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S.N. Nahar, A.J.M. Schmets and A. Scarpas
Determining Trace-elements in Bitumen by Neutron Activation Analysis
S.N. Nahar, A.J.M. Schmets and A. Scarpas
Section of Road and Railway Engineering
Faculty of Civil Engineering & Geosciences, Delft University of Technology 5 Stevinweg 1, 2628 CN, Delft, The Netherlands.
Tel: +31(0)152789597, Fax: +31(0)152785767, E-Mail: s.n.nahar @tudelft.nl
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Corresponding author: 15 Alexander Schmets
E-Mail: a.j.m.schmets@tudelft.nl
Submission date:
1 August 2014 20
Paper Number:
Total Number of Words
Words in text: = 4779 words 25 Tables: (4 × 250) = 1000 words equivalent
Figures: (5× 250) = 1250 words equivalent
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Total = 7029 words equivalent
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S.N. Nahar, A.J.M. Schmets and A. Scarpas
ABSTRACT
Trace elements and their concentrations play an important role in both chemical and physical
properties of bitumen. Instrumental Neutron Activation Analysis (INAA) is an analytical technique
to determine the trace elemental contents in bitumen at the bulk. This method requires irradiation of 5 the material with neutrons that transform the elements into radioactive isotopes. By analyzing the
activity of the individual nuclide, the concentration of each element is determined. In this work, we
perform trace elemental analyses of 13 bitumen, including 2 modified and 3 bitumen from the library
of strategic highway research program (SHRP). Vanadium, nickel and cobalt are present in all
bitumen and the first two metals are the most abundant among all the elements detected. Next to 10 vanadium and nickel, a significant amount of iron is found in 11 bitumen. The total number of trace
elements, identified in the these bitumen, varied from 17 to 28. Total trace metal content, i.e.
especially the sum of most abundant metals (vanadium and nickel) correlates well with the amount of
sulphur and asphaltene of the same bitumen. For modified bitumen, the concentration of trace
elements can be an indicator to measure the amount of modification. INAA provides a complete list 15 of trace elements in bitumen, where the concentrations varied (ppm to ppb) depending on the organic
constituents of the material. This method can be a fast screening tool to characterize the origin of
bitumen, with possible applications in the field of asphalt recycling (RAP and RAS).
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S.N. Nahar, A.J.M. Schmets and A. Scarpas
INTRODUCTION
Bitumen is composed of high molecular weight hydrocarbon molecules, many containing small
amounts of heteroatoms (sulphur, nitrogen and oxygen) and trace quantities of metals (1-3). Trace
metals usually occur as intrinsic component and are mainly associated with the asphaltene fraction of 5 bitumen (4). The asphaltene fraction is defined as the fraction that is not soluble in n-heptane. One
particular type of molecules that is known to be n-heptane insoluble and which is known to be
present in bituminous compounds, are so-called porphyrins; a group of heterocyclic molecular
compounds that are known to host trace metals, or form molecular complexes with those. The
presence of various metals in asphaltene does influence the association and agglomeration of the 10 molecules (4-9). As the mobility and the viscosity of the material is influenced by the asphaltene
association, trace metals play a significant role in the flow, and other chemomechanical, properties of
bitumen (3; 4).
Vanadium and nickel are the most abundant trace metals, found in almost all bitumen and
occur primarily in porphyrin-like organometallic complexes (4-6). Following vanadium and nickel, 15 iron is also present at significant concentration in many bitumen. Other metals such as magnesium,
calcium, chromium, cobalt, zinc and molybdenum are often present in small quantities (10; 11).
There are also some elements found in very small concentrations in bitumen and their presence
influence the molecular interactions within the material. But the concentration of these elements and
their association vary depending on the source of the bitumen. Knowledge of these elements can 20 provide useful information on the origin of the crude oil source; in principle the trace-metal makeup
of a bitumen provides a unique fingerprint of the origin of a bitumen. In principle, even mixtures of
bitumen from various crude sources can be unravelled by knowledge of the trace-metal content of the
crude sources.
There are a few analytical techniques that are most often used to characterize the trace 25 elements in petroleum. These methods are: optical emission spectroscopy, atomic absorption
spectroscopy, polarography and colorimetric analysis (12). Only the concentrations of the most
abundant trace elements (vanadium, nickel and iron) are usually measured in bitumen. In the
Strategic Highway Research Program (SHRP), the most abundant trace metals were measured
together with the concentrations of major elements (C, H, S, N and O). Within SHRP inductively 30 coupled plasma spectroscopy (ICP) was used to obtain concentrations of vanadium, nickel and iron
for the eight core SHRP bitumen (13).
In order to obtain a complete trace elemental mapping, a multi-element analytical technique,
instrumental neutron activation analysis (INAA) has sometimes been used in petroleum research (10;
12). INAA provides a bulk analysis of the material and can measure very low concentrations of 35 elements with high precision. This method is beneficial over the aforementioned analytical
techniques as the possible sources of contamination are minimal (10; 12). All the earlier mentioned
techniques involve chemical separations and pre-concentration of samples, which may introduce
sources of contamination and loss of volatiles (12), whereas INAA involves an easy sample
preparation that doesn’t involve any separation of components. There is no possible loss of volatile 40 compounds and the elemental compositions can be measured accurately.
INAA is a technique to probe the presence of trace elements in bitumen as its major
constituents, carbon, hydrogen and electronegative heteroatoms (N, O) seldom form any radioactive
isotope (14). This makes INAA an effective tool to measure the trace elements within bitumen,
without any interference. 45 The objectives of this study are to obtain into high detail the trace elemental maps and their
concentrations for 13 bituminous materials by INAA. The materials are obtained from different
sources, including two modified bitumen and three SHRP bitumen. The concentrations of the six
abundant trace metals, i.e. vanadium, nickel, iron, chromium, cobalt and zinc, present in these
bitumen, are compared. Later, the concentrations of vanadium, nickel and iron of three SHRP 50
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S.N. Nahar, A.J.M. Schmets and A. Scarpas
bitumen obtained by INAA are compared to the same measured by ICP in the SHRP program.
Further, a correlation is found between total trace metal contents of bitumen to fractions of hetero
atoms (especially sulphur) and asphaltene. Lastly, the consistency of elemental concentration is
checked from a pure bitumen and two modified bitumen derived from it.
5 MATERIALS & METHODS
Materials:
The bituminous materials, selected for INAA analysis are listed in Table 1. Among them, 11 are pure
bitumen from different sources and the other two are prepared by modifying a selected original
bitumen with two additives. AAA-1, AAM-1 and AAD-1 are selected from the bitumen library of 10 Strategic Highway Research Program. Another four bitumen designated as D-0114, D-0113, D-0184
and B (20/30) are obtained from NYNAS, Sweden. The crude origin of bitumen BNDM 90/130 and
BNDM 80/120 is Kazakhstan. Fina 70/100 has been obtained from Total and the 10 % w/w modified
bitumen are derived from this bitumen. One of the additives to the modified bitumen is ethylene
vinyl acetate (EVA) and the other is sasobit. EVA is the copolymer of ethylene and vinyl acetate and 15 sasobit (trade name) is a synthetic wax manufactured from natural gas or coal gasification using the
Fischer-Tropsch process (15).
Instrumental Neutron Activation Analysis (INAA):
INAA is an analytical technique for the precise determination and quantification of chemical 20 elements in a sample at very high sensitivity (<ppb). This method is capable of analyzing various
elements simultaneously and also sensitive enough to detect trace elements at very low
concentrations. The key prerequisites to analyze a sample by INAA include a source of neutrons,
suitable instrumentation for the detection and analysis of emitted gamma radiation and a detailed
knowledge of the radioactive activation of the elements by neutron irradiation and its characteristic 25 gamma-ray decay emission spectrum.
Figure 1 schematically presents the steps associated with an INAA experiment and illustrates
the process of activation of atomic nuclei present in the bitumen by the neutron capture. In this
method, the sample is exposed to a neutron flux in a nuclear reactor or any other neutron source.
During the irradiation process, radioactive nuclides are produced and emit distinctive gamma rays 30 that are detected by gamma-ray spectrometers. The wavelength or energy of this gamma radiation is
characterizing certain radionuclides and the intensity of the radiation is used to determine the
concentration of the activated element. A specific peak in the gamma-ray spectrum corresponds to a
certain element and in this way qualitatively the presence of an element is known. Further,
quantitative information on the concentration of an element is obtained from the peak area. 35 The nuclides formed after neutron activation will have different half-lives and can be
classified in three groups: (i) short (half- life seconds to hours), (ii) medium (hours to days) and (iii)
long-lived nuclides (days to weeks/months) (16). For all the elements measured in bitumen, nuclides
with short half-lives were measured in the first hours after irradiation. The medium-lived
radionuclides were measured between 3 to 6 days and the long lived nuclides were measured 3 weeks 40 after irradiation.
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S.N. Nahar, A.J.M. Schmets and A. Scarpas
FIGURE 1: Schematic representation of Neutron Activation Analysis steps and illustration of
the neutron capture process.
5
INAA Facility and Method of Analysis:
The bitumen samples were irradiated at the nuclear reactor and analyzed at the INAA facility of
Reactor Institute Delft of TU Delft. The short-lived nuclides were analyzed by the ‘SBP’ (fast rabbit)
facility and for the longer-lived nuclides; the irradiation was carried out in the ‘SUR’ facility. 10 The analysis was performed by following three key steps: (i) sample preparation (ii)
measurement and (iii) interpretation. Firstly, bitumen samples were prepared by taking a small
amount of material (~ 250 mg) by a spatula and placing them in separate polyethylene capsules. All
the samples were then sealed together with two additional capsules. One capsule was filled with the
reference material (NIST SRM 1632c, Coal) and the other was an empty capsule (blank). 15 At first, this cluster of sample capsules was placed close to the core of Delft nuclear reactor
in an irradiation container. A pneumatic irradiation tube system was used for transporting the
capsules to a location of high radiation intensity close to the reactor core. The samples were
irradiated for 10s in a thermal neutron flux of approximately 1.82×1017 neutrons m−2s−1. Next, the
samples were unpacked and the counting of short lived nuclides was immediately (7 minutes) carried 20 out, for 5 minutes by the ‘SBP’ coaxial GeLi detector.
Further, to determine the medium and long-lived nuclides, the batch of samples was
irradiated (after 3 days) for an hour in a thermal neutron flux of approximately 4.24×1016 n m−2s−1.
After 3 days of decay, the medium-lived nuclides were measured by ‘SUR’, a well type GeLi
detector. And after 3 weeks of decay, the long-lived nuclides were measured using the same detector. 25 The results of radiation peaks were analyzed and the intensity of each gamma-ray in the
spectrum was calculated from the peak area. After carrying out the necessary corrections of decay,
interference and fission products influences, the results were compared with the standard and the
concentration of the elements were obtained.
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S.N. Nahar, A.J.M. Schmets and A. Scarpas
EXPERIMENTAL RESULTS AND DISCUSSION
Results
The concentration of trace elements was obtained by INAA as described in the section above. From
the detailed elemental analysis, it was found that each bitumen contained different sets of trace 5 elements where the total number of elements varied from 17 to 28. The elements found in the
materials studied are: sodium (Na), aluminum (A1), silicon (Si), chlorine (Cl), potassium (K),
scandium (Sc), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni),
zinc (Zn), gallium (Ga), arsenic (As), selenium (Se), boron (Br), indium (In), antimony (Sb), iodine
(I), barium (Ba), tungsten (W), rhenium (Re), gold (Au), lanthanum (La), cerium (Ce), samarium 10 (Sm), ytterbium (Yb) and thorium (Th). Presence of these elements fingerprints the geochemical
origin of the bitumen and of its crude oil source. Among all these trace elements in bitumen,
vanadium, chromium, iron, cobalt, nickel and zinc are known to be the most abundant.
Concentrations of these elements are presented in Table 1. Figure 2 shows a comparison of
concentrations of the six abundant trace metals (V, Cr, Fe, Co, Ni, and Zn) in the original bitumen. 15 Besides, the total concentrations of these metals are presented in Figure 3.
TABLE 1: Concentrations of the Most Abundant Trace Metals in Bituminous Materials. 20
Bitumen
samples
Most abundant trace metals in bitumen samples (ppm)
Vanadium
(V)
Chromium
(Cr)
Iron
(Fe)
Cobalt
(Co)
Nickel
(Ni)
Zinc
(Zn)
SHRP AAA-1
183±3.7
0.57±0.01
6.7±2
0.17±0.01
91.5±5.5
-
SHRP AAM-1
60.6±1.2
1.22±0.11
251.2±7.5
0.27±0.02
50.7±0.5
6.12±0.5
SHRP AAD-1
315.4±6.3
2.27±0.11
14.2±4.3
0.42±0.02
133.8±5.4
1.27±0.3
D-0114
126±2.5
-
21.9±2.8
0.20±0.01
27.3±3.0
0.94±0.2
D-0113
642.2±13
0.65±0.13
-
0.96±0.03
83.1±5.8
1.12±0.4
D-0184
629.0±12
0.36±0.11
12.8±3.9
0.94±0.03
79.3±7.1
0.58±0.2
B (20/30)
834.8±17
0.29±0.15
-
0.68±0.03
86.4±6.9
14.79±0.7
BNDM 90/130
62.7±1.3
-
13.2±2.7
0.26±0.01
38.5±2.7
1.11±0.2
BNDM 80/120
99.9±2.0
0.25±0.08
39±3.1
0.15±0.01
44.5±4.0
1.95±0.4
Fina 70/100
192.2±3.8
-
31.8±9.5
0.25±0.01
58.2±4.1
1.50±0.3
Fina 70/100+
10% EVA
171.7±3.4
-
30.0±3.30
0.23±0.01
48.4±3.4
1.31±0.2
Fina 70/100+
10% sasobit
170.1±3.4
0.47±0.14
26.5±5.3
0.23±0.01
56.3±2.8
0.92±0.2
Sc-09-42
(40/60)
201.8±4.0
3.19±0.19
40.6±4.9
0.31±0.02
65.9±4.6
1.75±0.3
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S.N. Nahar, A.J.M. Schmets and A. Scarpas
FIGURE 2: Concentrations of the most abundant trace metals, vanadium (V), chromium (Cr),
iron (Fe), cobalt (Co), nickel (Ni) and zinc (Zn) in pure bitumen.
5 Some key observations from the elemental analyses are summarized below:
• Vanadium, nickel and cobalt are present in all bitumen.
• Vanadium has the highest concentration that is in the range of 60 to 835 ppm. The next most
abundant element is nickel and it is present in concentrations from 25 to 135 ppm.
• Iron is commonly present at concentrations below 50 ppm in all bitumen, except AAM-1. 10 This bitumen is very rich in iron with an average concentration of 250±7 ppm. Bitumen D-
0113 and B (20/30) do not contain any detectable amount of iron.
• Zinc is present in all bitumen except AAA-1. The concentration ranges from 1 to 15 ppm
where in most cases it is below 2 ppm. The maximum amount of zinc (15 ppm) is present in
B (20/30). 15
• Chromium is present in concentrations from 0.3 to 3 ppm in 7 bitumen and in one modified
bitumen (Fina 70/100+ 10% sasobit). And no detectable amount of chromium has been found
in bitumen D-0114, BNDM 90/130 and Fina 70/100. As the fresh bitumen Fina 70/100
doesn’t contain any chromium, it is obvious that the source of measured chromium must be
the sasobit additive. 20
• Cobalt is present in all bitumen at low concentrations (0.15 to 1 ppm).
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S.N. Nahar, A.J.M. Schmets and A. Scarpas
•
FIGURE 3: Total concentrations (ppm) of the most abundant trace metals, vanadium (V),
chromium (Cr), iron (Fe), cobalt (Co), nickel (Ni) and zinc (Zn) in pure bitumen.
• The total amount of INAA-detectable metals in all pure bitumen is presented in Figure 3. 5 Bitumen D-0113, D-0184 and B (20/30) are very rich in total metal, especially vanadium and
nickel occur in relatively high concentrations. Bitumen D-0114, BNDM 90/130 and BNDM
80/120 possess only a small concentration (< 200 ppm) of metals. The total metal content is a
good indicator for the susceptibility of the material to aging.
• The concentration of specific trace metals in bitumen can be a guide to the petroleum source. 10 For example, bitumen D-0113, D-0184 and B (20/30) are very rich in vanadium and nickel
content. The Venezuelan crude oil is rich in vanadium and the bitumen from Peru, Argentina
and Venezuela have also high nickel content (10). Thus, the enrichment of both the metals
suggests that these bitumen may have originated from these sources.
Common Trace Elements in SHRP Bitumen 15 There are 16 trace elements commonly present in all three SHRP bitumen, AAA-1, AAM-1, AAD-1
and their concentrations are presented in Table 2. Among these common elements, the most abundant
trace elements are: vanadium (60 to 315 ppm), nickel (51 to 134 ppm) and iron (7 to 251 ppm).
Whereas antimony and rhenium are only present at very low concentrations. And the concentrations
of antimony and rhenium range from 20 to 60 and 3 to 40 ppb respectively. 20
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S.N. Nahar, A.J.M. Schmets and A. Scarpas
TABLE 2: Concentrations of Common Trace Elements of Three SHRP Bitumen by INAA.
Common
elements in SHRP
Samples
Concentration of trace elements (ppm)
AAA-1
AAM-1
AAD-1
Sodium (Na)
12.40±0.12
13.90±0.28
29.80±0.27
Aluminum (Al)
2.10±0.42
11.80±0.59
2.20±0.44
Chlorine (Cl)
16.00±3.2
8.00±2.4
49.00±3.92
Vanadium (V)
183.00±3.66
60.60±1.21
315.00±6.3
Chromium (Cr)
0.57±0.11
1.22±0.11
2.27±0.11
Iron (Fe)
7.00±2.1
251.00±7.53
14.00±4.2
Cobalt (Co)
0.17±0.01
0.26±0.02
0.42±0.02
Nickel (Ni)
92.00±5.52
51.00±5.61
134.00±5.36
Gallium (Ga)
0.26±0.03
0.07±0.02
1.52±0.03
Arsenic (As)
0.18±0.005
0.42±0.008
0.08±0.005
Selenium (Se)
0.38±0.038
0.26±0.05
0.49±0.005
Bromine (Br)
0.12±.008
0.27±0.01
0.40±0.02
Molybdenum (Mo)
7.44±0.15
0.19±0.04
3.14±0.13
Antimony (Sb)
0.02±0.004
0.06±0.005
0.05±0.005
Rhenium (Re)
0.04±8E-4
0.003±9E-4
0.03±9E-4
There are total 19 different trace elements present in AAA-1 with the total amount of 282
ppm. AAM-1 has 28 trace elements and the total mass fraction is 370 ppm, whereas AAD-1 has the 5 highest concentration of elements; i.e., 468 ppm from 20 elements. Gold (Au), zinc (Zn), thorium
(Th) are absent in AAA-1, however ytterbium (Yb) is only present in this material. Besides,
scandium (Sc) and samarium (Sm) are absent in AAD-1 and tungsten (W) is only found in this
bitumen. AAM-1 contains additional 7 elements and they are potassium (5.1 ppm), barium (7 ppm),
lanthanum (0.076 ppm), cerium (0.11ppm), manganese (0.91 ppm), indium (0.03 ppm) and iodine 10 (0.7 ppm).
Comparison of Concentrations of Trace metals (V, Ni, Fe) in SHRP Bitumen Measured by
Different Techniques
The trace metals determined by INAA are compared to existing data reported in SHRP program for 15 SHRP bitumen: AAA-1, AAM-1, AAD-1 (17). In SHRP program, only three most abundant trace
metals, vanadium, nickel and iron were measured by inductively coupled plasma emission
spectrometry (ICP) (13). The comparison of the concentrations is made between these two sets of
measurements in Figure 2. The concentration of each metal measured by the individual techniques
are found to be the same, with only a small deviation. However, to probe lower concentrations, 20 INAA is far more sensitive (e.g. iron concentration of bitumen AAA-1).
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S.N. Nahar, A.J.M. Schmets and A. Scarpas
FIGURE 4: Comparison between concentrations of trace metals measured by INAA and ICP
in SHRP program for bitumen: AAA-1, AAM-1, AAD-1.
The concentrations of the most abundant trace metals measured by INAA, the concentrations 5 of the hetero elements (N, O, S) and asphaltene fractions of the SHRP bitumen are presented in Table
3. Here, the metals are known to be associated with the asphaltene fraction of bitumen in the form of
porphyrin like organometallic complexes in which the metallic cations are bonded to the hetero
atoms (4-6; 10).
10 TABLE 3: Hetero Elements, Trace Metals and Asphaltene content in SHRP Bitumen.
SHRP
Sample
Hetero elements*
(w/w %)
Asphaltene*
(w/w %)
Trace metals by INAA
(ppm)
Nitrogen
N
Oxygen
O
Sulphur
S
n-heptane
Vanadium
V
Nickel
Ni
Iron
Fe
V+Ni
AAA-1
0.5
0.6
5.5
16.2
183±3
92±5
7±2
275
AAM-1
0.55
0.5
1.2
4
61±1
51±0.5
251±7
112
AAD-1
0.77
0.9
6.9
20.5
315±6
134±5
14±4
449
*Data source: report: SHRP-A-645 (17)
From Table 3, it can be outlined that asphaltene content, trace metals and hetero atoms,
especially sulphur, exhibit good correlations. High amount of vanadium and nickel containing 15 bitumen is usually rich in asphaltene. AAD-1 possesses the highest amount of vanadium and nickel
(449 ppm) and it has the maximum asphaltene fraction of 20.5% (w/w). The next bitumen, rich in
metals (275 ppm) is AAA-1 and contains 16.2% (w/w) asphaltene. AAM-1 has the least vanadium
and nickel concentration of 112 ppm as well as the asphaltene content (4% w/w). However, a high
concentration of iron (251ppm) is detected in AAM-1 by INAA and the same is also characterized in 20 SHRP program by using ICP technique (255ppm). Besides, the higher the sulphur content in any
bitumen, the larger the asphaltene fraction. In the case of sulphur concentration, the SHRP bitumen
follow the same order of the total amount of vanadium and nickel (AAD-1˃ AAA-1˃ AAM-1).
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S.N. Nahar, A.J.M. Schmets and A. Scarpas
Consistency in Measured Concentrations of Trace Metals Measured by INAA
The consistency of INAA data can be checked from the metal concentration of Fina 70/100 and its
derived modified bitumen Fina 70/100 + 10% EVA and Fina 70/100 +10% sasobit. The comparison
data is presented in Figure 4 and Table 4. Both the 10% (w/w) modified bitumen showed 90% 5 vanadium content of the original bitumen, Fina 70/100. But minor inconsistency is observed in nickel
and iron concentrations of modified bitumen. Bitumen Fina 70/100+ 10% EVA has a nickel
concentration that is 83% relative to the pure bitumen, whereas for Fina 70/100+ 10% sasobit this is
96%, which is higher than the pure bitumen. Concentration of iron in Fina 70/100+ 10% EVA is 94%
(higher than original bitumen) and in Fina 70/100+ 10% sasobit is 83% of the original bitumen. 10
FIGURE 5: Consistency in concentrations of trace metals measured by INAA.
The inconsistency found in the modified bitumen samples can be a consequence of two
possible reasons. The additional amount of nickel (1.2 ppm) in sasobit and iron (3.4 ppm) in EVA 15 modified bitumen may have originated from the possible impurity of EVA and sasobit respectively.
It is plausible that these industrial grade additives may contain some foreign metals at very low
concentrations. Besides, the depreciation of 4 ppm nickel and 2.2 ppm iron can be the results of
inhomogeneity of the additive within the material. As small amount of sample (~ 250 mg) is
measured by INAA, material homogeneity can influence the data obtained. If a small amount of these 20 metals are present in unbound form in bitumen, it can also be a source of such inconsistency.
TABLE 4: Consistency of Trace Metal Concentrations Measured by INAA.
Bituminous
materials
Concentration of trace metals
(ppm)
Comparison of concentrations
(consistency)
Vanadium
V
Nickel
Ni
Iron
Fe
Vanadium
V
Nickel
Ni
Iron
Fe
Fina 70/100
192.20±3.8
58.21±4.1
31.76±9.5
V
o
Ni
o
Fe
o
Fina 70/100+ 10%
EVA
171.70±3.4
48.44±3.4
30±3.3
0.90V
o
0.83 Ni
o
0.94 Fe
o
Fina 70/100+ 10%
sasobit
170.10±3.4
56.31±2.8
26.47±5.3
0.90V
o
0.96 Ni
o
0.83 Fe
o
Vo, Nio, Feo = concentrations of vanadium, nickel and iron in pure Fina 70/100
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S.N. Nahar, A.J.M. Schmets and A. Scarpas
CONCLUSIONS
The concentration of the trace elements in eleven pure bitumen and two modified bitumen have been
successfully measured by neutron activation analysis, INAA. This elemental analysis shows the 5 characteristic chemical signature of individual bitumen and provides useful information about the
origin of the bitumen. In this study, bitumen D-0113, D-0184 and B (20/30) are found very rich total
metal content (i.e., vanadium and nickel). The well documented high concentration of vanadium and
nickel in Venezuelan crudes indicates that these materials possibly have originated from Venezuela
(10). Besides, vanadium rich crudes are known to contain high amounts of sulphur that is also 10 observed in this study (18). Thus, the chemical footprint together with the concentrations can indicate
the source of the respective material. Furthermore, the metals play an important role in the structure
of asphaltene molecule. The type and concentration of metals also influences the asphaltene
molecular association and its molecular aggregation characteristics (pipeline clogging).
AAD-1 is characterized by its high metal concentration, sulphur content and asphaltene 15 fraction, among all SHRP bitumen. Thus, total metal concentration correlates very well with the
sulphur and asphaltene fractions.
By neutron activation analysis the metal content of bitumen was measured, but one cannot
infer from this information alone in which chemical form these metals are present. Concentrations of
trace metals, especially vanadium and nickel, are good indicators for bitumen aging propensity (10; 20 12; 19; 20). These metals are present mainly in two forms in asphaltenes, i.e. porphyrinic and non-
porphyrinic (6). And, the minor fraction of vanadium and nickel are porphyrinic in nature.
Branthaver et al investigated the effect of metallo-porphyrins on bitumen oxidation and concluded
that vanadyl porphyrins can promote bitumen oxidation, while nickel porphyrins show less or no
activity in oxidation (18). However, the correlation of the metal concentration in bitumen and its 25 susceptibility to oxidation is not straightforward. The apparent reason is that the molecular
association in bitumen varies from source to source. This introduces different amounts and types of
oxidizable molecules. The type of metal and its porphyrinic and non-porphyrinic fractions mainly
govern the potential to bitumen oxidation.
INAA is able to rapidly characterize bitumen by simultaneous analyses of multiple chemical 30 elements. The method characterizes the bulk of the material and provides a complete map of trace
elements. By INAA, one can perform the analyses of trace elements present at very low
concentrations in bitumen with high precision. The complete analysis can be performed at relatively
low cost (estimation of commercialized INAA analysis is a few hundred dollars per bitumen sample).
A unique possible application of INAA can be, to identify the original bituminous ingredients 35 in recycled asphalt pavement (RAP) or recycled asphalt shingles (RAS) in a stock pile. By extracting
the bitumen from the RAP or RAS and carrying out the neutron activation analysis, a chemical
signature of the bitumen and a primary idea about the source can be obtained. Again from the
analyses of the modified binders, it is proposed that, INAA can be a suitable tool to characterize the
homogeneity of the additive to the bitumen matrix in different modified binders. 40
ACKNOWLEDGEMENTS
We acknowledge the bitumen providers and Troy Pauli from Western Research Institute (Laramie,
USA) for the SHRP bitumen. We thank Mehmet Sarilar from Neutron Activation Facility, Reactor 45 Institute TU Delft, for carrying out the analyses. Financial support from the national IOP Self
Healing Materials program (AgentschapNL, the Hague, the Netherlands) under grant no. SHM01056
is gratefully acknowledged.
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13
S.N. Nahar, A.J.M. Schmets and A. Scarpas
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