EVALUATION OF ASPHALT COMPOSITION LABORATORY DETERMINATION
METHODS
iktorasudriusVaitkus2, Alfredas Laurinavičius3, Donatas Čygas4
Vilnius Gediminas Technical University, Sauletekio av. 11, 10223 Vilnius-40, Lithuania
1
E-mail: viktoras.vorobjovas@ap.vtu.lt, 2E-mail: akml@ap.vtu.lt,
3
E-mail: alfla@ap.vtu.lt, 4E-mail: dcyg@ap.vtu.lt
Abstract. The majority of Lithuanian road material testing laboratories uses the chlorinated solvents for the
determination of the hot mixed asphalt (HMA) mixtures in order to separate the binder from the aggregates. The
separation-with-solvents method carries out the main function, separates the mineral aggregates and the binder.
However, the methods using the solvents are expensive, require big experience and are not safe. With the constantly
growing requirements for health and environmental protection it is aimed to reduce the use of chlorinated solvents in
laboratory investigations. For this purpose the new methods are being created to determine the HMA content. One of
the new methods is the ignition method.
Keywords: asphalt content, extraction, ignition, gradation, binder content.
1.
Introduction
Based on 2006 data, nearly 60 % of Lithuanian state
roads have asphalt pavement. Asphalt pavement is the
most widely used type of pavement in the world. Asphalt
pavements are strong and strainth, having good skidresistance [1, 2, 3]. Asphalt quality is highly dependant
on the type and quality of the composing materials of the
mixture. There are cases when asphalt pavement fails
before the end of the predicted service life. It also
happens that the paving characteristics of asphalt do not
match the required ones. Asphalt pavement has to
withstand the long-term static and the short-term repeated
dynamic loads, caused by the standing or moving
vehicles at different time of the year. The most
characteristic asphalt properties are: elasticity, viscosity
and plasticity [2]. The properties vary in a very wide
range, depending on ambient temperature, speed of the
applied loads and duration of the load impact.
Asphalt is multi-component conglomerate material,
the separate mineral particles of which is in touch with
the other particles and is covered with binder, binding the
particles into a single conglomeration. Asphalt structure
is characterized by the size and the shape of mineral
particles, interrelation between the particles of different
size, the properties of the aggregate, also the content,
structure and the properties of the binding material, the
type of interrelation between the binder and the mineral
particles. For practical purposes the most important is the
optimal asphalt structure, which ensures the best
properties of the mixture. The optimal structure not only
reflects the best characteristics of asphalt properties, but
also ensures the highest mechanical stability of the
material in pavement. The main condition to ensure the
highest strength of asphalt is: a dense mineral structure of
the mix, which could be achieved by a proper selection of
gradation, also the largest possible compaction of mineral
particles and the optimum bitumen content for a certain
mineral composition of the mix under the existing
conditions of mixing and compacting [2].
The produced HMA mixture should meet the project
requirements. The main characteristic of asphalt lies in its
composition - bitumen content and gradation. Bitumen is
a very important component of an asphalt mixture,
ensuring pavement strength and durability [4]. Bitumen
content and gradation, required for the asphalt mixture, is
determined by laboratory testing. Extraction with
chlorinated solvents is one of the most popular and most
widely used methods in the world and in Lithuania.
However, this method is expensive, relatively timeconsuming, difficult to perform and hazardous to the
environment. Taking into consideration the growing
requirements for health and environmental protection,
and following the EU Council Directive 98/24/EC on the
“Protection of the Health and Safety of Workers from the
Risks Related to Chemical Agents at Work” the aim is to
reduce the use of chlorinated solvents at the workplaces.
Therefore, we are seeking for new alternative methods to
determine the composition of asphalt mixture.
In 1969 the scientists of US Clemson University J.D.
Antrim and H.W. Busching [5] suggested the use of a
new method for the determination of bitumen content in
an asphalt mixture based on the bitumen ignition. The
furnace, used in this method, was created in the National
Center for Asphalt Technology (NCAT). Investigation of
the accuracy of the results, obtained by this method,
showed that this method is as accurate as the extraction
method. The ignition method is still new in our country,
thus, it is necessary to study the reliability of results of
testing HMA mixtures in Lithuania.
This paper gives the analysis and the comparison of
two different methods for the determination of asphalt
content: ignition method and the most frequently-used in
the world and in Lithuania – extraction with chlorinated
solvents.
2.
Overview of the previous investigations
The methods, used to determine the HMA content,
could be divided into two groups: using organic solvents
and using the furnaces. Most of Lithuanian laboratories
for the determination of asphalt content in a mixture use
the chlorinated solvents, in order to separate binder from
mineral aggregates. One of these methods is extraction.
The main disadvantage of extraction is that sometimes, in
the process of extraction, part of mineral particles flows
out through the top of a thin-walled cylinder together
with the extract and this reduces the data reliability [6].
The other methods to determine the asphalt content
of HMA mixture are the methods of ignition. In 1969 the
studies by the scientists of Clemson University (USA)
revealed that the complete combustion of the binder
could be achieved by subjecting HMA mixture at a
temperature of 843°C. They also noted that the burning of
aggregate at such a temperature could possibly cause the
mass loss of the whole sample. Although the mass loss of
granite materials was negligible, dolomite materials lost a
significant amount of its mass. The scientists noted that
during the ignition testing of 1000 g aggregates at a
temperature of 843°C for 30 minutes in order to
determine the binder content of asphalt mixture, the
measured content could vary from the true binder content
up to 1% [5].
Subsequent investigations of the new method were
continued in the U.S. National Center for Asphalt
Technology (NCAT) by Elton R. Brown, Nicholas E.
Murphy, Li Yu and Stuart Mager [5]. Their tests solved
many questions, identified by Antrim and Busching. First
of all, a new furnace was created. In a new furnace the
asphalt mixture was burnt at a temperature setting of
593°C but not 843°C, resulting in a significantly lower
change in the results of the binder content due to ignition
of mineral aggregates. The tests showed that the
aggregate residue, remaining after ignition, is suitable to
determine gradation of the asphalt mixture. Also it was
noted that the results of burning at a temperature of
593°C are more accurate than 843°C. The new dishes
were created, which reduced the burning time from 4,5
hours to 30-40 minutes. Further investigations with a new
furnace resulted in the creation of ignition method to
determine the binder content of HMA mixture and from
the remaining burnt mineral aggregate – to determine the
gradation. In order to determine the exact binder content
the correction factor is necessary for some aggregates. No
correction factor is needed for aggregate gradation. One
of the main conclusions, made by Elton R. Brown,
Nicholas E. Murphy, Li Yu and Stuart Mager, was that
the accuracy of ignition method is as good as of the
extraction method [5].
In 1995 E. R. Brown and Stuart Mager conducted a
special study to determine the accuracy of the ignition
method. For this purpose they used the method,
developed by NCAT. 12 laboratories throughout the U.S.
were selected for the study. Each of them was supplied
with 1 furnace and the test procedure for the
determination of binder content of HMA mixture by
ignition method and was sent 4 different HMA mixture
types. The study and the statistical analysis of the results
showed that the ignition method is more accurate than the
extraction method. In order to obtain a sufficient
accuracy of the results it was important to identify the
correction factors [7].
In 2002 Brian D. Prowell conducted analogical study
as that of E. R. Brown and Stuart Mager. Brian D.
Prowell used the same ignition method and not a standard
ignition furnace but the infrared furnace. The study was
based on the previously prepared asphalt mixtures with
the already known content by using the standard and the
infrared furnace. The study and the statistical analysis of
the results showed that, when using a new type of
infrared furnace, the test results are more accurate.
Aditionaly, it was determined that the correction factors
for the infrared furnace were generally smaller than those
for the standard furnace [8].
3.
Experimental investigations for the determination
of asphalt content
3.1. Selection of samples for experimental investigations
28 cores, taken from the road pavement, were
selected by an accidental order in the laboratory. The
composition of the cores selected was determined by the
use of both extraction and ignition methods.
The majority of samples were the mixtures from the
top layers of the pavement. Therefore, in order to study
the more frequently-used asphalt mixtures in the second
part of investigations, asphalt mixtures, used for the
lower pavement layers were prepared in the laboratory. 4
asphalt mixtures of different grade were prepared. 6
samples were produced from each mixture and 4 samples
– from one mixture.
Since the smallest possible mass of the sample,
required for the extraction method is 800 grams and for
the ignition method - 500 grams, the test was conducted
for the sample mass of (1100±100) grams, since the
sample should represent the content of the mixture to be
tested.
Aggregate content, % of mass
By ignition
By extraction
By ignition
By extraction
>2
By extraction
0,09 - 2
By ignition
< 0,09
By extraction
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
Bitumen
content, % of
mass1)
By ignition
Sample No.
Table 3.1. Determined composition of samples, taken from
asphalt pavement.
Grade of
mixture
4,18
5,58
5,36
5,39
5,44
5,31
5,33
5,61
5,46
5,44
5,14
6,29
6,23
6,07
6,13
6,00
5,95
5,93
6,04
5,66
5,24
5,66
5,64
5,98
5,47
5,09
6,25
5,56
6,00
6,06
5,57
5,94
5,85
5,82
5,67
5,79
5,62
6,04
4,72
6,56
5,79
6,09
6,39
5,92
6,05
5,96
6,50
5,59
5,52
5,35
5,82
5,82
5,93
4,93
6,06
5,59
6,63
9,67
6,51
6,43
6,82
6,33
8,35
9,09
9,65
7,57
8,62
8,09
8,04
7,56
7,41
7,35
7,61
8,19
7,54
7,64
8,39
7,32
4,51
5,78
9,32
6,87
7,70
6,59
10,70
10,50
6,90
7,30
7,20
7,40
9,60
10,90
11,00
6,70
8,80
8,90
8,80
8,40
8,50
8,60
9,00
9,50
9,30
10,40
9,00
8,60
7,50
7,40
10,20
6,60
8,50
6,70
26,24
35,50
38,44
34,18
35,00
34,53
38,31
39,43
36,98
40,63
32,96
27,77
36,90
37,28
36,51
38,10
38,32
37,05
39,64
31,95
30,46
37,80
32,81
35,56
40,28
36,73
40,05
35,08
31,50
33,80
39,30
35,10
33,70
34,20
38,00
36,40
33,00
32,60
27,50
21,00
32,00
33,50
37,00
35,80
38,40
35,40
40,30
30,20
29,30
27,60
34,30
34,10
41,60
33,30
37,60
32,60
67,13
54,82
55,05
59,38
58,19
59,14
53,34
51,48
53,37
51,80
58,42
64,14
55,07
55,16
56,08
54,55
54,07
54,76
52,82
60,41
61,15
54,88
62,68
58,66
50,41
56,40
52,25
58,33
57,90
55,70
53,80
57,60
58,90
58,40
52,40
52,70
56,20
60,70
63,70
70,10
59,10
58,10
54,50
55,60
52,60
55,10
50,40
59,40
61,70
63,80
58,20
58,50
48,20
60,10
53,90
60,70
0/16S-V
0/16S-V
0/11S-V
0/11S-V
0/11S-V
0/11S-V
0/11S-V
0/11S-V
0/11S-V
0/11S-V
0/16S-A
0/11S-M
0/16-Vn
0/16-Vn
0/16-Vn
0/16-Vn
0/16-Vn
0/16-Vn
0/16-Vn
0/16-Vn
0/16-Vn
0/16-Vn
0/11-V
0/11-V
0/11-V
0/11-V
0/11-V
0/11-A
Note: the specified binder content exceeds 100 % of the
aggregate mixture mass.
Table 3.2. Determined composition of laboratory-prepared
asphalt samples.
Grade of mixture
0/16S-A
0/16S-A
0/22-Cs
0/16S-A
Grade of bitumen
B 50/70
B 70/100
B 50/70
67,0
67,0
67,0
67,0
67,0
67,0
67,0
67,0
67,0
67,0
67,0
67,0
67,0
67,0
67,0
67,0
67,0
67,0
67,0
67,0
67,0
67,0
B 50/70
69,4
63,7
68,8
65,1
67,1
66,6
66,3
66,0
64,2
64,7
62,8
61,5
64,9
63,7
64,8
64,3
65,5
64,4
65,6
66,6
67,3
66,5
Granite
65,8
64,3
66,6
65,2
66,4
63,8
64,6
64,5
65,4
65,3
63,4
64,4
65,1
64,3
65,0
64,2
67,6
66,6
64,6
67,3
66,2
64,7
Granite
27,0
27,0
27,0
27,0
27,0
27,0
27,0
27,0
27,0
27,0
27,0
27,0
27,0
27,0
27,0
27,0
26,0
26,0
26,0
26,0
26,0
26,0
Crushed
granite
20,7
24,8
20,6
23,8
22,1
22,8
22,7
22,4
23,6
22,8
24,5
24,5
27,4
28,5
27,5
28,1
22,3
23,7
21,9
21,1
20,7
20,9
Dolomite
By extraction
24,6
26,5
24,3
25,1
24,3
26,6
26,1
26,2
24,8
24,6
26,1
24,7
29,0
30,1
29,8
29,9
24,0
24,6
25,9
23,9
24,8
25,9
Job mix formula
6,0
6,0
6,0
6,0
6,0
6,0
6,0
6,0
6,0
6,0
6,0
6,0
6,0
6,0
6,0
6,0
7,0
7,0
7,0
7,0
7,0
7,0
By ignition
9,9
11,6
10,6
11,1
10,9
10,6
11,0
11,6
12,3
12,4
12,8
14,0
7,7
7,8
7,7
7,6
12,2
11,9
12,5
12,3
12,0
12,6
By extraction
By ignition
9,6
9,1
9,1
9,7
9,3
9,6
9,3
9,4
9,7
10,1
10,5
10,9
5,9
5,6
5,2
5,9
8,4
8,8
9,5
8,8
9,0
9,4
>2
Job mix formula
Job mix formula
3,4
3,8
4,2
4,6
5
5,4
3,4
3,8
4,2
4,6
5
5,4
3,4
3,8
4,2
4,6
3,8
4,2
4,6
5
5,4
5,8
By ignition
3,46
4,03
4,06
4,72
4,91
5,28
3,42
3,81
4,34
4,64
5,32
5,75
3,4
3,82
4,08
4,44
5,55
5,32
4,66
5,59
4,21
3,9
0,09 - 2
By extraction
By extraction
3,34
3,7
3,98
4,35
4,62
5,19
3,4
3,7
3,87
4,07
4,68
4,94
3,33
3,73
4,05
4,43
5,61
5,32
5,11
5,59
4,59
4,45
Job mix formula
Sample No.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
< 0,09
Type of aggregate
Aggregate content, % of mass
Bitumen content,
% of mass1)
By ignition
3.2. Evaluation and analysis of the results of
experimental investigations
After extraction, ignition and screening of the
samples, taken from asphalt pavement, the analysis of the
results was carried out. Tables 3.1 and 3.2 give the results
of investigations.
In the Laboratory of Road Research of the
Department of Roads of Vilnius Gediminas Technical
University the composition of 28 samples, taken from
asphalt pavement and of 22 laboratory-prepared samples
was determined. Investigations were performed by using
the extraction method with chlorinated solvent
(trichloroethylene) and the ignition method. The job-mix
formula of the samples, taken from the pavement, and a
precise grading and binder content of the laboratoryprepared samples were known.
The aim of this investigation was to evaluate the
accuracy of extraction and ignition methods as well as
their relationship. The extraction method is widely used
all over the world and in Lithuania, while the ignition
method is still new and rarely used, though it is more
effective than the extraction.
Note: the specified binder content exceeds 100 % of the
aggregate mixture mass.
After all the asphalt samples were investigated and a
statistical analysis of the results was made, the
distribution and correlation charts were presented (Fig.
3.1 - 3.8). The following correlations were obtained:
 between bitumen content – r = 0,899;
 between the fractions of aggregate < 0,09 mm - r
= 0,837;
 between the fractions of aggregate 0,09-2 mm - r
= 0,916;
 between the fractions of aggregate > 2 mm - r =
0,839.
Investigation results show that the lowest correlation
r = 0,837 is between the fractions of aggregate < 0,09
mm, the highest correlation – r = 0,916 is between the
fractions of aggregate 0,09-2 mm.
Figure 3.1 shows that the bitumen content in the
asphalt sample, determined by the ignition method, is not
always higher than that determined by the extraction
method. The difference in the bitumen content between
the ignition and extraction methods differs for all grades
of asphalt mixture.
Data in Figure 3.2 illustrates that nearly in all
samples the content of < 0,09 mm fraction of aggregate,
determined by the ignition method, is lower than that by
the extraction method. This means that part of < 0,09 mm
aggregate particles could be removed during the burning
process together with smoke and other burning products
in a disperse phase or did not stick to the filter in the
centrifuge during the extraction and was washed-out
together with trichloroethylene.
Figure 3.3 shows that nearly in all samples the
content of 0,09-2 mm fraction of aggregate, determined
by the ignition method, is higher than that by the
extraction method. This could happen because in the
burnt sample the aggregate particles of < 0,09-2 mm
fraction fused together, thus, making a larger part of 0,092 mm fraction.
Bitumen content, % of mass
7,00
6,50
6,00
5,50
By Ignition
5,00
By Extraction
4,50
4,00
3,50
3,00
0
5
10
15
20
25
30
35
40
45
50
55
Sample
Aggregate content, % of mass
Fig. 3.1. The determination bitumen content in the tested samples
16,00
14,00
12,00
By Ignition
10,00
By Extraction
8,00
6,00
4,00
0
5
10
15
20
25
30
35
40
45
50
55
Sample
Aggregate content, % of mass
Fig. 3.2. The determined content of < 0,09 mm fraction of aggregate in the tested samples
45,00
40,00
35,00
By Ignition
By Extraction
30,00
25,00
20,00
0
5
10
15
20
25
30
35
40
45
50
55
Sample
Aggregate content, % of mass
Fig. 3.3. The determined content of < 0,09-2 mm fraction of aggregate in the tested samples
70,00
65,00
60,00
By Ignition
By Extraction
55,00
50,00
45,00
0
5
10
15
20
25
30
35
40
45
50
55
Sample
Fig. 3.4. The determined content of > 2 mm fraction of aggregate in the tested samples
Fig. 3.5. Correlation of determined bitumen content in all test
samples.
Fig. 3.6. Correlation of the determined content of < 0,09 mm
fraction of aggregate in all test samples.
Fig. 3.7. Correlation of the determined content of 0,09-2 mm
fraction of aggregate in all test samples.
Fig. 3.8. Correlation of the determined content of > 2 mm
fraction of aggregate in all test samples.
Fig. 3.9. Statistical evaluation of the difference between the
bitumen value and the job mix value in all test samples.
Fig. 3.10. Statistical evaluation of the difference between the
value of < 0,09 mm fraction of aggregate and the job mix value
in all test samples.
Fig. 3.11. Statistical evaluation of the difference between the
value of 0,09-2 mm fraction of aggregate and the job mix value
in all test samples.
Fig. 3.12. Statistical evaluation of the difference between the
value of > 2 mm fraction of aggregate and the job mix value in
all test samples.
The analysis of the difference between the
investigation results and the job mix formulas gave the
values of differences. The values were subjected to the
statistical analysis and the dispersion diagrams were
obtained (Fig. 3.9 – 3.12). The diagrams show the
distribution of investigation results, obtained by using the
ignition and extraction methods.
Conclusions
Based on the overview of previous investigations and
a statistical analysis and evaluation of investigation
results the following conclusions and recommendations
could be given:
1) HMA mixtures and their components shall
correspond to the traffic and climatic conditions.
The HMA mixture production process shall be
continuously checked and subjected to the
quality control. This requires a proper sampling
of asphalt mixtures and the use of certain
methods to determine their composition;
2) The test by using the ignition method is twice as
short as the extraction method. Thus, the test is
quick and more effective. Also the ignition
method is cheaper and more safe than the
extraction method;
3) In accordance with the EU Council Directive
98/24/EC on the “Protection of the Health and
Safety of Workers from the Risks Related to
Chemical Agents at Work” it is aimed to create
the more strict conditions for using, storing and
working with chlorinated materials, therefore, in
order to use less hazardous methods, it is
necessary to conduct more comprehensive
investigations and to determine the accuracy and
reliability of the ignition method;
4) Investigation results showed that the bitumen
content after ignition of samples is not equal to
the bitumen content of extracted samples. The
difference depends on the grade of asphalt
mixture (type and grade of components). In
HMS mixtures, containing dolomite aggregate,
the bitumen content, determined by the ignition
method, is higher than that determined by the
extraction. When granite aggregate is used the
results are opposite;
5) Statistical analysis of investigation shows a
strong correlation r ≈ 0,9 between the methods.
Therefore, it could be stated that the ignition
method is as accurate as the extraction method
for the determination of asphalt content.
However, bitumen content in the burnt asphalt
samples is more scattered from the point of view
of the job mix formula, and the determined
scattering of bitumen content in the extracted
samples is very low, the average of values is
close to the bitumen content of job mix formula;
6) Statistical analysis of investigation shows that
the grading of extracted asphalt samples is less
scattered from the point of view of the job mix
formula than of the burnt samples. However, the
difference between the content of fractions and
the job mix formula in the burnt asphalt samples
is less than in the extracted samples;
7) In order to get reliable results for each grade of
the HMA mixture it is necessary to perform
additional investigations of mixture composition, to ensure the correspondence of test
sample to the job-mix formula and at least 20
tests for one grade of the mixture. In the result
the correction factors could be determined.
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