temperature properties of foamed WMA and HMA, the failure temperature [15] was employed. The failure temperature was obtained
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from the relationship between rutting resistance factor G⁄/sind and temperature when rutting resistance factor G⁄/sind is at 1.0 kPa. And then the failure temperatures of foamed WMA and HMA with different RAP binder content are illustrated in Fig. 6. Compared to foamed warm-mix asphalt, the addition of RAP binder could improve the failure temperature of asphalt. Meanwhile, the failure temperature of foamed warm-mix recycled asphalt increases with the increase of RAP binder content. In other word, adding RAP binder is beneficial for the high temperature performance of foamed warm-mix asphalt, and the higher the RAP binder content is, the better high temperature performance of foamed warm-mix recycled asphalt is. And the results are consistent with that the higher content of RAP is used in asphalt pavement by WMA technology [16]. Compared to foamed warm-mix recycled asphalt, the failure temperature of hot mix recycled asphalt with different RAP binder content are higher than that of foamed warm-mix recycled asphalt, which indicates that the hot mix recycled asphalt is better than that of foamed warm-mix recycled asphalt. The more the RAP binder content is the higher the failure temperature of foamed warmmix recycled asphalt, and when the RAP binder content increase from 40wt% to 60wt% the failure temperature has a great improvement. 3.3. Temperature sensitivity The temperature sensitivity of asphalt binder has a great influence on the road service performance of asphalt pavement. And the better temperature sensitivity could improve the high and low temperature performance of asphalt [17]. Meanwhile, the storage modulus G0 and loss modulus G00 are sensitive to temperature. Therefore, the complex number index [18] obtained from the relationship between G0 , G00 , and temperature was selected to evaluate the temperature sensitivity of foamed warm-mix recycled asphalt and hot mix recycled asphalt. The relationship between storage modulus G0 and temperature and the relationship between loss modulus G00 and temperature of foamed warm-mix recycled asphalt and hot mix recycled asphalt are presented in Figs. 7and 8. It can be found that the linear correlation between lgG0 , lg G00 , and lgT is better. And the absolute slope values for the regression equations of foamed warm-mix recycled asphalt and hot mix recycled asphalt with different RAP binder content are listed in Table 2. The literature [18] reported that the
Fig. 3. The G0 and G00 values of foamed WMA.
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Fig. 4. The G0 and G00 values of HMA.
Fig. 5. The G⁄/sin d values of foamed WMA and HMA.
lower the slope values of regression equations are the better the temperature sensitivity of asphalt is. As shown in Table 2, with the increase of RAP binder content, the slope value of storage modulus G0 and loss modulus G00 decrease, which suggests that adding RAP binder could improve the temperature sensitivity of foamed warm-mix asphalt. Compared to hot mix recycled asphalt, the slope value of foamed warm-mix recycled asphalt is higher than that of foamed warmmix recycled asphalt at the same RAP binder content. In a word, the temperature sensitivity of hot mix recycled asphalt is better than that of foamed warm-mix recycled asphalt with the same RAP binder content. 3.4. Fatigue resistance
Fig. 6. Failure temperatures of foamed WMA and HMA.
Fatigue resistance performance of asphalt binder has significant influence on the service life of asphalt pavement [19]. To evaluate the fatigue resistance of foamed warm-mix recycled asphalt and hot mix recycled asphalt, the fatigue resistance factors G⁄sind were obtained from temperature sweep tests at the temperature
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Fig. 7. Logarithm of storage modulus G0 for foamed warm-mix recycled asphalt and hot mix recycled asphalt.
Fig. 8. Logarithm of loss modulus G00 for foamed warm-mix recycled asphalt and hot mix recycled asphalt.
Table 2 Absolute Slope Values for the Regression Lines in Figs. 7 and 8. RAP binder content/wt%
0 20 40 60 80
Absolute value of slope for lgG0 regression equation
Absolute value of slope for lgG00 regression equation
Foamed WMA
HMA
Foamed WMA
HMA
62.446 60.964 59.099 57.629 57.398
60.509 59.647 58.054 55.918 54.510
42.900 41.448 40.507 39.494 38.913
41.392 40.994 39.954 38.889 37.079
range from 10 °C to 50 °C. And the relationship between lg G⁄sind and temperature are illustrated in Fig. 9. According to the literatures [15], the lower fatigue resistance factor G⁄sind indicates the better fatigue resistance. As shown in Fig. 9, compared to foamed warm-mix asphalt, the fatigue resistance factor G⁄sind of foamed warm-mix recycled asphalt becomes higher, which indicates that the RAP binder has bad effects on the fatigue resistance of asphalt. Meanwhile, with the increase of RAP binder content, the fatigue resistance factor G⁄sind of foamed warm-mix recycled asphalt increase, and when the RAP binder
content increase higher, the asphalt become more sensitivity to fatigue cracking. In order to quantify the influence of RAP binder content on the fatigue resistance of foamed warm-mix recycled asphalt and hot mix recycled asphalt, the ultimate fatigue temperature was employed and presented in Table 3. It is shown that with the increase of RAP binder content, the fatigue temperatures of foamed warm-mix recycled asphalt and hot mix recycled asphalt increase, which indicates that adding RAP binder could compromise the fatigue performance of asphalt. Furthermore, the fatigue temperature
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Fig. 9. Temperature dependence of G⁄sind of foamed warm-mix recycled asphalt and hot mix recycled asphalt.
RAP binder content/ wt%
Ultimate failure temperature/°C
times higher than that of samples with the RAP binder content from 40% to 60%. In a word, the optimum RAP binder content of foamed warm-mix recycled asphalt is more than that of hot mix recycled asphalt.
Foamed WMA with RAP binder
HMA with RAP binder
3.5. Microstructure
0 20 40 60 80
18.56 20.89 23.10 25.62 33.51
21.16 25.27 29.80 33.72 38.06
Table 3 Ultimate failure temperature of foamed warm-mix recycled asphalt and hot mix recycled asphalt.
of foamed warm-mix recycled asphalt is lower than that of hot mix asphalt, that is to say that the fatigue resistance of foamed warmmix recycled asphalt is better. However, the variation amplitude of ultimate fatigue temperature presents a significant difference as the RAP binder content increases. The change of ultimate fatigue temperature with the RAP binder content from 60% to 80% is four
In this study, the Fourier Transform Infrared (FTIR) Spectroscopy (Nexus, Thermo Nicolet) tests were used to evaluate the influence of RAP binder content on the microstructure of foamed warm-mix recycled asphalt and hot mix recycled asphalt and the difference between foamed warm mix recycled asphalt and hot mix recycled asphalt. And the FTIR of foamed warm-mix recycled asphalt and hot mix recycled asphalt with different RAP binder content are presented in Fig. 10. As for recycled system, the chemical reaction is mainly focused on the aging degree of asphalt. Therefore, the band of methyl group at 1375 cm1 and the band of CAO bond at 1033 cm1 were selected to characterize the aging degree of asphalt, and the ratio
Fig. 10. FTIR of foamed warm-mix recycled asphalt and hot mix recycled asphalt with different RAP binder content.
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F. Dong et al. / Construction and Building Materials 134 (2017) 594–601 Table 4 The ratio of A1033/A1375 of foamed warm-mix recycled asphalt and hot mix recycled asphalt. RAP binder content/%
0 20 40 60 80
Foamed WMA with RAP binder
HMA with RAP binder
A1375
A1033
A1033/A1375
A1375
A1033
A1033/A1375
2.325 3.978 2.732 3.321 2.103
0.467 1.272 0.897 1.324 0.885
0.2008 0.3197 0.3275 0.3986 0.4210
2.704 3.912 2.573 2.907 2.474
0.669 1.358 0.906 1.210 1.092
0.2475 0.3472 0.3521 0.4163 0.4412
of A1033/A1375 of foamed warm-mix recycled asphalt and hot mix recycled asphalt are listed in Table 4. According to Beer’s law [20], the peak intensity ratio is equal to the area ratio between the two bands at 1033 cm1 and 1375 cm1. And the higher the ratio of A1033/A1375 is, the deeper the aging degree of asphalt is. As shown in Table 4, with the increase of RAP binder content, the ratio of A1033/A1375 increase. Meanwhile, the ratio of A1033/A1375 of HMA with RAP binder is higher than that of foamed HMA. It is suggested that the foaming process could slow down the aging degree of asphalt, and the aging degree of hot mix recycled asphalt is deeper than that of foamed warm mix recycled asphalt. 4. Conclusions The influence on the viscosity-temperature performance, rheological properties, temperature sensitivity, fatigue resistance, and microstructure of foamed warm mix recycled asphalt and hot mix recycled asphalt with different RAP binder content were investigated by Brookfield viscosity tests, DSR tests, and FTIR tests. The results show that the RAP binder content has great effect on the performance of foamed warm mix recycled asphalt and hot mix recycled asphalt. (1) Adding the RAP binder can improve the high temperature performance and temperature sensitivity of foamed warmmix recycled asphalt, while it compromises the fatigue resistance of asphalt. (2) The fatigue resistance of foamed warm mix recycled asphalt is better than that of hot mix recycled asphalt, while the high temperature performance and temperature sensitivity are worse. (3) The foaming process could slow down the aging degree of asphalt, and the aging degree of hot mix recycled asphalt is deeper than that of foamed warm mix recycled asphalt. (4) The optimum RAP binder content of foamed warm mix recycle asphalt is more than that of hot mix recycled asphalt.
Acknowledgments This work was supported by the National Natural Science Foundation of China (51278173), the Natural Science Foundation of Jiangsu Province for Distinguished Young Scholar (BK20150038), the Fundamental Research Funds for the Central Universities
(2015B21614), and project funded by China Postdoctoral Science Foundation (2016M591759). References [1] R.R. De Lira, D.D. Cortes, C. Pasten, Reclaimed asphalt binder aging and its implications in the management of RAP stockpiles, Constr. Build. Mater. 101 (2015) 611–616. [2] X. Shu, B.S. Huang, E.D. Shrum, X.Y. Jia, Laboratory evaluation of moisture susceptibility of foamed warm mix asphalt containing high percentages of RAP, Constr. Build. Mater. 35 (2012) 125–130. [3] L.I. Al-Qadi, M. Elseifi, S.H. Carpenter, Reclaimed asphalt pavement-a literature review. Research Report, 2007; FHWA-ICT-07-001. [4] T. Al-Rousan, I. Asi, O. Al-Hattamleh, H. Al-Qablan, Performance of asphalt mixes containing RAP, Jordan J. Civil Eng. 2 (3) (2008) 218–227. [5] B.T. Tran, R.A. Hassan, Performance of hot-mix asphalt containing recycled asphalt pavement, J. Trans. Res. Board 2205 (2011) 121–129. [6] I. Widyatmoko, Mechanistic-empirical mixture design for hot mix asphalt pavement recycling, Constr. Build. Mater. 22 (2008) 77–87. [7] H. Usama, Effect of the Repeated Recycling on Hot Mix Asphalt Properties, University of Nottingham, 2013. [8] A. Copeland, Sustaining our highways: A national perspective on RAP usage & best practices for recycled asphalt pavement. Presented at the pavement performance prediction symposium, Laramie, Wyoming, 2008. [9] F. Xiao, S. Amirkhanian, C.H. Juang, Rutting resistance of rubberized asphalt concrete pavements containing reclaimed asphalt pavement mixtures, J. Mater. Civ. Eng. 19 (6) (2007) 475–483. [10] J. D’Angelo, Warm-mix Asphalt: European Practice, Federal Highway Association, Washington, DC, 2008 (FHWA-PL-08-007). [11] Y.H. Yang, Y.B. Wu, J.G. Qiao, The Study on the performance of aspha-min warm mix asphalt binders, J. China Foreign Highway 34 (3) (2014) 291–294. [12] C. Wang, P.W. Hao, F. Ruan, Determination of the production temperature of warm mix asphalt by workability test, Constr. Build. Mater. 48 (2013) 1165– 1170. [13] Z. Leng, A. Gamez, I.L. Al-Qadi, Mechanical property characterization of warm mix asphalt prepared with chemical additives, J. Mater. Civ. Eng. 26 (2) (2014) 304–311. [14] A. Ali, A. Abbas, M. Nazzal, Effect of temperature reduction, foaming water content, and aggregate moisture content on the performance of foamed warm asphalt, Constr. Build. Mater. 48 (2013) 1058–1066. [15] X. Yu, Z. Leng, Y. Wang, Characterization of the effect of foaming water content on the performance of foamed crumb rubber modified asphalt, Constr. Build. Mater. 67 (2014) 279–284. [16] B. Putman, F. Xiao, Investigation of warm mix asphalt (WMA) technologies and increased percentages of reclaimed asphalt pavement (RAP) in asphalt mixtures, FHWA-SC-12-05, 2012. [17] L.Z. Wang, J.M. Wei, Y.Z. Zhang, Development of alternative parameters to evaluate the temperature susceptibility of asphalt binders, Int. J. Pavement Res. Tech. 2 (2) (2009) 75–81. [18] X. Yu, H.W. Sun, Y.L. Luo, Research on the evaluation index of temperature sensitivity of CRMA, J. Build. Mater. 16 (2) (2013) 265–270. [19] H.F. Liu, Research on Nonlinear Fatigue Damage Properties of Asphalt Mixture Based on the Decay of Strength and Stiffness, Changsha University of Science and Technology, 2012. [20] Q.Q. Zhang, W.Y. Fan, T.Z. Wang, G.Z. Nan, S. Jaka, Influence of emulsification on the properties of styrene-butadene-styrene chemically modified bitumens, Constr. Build. Mater. 29 (2012) 97–101.
Contents lists available at ScienceDirect
Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
Comparison of high temperature performance and microstructure for foamed WMA and HMA with RAP binder Fuqiang Dong, Xin Yu ⇑, Bo Xu, Tianyu Wang College of Civil and Transportation Engineering, Hohai University, Nanjing, Jiangsu Province 210098, PR China
h i g h l i g h t s RAP binders improve the high temperature performance and temperature sensitivity. RAP binders compromise the low temperature performance and fatigue resistance. The optimum RAP binder content of foamed WMA is more than that of HMA.
a r t i c l e
i n f o
Article history: Received 7 August 2016 Received in revised form 26 October 2016 Accepted 21 December 2016
Keywords: RAP binder Foamed warm mix recycled asphalt Hot mix recycled asphalt High temperature performance Microstructure
a b s t r a c t The foamed warm-mix recycled asphalts and hot mix recycled asphalt with different reclaimed asphalt pavement (RAP) binder contents (0wt%, 20wt%, 40wt%, 60wt%, and 80wt%) were prepared in laboratory. The influence on the viscosity-temperature performance, rheological properties, temperature sensitivity, fatigue resistance, and microstructure were investigated by conventional tests, Brookfield viscosity tests, Dynamic Shear Rheometer (DSR) tests, and Fourier Transform Infrared Spectroscopy (FTIR) tests. The results show that the RAP binder content has great effect on the performance of foamed warm mix recycled asphalt and hot mix recycled asphalt, and there is different change between foamed warm mix recycled asphalt and hot mix recycled asphalt. Compared to foamed warm-mix asphalt, foamed warm-mix recycled asphalt provides better high temperature performance and temperature sensitivity. Adding the RAP binder compromise the fatigue resistance of asphalt and with the increase of RAP binder content, the fatigue resistance of asphalt becomes worse. And the high temperature performance and temperature sensitivity of hot mix recycled asphalt is better than that of foamed warm mix recycled asphalt, while the fatigue resistance is on the contrary. By the microstructure analysis, the foaming process could slow down the aging degree of asphalt, and the aging degree of hot mix recycled asphalt is deeper than that of foamed warm mix recycled asphalt. The optimum RAP binder content of foamed warm mix recycle asphalt is more than that of hot mix recycled asphalt. Ó 2016 Elsevier Ltd. All rights reserved.
1. Introduction The use of recycled materials for road construction has been widely promoted due to environmental and economic benefits. It is reported that billions of dollars are spent annually in resurfacing and reconstruction of asphalt pavements [1] and over 500 million tons of asphalt are produced each year in the USA, which has brought considerable environmental burdens [2]. The reuse of reclaimed asphalt pavements (RAP) in asphalt layers can offer a sustainable alternative for pavement resurfacing and replacement.
⇑ Corresponding author. E-mail addresses: [email protected] (F. Dong), [email protected] (X. Yu), [email protected] (B. Xu), [email protected] (T. Wang). http://dx.doi.org/10.1016/j.conbuildmat.2016.12.106 0950-0618/Ó 2016 Elsevier Ltd. All rights reserved.
Hot-mix asphalt (HMA), which is the most widely used all over the world, is a material which can be recycled in 100% and could be totally reused to construct new asphalt layers in flexible pavements [3]. And many researches focused on the performance of hot-mix recycled asphalt and hot-mix recycled asphalt mixtures [4–6]. There are several advantages using hot recycling technology, and the performance of hot recycled asphalt mixtures are not worse than that of hot asphalt mixtures with new materials, and then the shortage of RAP materials could be covered by the different new aggregate and asphalt binder [7]. However, the higher construction temperature, the further aging of recycled and new asphalt and the more consumption of energy limit the development of hot recycling technique for asphalt pavement [8]. A low-carbon and saved energy technology, which is known as Warm Mix Asphalt (WMA), is developed to meet the increasingly
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stringent environmental regulations. The WMA technology could decrease the mixing and compacting temperatures by 30–50 °C, and reduce the emissions of SOx, NOx, CO2, and volatile organic compounds (VOC’s) by 15–70% [9,10]. Recently, there are three types of WMA technologies commonly used: (a) organic additives [11,12], (b) chemical additives [13], and (c) water foaming process or water containing additives [14] which reduce the mixing temperature by foaming the liquid asphalt to expand. Among the above technologies, the foaming technology involves minimal cost for the additives and is the most widely used in USA. However, when it comes to the combination of WMA and RAP, there are less research about the question that whether the blending efficiency between RAP binder and new asphalt is better or not, and how about the difference between foamed WMA and HMA with RAP binders. And few of them have focused on comparison of the high temperature performance and microstructure of the foamed warm mix recycled asphalt and hot mix recycled asphalt. Therefore, the objective of this paper is to investigate the influence of RAP binder content of viscosity-temperature performance, rheological properties, temperature sensitivity, fatigue resistance, and microstructure by Brookfield viscosity tests, DSR tests, and FTIR tests. 2. Materials and testing methods 2.1. Materials The 60/80 penetration grade of virgin asphalt produced by Ssangyong asphalt plant of South Korea was selected to prepare the foamed warm-mix asphalt, foamed warm-mix recycled asphalt and hot mix recycled asphalt, and the properties of virgin asphalt are summarized in Table 1. And the RAP materials were recycled from the asphalt road in Zhejiang province and the service life is about 5 years. Then the RAP binder was extracted from RAP materials by the rotary evaporator method using extracted liquid. The properties of RAP binder are listed in Table 1. 2.2. Preparation for foamed warm-mix recycled asphalt samples Firstly, the foamed warm-mix asphalt samples were prepared by Wirtgen foaming machine, and the conditions of foaming process as follows: the foaming water content is 1.5% (by the weight of virgin asphalt), and the temperature of virgin asphalt and the foaming water were controlled at 150 °C and 30 °C, respectively. The foamed warm-mix asphalt samples were then ready for preparing the foamed warm-mix recycled asphalt samples. Secondly, the foamed warm-mix recycled asphalt samples were prepared with foamed warm-mix asphalt and RAP binder by stirring for 30 min at 125 °C. The RAP binder contents used in this study were 20%, 40%, 60% and 80% by weight of foamed warmmix asphalt.
And then, the samples were conducted by Rolling Thin Film Oven Test (RTOFT) tests to stimulate the process of mixing and compaction of hot-mix asphalt mixtures. Also the samples were conducted by Pressure Aging Vessel (PAV) to stimulate the oxidation process of the asphalt during the first five years. 2.3. Preparation for hot-mix recycled asphalt samples The hot-mix recycled asphalt samples were prepared by a stirring mixer. Firstly, the virgin asphalt and RAP binder were heated to fluid condition at about 120–140 °C. Secondly, the RAP binder (20%, 40%, 60% and 80% by weight of virgin asphalt) was added to virgin asphalt at 150 °C and mixed for 30 min. And then the samples were conducted by RTOFT tests and PAV tests to stimulate the short-aging process and long-aging process. 2.4. Test and evaluation methods In this study, the comparison of foamed warm-mix recycled asphalt and hot-mix recycled asphalt with different RAP binder content were investigated and the high temperature performance including viscosity-temperature characteristic, failure temperature, temperature sensitivity and fatigue resistance as well as microstructure of above samples were evaluated by Dynamic Shear Rheometer (DSR) tests and Fourier Transform Infrared Spectroscopy (FTIR) tests. The flow chart of the experiment program was illustrated in Fig. 1. 2.4.1. Rotational viscosity tests The viscosity-temperature characteristic can be used to evaluate the high temperature performance of asphalt, and the workability of asphalt mixture could be obtained. And the Brookfield viscometer (Model DV-II+, Brookfield Engineering Inc., USA) was employed to determine the viscosity of foamed warm-mix recycled asphalt and hot-mix recycled asphalt at the temperatures of 90 °C, 100 °C, 110 °C, 120 °C, 130 °C, 135 °C, and 140 °C. 2.4.2. Rheological performance tests It is an effective and common method to evaluate the performance of asphalt by rheological tests. In this study, a TAAR1500EX DSR was employed to determine the rheological performance of foamed WMA and HMA with different RAP binder content. And the test conditions are 25 mm diameter plates and 1 mm gap. And the failure temperature and complex number index were calculated by the relationship between storage modulus (G0 ), loss modulus (G00 ) and rutting resistance factor (G⁄/sind) and temperature (T) obtained from the temperature sweep tests at the temperature range from 40 °C to 80 °C. The ultimate fatigue temperature was calculated by the relationship between fatigue resistance factor (G⁄sind) and temperature (T) obtained from the temperature sweep tests at the temperature range from 10 °C to 50 °C.
Table 1 Properties of the virgin asphalt and RAP binder. Property
Test Standards
Virgin asphalt
RAP binder
Penetration (25 °C)/(0.1 mm) Ductility (15 °C)/(cm) Softening point/(°C) Density (15 °C)/(g/cm3) Solubility (trichloroethylene)/(%) Components
ASTM D ASTM D ASTM D ASTM D ASTM D T0618
70 >100 48.2 1.035 99.8 27.31 41.34 26.27 5.38
11 0.4 71.7 1.062 99.6 9.25 21.39 40.84 27.61
Saturate/wt% Aromatic/wt% Resin/wt% Asphaltene/wt%
5 113 36 70 2042
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Fig. 1. The flow chart of the experiment program.
2.4.3. Microstructure characteristic In order to characterize the difference of microstructure between foamed WAM and HMA with different RAP binder content, the Fourier Transform Infrared (FTIR) Spectroscopy (Nexus, Thermo Nicolet) tests was used in wavenumbers ranging from 500 cm1 to 4000 cm1. The samples dissolved by solvent of carbon tetrachloride smeared on the KBr pellet and then the sample was measured on the FTIR. 3. Results and discussions 3.1. Viscosity-temperature performance The viscosity-temperature characteristic is an important index for evaluating the high temperature performance and workability of asphalt binders. So the influence of RAP binder content on the viscosity of foamed WMA and HMA samples and the comparison of between foamed WMA and HMA were investigated in this study. And then the viscosity of foamed WMA and HMA are presented in Fig. 2.
As shown in Fig. 2, it could be concluded that there are great difference in viscosity between foamed WMA and HMA, and the RAP binder content has significant influence on the viscosity of both foamed WMA and HMA. On the whole, the viscosity of foamed WMA and HMA decreases at various different levels as the testing temperature is increasing. When it comes to the foamed WMA, with the increase of RAP binder content the viscosity of asphalt increases, because the components of RAP binder and virgin asphalt binder have major difference and the addition of RAP binder change the components of recycled asphalt system. Meanwhile, the higher the RAP binder content is the greater changing the viscosity of asphalt is becoming. Moreover, compared to foamed WMA, the viscosities of HMA are higher than that of foamed WMA with different RAP binder content at different testing temperature. On the one hand, more RAP binder improves the hard components of system. On the other hand, the mixing and compaction temperatures of HMA are higher than those of foamed WMA by 30–50 °C, and the higher temperature could accelerate the aging levels of asphalt and increase the content of hard components. In other words, the RAP binder could improve the high
Fig. 2. The viscosity-temperature characteristic difference between foamed warm-mix recycled asphalt and hot-mix recycled asphalt.
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temperature performance of asphalt, and the high temperature performance of HMA is better than that of foamed WMA, while the workability of foamed WMA is better than that of HMA. 3.2. Failure temperature As we all known, rheological properties are very sensitive to the changes of component of asphalt binders. Therefore, the storage modulus G0 , loss modulus G00 , and rutting resistance factor G⁄/sind were obtained from the temperature sweep tests by DSR to evaluate the high temperature performance of foamed WMA and HMA. The influence of RAP binder content on the storage modulus G0 and loss modulus G00 of foamed WMA and HMA samples are presented in Figs. 3 and 4. As shown, the temperature has a significant effect on the evolution of G0 and G00 , and G0 as well as G00 decreases dramatically with the increase of temperature. Meanwhile, loss modulus G00 is always higher than storage modulus G0 , which indicates that the rheological behavior is dominated by viscous properties and the viscous component is more than elastic component. Moreover, the gap of G0 and G00 becomes narrower with the RAP binder content increasing, which is due to the difference of component between base asphalt and RAP binder. Compared to foamed warm-mix asphalt, RAP binder could improve the value of G0 and G00 , especially the G0 , which suggests that elastic component increase after adding RAP binder. Form Figs. 3–5, it can be concluded that RAP binder content has great influence on the storage modulus G0 , loss modulus G00 , and rutting resistance factor G⁄/sind of both foamed WMA and HMA, and there are great difference in rheological properties between foamed WMA and HMA. With the increase of RAP binder content, the storage modulus G0 , loss modulus G00 , and rutting resistance factor G⁄/sind all increase dramatically. Compared to foamed WMA, the above rheological properties of HMA are higher than those of foamed WMA with different RAP binder content. Meanwhile, the difference in rheological properties between foamed WMA and HMA becomes greater when the RAP binder content is increasing. The reasons are that the more RAP binder improves the hard components in this system, and the higher mixing and compaction temperature for HMA accelerate the aging degree of asphalt binder. In order to evaluate the influence on the RAP binder on the high temperature properties of foamed WMA and HMA, the failure temperature [15] was employed. The failure temperature was obtained
597
from the relationship between rutting resistance factor G⁄/sind and temperature when rutting resistance factor G⁄/sind is at 1.0 kPa. And then the failure temperatures of foamed WMA and HMA with different RAP binder content are illustrated in Fig. 6. Compared to foamed warm-mix asphalt, the addition of RAP binder could improve the failure temperature of asphalt. Meanwhile, the failure temperature of foamed warm-mix recycled asphalt increases with the increase of RAP binder content. In other word, adding RAP binder is beneficial for the high temperature performance of foamed warm-mix asphalt, and the higher the RAP binder content is, the better high temperature performance of foamed warm-mix recycled asphalt is. And the results are consistent with that the higher content of RAP is used in asphalt pavement by WMA technology [16]. Compared to foamed warm-mix recycled asphalt, the failure temperature of hot mix recycled asphalt with different RAP binder content are higher than that of foamed warm-mix recycled asphalt, which indicates that the hot mix recycled asphalt is better than that of foamed warm-mix recycled asphalt. The more the RAP binder content is the higher the failure temperature of foamed warmmix recycled asphalt, and when the RAP binder content increase from 40wt% to 60wt% the failure temperature has a great improvement. 3.3. Temperature sensitivity The temperature sensitivity of asphalt binder has a great influence on the road service performance of asphalt pavement. And the better temperature sensitivity could improve the high and low temperature performance of asphalt [17]. Meanwhile, the storage modulus G0 and loss modulus G00 are sensitive to temperature. Therefore, the complex number index [18] obtained from the relationship between G0 , G00 , and temperature was selected to evaluate the temperature sensitivity of foamed warm-mix recycled asphalt and hot mix recycled asphalt. The relationship between storage modulus G0 and temperature and the relationship between loss modulus G00 and temperature of foamed warm-mix recycled asphalt and hot mix recycled asphalt are presented in Figs. 7and 8. It can be found that the linear correlation between lgG0 , lg G00 , and lgT is better. And the absolute slope values for the regression equations of foamed warm-mix recycled asphalt and hot mix recycled asphalt with different RAP binder content are listed in Table 2. The literature [18] reported that the
Fig. 3. The G0 and G00 values of foamed WMA.
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Fig. 4. The G0 and G00 values of HMA.
Fig. 5. The G⁄/sin d values of foamed WMA and HMA.
lower the slope values of regression equations are the better the temperature sensitivity of asphalt is. As shown in Table 2, with the increase of RAP binder content, the slope value of storage modulus G0 and loss modulus G00 decrease, which suggests that adding RAP binder could improve the temperature sensitivity of foamed warm-mix asphalt. Compared to hot mix recycled asphalt, the slope value of foamed warm-mix recycled asphalt is higher than that of foamed warmmix recycled asphalt at the same RAP binder content. In a word, the temperature sensitivity of hot mix recycled asphalt is better than that of foamed warm-mix recycled asphalt with the same RAP binder content. 3.4. Fatigue resistance
Fig. 6. Failure temperatures of foamed WMA and HMA.
Fatigue resistance performance of asphalt binder has significant influence on the service life of asphalt pavement [19]. To evaluate the fatigue resistance of foamed warm-mix recycled asphalt and hot mix recycled asphalt, the fatigue resistance factors G⁄sind were obtained from temperature sweep tests at the temperature
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Fig. 7. Logarithm of storage modulus G0 for foamed warm-mix recycled asphalt and hot mix recycled asphalt.
Fig. 8. Logarithm of loss modulus G00 for foamed warm-mix recycled asphalt and hot mix recycled asphalt.
Table 2 Absolute Slope Values for the Regression Lines in Figs. 7 and 8. RAP binder content/wt%
0 20 40 60 80
Absolute value of slope for lgG0 regression equation
Absolute value of slope for lgG00 regression equation
Foamed WMA
HMA
Foamed WMA
HMA
62.446 60.964 59.099 57.629 57.398
60.509 59.647 58.054 55.918 54.510
42.900 41.448 40.507 39.494 38.913
41.392 40.994 39.954 38.889 37.079
range from 10 °C to 50 °C. And the relationship between lg G⁄sind and temperature are illustrated in Fig. 9. According to the literatures [15], the lower fatigue resistance factor G⁄sind indicates the better fatigue resistance. As shown in Fig. 9, compared to foamed warm-mix asphalt, the fatigue resistance factor G⁄sind of foamed warm-mix recycled asphalt becomes higher, which indicates that the RAP binder has bad effects on the fatigue resistance of asphalt. Meanwhile, with the increase of RAP binder content, the fatigue resistance factor G⁄sind of foamed warm-mix recycled asphalt increase, and when the RAP binder
content increase higher, the asphalt become more sensitivity to fatigue cracking. In order to quantify the influence of RAP binder content on the fatigue resistance of foamed warm-mix recycled asphalt and hot mix recycled asphalt, the ultimate fatigue temperature was employed and presented in Table 3. It is shown that with the increase of RAP binder content, the fatigue temperatures of foamed warm-mix recycled asphalt and hot mix recycled asphalt increase, which indicates that adding RAP binder could compromise the fatigue performance of asphalt. Furthermore, the fatigue temperature
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Fig. 9. Temperature dependence of G⁄sind of foamed warm-mix recycled asphalt and hot mix recycled asphalt.
RAP binder content/ wt%
Ultimate failure temperature/°C
times higher than that of samples with the RAP binder content from 40% to 60%. In a word, the optimum RAP binder content of foamed warm-mix recycled asphalt is more than that of hot mix recycled asphalt.
Foamed WMA with RAP binder
HMA with RAP binder
3.5. Microstructure
0 20 40 60 80
18.56 20.89 23.10 25.62 33.51
21.16 25.27 29.80 33.72 38.06
Table 3 Ultimate failure temperature of foamed warm-mix recycled asphalt and hot mix recycled asphalt.
of foamed warm-mix recycled asphalt is lower than that of hot mix asphalt, that is to say that the fatigue resistance of foamed warmmix recycled asphalt is better. However, the variation amplitude of ultimate fatigue temperature presents a significant difference as the RAP binder content increases. The change of ultimate fatigue temperature with the RAP binder content from 60% to 80% is four
In this study, the Fourier Transform Infrared (FTIR) Spectroscopy (Nexus, Thermo Nicolet) tests were used to evaluate the influence of RAP binder content on the microstructure of foamed warm-mix recycled asphalt and hot mix recycled asphalt and the difference between foamed warm mix recycled asphalt and hot mix recycled asphalt. And the FTIR of foamed warm-mix recycled asphalt and hot mix recycled asphalt with different RAP binder content are presented in Fig. 10. As for recycled system, the chemical reaction is mainly focused on the aging degree of asphalt. Therefore, the band of methyl group at 1375 cm1 and the band of CAO bond at 1033 cm1 were selected to characterize the aging degree of asphalt, and the ratio
Fig. 10. FTIR of foamed warm-mix recycled asphalt and hot mix recycled asphalt with different RAP binder content.
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F. Dong et al. / Construction and Building Materials 134 (2017) 594–601 Table 4 The ratio of A1033/A1375 of foamed warm-mix recycled asphalt and hot mix recycled asphalt. RAP binder content/%
0 20 40 60 80
Foamed WMA with RAP binder
HMA with RAP binder
A1375
A1033
A1033/A1375
A1375
A1033
A1033/A1375
2.325 3.978 2.732 3.321 2.103
0.467 1.272 0.897 1.324 0.885
0.2008 0.3197 0.3275 0.3986 0.4210
2.704 3.912 2.573 2.907 2.474
0.669 1.358 0.906 1.210 1.092
0.2475 0.3472 0.3521 0.4163 0.4412
of A1033/A1375 of foamed warm-mix recycled asphalt and hot mix recycled asphalt are listed in Table 4. According to Beer’s law [20], the peak intensity ratio is equal to the area ratio between the two bands at 1033 cm1 and 1375 cm1. And the higher the ratio of A1033/A1375 is, the deeper the aging degree of asphalt is. As shown in Table 4, with the increase of RAP binder content, the ratio of A1033/A1375 increase. Meanwhile, the ratio of A1033/A1375 of HMA with RAP binder is higher than that of foamed HMA. It is suggested that the foaming process could slow down the aging degree of asphalt, and the aging degree of hot mix recycled asphalt is deeper than that of foamed warm mix recycled asphalt. 4. Conclusions The influence on the viscosity-temperature performance, rheological properties, temperature sensitivity, fatigue resistance, and microstructure of foamed warm mix recycled asphalt and hot mix recycled asphalt with different RAP binder content were investigated by Brookfield viscosity tests, DSR tests, and FTIR tests. The results show that the RAP binder content has great effect on the performance of foamed warm mix recycled asphalt and hot mix recycled asphalt. (1) Adding the RAP binder can improve the high temperature performance and temperature sensitivity of foamed warmmix recycled asphalt, while it compromises the fatigue resistance of asphalt. (2) The fatigue resistance of foamed warm mix recycled asphalt is better than that of hot mix recycled asphalt, while the high temperature performance and temperature sensitivity are worse. (3) The foaming process could slow down the aging degree of asphalt, and the aging degree of hot mix recycled asphalt is deeper than that of foamed warm mix recycled asphalt. (4) The optimum RAP binder content of foamed warm mix recycle asphalt is more than that of hot mix recycled asphalt.
Acknowledgments This work was supported by the National Natural Science Foundation of China (51278173), the Natural Science Foundation of Jiangsu Province for Distinguished Young Scholar (BK20150038), the Fundamental Research Funds for the Central Universities
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