INFLUENCE OF MINERAL FILLER ON VOLUMETRIC PROPERTIES OF HOT MIX
ASPHALT
Vivian Silveira dos Santos Bardini *
* Universidade de São Paulo, São Carlos, [email protected]
José Leomar Fernandes Júnior
Universidade de São Paulo, São Carlos, Brazil
[email protected]
Luis Miguel Gutiérrez Klinsky
Centro de Pesquisas Rodoviarias – Grupo CCR, Brazil
[email protected]
ABSTRACT: It has long been recognized the importance of the role of fillers in the hot mix asphalt (HMA)
behavior. The filler fills the voids between the coarse and fine aggregates in the mixtures and changes the
properties of asphalt binders, because it acts as an active part of the mastic. In the HMA design, the mastic
influences the lubrication of the larger aggregates particles and affects the voids in mineral aggregate, the
compaction characteristics and the optimum asphalt binder content. The HMA volumetric properties are
necessary requirements to ensure a good performance, and these properties are directly influenced by the mixture
grading, aggregates surface characteristics and compaction energy. This research evaluated the mineral filler
influence on the volumetric properties of HMA, the Voids in Mineral Aggregates (VMA) and Voids Filled with
Asphalt (VFA). HMA were prepared with an asphalt binder of 50-70 (0.1mm) penetration, varying mineral
aggregate (basalt and granite), filler type (hydrated lime, Portland cement, limestone and silica) and filler content
(0.6; 0.9 and 1.2 % in the HMA grading). The results showed that, HMA with 4% of Air Voids, the VMA and
the VFA decreases when the filler content increases and is dependent on filler content. Also, it was noted that the
optimum asphalt binder content decreases as the filler in the HMA content increases and it is greatly influenced
by the filler type.
KEY WORDS: mineral filler, hot mix asphalt, volumetric properties
1. INTRODUCTION
Years of experience has shown that the filler plays an important role in asphalt mixtures behavior. The filler fills
the voids between the coarse and fine aggregates in the mixtures and changes the asphalt binders properties,
because it acts as an active part of the mastic (combination of asphalt binder, fillers and air). The mastic quality
influences all the mechanical properties of asphalt mixtures, as well as workability. The fatigue process, a
phenomenon affected by the development and growth of micro cracks in mastic, is strongly related to the asphalt
binder characteristics, the filler properties and the physical-chemical interaction between both, which is affected
mainly by the filler fineness and features surface.
Mineral filler is a mineral material, inert to the other components of the asphalt mixture, finely divided, at least
65% passing the sieve opening of 0.075 mm square mesh. However, as a result of the small size of the particles
and their surface characteristics, the filler acts as an active material, manifested in the interface filler / asphalt
binder properties.
The mineral filler is a material consisting of mineral particles from the coarse and / or fine aggregates, employed
in the asphalt mixture or from other sources such as limestone powder, hydrated lime, Portland cement. It can
improve the rheological, mechanical, and thermal behavior and water susceptibility of asphalt mixtures. Mineral
filler, also, can be used as filling material between the spaces of the coarse and fine aggregates, modifying
workability, water resistance and aging resistance.
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Two mechanisms describe the role played by the filler in asphalt mixture: the filler provides additional points of
contact between the larger aggregates and can be considered as a continuation of the fraction of asphalt
aggregate mixture, and the filler increases the stability of the mixture by increasing the viscosity of the asphalt
binder and changing their properties. It is evident that all the fillers have two functions in the asphalt mixture,
but depending on the characteristics of the aggregate, the asphalt binder and fillers, a feature predominate [1].
In the mixture design, the mastic influences coarse aggregate lubrication and voids in mineral aggregate,
compaction characteristics and the optimum asphalt binder content. The mastic stiffness affects the resistance of
HMA to permanent deformation at high temperatures, fatigue strength at intermediate temperatures and
resistance to cracking at low temperatures.
The volumetric properties of asphalt mixtures are commonly used to ensure proper performance of pavements.
In 1915, [2] noted the importance of volumetric proportions of the components of asphalt mixtures with respect
to performance of pavements. In the 1940s, Marshall proposed the incorporation of conceptual voids volume and
degree of saturation of the voids of the mixtures by asphalt (voids filled with asphalt) for the design of asphalt
mixtures. By the 1950s, [3] spread the concept of voids in mineral aggregate, highlighting the importance of its
use to ensure pavement durability.
The volumetric properties of mixtures are the basis for the development of projects and have an important
influence on asphalt mixtures performance. The main factors that control and alter these volumetric properties
are: grain size, the volume of aggregate in the mix, the degree of compaction, the asphalt content and the type
and amount of fillers in the mixture.
This research evaluated the mineral filler influence on the volumetric properties of HMA, the Voids in Mineral
Aggregates (VMA) and Voids Filled with Asphalt (VFA). The factorial experiment was designed to evaluate the
factors that can influence hot mix asphalt volumetric properties, such as: type of aggregate, type and content of
mineral filler.
2. LITERATURE REVIEW
2.1 Importance of Volumetric Properties in Asphalt Mixtures
Currently, the volumetric properties of asphalt mixtures are subdivided and classified as primary and secondary
volumetric parameters [4]. The primary volumetric parameters are directly related to the relative volumes of the
individual components of the mixtures: air voids (Vv); aggregates volume (Vs), and asphalt binder volume (Vb).
It is important to consider that the aggregate cavities porous (pore space) and the asphalt portion absorbed share
the same space. It means that the sum of the volumes (Vb + Vs) is larger than their combined volumes (Vb + s).
This phenomenon leads to a subdivision of the primary volumetric parameters:
 Effective binder volume (V be): volume of asphalt not absorbed by the aggregate;
 Absorbed binder volume (V ba): volume of asphalt absorbed into the external pore structure of the
aggregates;
 Effective volume of aggregate (V se): aggregate volume including the volume of pores permeable to
water and the volume of pores permeable to the asphalt;
 Bulk volume of aggregate (V sb): aggregate volume that includes volume permeable porous to water but
not to the asphalt;
 Apparent volume of aggregate (V sa) only the solid volume of the aggregate excluding the volume of
permeable pores to water or asphalt.
Secondary volumetric parameters (or volumetric properties of mixtures) are Void Volume (Vv), Voids in
Mineral Aggregates (VMA) and Voids Filled with Asphalt (VFA), that are determined based on the primary
volumetric parameters. Conceptually, these parameters can be defined as:
 Void volume (Vv): is the air volume (Var) between the aggregate particles surrounded by the film of
asphalt, expressed as a percentage of the total volume of the compacted mixture;
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

Voids in Mineral Aggregates (VMA): is the sum of the void volume (Vv) and volume effective asphalt
(VEAC), expressed as a percentage of the total volume of the compacted mixture;
Voids Filled with Asphalt (VFA): is the degree of VMA filled by asphalt, expressed in percentage.
The methods commonly used in asphalt mixtures design incorporate volumetric criteria, which is calculated
from the volumetric proportions of the constituent materials of the mixtures. The Marshall and Superpave
methods [5], determine the optimum asphalt binder using HMA volumetric properties (Vv, VMA and VFA). The
Superpave method also evaluates the filler content in the mixture and the percentages of initial and maximum
compaction as a function of the number of gyrations in the Superpave Gyratory Compactor (SGC).
The asphalt mixtures are expected to be stable enough to prevent permanent deformations, flexible enough to
delay fatigue cracks development and durable to resist traffic action, weather and time. To achieve optimum
performance properties, it must be established a balance between the skeletal structure formed by aggregates and
asphalt binder amount added to the mix. The mixture should be formed by aggregates sizes, shapes, angularity
and surface textures that allow enough space for the addition of the adequate amount of asphalt to ensure
durability and flexibility of the mixture.
The Superpave method [5] suggests the volumetric parameters of Vv, VMA and VFA to design of asphalt
mixtures. It is established a Vv of 4% as the main parameter to select the optimum asphalt binder content.
Excessive Vv or VFA and inadequate VMA suggest potential durability problems. Also, insufficient Vv or
excessive VFA indicate potential rutting. Superpave Method establishes minimum values of VMA (Table 1),
based on the mixture Nominal Maximum Size (NMS) and minimum and maximum values of the VFA, based on
traffic volume (Table 2).
Table 1. Minimum VMA recommended [5]
Mixture Nominal
Minimum
Maximum Size (NMS) VMA
(mm)
(%)
9,5
15
12,5
14
19,0
25,0
37,5
13
12
11
Table 2. VFA criteria [5]
Traffic
Design VFA
(ESALs)
(%)
5
<3 x 10
70 - 80
>3 x 105
65 - 78
< 1 x 108
65 - 75
8
65 - 75
< 1 x 10
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3. MATERIALS
This research used granite aggregates, from Quarry St. Jerome, located in Valinhos / SP - Brazil, and basaltic
aggregates, from Bandeirantes Quarry, located in São Carlos / SP - Brazil. The aggregates properties were
determined using specific gravity and water absorption of coarse aggregate [6] and specific gravity and water
absorption of fine aggregate [7]. Table 3 summarizes the aggregates properties results.
Table 3. Aggregates physical properties
Coarse 1 Coarse 2 Fine
Mineral Filler
Test
Apparent specific gravity (g/cm3)
2.965
2.976
3.068
2.853
Bulk specific gravity (g/cm3)
2.828
2.810
2.844
-
Water Absorption (%)
1.635
1.986
2.570
-
Apparent specific gravity (g/cm3)
2.635
2.622
2.661
Bulk specific gravity (g/cm3)
2.601
2.567
2.487
-
Water Absorption (%)
0.496
0.815
2.627
-
Basaltic
aggregate
Granite
aggregate
The aggregate gradation was determined using that recommended by the Superpave method [8], through a series
of sieves: 0.075 mm, 0.15 mm, 0.30 mm, 0.60 mm, 1.18 mm, 2.36 mm; 4.75 mm, 9.5 mm, 12.5 mm, 19.0 mm
and 25.0 mm. Table 4 shows aggregates gradation.
Sieve Size
(mm)
25
19
12.5
9.5
4.75
2.36
1.18
0.6
0.3
0.15
0.075
Table 3. Aggregate gradation
Coarse 1
Coarse 2 Fine
Coarse 1
100
84.89
9.47
0.85
0.00
0.00
0.00
0.00
0.00
0.00
0.00
Basaltic
100
100
100
100
28.15
0.00
0.00
0.00
0.00
0.00
0.00
100
100
100
100
96.60
66.16
43.29
30.99
23.81
15.85
10.39
100
100
25.55
8.49
0.00
0.00
0.00
0.00
0.00
0.00
0.00
Coarse 2
Fine
Granite
100
100
100
99.2
32.86
2.24
0.40
0.00
0.00
0.00
0.00
100
100
100
100
98.00
75.00
55.00
40.00
29.00
17.00
9.60
It was used an asphalt binder of 50-70 (0.1mm) penetration (AC 50/70), fabricated by Betunel S.A., located in
Ribeirão Preto/ SP – Brazil. Table 4 presents the asphalt binder characteristics.
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Table 4. Characterization of the AC 50/70 asphalt binder.
Method
Property
Specification Result
Unit
ASTM
Penetration
D5
50 a 70
50
0,1 mm
Softening Point
D 36
46 min
48.6
°C
Brookfield Viscosity @ 135°C D 4402
274 min
377
cp
Brookfield Viscosity @150°C D 4403
112 min
187
cp
Brookfield Viscosity @177°C D 4404
57 a 285
69
cp
Silica powder, hydrated lime (CHIII), lime powder and Portland cement were used as fillers in HMA. The
specific gravity of the fillers was determined according to [9], and the results are shown in Table 5. Pinnila [10]
established a relationship between filler type and specific surface, which is also shown in Table 5.
Table 5. Physical properties of mineral fillers
Specific Gravity
Specific Surface,
Mineral Filler
3
(g/cm )
(cm2/g) (1)
2.635
2500 – 3500
Silica Powder
2.749
2800 – 3500
Lime Powder
2.350
5000 - 15000
Hydrated Lime
3.030
2200 – 2750
Portland Cement
(1)
Pinnila (1965)
4. METHOD
Factors described in Table 6 were used in a factorial experiment to assess their influence in HMA volumetric
properties. Three aggregate gradations (Table 7) were composed varying the filler content, according to
Superpave specification, i.e., attending the control points and according to the recommendation of avoiding the
restricted zone. Gradations passing above the restriction zone were chosen, as recommended by Bardini [11], to
satisfactorily reach a Vv of 4%.
Factors
Aggregate type
Asphalt Binder type
Filler type
Filler Content
Table 6. Independent variables or factors
Factors Levels
2 (basaltic and granite)
1 (50/70)
4 (Portland cement, Hydrated lime, limestone powder, silica powder)
3 (2,5; 5,0; 7,5)
The viscosity of 1.7 Poises and 2.8 Poises was established to define the mixing and compaction temperatures,
respectively. Aggregates gradation of HMA specimens was individually prepared. After asphalt binder addition
and mixing, samples were maintained for two hours at compaction temperature to simulate short term aging and
ensure the asphalt binder absorption by the aggregates.
Superpave volumetric mix design [5] was used to obtain optimum asphalt binder content. The initial, design, and
maximum number of gyrations used were 8, 100, and 160, respectively which represent a design traffic level (20
year) of 3-30 million ESALs. Compaction was carried out to Nmaximum to determine optimum asphalt content (4
percent voids), and for the volumetric characterization, compaction was carried out to Ndesign.
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Table 7. Aggregate gradations
Sieve Size
(mm)
25
19
12.5
9.5
4.75
2.36
1.18
0.6
0.3
0.15
0.075
Percent Passing
100 100 100
95 95 95
85 85 85
75 75 75
55 55 55
40 40 40
30 30 30
21 21 21
16 16 16
10 10 10
2.5
5.0
7.5
The first property to be determined is the bulk specific gravity (Gmb) of the sample after determining the weight
in air and the weight submerged in water (Equation 1).
Equation 1
where:
Gmb: bulk specific gravity;
WD: dry weight (g);
Wsub: weight submerged in water (g).
The theoretical maximum specific gravity (DMT or Gmm), or Rice specific gravity, is the ratio of the weight in
air of a unit volume of an non compacted bituminous mixture at a stated temperature to the weight of an equal
volume of gas-free distilled water at a state temperature (Equation 2).
Equation 2
where:
Gmm: maximum specific gravity if mixture;
A: sample dry weight (g);
D: kitassato weight filled with water, in function of the temperature (g);
E: set of kitassato, water and sample weight (g).
The air voids (Vv) is obtained from Equation 3.
(
)
Equation 3
where:
Vv: air voids (%).
VMA is obtained from Equation 4 and 5.
(
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Equation 4
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Equation 5
where:
VMA: voids in mineral aggregate (%);
Pb: asphalt content;
Ρagg: aggregate specific gravity;
ρwater: water specific gravity = 1 g/cm3;
VEAC: void volume filled by asphalt binder (%).
The VFA is obtained from Equation 6.
Equation 6
where:
VFA: voids filled with asphalt (%).
5. RESULTS
Figure 1, Figure 2 and Figure 3 shows the optimum asphalt binder content, the VMA and the VFA, respectively,
of HMA composed by granite (a) and basalt (b). The optimum asphalt content was determined to reach 4% of
Vv, as well as all specimens were prepared to evaluate the volumetric properties.
HMA with Vv of 4% showed that as the filler content increases, the VMA and the VFA increases. Also, was
noted that the filler type influenced these parameters. The optimum asphalt binder content decreased as the filler
content increased, and was greatly influenced by the filler type.
Aggregate type influenced either the optimum asphalt content, the VMA and the VFA. It was noted that the
mixtures composed by the basalt had higher values of the volumetric properties. HMA with hydrated lime
showed the lowest optimum asphalt content, maybe due to the higher specific surface of this filler, which can
result in a large surface activity.
(a)
(b)
Figure 1. Optimum asphalt binder content: (a) granite (b) basalt
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(a)
(b)
Figure 2. Voids in Mineral Aggregates (VMA): (a) granite (b) basalt
(a)
(b)
Figure 3. Voids Filled with Asphalt (VFA): (a) granite (b) basalt
A factorial experiment was performed to investigate the effect of the type and amount of filler and type of
aggregate on the volumetric properties. The Analysis of Variance (ANOVA) was used to assess the influences of
each factor. Factorial experiment data is summarized in Table 8, the ANOVA values are summarized in Table 9,
and the response of influent factors is shown on Table 10. It was assumed f0 values considering α = 0.05, if
F0>f0, the factor is influent, but if F0<f0, the factor is not influent.
It can be concluded that the type of aggregate and filler content influenced all the volumetric parameters and the
type of filler influenced the optimum asphalt content and the VFA only if the α=0.10. Table 10 shows that
optimum asphalt content is the more influenced parameter by the filler content.
6. CONCLUSIONS
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The volumetric properties of asphalt mixtures are a fundamental requirement for HMA projects, to achieve good
performance of the pavement in the field. This paper studied filler type and content influence in HMA
volumetric parameters.
HMA with Vv of 4% showed that the VMA and the VFA decreases as the filler content increases. Lower values
of VMA and VFA usually represent thin asphalt film. Thus, can be affirmed that using higher amounts of filler,
leads to HMA with thinner asphalt film, which could be detrimental for mixture durability. It was noted that
aggregate type influenced the volumetric properties. HMA composed by basalt aggregate had the higher values
of VMA, VFA and optimum asphalt binder content.
The factorial experiment result, performed using ANOVA, showed that the filler content is the factor that
influences the most the volumetric parameters. Also was verified that type of filler does not influence the HMA
volumetric parameters.
basalt
granite
Table 8. Volumetric parameter data to analysis of variance experiment
Type of
Filler Optimum Asphalt
VMA (%) VFA (%)
filler
content
Binder (%)
2.5
4.65
14.42
72.50
hidrated
5.0
4.10
13.98
71.14
lime
7.5
4.00
13.89
71.20
2.5
4.80
14.56
72.91
limestone
5.0
4.05
13.93
71.22
7.5
3.75
13.92
68.09
2.5
4.75
14.49
72.83
Portland
5.0
4.35
14.24
71.36
cement
7.5
4.00
13.86
71.14
2.5
4.50
13.99
74.20
silica
5.0
4.40
14.40
70.76
7.5
4.00
13.86
71.14
2.5
4.80
14.61
72.73
hidrated
5.0
4.50
14.26
72.30
lime
7.5
4.44
14.22
72.18
2.5
4.80
14.59
72.59
limestone
5.0
4.37
14.21
71.40
7.5
4.10
13.88
71.50
2.5
4.90
14.66
72.63
Portland
5.0
4.75
14.56
72.45
cement
7.5
4.30
13.74
74.35
2.5
5.00
14.76
72.89
silica
5.0
4.60
14.39
72.19
7.5
4.20
14.07
71.51
Table 9. ANOVA data summary
F0
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f0
f0
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Optimum Asphalt Binder
VMA
VFA
(=0.05)
(=0.10)
33.47
7.15
7.61
4.26
2.93
2.83
0.20
2.54
3.01
2.33
63.59
20.04
9.43
3.4
2.54
0.21
0.74
1.63
0.56
0.58
1.41
0.69
5.00
1.76
3.01
3.4
2.51
2.33
2.54
2.04
A
(Type of aggregate)
B
(Type of filler)
C
(Filler content)
AB
AC
BC
Factor
Table 10. Factors and interaction influence
Response
A
(Type of aggregate)
B
(Type of filler)
C
(Filler content)
AB
AC
BC
Optimum Asphalt Binder
VMA
VFA
Yes
yes
yes
No
no
no
Yes
yes
yes
No
No
No
no
no
no
no
no
no
ACKNOWLEDGEMENT: The authors thank the Brazilian promoting agency CNPQ ("National Counsel of
Technological and Scientific Development") for the PhD scholarship given.
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[1]
[2]
[3]
[4]
[5]
[6]
[7]
[8]
[9]
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American Society for Testing and Materials. Philadelphia.
ASTM 188 (2009) Standard Test Method for Density of Hydraulic Cement. American Society for
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2013 IJPC Paper 156-1
2013 IJPC − International Journal of Pavements Conference, São Paulo, Brazil Page 10
[10] Pinnila, A. (1965) “O sistema fíler-betume, algumas considerações sobre sua importância nas
misturas densas” Conselho Nacional de Pesquisa. Instituto de Pesquisas Rodoviárias.
[11] Bardini, V S S (2008) “Estudo de viabilidade técnica da utilização de cinzas da queima da casca
de Pinus em obras de pavimentação asfáltica” Thesis (master's degree) – School of Engineering
of São Carlos, University of São Paulo.
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2013 IJPC − International Journal of Pavements Conference, São Paulo, Brazil Page 11