Chemical characterization and oxidative aging of bio-asphalt and its compatibility with petroleum asphalt

Journal of Cleaner Production xxx (2016) 1e11

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Chemical characterization and oxidative aging of bio-asphalt and its compatibility with petroleum asphalt Xu Yang a, Julian Mills-Beale b, Zhanping You c, * a

Department of Civil and Environmental Engineering, Michigan Technological University, 1400 Townsend Drive, Houghton, MI, 49931, USA Department of Civil Engineering, California Baptist University, 8432 Magnolia Ave., Riverside, CA, 92504, USA c Department of Civil and Environmental Engineering, Michigan Technological University, 1400 Townsend Drive, Houghton, MI, 49931-1295, USA b

a r t i c l e i n f o

a b s t r a c t

Article history: Received 18 May 2016 Received in revised form 26 October 2016 Accepted 16 November 2016 Available online xxx

The objective of this paper is to characterize the elemental composition, chemical compounds, oxidative aging and the compatibility of bio-asphalt modified with bio-oil. A petroleum asphalt was modified with treated and untreated bio-oil at 2%, 5% and 10% by weight to prepare bio-asphalt, respectively. Gas chromatographyemass spectrometry (GC-MS) was employed to characterize the chemical compounds in the bio-oil. The Fourier Transform Infrared Spectroscopy (FTIR) was utilized to explore the influence of bio-oil on the aging performance of asphalt. The compatibility of bio-oil with petroleum asphalt was investigated using automated flocculation titrimetry (AFT) based on flocculation stability. The elemental composition analysis revealed a higher amount of oxygen in the bio-oil. The GC-MS results showed the presence of chemical compounds with low boiling temperatures, which have potential environmental impacts and health concerns if used in hot mix asphalt. The FTIR results indicated the presence of aromatic and nitrogenous compounds, alcohols, ethers, ketones, carboxylic acids, aldehydes, esters, acyls, alkanes, polymeric OeH, NH2 and water. The AFT results implied a stable and compatible mixture of 2% bio-asphalt. The study also suggested that with an increase in the fraction of bio-oil, the compatibility with petroleum asphalt would decrease. © 2016 Elsevier Ltd. All rights reserved.

Keywords: Bio-oil Bio-asphalt Elemental composition Compatibility Chemical compounds Fourier Transform Infrared Spectroscopy (FTIR) Automated Flocculation Titrimetry (AFT)

1. Introduction Asphalt pavement engineers and researchers have been seeking materials that would guarantee the structural integrity and performance of asphalt pavement without compromising the environment. Warm mix asphalt with lower emissions (Almeida-Costa
nchez and Benta, 2016; Dinis-Almeida and Afonso, 2015; Sol-Sa et al., 2016), recycled asphalt and concrete pavements (Mills-Beale and You, 2010; Shu et al., 2012), and asphalt with scrap tire rubbers (Fakhri and Saberi, 2016; Oliveira et al., 2013) are cleaner materials that have been well explored in industry. Bio-oils derived from biomasses present an innovative and interesting alternative to the existing petroleum-based asphalt due to its renewability and environmental friendliness (Fini et al., 2010; Podolsky et al., 2016). The blending of bio-oil and traditional petroleum asphalt is also referred to as bio-asphalt. In addition to easing the pressure on

* Corresponding author. E-mail addresses: [email protected] (X. Yang), [email protected] (J. MillsBeale), [email protected] (Z. You).

existing landfills, the production of bio-oil from wood waste will reduce the continued dependence on crude resources for asphalt. Crude oil consumption has experienced a significant increase in recent years in the United States. The 19.3 million acres of timber land, 385 million cubic feet of trees and 458.2 million cubic feet of unused annual growth and residues in Michigan present an ideal opportunity for the exploration of bio-asphalt development in the state (Mueller et al., 2010). Additionally, the rising dumping fees associated with hauling wood waste over long distances to dumping sites can be compensated if the waste can be developed into an economically beneficial bio-asphalt product. Compared to petroleum asphalt, the benefits of bio-oil are mainly the renewability and recycling of waste. As mentioned above, Michigan has a large amount of wood resources that can be potentially used to generate bio-oils. Most importantly, bio-oils can be generated from many waste materials, which are costly to deal with if not properly recycled. According to the review by Yan et al. (2015), 20% of the transportation fuels will be produced from lignocellulosic biomass as an alternative of traditional fossil fuel by 2030. The generation of biooil is similar to the approaches of producing bio-fuels. Many types

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Please cite this article in press as: Yang, X., et al., Chemical characterization and oxidative aging of bio-asphalt and its compatibility with petroleum asphalt, Journal of Cleaner Production (2016), http://dx.doi.org/10.1016/j.jclepro.2016.11.100

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X. Yang et al. / Journal of Cleaner Production xxx (2016) 1e11

Abbreviations AFT BTX CHON FTIR FR GC-MS IC]O IS]O NTB PAV RTFO SARA SBN TB

Automated Flocculation Titrimetry Benzene, touelene and xyrenes Carbon, hydrogen, oxygen, and nitrogen Fourier Transform Infrared Spectroscopy Flocculation ratio Gas Chromatography Mass Spectrography Carbonyl index Sulphoxide index Non-treated bio-oil Pressure aging vessel Rolling thin film oven Saturates, aromatics, resin, and asphaltene Solubility number Treated bio-oil

of biomass materials can be used for bio-oil development, such as animal waste (Fini et al., 2011; You et al., 2011), wood waste (Yang et al., 2013, 2014a), agricultural waste (Raouf and Williams, 2010), microalgae (Chailleux et al., 2012), and waste cooking oil (Sun et al., 2016). Thermochemical processes such as hydrolysis, pyrolysis, gasification and liquefaction are used to turn biomasses into bioproducts (Pandey et al., 2015). Hydrolysis is a common approach to produce the bio-product furfural which can be used to generate furfuryl alcohol (Yan et al., 2014). Among them, fast pyrolysis is the most widely used technique due to various advantages such as simplicity, high yield rate and low cost (Akhtar et al., 2010; Bridgwater and Peacocke, 2000; Mohan et al., 2006). The yield rate for corn stover, wheat straw, or switch grass can be as high as 78% by weight using the fast pyrolysis (Laird et al., 2009). Three components can be generated from the fast pyrolysis: bio-char, gases, and liquids. The liquid is regarded as the bio-oil. The yield rate is also affected by the temperature (Silva et al., 2016; Westerhof et al., 2009). Some researchers have proposed approaches to estimate the pyrolysis output based on the feedstock properties and the reaction condition (Lim et al., 2016). A certain moisture content is contained in raw bio-oils depending on the type of biomass. The components of bio-oils can be separated through fractional distillation. The fraction distillation for corn stover bio-oil showed that water is in the light fraction; aromatic and oxygenated compounds are in the light to middle fractions; and phenolic compounds fall into the heavy fraction (Capunitan and Capareda, 2013). The water contents of bio-oil developed from some vegetal sources can be higher than 40% (Williams and Tang, 2009). It was reported that the components of bio-oil can also fall into the four typical compounds in petroleum asphalt, which are saturates, aromatics, resin, and asphaltenes (Fini et al., 2011; Miao and Wu, 2004). The pH of biooils was reported to be in the range between 2.5 and 3.5 (Ba et al., 2004; Czernik and Bridgwater, 2004). The elemental composition of bio-oils is different from petroleum asphalt, with a noticeably higher content of oxygen in bio-oils, and the elemental composition of bio-oils from different biomasses may vary significantly (Czernik and Bridgwater, 2004; Fini et al., 2011; Metwally and Williams, 2010). Asphalt by nature, is adhesive to bond aggregates together when applied in the pavement industry. Since bio-oil has similar chemical compounds as that in petroleum asphalt, many previous studies have explored the potential of using bio-oil in the pavement industry (Fini et al., 2011; Raouf and Williams, 2011; Wen et al., 2012; Yang et al., 2013). The easiest way of applying bio-oil to the pavement industry is to blend bio-oil into petroleum asphalt to form

bio-asphalt. The pavement purposed performance of bio-asphalt binders and bio-asphalt mixtures have been investigated recently (Sun et al., 2016; Yang et al., 2014a). The performance of bioasphalts developed from different bio-oil sources can vary significantly. For instance, the forest waste bio-asphalts were found to increase the high temperature performance of traditional asphalt while adversely affecting the low temperature binder properties (Raouf and Williams, 2011; Williams and Tang, 2009; Yang et al., 2013). On the contrary, the bio-asphalt from swine waste and cooking oil was found to weaken the high temperature performance but improve the low temperature performance (Fini et al., 2011; Sun et al., 2016; Wen et al., 2012). Additional additives were sometimes blended into bio-asphalt to improve performance in certain aspects, such as nanomaterials (Onochie et al., 2013) and crumb rubber (Peralta et al., 2012). Meanwhile, many previous studies have indicated that the aging of bio-asphalt is quicker than petroleum asphalt (Mills-Beale et al., 2014; Onochie et al., 2013). Yang et al. (2014b) attributed the aging of wood waste bio-asphalt to the loss of lightweight molecular components, oxidation, and polymerization. In regards to the performance of asphalt mixture containing bio-asphalt, it was reported that the waste wood bioasphalt can improve fatigue resistance and has no significant effect on rutting or tensile strength (Yang et al., 2014a). The study on the high reclaimed asphalt pavement containing swine waste bioasphalt showed that the presence of bio-asphalt can improve workability, fatigue and cracking resistance, and has no adverse effect on moisture susceptibility and rutting resistance (Mogawer et al., 2016). Bio oil has also been used as an additive and rejuvenator for petroleum asphalt. Gong et al. (2016) found that the bio-oil derived from biodiesel residue can improve the performance of aged asphalt because it can compensate the loss of lightweight components and may interact with the polymers in modified asphalt. Oldham et al. (2015) investigated the bio-oils generated from swine manure as a rejuvenator for asphalt binder containing asphalt shingles and found that the addition of such bio-oil can lead to a reduction in viscosity and an improvement in fracture energy. Garcia et al. (2016) investigated the potential of using sunflower oil capsules as a rejuvenator to extend the life of asphalt mixture. Podolsky et al. (2016) found that the bio-additive derived from corn biomass, can serve as a warm mix additive and reduce the mixing and compaction temperatures by as much as 30
C. To thoroughly understand the paving performance of wood waste bio-asphalt, it is important to understand the basic properties of bio-oil and bio-asphalt. Although the rheological and mechanical performance of wood waste bio-asphalt and the elemental analysis has been reported in some previous studies, the lack of understanding of the elemental composition, chemical compounds, oxidative aging and the compatibility of bio-asphalt is inadequate for immediate implementation of bio-asphalt. To build on the body of knowledge available on wood waste bio-asphalt, it is pertinent to understand the aging behavior from the standpoint of the chemical functional group and also investigate the molecular asphaltenemaltene precipitation behavior. The impact of the chemical compounds on the environment and health during asphalt mix production has not been reported in previous studies. The compatibility between petroleum asphalt and bio-oil has been rarely investigated in existing literature. This study will fill these research gaps based on the literature review. The objective of this paper is to characterize the elemental composition, chemical compounds, oxidative aging and the compatibility of bio-asphalt modified with bio-oil. The expected contribution of this study is to reveal the feasibility of using bio-oil in pavement engineering and the potential concerns to be faced. In order to achieve the research objective, the following research

Please cite this article in press as: Yang, X., et al., Chemical characterization and oxidative aging of bio-asphalt and its compatibility with petroleum asphalt, Journal of Cleaner Production (2016), http://dx.doi.org/10.1016/j.jclepro.2016.11.100

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activities were planned: 1) analyze the elemental composition and chemical components of wood waste bio-oil; 2) characterize the physio-chemical aging performance of pure wood waste bioasphalt, petroleum asphalt and bio-asphalt using Fourier transform infrared spectroscopy (FTIR); 3) investigate the compatibility between petroleum asphalt and bio-oils using the automated flocculation titrimetry (AFT). The paper is organized as follows. Firstly, the methods to achieve the goals and the materials to be used were described. Then the experimental design to analyze the elemental composition, chemical components, oxidative aging and compatibility of bio-asphalt were provided. Next, the results were documented and discussed to evaluate the potential benefits and disadvantages of bio-asphalt in pavement industry. Lastly, the summary and the conclusions were drawn. The main challenges and the future research were also stated at the end of the paper. 2. Materials and methods 2.1. Material preparation 2.1.1. Raw wood waste materials The feed stock used for the production of bio-asphalt was typical Michigan wood collected from saw mills in the form of wood chips, sawdust and shavings. The wood chips were of average dimensions of 2.0 in. (51 mm) length, 0.5 in. (12.8 mm) breadth and 0.25 in. (6.4 mm) thickness. The thicknesses of the wood shavings were averaged at about 1 mm to allow easy feeding to the pyrolysis plant. Wood shaving particle sizes of approximately 0.7 mm have been shown to provide optimal bio-oil yield rates. The wood types collected were Aspen, Basswood, Red Maple, Balsam, Maple, Pine, Beech and Magnolia. 2.1.2. Generation of bio-oils from wood wastes Among the known types of conversion methods for producing bio-oils (Haarlemmer et al., 2016; Itoh et al., 1994; Mohan et al., 2006; Orozco et al., 2011; Yorgun and Yıldız, 2015), the Mohan fast pyrolysis approach was selected (Mohan et al., 2006). Mohan fast pyrolysis is a process in which biomass materials are heated under accelerated conditions in a vacuum resulting in decomposition into solid bio-char, vapors and aerosols (Mohan et al., 2006). Significant benefits of the fast pyrolysis conversion approach over other technologies are a relatively higher bio oil yield rate (Bridgwater, 1999) and a lower heating temperature (Qiang et al., 2009). Furthermore, the process allowed for very quick devolatilization, flexibility of operation, and easy collection of the final product. A 25 KW pyrolysis plant developed at the Iowa State University Center for Sustainable Energy Technologies (CSET) was used during this research. In the thermopyrolysis step, the wood waste chips, shavings and sawdust were dried at about 100
C for a 24-h period, and subsequent pyrolysis between 425 and 500
C. Accelerated vaporization was then conducted on the products from the pyrolysis stage at a rate of microseconds. Finally, the resulting volatiles were condensed before the bio-oil product was obtained and refined. During the conversion, end products of bio-char and bio-gas were recycled back as regenerating fuel. The final bio-oil was collected and treated to drive off moisture before it was tested for pH, moisture content, solids and insoluble content properties. 2.1.3. Preparation of bio-asphalt The bio-asphalt was prepared by adding bio-oil into petroleum asphalt. Three different bio-oil fractions were used: 2%, 5% and 10% by weight. The base asphalt used was a performance graded asphalt PG58-28. The mixing of the bio-oil into the petroleum asphalt binder was achieved using a high speed shear mixer at the speed of

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approximately 1500 rpm for 30 min at 120
C. Three replicate samples each of the 2%, 5% and 10% bio oil modified samples were then used together with the control petroleum asphalt for the characterization used in this research. 2.2. Methods The research objectives are accomplished through a few steps. First, the bio-oil was generated from raw waste wood materials. Then the elemental composition of bio-asphalt is obtained using an element analyzer. Next, the chemical components of the bioasphalt are investigated through GC-MS characterization. The bioasphalt is mixed with petroleum asphalt to produce bio-asphalt. The oxidative aging of the bio-asphalt is analyzed through the changes in chemical bond of the FTIR. The oxidation related bond indices, carbonyl (C]O) and sulphoxide (S]O), are analyzed for the unaged and aged bio-asphalts. Oxidative aging is carried out through the standard rolling thin film oven (RTFO, short-term aging) and pressure aging vessel (PAV, long term aging) tests. The automated flocculation titrimetry (AFT) was utilized to analyze the compatibility between the bio-asphalt and petroleum asphalt. The roadmap of this study is shown in Fig. 1. The details of each step will be described below. 2.2.1. Elemental composition and GC-MS characterization The elemental composition acquisition of asphalt has been reported in many previous studies (Greenfield et al., 2015; Michalica et al., 2007). Carbon, Hydrogen and Nitrogen (CHN) investigations on the bio oils were undertaken using a Perkin-Elmer Model 2400 Series II CHN/S elemental analyzer on approximately 2 mg sized samples. The test revealed the contributions of each of these elements in the pyrolysis oil. Furthermore, in order to determine the chemical compound fractions in the bio oil, a Varian Saturn-2200 mass spectrometer linked with a Varian CP-3800 Gas Chromatograph was used. It had a 30 m long Frontier-UA5 GC capillary column with 0.25 mm film thickness. The Gas chromatographyemass spectrometry (GC-MS) investigation was useful in ascertaining the key chemical compounds; then an attempt was made to relate these compounds to fundamental performance properties in the bio oils. GC-MS has been applied in many previous studies to analyze the chemical compounds of organic materials (Bala et al., 2015; Bortolomeazzi et al., 2007; Branca et al., 2003). 2.2.2. Fourier transform infra-red (FTIR) characterization FTIR has been widely applied to identify the functional groups in chemicals and to analyze the aging behavior of asphalt (Cong et al., 2016; Yan et al., 2016; Yu et al., 2017). In this study, the FTIR investigations were conducted on the petroleum asphalt, untreated, and treated bio-asphalts to characterize the chemical functional groups and the oxidation aging performance. The Jasco FTIR-4200 spectrometer was utilized to test the control binder (0% bio-oil), 2%, 5%, 10% and 100% bio-asphalt by weight. The asphalt binders

Fig. 1. Roadmap of this study.

Please cite this article in press as: Yang, X., et al., Chemical characterization and oxidative aging of bio-asphalt and its compatibility with petroleum asphalt, Journal of Cleaner Production (2016), http://dx.doi.org/10.1016/j.jclepro.2016.11.100

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X. Yang et al. / Journal of Cleaner Production xxx (2016) 1e11

were then spread on silicon slides with a thickness of about 0.5 mm. For optimum FTIR spectra results, a maximum asphalt coating thickness of about 1 mm was achieved. The resolution of the FTIR test was 4 cm1.

where doil ¼ solubility constant of the bio-asphalt blend; d10 ¼ solubility constant of iso-octane (titrant); d10 is 6.99 (cal/ mL)0.5 for iso-octane (titrane); dT ¼ solubility constant of toluene; dT is 8.93 for toluene (solvent).

2.2.3. AFT characterization In the automated flocculation titrimetry (AFT) investigations, the degree of molecular compatibility of the Michigan wood bio-oil and petroleum asphalt binder was evaluated. This degree of chemical compatibility was studied in terms of homogenous solubility. This process attempted to reveal how the higher molecular asphaltene fractions in the base asphalt either conglomerate or disperse in the lower molecular maltene fractions when the foreign bio oil was added as a modifier. Tests were run on two samples: the control base asphalt and the 2% treated bio oil, with three replicate tests conducted on each specimen. Also known as the automated Heithaus titrimetry (Koehler, 2011), the investigation was conducted between 20 and 100
C. Next, the Heithaus compatibility parameters were found, and the flocculation point was determined spectroscopically. The asphaltene content in petroleum-based asphalt binders is the fraction insoluble in n-heptane but soluble in toluene (Pfeiffer and Saal, 1940). The control (0%) and 2% treated bio-asphalt binder was firstly dissolved in toluene at different chemical concentrations and later titrated with iso-octane or nheptane between 20
C and 100
C to establish the flocculation and Heithaus engineering compatibility indices. The test data was then analyzed to evaluate the colloidal stability of the mixture. The test was conducted at the polymer research laboratory of Koehler Instruments in New York. Due to limited bio-asphalt materials, the AFT characterization was done on only the control and the 2% bio-asphalt. This was considered satisfactory since the idea behind the AFT investigations was to find out what happens to the flocculation of asphaltene molecules in the petroleum asphalt upon adding the bio-asphalt sample. The compatibility between the bio-oil and the petroleum asphalt was studied based on Equation (1) and the Wiehe compatibility model (Wiehe and Kennedy, 2000)

3. Results and discussion

dcr ¼ F0d0 þ F10d10 þ FTdT

(1)

where SFi ¼ 1; dcr ¼ the critical solubility constant; F0 ¼ volume fraction of the bio-asphalt; d0 ¼ solubility constant of asphalt; F10 ¼ volume fraction of iso-octane; d10 ¼ solubility constant of isooctane (titrant), d10 is 6.99 (cal/mL) 0.5 for iso-octane (titrane); FTdT ¼ volume fraction of toluene, and solubility constant of toluene, dT is 8.93 for toluene (solvent). The measurement of the solvency of the asphalt oil fractions (maltene) for the asphaltene fractions is given by Equation (2)

SBN ¼ 100

ðdoil  d10 Þ ðdT  d10 Þ

(2)

3.1. Elemental compositions The common proportions of carbon, hydrogen, oxygen, and nitrogen (CHON) elements in the bio-oil product in this study were found to be 58.8%, 6.62%, 34.31%, and 0.27%, respectively, as shown in Table 1. For a comparative study, the elemental compositions of three other types of petroleum asphalts and bio-oils from other sources were also provided from previous literature. It can be observed that the elemental compositions of Michigan wood waste bio-oil were significantly different from the petroleum asphalt. Specifically, the bio-oil had visibly lower carbon and higher oxygen contents than petroleum asphalt. This is mainly attributed to the moisture and high oxygen content of the raw material. Comparison among bio-oils from different sources showed that the elemental compositions of bio-oils varied significantly among different biomass sources. It looks like the vegetal biomass yielded bio-oils with lower carbon content and higher oxygen content than animal waste. The H/C ratio of different types of bio-oils were also provided. It was found that the petroleum asphalt had a higher H/C ratio than other bio-oils. A saturated hydrocarbon has an H/C ratio close to 2. There is some amount of asphaltenes and aromatics in petroleum asphalt, so the H/C ratio is lower than 2. Compared to the petroleum asphalt, bio-oils had an even lower H/C ratio. This could have resulted from a higher amount of aromatics and apshaltenes, or from a higher amount of CeOeC and C]O bonds because the CeOH bond does not change the H/C ratio. The review by Mohan et al. (2006) showed that there is a large amount of CeOeC and C]O bonds and aromatics in the cellulose, hemicellulose, and lignin, which are the main components of wood. Previous research has shown that relative amounts of CHON in hydrocarbon-related compounds impacts the functional or polar group formations (Roberts et al., 1996). It is believed that the difference in CHON proportions in the petroleum asphalt compared to the bio oil will account for the inherent differences of the molecular and rheological properties, as reported in literature. The different elemental composition indicates different type of chemical compounds in the bio-oils, and further implies different properties when used as an adhesive material. 3.2. GC-MS compound compositional analysis The chemical compounds and their fractions in the bio-oil from Michigan wood wastes were obtained through the GC-MS, as shown in Table 2. The results showed that the dominant chemical functional compounds are levoglucosan; 2, 6 dimethoxyphenol; 2-

Table 1 Elemental Composition in asphalts and bio-oils. Asphalt and bio oil type

Carbon (%)

Hydrogen (%)

Oxygen (%)

Nitrogen (%)

H/C ratio

Michigan wood waste Petroleum asphalt type 1 (Fini et al., 2011) Petroleum asphalt type 2 (Michalica et al., 2008) Petroleum asphalt type 3 (Michalica et al., 2008) Wood waste (Czernik and Bridgwater, 2004) Swine-waste bio oil (Fini et al., 2011) Cornstover (Metwally and Williams, 2010) Oakwood (Metwally and Williams, 2010)

58.80 81.60 85.20 83.17 56.4 72.58 46.5 60.5

6.62 11.80 10.30 10.28 6.2 9.76 5.9 6.5

34.31 0.9 1.25 1.33 37.3 13.19 46.2 34.6

0.27 0.77 0.58 0.45 0.1 4.47 e e

1.35 1.74 1.45 1.48 1.32 1.61 1.52 1.29

Please cite this article in press as: Yang, X., et al., Chemical characterization and oxidative aging of bio-asphalt and its compatibility with petroleum asphalt, Journal of Cleaner Production (2016), http://dx.doi.org/10.1016/j.jclepro.2016.11.100

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Table 2 Chemical compound analysis of bio-asphalt fractions. Chemical compound

Furfural 3-methyl-1, 2-cyclopentandione phenol 2-methoxyphenol o-cresol m-cresol 2-methoxy-4-methylphenol p-cresol 2-methoxy-4-vinylphenol eugenol 2,6 dimethoxyphenol isoeugenol levoglucosan 4-allyl-2,6 dimethoxyphenol 3,5 dimethoxy-4-hydrobenzaldehyde

GC-MS % wt.

0.054 0.245 0.027 0.144 0.065 0.077 0.176 0.034 0.444 0.093 0.409 0.444 3.721 0.309 0.386

Formula

C5H4O2 C6H8O2 C6H6O C7H8O2 C7H8O C7H8O C8H10O2 C7H8O C9H10O2 C10H12O2 C8H10O3 C10H12O2 C6H10O5 C11H14O3 C9H10O4

Boiling point (
C) *(National Center for Biotechnology Information, 2016)

Acidity (pKa)** (National Center for Biotechnology Information, 2016)

HMIS/NFPA health hazardþ (ScienceLab.com, 2016)

Water solubility (g/L) (National Center for Biotechnology Information, 2016)

162 e 182 204 191 203 221 202 224 225 261 266 384 300 192

e e 9.9 9.98 10.3 10.1 e 10.3 e 10.19 9.97 9.88 e e 7.8

3 e 3 2 3 3 2 3 1 2 2 2 1 2 1

83 e 83 18.7 31 23.5 e 24 e 2.5 20 0.81 e e <1

þþ

Note, ‘*’: @ 760mm Hg; ‘**’: the lower the pKa the more acidic, the pKa of water is 16; ‘þ’: value ranges from 0 to 4, 0-minimal hazard, 1-slight hazard, 2-moderate hazard, 3serious hazard, and 4-severe hazard; ‘þþ’: a common threshold of solubility is 1 g/L.

methoxy-4-vinylphenol; 2-methyl-1-2-cyclopentandione and 4allyl-2, 6-dimetoxyphenol. The corresponding formulas were also provided. It can be seen that most of these chemical compounds contain aromatic rings. Asphalt materials require a high temperature (around 160
C for hot mix asphalt) when mixing with aggregates to produce asphalt mixtures for paving on roads. Bio-oils, if used in hot mix asphalt, need to withstand that high temperature. Mass loss during production (mixing and compaction) is an important index of asphalt quality. Superpave asphalt specification requires a maximum value of 1% mass loss during the production process (Asphalt Institute, 2003). The boiling points of the compounds were provided to estimate the evaporation during the production. It can be seen that the boiling points of many compounds were lower than 200
C, which is close to the production temperature of hot mix asphalt. This implies that the mass loss caused from compound evaporation could be a concern when such bio-oil is used in hot mix asphalt. In fact, the high mass loss of bioasphalt from wood waste has been observed in a previous study by conditioning the bio-asphalt with abundant fresh air at 163
C (Yang et al., 2014b). In comparison, petroleum asphalt is the refinery residue of crude oil. The distillation temperature in the refinery process can be as high as 400
C, which is higher than the boiling temperature of all the compounds in Table 2. This is the reason that the mass loss of petroleum asphalt is very low. While the detailed chemical compounds using GC-MS were rarely reported in previous studies, a recent study revealing the chemical compounds of asphalt volatiles using dynamic headspace and GCMS implies a much lower concentration of these compounds in asphalt (Boczkaj et al., 2016). If the mass loss is high, the impact of the bio-asphalt smokes on human health and environment is a potential concern. In regards to this, the health hazard of these compounds were provided according to the categorization of health management information systems (HMIS) and the national fire protection association (NFPA). It is mainly evaluated based on the toxicity to the eye, skin, and inhalation. The health hazard ranges from zero to four, and a higher number indicates a more severe hazard. It was observed that most of the compounds had a health hazard of moderate hazard or serious hazard, implying that the smoke produced by bio-asphalt could threaten human health during the production. Workers may need protection in the mixing plant or compaction site. In addition, the acidity of asphalt is also an important property. In regards of this, it may be better to use the bio-oils in warm mix

asphalt or cold mix asphalt because the production temperature in these cases were much lower. Warm mix asphalt can produce asphalt mix at temperatures 20-50
C lower than hot mix asphalt (Almeida-Costa and Benta, 2016; Dinis-Almeida and Afonso, 2015;
nchez et al., 2016). Cold mix asphalt can be produced at Sol-Sa ambient temperatures (Ferrotti et al., 2014; Rahman et al., 2016). If bio-oils can be used in warm mix asphalt or cold mix asphalt, the environmental impact and health concerns could be greatly reduced. The acidity of the compounds are also listed in Table 2. Because most aggregates used in pavements are weakly alkaline, it is desirable that the asphalt binder is weakly acidic to form a strong asphalt-aggregate interface. Most petroleum asphalts exhibis slight acidity. A lower pKa value corresponds to a higher acidity. Specifically, the pKa value of water is 16. The pKa values of most of the compounds were around 10, indicating the acidity of bio-oil. This agrees with the previous findings that wood waste bio-oils have pH values around 2.0e3.0 (Ba et al., 2004; Czernik and Bridgwater, 2004). This indicates that the bio-asphalt is able to obtain a good adhesion with aggregate. For the long-term performance, the water solubility of these chemical compounds were also provided considering that moisture related damage is a common distress of asphalt pavement. It was found that many of the compounds were soluble in water with a common threshold of 1 g/L in solubility. Therefore, mass loss under repeated water flow could also be a concern for wood waste bio-asphalt. More research need to be considered to fully evaluate the water solubility of the bio-oil. 3.3. FTIR results 3.3.1. Functional groups and physiochemical properties FTIR spectra were generated for the pure petroleum asphalt, untreated and treated bio-asphalt specimens. The first part of the FTIR is the graphical representation of spectra as a graph of absorbance against wavenumber. The absorbance spectra for the control petroleum asphalt, treated and untreated bio-asphalts were overlaid or superimposed on each other to understand the relative variations in the functional groups of the three different materials. In Fig. 2, the superimposed FTIR spectra are provided for the petroleum asphalt, 100% untreated and treated bio-oils. Firstly, it can be observed that the absorbance spectra trends for the petroleum asphalt and the untreated bio-asphalt (NTB) and treated bioasphalt (TB) are different. However, the two bio-asphalt samples,

Please cite this article in press as: Yang, X., et al., Chemical characterization and oxidative aging of bio-asphalt and its compatibility with petroleum asphalt, Journal of Cleaner Production (2016), http://dx.doi.org/10.1016/j.jclepro.2016.11.100

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under treated and untreated conditions, have similar spectra since they are from the same wood source. An attempt was made to characterize the functional groups from the absorbance peaks generated for these samples. The functional groups identified from the spectra for the petroleum asphalt and the bio-oils are provided in Table 3. A significant difference between the petroleum asphalt and biooils can be observed from Table 3 and Fig. 2. Unlike the petroleum asphalt in which the CeH bending is dominant, the bio-oils exhibited a larger amount of other functional groups including CeO stretching, C]O stretching, and the OeH stretch, mainly attributed to by the large amount of oxygen in the bio-oils. Overall the results of the functional groups from FTIR are consistent with the results revealed from the elemental composition and chemical compounds. In petroleum asphalt, the carbon and hydrogen are more than 90% of the total elemental compositions, while in the bio-oils this value is only around 65%. The functional groups of C]O and OeH stretching implies the presence of acids, which can explain the low pH value of bio-oils. Additionally, ketones, aldehydes, ester, and acyls probably were also present in the bio-oils. The performance of asphalt binder is determined by the rheological, fatigue and oxidative properties, which are affected by the chemical components. It is expected that the rheological properties of bio-oils are different from the petroleum asphalt. Some previous studies have revealed the experimental difference between bioasphalt and petroleum asphalt, including the viscosity, stiffness, temperature sensitivity, aging resistance, etc. (Mills-Beale et al., 2014; Yang and You, 2015; Yang et al., 2013). The FTIR spectra of the petroleum asphalt and the 2%, 5% and

10% bio-asphalts before and after RTFO aging are shown in Fig. 3. Overall, the peak heights of all petroleum asphalt and bio-asphalts presented similar patterns. This is, in part, due to the low concentration of bio-oils. It also indicates that the absorbance intensity of the functional groups bio-oils had no big difference from that in petroleum asphalt, according to the Bouguer-Lambert-Beer law (Ingle and Crouch, 1988). From Fig. 3, it is evident that the absorbance growth heights increased with increasing amounts of untreated bio-asphalt. It is believed that the modified petroleum asphalt had a greater bond strength between molecules since the higher the content of the untreated bio-asphalt, the more the molecular functional groups can absorb infrared light. From Fig. 3, the control and 2% bio-asphalt had a similar spectrum, which was unexpected, and could be attributed to excessive binder coating on the surface of the FTIR silicon slide. Typically, the 2% treated bioasphalt was anticipated to have a higher absorption spectra curve than the control binder. Furthermore, the 10% treated bio-asphalt absorption spectra were seen to be higher than that of the 5% bio-asphalt. No extra peaks were found in addition to the existing peaks in petroleum asphalt or bio-oils, indicating a high chance of no chemical reaction between them. 3.3.2. Carbonyl and sulphoxide aging behavior The investigation of the carbonyl bonding index and sulphoxide bonding behaviors within the base asphalt and bio-asphalt binders are crucial in understanding the morphological behavior of the samples on the chemical bonding level. This carbonyl and sulphoxide bonding, termed as the carbonyl and sulphoxide indices, respectively, were postulated to represent the degree of oxidative hardening or aging within organic compounds (Lamontagne et al., 2001). From the FTIR spectra obtained for the control and bioasphalt specimens, the quantitative analysis of the carbonyl index (IC]O) and sulphoxide index (IS]O) are determined as shown in Equations (3) and (4).

Ic¼o ¼

Is¼o ¼

Fig. 2. FTIR spectra for pure petroleum asphalt, untreated and treated bio-asphalt at their unaged condition.

Area of the carbonyl band around 1700cm1 Area of the spectral bands between 2000 and 600 cm1 (3) Area of the sulphoxide band around 1030 cm1 Area of the spectral bands between 2000 and 600 cm1 (4)

In order to investigate the rate of aging due to the carbonyl and sulphoxide bonds, these two indices are incorporated in this research. The aging indices are first conducted on the unaged

Table 3 Functional groups identified for the control petroleum asphalt. Asphalt type

Functional groups

Absorption wavenumbers (cm1)

Class of compound

Asphalt

CeH in plane bending S¼O CH3 C¼C ring stretch CH2 (methylene) and CH3 (methyl) CeH in plane bending CeO stretching, OeH bending CeH bending eNO2 stretching NeH bending Aromatic C]C stretching C]O stretching CeH stretching OeH stretching NeH stretching

700e900 997e1043 1372 and 1445 1595 2803e3066 507e730 933e1390 1384e1482 1482e1560

Aromatic compounds Sulphoxide Aliphatic compounds Aromatic compounds Aliphatic compounds Aromatic compounds Alcohols, ethers Alkanes Nitrogenous compounds Aromatic compounds Aromatic compounds Ketones, carboxylic acids, aldehydes, esters, acyls Alkanes Polymeric OeH, water NH2

Bio-oils

1650e1812 2799e3040 3045e3690 3045e3690

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the bio-asphalt becomes stiffer than petroleum asphalt after RTFO and PAV aging (Mills-Beale et al., 2014; Yang et al., 2014a, 2014b). Asphalt oxidation and hardening are key factors of asphalt degradation, which cause asphalt distresses such as fatigue and thermal cracking (Lo Presti et al., 2016; Pasandín et al., 2015). More experimental tests are needed to obtain a full picture of how aging affects the road purposed performance of bio-asphalt.

3.4. AFT results 3.4.1. Light transmittance-time curve analysis In Fig. 5, the trace of light intensity versus time is given for the flocculation titration of the 0% and 2% bio-asphalt binders, respectively. Three replicates were tested. In the first part of the curve, the light transmission intensity increases because the asphaltenes remain in solution while the bio-asphalt binder matrix is gradually diluted. At this stage, the concentration of the bioasphalt binder matrix decreases with the addition of the titrant, iso-octane. The relevant equation, equation (5), expresses the oil concentration to model this process:

ci ¼ ½V0 =ðV0 þ Vt Þc0

Fig. 3. FTIR spectra for the control and bio-oil asphalt blends in the unaged condition: a) untreated bio-oil; and b) treated bio-oil.

materials and finally the RTFO and PAV aged specimens. This provides an understanding of the aging rates at the molecular bond level within the functional groups. Fig. 4a) and b) show bar charts of the results of the aging index analysis done on the control, untreated and treated bio-asphalts. The results showed increasing carbonyl and sulphoxide aging indices with increasing rates of both the untreated and treated bio-asphalt content. The functional groups in the untreated and treated bio-asphalt are believed to interact with the functional groups of the petroleum asphalt binder which results in the formation of a stronger bond network and, thus, an increase in the carbonyl and sulphoxide bonding indices. As asphalt binders typically undergo short and long-term aging, it was pertinent that the aging behavior of the RTFO and PAV aged specimens be investigated. From Fig. 4c) and d), e) and f), the carbonyl and sulphoxide aging indices for both the untreated and treated bio-asphalt samples after RTFO and PAV aging are provided in bar charts. Both the sulphoxide and carbonyl aging indices are observed to increase with increasing percent of untreated and treated bio-asphalt after RTFO and PAV aging. This can be attributed to the formation of stronger oxidation bonding chains initiated by the presence of bio-asphalt. It is also observed that the aging indices for the untreated and treated bioasphalt samples are close to each other, which means that after RTFO and PAV aging, the effect of the moisture and volatiles present in the untreated bio-asphalt have been reduced and the molecular structure of untreated bio-asphalt is similar to that of the treated specimen. The higher aging indices from the FTIR analysis are consistent with previous results on the rheological properties that

(5)

where c0 ¼ the initial oil concentration; V0 ¼ the initial volume of sample; Vt ¼ volume of iso-octane titrant. From Fig. 5, the transmittance all drop in value before beginning to rise. This initial drop is because that, at the start of the investigations, the petroleum asphalt (0% bio-asphalt) binder or 2% bio-asphalt is added to the toluene solvent. This leads to an increase in concentration of the mixtures and thus a decrease in light transmittance. Upon commencement of the flocculation titration process by addition of the titrant, iso-octane, the petroleum asphalt/toluene or 2% bio-asphalt/toluene mixtures begin to undergo dilution and, thus, increased the light transmittance behavior. As the titration continues, a point is attained where the flocculation of the asphaltene molecules within the mixture starts. At the onset of this flocculation of these asphaltene molecules, scattering of the light rays will begin to occur and the transmittance intensities begin to decrease. It has been studied that at this maximum peak of light transmittance intensity, there are sufficient asphaltene from the bio-asphalt binder matrix to scatter the light rays, and this is the point where the dilution process is counteracted (Andersen, 1999). The flatter slopes in Fig. 5 suggests reasonable titration rates that are not too high and, thus, exhibit less severe local precipitation at equilibrium conditions.

3.4.2. Flocculation ratio investigations In understanding and interpreting the results of the automated flocculation titrimetry, two approaches were used. Brief descriptions of the two approaches are shown herein. A key parameter of interest is the flocculation ratio (FR) of the bio-asphalt matrix. This flocculation ratio is defined as the minimum amount of the toluene solvent necessary to keep the asphaltene of the bioasphalt matrix in solution in the precipitant-toluene mixture. This definition has been given by Heithaus (1962). Therefore, the FR is expressed as the volume fraction of the solvent at the onset of the precipitation of the asphaltene content. Another interesting parameter used in the investigations is the inverse dilution ratio (I/ X) or concentration of the mixture (C in g/mL), defined as the ratio of the volume of asphaltene precipitant to the volume of mass residue. The relevant equations used in evaluating the FR and the C parameters are:

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Fig. 4. Bar chart of bond (Carbonyl and Sulphoxide) indices: a) unaged NTB; b) unaged TB; c) RTFO-aged NTB; d) RTFO-aged TB; e) PAV-aged NTB; f) PAV-aged TB.

FR ¼ Vs =ðVs þ Vt Þ

(6)

C ¼ Wa =ðVs þ Vt Þ

(7)

where FR ¼ flocculation ratios; Wa ¼ weights of asphalt; Vs ¼ Constant volume of toluene solvent; Vt ¼ Volume of titrant required to initiate flocculation. The Heithaus parameters of interest from the investigations are Cmin, defined as the quantity of the iso-octane titrant that would be just enough to cause asphaltene precipitation in the 0% and 2% bioasphalt binder, and FRmax, defined as a measure of the solubility parameter, at which asphaltene flocculation occurs in the bioasphalt binder matrix as a whole. The peptizing power (Po), peptizability of the asphaltenes (Pa) and the state of peptization (P) of

the control petroleum asphalt and the treated bio-asphalt binder matrix can then be determined from Equations (8)e(10).

P0 ¼ FRmax ðXmin þ 1Þ

(8)

Pa ¼ ð1  FRmax Þ

(9)

P ¼ ðXmin  1Þ

(10)

Using FRmax, the insolubility number (IN) can be calculated from Equation (11).

IN ¼ 100*FRmax

(11)

All the necessary Heithaus compatibility or solubility parameters are presented in Table 4. For stability of the asphaltene in both

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Fig. 5. Titration time against light transmittance for: a) the base asphalt; and b) the base asphalt blended with 2% bio-asphalt.

the 0 and 2% treated bio-asphalt samples, the insolubility number, IN, which measures the degree of insolubility of the asphaltene present, must be less than the solubility blending number, SBN, which measures the solvency of the oil for asphaltene. From Table 4, the SBN for both the 0 and 2% treated bio-asphalt binder were greater than their IN; thus adding the bio-oil into the petroleum asphalt creates a stable and compatible mixture. However, the SBN of the 0% bio-asphalt (control petroleum asphalt) was lower than the SBN of the 2% treated bio-asphalt, suggesting that modifying petroleum asphalt with treated bio-oil can cause some of the asphaltene fractions to be unstable but not sufficient enough to cause insolubility and initiate phase separation problems for the mixture. It will be interesting to determine the optimum percent of bio-oil that can induce high flocculation of the asphaltenes and cause undesirable phase separation between the molecules in the mixture. In all cases, the Po, Pa and P of the 2% treated bio-asphalt were found to be lower than those of the petroleum asphalt. In terms of the peptizing power, Po, it can be deduced that once the 2% treated bio-oil was added to the control petroleum asphalt, the solvent power of the maltene fractions in the binder matrix was reduced at the final stage after the asphaltenes had begun to flocculate. The overall compatibility of the asphaltenes in the maltenes of the petroleum asphalt, P value, is better than the 2% treated bioasphalt. Typically, the addition of the treated bio-asphalt can be said to possess functional groups that “attack” the maltene components of the petroleum asphalt and reduce their ability to initiate and propagate dispersal in the maltenes. This is not problematic in affecting the compatibility since the SBN of the 2% treated bioasphalt is still greater than the IN.

4. Summary and conclusions This study was motivated by the lack of understanding of the elemental composition, chemical compounds, oxidative aging and the compatibility with petroleum asphalt of bio-oil. It investigated the chemical composition and aging behavior of bio-asphalt generated from wood wastes in Michigan and its compatibility of petroleum asphalt. Two types of bio-asphalt (untreated and treated) were added into petroleum asphalt to prepare bio-asphalt. The Gas chromatographyemass spectrometry (GC-MS) was utilized to characterize the elemental composition of bio-asphalt; the Fourier Transform Infrared Spectroscopy (FTIR) technique was utilized to analyze the functional groups and the aging behavior of

Table 4 Compatibility parameters for 0 and 2% treated bio-asphalt. Compatibility Parameters

0% (CTL)

2% (AFT M B0)

Flocculation ratio (FR) Cmin Solubility number (SBN) Heithaus (Frmax) Peptizing power (Po) Peptizability of asphaltenes (Pa) State of peptization (P) Insolubility number (IN)

0.321 0.526 105.98 0.365 1.06 0.635 2.9 36.53

0.361 5.319 44.45 0.366 0.434 0.34 1.188 36.56

bio-asphalt. The Automatic Flocculation Titration (AFT) process was carried out to investigate the compatibility between the bioasphalt and petroleum asphalt. The findings in this paper provides a thorough understanding of some basic properties of bio-oil and some potential issues if it is applied in pavement industry. It can guide the research direction of promoting bio-oil implementation in pavement engineering. Based on the test results and discussion, the conclusions of this study can be drawn as below: 1) The amount of oxygen in bio-oils was significantly higher than petroleum asphalt according to the elemental composition analysis, which is due to the large amount of CeOeC and C]O bonds in cellulose, hemicellulose, and lignin. 2) Many chemical compounds and their concentrations can be successfully identified from the GC-MS. The concentration of these chemical compounds were much higher than petroleum asphalt. The mass loss, environmental impacts and health concerns during hot mix asphalt production could be concerns due to the low boiling points and toxicity of some compounds. Such concerns can be greatly reduced if bio-oils are used in warm mix asphalt or cold mix asphalt. 3) The functional group analysis of FTIR showed the presence of acids, ketones, aldehydes, ester, acyls, etc. in the bio-oils. The aging indices from FTIR showed that the addition of bio-oil into petroleum asphalt exhibited an increased aging rate according to the FTIR analysis, which may not be desirable for the longterm performance of asphalt mixtures. 4) Treated bio-oil, containing limited quantities of water, can be successfully used as a modifier in petroleum-based asphalt with good compatibility with petroleum-based asphalt. With the addition of a higher dosage of bio-oil into petroleum asphalts, conglomeration or assemblage of the asphaltenes will be reached with possible undesirable stiffening effects or loss of some elastic characteristics of the asphalt binder.

Please cite this article in press as: Yang, X., et al., Chemical characterization and oxidative aging of bio-asphalt and its compatibility with petroleum asphalt, Journal of Cleaner Production (2016), http://dx.doi.org/10.1016/j.jclepro.2016.11.100

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Future research This study mainly investigated some basic properties of wood waste bio-oil and bio-asphalt. More tests need to be conducted to fully evaluate the potential of using bio-oil in pavement industry. The investigation of the chemical compounds in the smoke of bioasphalt during asphalt production will provide a direct vision of the environmental and health impacts. Laboratory distillation of bioasphalt may be able to achieve this goal. In addition, the mass loss and polymerization during bio-asphalt aging shall be quantified. More efforts need to be carried out to reduce the aging of bioasphalt. Further, it has been observed that petroleum asphalt and bio-oil have a good compatibility when the bio-oil content is low. The critical percentage of bio-oil that results in an incompatible blend still needs to be discovered. In addition to the AFT test investigated in this study, other approaches such as the storage stability test is also a potential option to evaluate this. Acknowledgments The research work was partially sponsored by the Federal Highway Administration through the Michigan Department of Transportation (MDOT) under the contract number of ORE0902. The authors also appreciate the guidance and involvement of Nathan Maack, Andre Clover, Benjamin Krom, and John Barak of MDOT. The graduate research assistantships to Julian Mills-Beale and Xu Yang from MDOT through Michigan Technological University is acknowledged. MDOT assumes no liability for its content or use thereof. The content of this report reflects the views of the authors, which is responsible for the accuracy of the information presented herein. The contents may not necessarily reflect the views of MDOT and do not constitute standards, specifications, or regulations. This research could not have been completed without the contributions of Dr. R. Christopher Williams, who was a subcontractor for this project. The authors would like also appreciate the help of Dr. Ying Liu and Dr. Raj Shah from Koehler Instrument Company, New York, for the AFT test. References Akhtar, J., Kuang, S.K., Amin, N.S., 2010. Liquefaction of empty palm fruit bunch (EPFB) in alkaline hot compressed water. Renew. Energy 35, 1220e1227. Almeida-Costa, A., Benta, A., 2016. Economic and environmental impact study of warm mix asphalt compared to hot mix asphalt. J. Clean. Prod. 112 (Part 4), 2308e2317. Andersen, S.I., 1999. Flocculation onset titration of petroleum asphaltenes. Energy Fuels 13, 315e322. Asphalt Institute, 2003. Superpave Performance Graded Asphalt Binder Specifications and Testing. Asphalt Institute, Lexington, KY. Ba, T., Chaala, A., Garcia-Perez, M., Roy, C., 2004. Colloidal properties of bio-oils obtained by vacuum pyrolysis of softwood bark. Storage stability. Energy & Fuels 18, 188e201. Bala, D.D., de Souza, K., Misra, M., Chidambaram, D., 2015. Conversion of a variety of high free fatty acid containing feedstock to biodiesel using solid acid supported catalyst. J. Clean. Prod. 104, 273e281. Boczkaj, G., Makos, P., Przyjazny, A., 2016. Application of dynamic headspace and gas chromatography coupled to mass spectrometry (DHS-GC-MS) for the determination of oxygenated volatile organic compounds in refinery effluents. Anal. Methods 8, 3570e3577. Bortolomeazzi, R.S.N., Toniolo, R., Pizzariello, A., 2007. Comparative evaluation of the antioxidant capacity of smoke flavouring phenols by crocin bleaching inhibition, DPPH radical scavenging and oxidation potential. Food Chem. 100, 1481e1489. Branca, C., Giudicianni, P., Di Blasi, C., 2003. GC/MS characterization of liquids generated from low-temperature pyrolysis of wood. Ind. Eng. Chem. Res. 42, 3190e3202. Bridgwater, A.V., 1999. Principles and practice of biomass fast pyrolysis processes for liquids. J. Anal. Appl. Pyrolysis 51, 3e22. Bridgwater, A.V., Peacocke, G.V.C., 2000. Fast pyrolysis processes for biomass. Renew. Sustain. Energy Rev. 4, 1e73. Capunitan, J.A., Capareda, S.C., 2013. Characterization and separation of corn stover bio-oil by fractional distillation. Fuel 112, 60e73.

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Please cite this article in press as: Yang, X., et al., Chemical characterization and oxidative aging of bio-asphalt and its compatibility with petroleum asphalt, Journal of Cleaner Production (2016), http://dx.doi.org/10.1016/j.jclepro.2016.11.100