TYPE Original Research

PUBLISHED 03 March 2023

DOI 10.3389/fmats.2023.1151479

Durability behavior of asphalt

OPEN ACCESS mixtures in regard to material
EDITED BY
Zhanping You,
Michigan Technological University,
properties and gradation type
United States

REVIEWED BY Tonggeng Ji 1, Peiwen Hao 2*, Hongwei She 1, Kai Yang 3,

Hui Yao,
Beijing University of Technology, China
Hongxiang Li 2, Dong Wang 3, Rui Kang 1 and Jingwen Liu 2
Tao Ma, 1
Henan Airport Group Co, LTD, Zhengzhou, China, 2School of Highway, Chang’an University, Xi’an, China,
Southeast University, China 3
Northwest Civil Aviation Airport Construction Group Co, LTD, Xi’an, China
Ke Zhang,
Fuyang Normal University, China

*CORRESPONDENCE
Peiwen Hao,
superpave@163.com The main objective of this study is to compare the differences between different
SPECIALTY SECTION
gradation types of mixtures (stone matrix asphalt (SMA), large stone asphalt (LSA),
This article was submitted stone asphalt concrete (SAC), and superior performing asphalt pavements
to Structural Materials, (Superpave)) and conventional dense-graded mixtures (asphalt concrete (AC)) in
a section of the journal
Frontiers in Materials
terms of resistance to rutting, moisture damage, low-temperature cracking, and
water permeability. The paper reports a study of the effect of different asphalt
RECEIVED 26 January 2023
ACCEPTED 15 February 2023 binders on the performance of asphalt mixtures. The experimental results
PUBLISHED 03 March 2023 demonstrated that the gradation types had a significant effect on the
CITATION
engineering performance of asphalt mixtures. SMA20, SAC20, and
Ji T, Hao P, She H, Yang K, Li H, Wang D, LSA30 exhibited lower rutting potential than AC20. In addition, SAC20 had a
Kang R and Liu J (2023), Durability larger stripping ratio, while AC13 had a smaller stripping ratio. The stone matrix
behavior of asphalt mixtures in regard to
material properties and gradation type. asphalt displayed the largest failure strain, while the SAC had the smallest, and
Front. Mater. 10:1151479. Superpave ranged between SMA and SAC. SAC20 had the maximum permeability
doi: 10.3389/fmats.2023.1151479 coefficient, followed by SMA20 and AC20, and Superpave20 had the smallest. The
COPYRIGHT nominal maximum aggregate sizes significantly affected the resistance to
© 2023 Ji, Hao, She, Yang, Li, Wang, Kang
permanent deformation, resistance to low-temperature cracking, and moisture
and Liu. This is an open-access article
distributed under the terms of the sensitivity of the asphalt mixtures. Styrene–butadiene–styrene (SBS)-modified
Creative Commons Attribution License asphalt was found to significantly improve the performance of asphalt mixtures
(CC BY). The use, distribution or
compared with ordinary asphalt.
reproduction in other forums is
permitted, provided the original author(s)
and the copyright owner(s) are credited KEYWORDS
and that the original publication in this
journal is cited, in accordance with asphalt mixture, gradation, SMA, LSA, SAC, Superpave, characteristics
accepted academic practice. No use,
distribution or reproduction is permitted
which does not comply with these terms.
1 Introduction
As trucks have become larger and operation frequency has increased in recent years, the
wheel loads and tire pressures have exceeded the bearing capacity of traditional pavement. As
a result, rutting, deformation, and fatigue cracking of flexible pavements are becoming more
prevalent. Investigations have revealed that asphalt concrete does not have sufficient
durability against heavy loads, which is affected by several factors such as properties of
aggregates and asphalt, asphalt content, and environmental conditions (Izzo et al., 1997;
Kandhal and Mallick, 2001; Ma et al., 2017; Ding et al., 2019; Zhu et al., 2020).
Road engineers and researchers are always looking for new solutions to address this
problem. They have found that modification of asphalt binders can moderately improve the
performance of hot mix asphalt (HMA). In particular, the introduction of polymers into the
asphalt matrix increases its high-temperature viscosity, which contributes to the resistance of
HMA to rutting during hot weather. Some specific types of polymer-modified asphalt are
also able to reduce the stiffness of HMA at low-temperature. However, the investigations

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Ji et al. 10.3389/fmats.2023.1151479

have confirmed that modification of asphalt alone cannot the aggregate are more important to the performance of the
completely resolve serious rutting and cracking distress in mixture. The SHRP gradation specification contains a restriction
pavements (Kandhal and Mallick, 2001; Mokhtari and Nejad, 2012). zone to avoid the bulge close to 0.6 mm in the gradation curve
Pavement engineering scholars have found that the properties (the control point of the restriction zone is determined by the
and gradation types of mineral aggregates can significantly affect the nominal maximum size of the aggregate). According to the
mechanical strength (resilient modulus and tensile strength) and Superpave specification, any gradation that passes above or
engineering performances (permanent deformation, low- below the restriction zone but within the relevant control
temperature cracking, and moisture sensitivity) of hot mix points is expected to produce a good performance mixture
asphalt mixtures (Sebaaly et al., 1997). Furthermore, it is (Kandhal and Cooley, 2001).
beneficial to adjust the gradation composition of the aggregate to Dense-graded asphalt concrete (AC) is composed of aggregates,
improve the performance of asphalt pavements while not changing mineral powders, and asphalt binders, where the aggregate particles
the source and type of aggregate (Park et al., 2022). HMA mixtures are continuously graded and interlocked. The void ratio of dense-
are classified into five main categories based on gradation: stone graded asphalt concrete after compaction is less than 10% (Fang
matrix asphalt (SMA), stone asphalt concrete (SAC), large stone et al., 2019; Ferreira et al., 2020; Khasawneh and Alsheyab, 2020).
asphalt (LSA), superior performing asphalt pavements (Superpave), Many scholars have studied the influence of characteristics,
and conventional dense-graded asphalt concrete (AC) (Fang et al., gradation, and nominal maximum size of aggregate on the
2019; Ferreira et al., 2020; Khasawneh and Alsheyab, 2020; mechanical behavior and engineering performance of mixtures
Devulapalli et al., 2022). using methods based on different theories. Most findings
SMA was developed in Germany in the 1960s. It is a indicated that the aggregate gradation has a significant impact on
deformation-resistant, durable paving material for heavily the resistance to rutting and permanent deformation of asphalt
trafficked roads. SMA has been used as a durable asphalt pavements (Kandhal and Mallick, 2001; Ferreira et al., 2020;
pavement option for city streets and highways in Europe, Khasawneh and Alsheyab, 2020; Lira et al., 2021; Zhu et al.,
Australia, the United States, and Canada. SMA has a high 2021; Devulapalli et al., 2022; Park et al., 2022).
content of coarse aggregates that are interlocked to form a However, previous studies have focused on a specific gradation
stone skeleton that resists permanent deformation. The stone type, such as dense-graded asphalt concrete (DGAC), stone matrix
skeleton is filled with a mastic consisting of asphalt and filler, asphalt (SMA), and asphalt-treated base (ATB), and mainly vary the
into which fibers are incorporated to impart sufficient asphalt aggregate gradations by varying the proportion of different sizes of
stability and inhibit the loss of binder during transport and aggregates through different calculation methods (Zhu et al., 2021;
placement. A typical SMA composition consists of 70%–80% Devulapalli et al., 2022). Little attention has been paid to the
coarse aggregate, 8%–12% filler, 6.0%–7.0% binder, and 0.3% differences between the performance of mixtures composed of
fibers. Engineering practices in Europe have proven SMA to be different gradation types and nominal maximum aggregate sizes
more durable and resistant to rutting than dense-graded mixes when their properties, specifications, and sources are the same. In
(Mogawer and Stuart, 1994; Mokhtari and Nejad, 2012; addition, the effect of different asphalt binders on the properties of
Devulapalli et al., 2022). asphalt mixtures consisting of different nominal maximum
Stone asphalt concrete (SAC) is a gap-graded HMA that is aggregate sizes (with the same gradation type) has not been
similar to a stone matrix asphalt (SMA) but tends to be more of a clarified. Therefore, the main objectives of this study were to
dense-graded mixture and is primarily designed to eliminate the comparatively investigate the differences in terms of resistance to
requirement for expensive modified binders or fibers. Fairly good rutting, water damage, low-temperature cracking, and water
stone-to-stone contact is achieved by the structural skeleton permeability for different mixture gradation types (SMA, LSA,
formed by the coarser aggregates. The increased stone-to- SAC, Superpave, and AC). The study also evaluated the effect of
stone contact is intended to provide greater rutting resistance. different asphalt binders on the mixture performance.
SAC mixes have a higher binder content than dense-graded
mixes, thus providing a thicker asphalt film. The thicker
asphalt film should resist moisture damage and aging better 2 Materials and methods
than conventional mixtures (Liu, 2011).
Large stone asphalt (LSA) is defined as an aggregate with a 2.1 Materials
maximum size of more than 25 mm. The use of a large stone mixture
could minimize or eliminate the rutting of heavy-duty asphalt Two types of binder were used in the study: a base asphalt with
pavement (Abdulshafi et al., 1999). penetration ranging from 60 to 80 (labeled as Pen 60/80) and a
Superpave mixtures originated from a new mix design system styrene–butadiene–styrene (SBS)–polymer-modified asphalt binder
proposed by the Strategic Highway Research Program (SHRP) (labeled as SBS MA) from KLMY Petroleum INC. The Pen 60/
that includes asphalt binder specifications for performance 80 binder was used in this study to evaluate the effect of aggregate
classification and a series of advanced mixture tests. In gradation and nominal maximum aggregate size on the pavement
addition, the system focuses on binder characteristics, performance of the HMA mixture, and the SBS MA was used to
aggregate quality, and gradation. SHRP binder specifications investigate the effect of different binder types on the performance of
are used to characterize asphalt properties related to rutting the HMA mixture. The properties of binders are provided in Table 1.
and cracking; however, the binder is only a relatively minor To achieve the objectives of this study, the midpoint values of
component of the HMA. Therefore, the quality and gradation of different gradation curves were selected as representative of different

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TABLE 1 Properties of binders.

Item Unit Asphalt binders

Pen 60/80 SBS MA

Penetration (25 °C) 1/10 mm 73 64

Softening point °C 47 64

Ductility (15 °C) cm >140 92

Solution % 99.8 —

3
Density g/cm 1.034 1.028

Thin film oven aging (163 °C, 5 h) Loss ratio % 0.02 0.01

Penetration ratio % 64.4 82.7

The coarse and fine aggregates in the study were limestone, while the filler was limestone powder. The technical indexes of aggregates are listed in Table 2.

TABLE 2 Technical indexes of aggregates.

Category Apparent specific gravity (g/cm3) Absorption (%) Los Angeles abrasion (%) Robustness (%)
Coarse aggregates 20–30 mm 2.709 0.61 16.3 8.4

10–20 mm 2.723 0.57 11.7 6.3

5–13 mm 2.716 0.65 13.2 5.6

3–5 mm 2.713 1.24 14.8 3.7

Fine aggregates Crushed stone 2.740 1.76 - 2.1

Coarse sand 2.626 1.17 - 2.9

Fine sand 2.639 1.58 - 3.9

Filler 2.710 - - -

TABLE 3 Aggregate gradation of asphalt mixtures.

Sieve size (mm) Aggregate gradation

AC13 AC20 SMA20 SAC20 SUPER20A SUPER20B LSA30

37.5 - - - - - - 100

26.5 - 100 100 100 100 100 95

19 - 97.5 97.5 97.5 95 95 -

16 100 - - 86 - - -

13.2 97.5 82.5 82.5 74.5 - - 68

9.5 - - 58.5 - - -

4.75 62.5 55 35 35 - - 44

2.36 42.5 42.5 27.5 26.5 33 38 32

1.18 - - - 20 20 30 -

0.6 24 24 - 16 15 22 -

0.3 15.5 15.5 16.5 13.5 11 15 11

0.15 11 11 - 11.5 - - -

0.075 6 6 10.5 8 4 5 4

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TABLE 4 Requirements for the Marshall design method. 2.2 Asphalt mixture preparation and tests
Item Unit Requirement Note
2.2.1 Asphalt mixture preparation
Blows times 75 (with 4.5-kg hammer) - Engineering practice has confirmed that the Marshall
112 (with 10.2-kg LSA30
volume design method has the advantages of simplicity and
hammer) efficiency (MOT, 2011). To exclude the differences in mixes
performance due to different preparation methods, the optimum
Stability kN >8.8 -
asphalt content of the asphalt mixes in this study was
>19.6 LSA30 determined using the standard Marshall method. It should be
Flow value 1/ 20–40 - noted that the SMA20 mixture required the addition of SBS-
10 mm modified asphalt with 0.4% (by weight of the mixture) fiber.
30–60 LSA30
Table 4 show the specific requirements (MOT, 2004) of the
Air void content % 2–5 - Marshall design method and the parameters of different asphalt
mix volume indexes, respectively.
Voids filled with % 75–85 -
asphalt (VFA) Figure 1 shows that the dense-graded mixture AC and
SUPER20 have higher stability and lower flow values than
SMA20 and SAC20. As for AC mixtures, the optimum asphalt
gradation types, where the nominal maximum aggregate size was content decreased with the increase of nominal maximum aggregate
selected as 20 mm (AC20, SMA20, SAC20, and Superpave20 (noted size, which is mainly attributed to the fact that the finer the
as SUPER20)). In addition, the nominal maximum aggregate size aggregate, the larger its specific surface area, the more asphalt
was set to 30 mm (i.e., LSA30), considering that the maximum content it adsorbs, and the thicker the asphalt film on the
nominal aggregate size of LSA mixtures should not be less than aggregate surface. The LSA30 mixture has the lowest voids filled
25 mm. A group of dense-graded asphalt mixtures (AC13) was with asphalt (VFA), which is related to a larger air void and lower
added to compare and analyze the effect of different asphalt binders asphalt content. Meanwhile, the AC13 mixture presented higher
and nominal maximum aggregate size on the mixture performance. voids in mineral aggregate (VMA) value than the other mixtures,
The various gradation types are shown in Table 3. resulting in a higher asphalt content for the AC13 mixture.

FIGURE 1
Volume parameters and optimum asphalt content of asphalt mixtures: (A) density, (B) mashall stability and flow, (C) air voids content, (D) voids in
mineral aggregates, VMA (E) voids filled with asphalt, VFA, and (F) optimum asp halt content.

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FIGURE 2
Dynamic stability versus gradation types under different tire pressures: (A) 0.7 MPa and (B) 1.44 MPa.

2.2.2 Asphalt mixture tests 150 kPa (24 h) and 500 kPa (24 h) for water pressure and 20 °C for
Wheel tracking tests were conducted on all the mixtures based on temperature.
JTG E20-2011 (MOT, 2011). The AC13, AC20, SMA20, SAC20, and
SUPER20 mixture samples were prepared at 300 mm length, 300 mm
width, and 50 mm thickness, while the samples of LSA30 were 3 Experimental results and discussions
prepared at 300 mm length, 300 mm width, and 10 cm thickness.
The test temperature was 60 °C with a tire pressure of 0.7 MPa and 3.1 Wheel tracking tests
1.44 MPa. Dynamic stability (DS) is used as an indicator of the high-
temperature rutting resistance of asphalt mixtures. The larger the DS of The effect of gradation types on the rutting resistance of asphalt
the asphalt mixture, the better the mixture’s ability to resist high- mixtures with different tire pressures is illustrated in Figure 2. The
temperature permanent deformation. experimental results indicated that different gradation types of
A moisture damage test was conducted on all the mixtures based mixtures exhibited distinct high-temperature rutting resistance
on JHA3-7-4 (Japan Road Association, 1996). The test temperature potential.
was 60 °C in the water. Mixture samples (500 mm in length, 300 mm When the nominal maximum aggregate size was set to 20 mm
in width, and 50 mm in thickness) were tested for 6 h by the and the tire pressure was 0.7 MPa, as shown in Figure 2A, the best
immersion water wheel tracking test. The stripping ratio (SA) rutting resistance (maximum dynamic stability) was obtained for
can be calculated as follows: both the SMA and SAC mixtures, which was mainly attributed to the
Sb large amount of coarse aggregates in the gradation forming a stable
SA
, (1) skeletal structure, thus improving the resistance to permanent
Sa + Sb
deformation (rutting) of the asphalt mixture (Devulapalli et al.,
where Sa represents the non-stripping area in cm2, and Sb is the 2022). The dynamic stability of SUPER20A is slightly greater than
stripping area in cm2. The larger the SA value, the better the that of SUPER20B, which was due to the larger proportion of coarse
resistance to water damage and the lower the water sensitivity of aggregate in the former. AC20 has the least dynamic stability
the asphalt mixture. because, on one hand, the higher fraction of fine aggregate in the
Three-point bending tests were carried out to evaluate the low- gradation absorbed more free asphalt, and on the other hand, the
temperature cracking resistance performance of the asphalt mixture. synthetic gradation of coarse and fine aggregates formed a
In the study, samples with 250 mm length, 30 mm width, and suspended dense structure in the asphalt mixture. The
35 mm thickness were prepared, and the test was carried out LSA30 mixture has the largest nominal maximum aggregate size
at −10°C with a loading rate of 50 mm/min (MOT, 2011). and the highest coarse aggregate content. Meanwhile, the aggregates
Bending stress, failure strain, and stiffness were employed to can contact and embed each other to achieve greater structural
characterize the low-temperature cracking resistance performance stability, so its mixture has the best rutting resistance.
of the HMA mixture. Obviously, the higher the failure strain and A comparative analysis of the dynamic stability of AC13 and
bending stress, the better the low-temperature crack resistance of the AC20 mixtures revealed that the high-temperature rutting resistance
asphalt mixture. of the mixture was positively proportional to the nominal maximum
The permeability test was conducted according to JIS A aggregate size. In other words, the dynamic stability of AC20 was
1218–1990 (Japan Road Association, 1996). Test conditions were significantly higher than that of AC13 because the former contained

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thickness, which led to a larger stripping ratio. Compared to the

SAC20 mixture, the proportion of coarse aggregate in the
SUPER20 mixture was slightly lower, while the SMA mixture
showed the best resistance to moisture damage due to the
presence of fibers, which fixed more asphalt and formed a
thicker asphalt film (Devulapalli et al., 2022). Despite the higher
fine aggregate content and the greater asphalt film thickness in the
AC20 mixture, its dense suspension structure had difficulty
supporting the repeated operation of the test wheel and exhibited
a lower level of moisture damage. The stripping ratio dramatically
increased when a larger size aggregate such as LSA30 was employed,
which was mainly attributed to the greater void content and coarse
aggregate percentage within the mixture. The stripping ratio of the
AC13 mixture was minimal due to the lesser void ratio.
Comparing AC13 and AC20, it was found that the stripping
ratio of the mixture increased with the increasing nominal
maximum aggregate size. In other words, the larger the nominal
maximum aggregate size, the higher the moisture damage and the
worse the water stability. In a word, the aggregate gradation types
FIGURE 3 and nominal maximum aggregate sizes significantly affected the
Stripping ratio versus gradation types.
resistance of the mixture to moisture damage.

3.3 Three-point bending tests

more large-size aggregates and formed a certain skeletal structure
that was able to resist the potential permanent deformation (Fang Figure 4 plots the results of beam bending tests of mixtures with
et al., 2019). different gradation types at −10 °C. Normally, the higher the failure
The tire pressure was elevated to 1.44 MPa, as shown in stress and failure strain and the lower the fracture stiffness of asphalt
Figure 2B. Similar to Figure 2A, the LSA30 mixture has the mixtures, the better its low-temperature cracking resistance.
largest dynamic stability, followed closely by SAC20, SMA20, It can be seen from Figure 4A that when the nominal maximum
SUPER20, and AC20, and the smallest was AC13. It should be aggregate size was constant, the failure stresses of mixtures with
noted that the dynamic stability of SAC20 was slightly superior to different gradation types were quite similar (except for the SMA
that of SMA20 at higher tire pressure, although contact or an mixture). Even if the nominal maximum particle size was adjusted to
aggregate skeleton had been achieved for both gradations. This 13 mm or 30 mm, the failure stresses of mixtures with different
outcome is mainly because the internal void content of the gradation types were almost the same. In other words, the effect of
SAC20 mixture (2.9%) was lower than that of the gradation type on the low-temperature failure stresses of the
SMA20 mixture (3.6%), so the former has less space for the mixtures was not significant, which might be explained by the
mixture to deform at high tire pressure. Thus, the synergistic capability of the embedded structure of coarse
SAC20 mixture presented better anti-rutting performance. aggregate and the asphalt mastic to resist the bending and tensile
The aforementioned analysis revealed that aggregate gradation loads.
significantly affected the high-temperature rutting resistance of the Figure 4B confirms that the effect of aggregate gradation type on
mixture, and the more coarse aggregate content in the gradation and the failure strain of the mixture was more pronounced. Specifically,
the larger the nominal maximum particle size, the better the high- when the nominal maximum aggregate size was retained at 20 mm,
temperature resistance of the mixture to permanent deformation. the SMA20 mixture presented the maximum failure strain, while the
failure strains of SAC20 and AC20 mixtures were smaller, and that
of the SUPER20 mixture was between SMA20 and SAC20. This
3.2 Wheel tracking tests under immersion in phenomenon can be explained by the fact that the SMA mixture has
water a thicker effective asphalt film compared with AC20, SAC20, and
SUPER20. The LSA30 mixture has the lowest low-temperature
The results of wheel tracking tests of mixtures with different failure strain, which was associated with a lower asphalt content.
gradation types under water immersion are presented in Figure 3. In addition, when the same dense-graded mixture, such as AC, was
When the nominal maximum aggregate size was fixed at 20 mm, employed, the failure strain of the mixture decreased with increasing
the order of stripping ratio of the asphalt mixture was as follows: nominal maximum aggregate size. In other words, the mixture with
SAC > SUPER > AC > SMA. It is generally believed that the thicker a higher percentage of coarse aggregates (AC20) experienced worse
the asphalt film wrapped around the aggregate, the lower the resistance to low-temperature cracking, owing to the lesser amount
moisture damage suffered by the mixture. Obviously, the higher of asphalt and the thinner effective asphalt film.
coarse aggregate content and relatively low specific surface area in It can be seen from Figure 4C that the variation of the failure
SAC20 resulted in less asphalt coating and reduced asphalt film stiffness of the mixture was almost opposite to the failure strain at

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FIGURE 4
Low-temperature cracking parameters versus gradation types: (A) failure stress, (B) failure strain, and (C) failure stiffness.

the failure stiffness of the mixtures was determined by the

combination of failure stress and failure strain. The failure
stiffness of the AC20 mixture was slightly higher than that of the
AC13 mixture.
The aforementioned analysis suggested that the aggregate
gradation type and nominal maximum aggregate size would
significantly affect the failure strain of the mixture, but the
mechanism of its effect on the failure stress and failure stiffness
has yet to be clarified.

3.4 Water permeability test

Figure 5 shows the permeability coefficients for the different

gradation types of mixtures. For the mixture with a nominal
maximum aggregate size of 20 mm, SAC20 had a much higher
permeability coefficient than the other types of mixtures. AC20 and
SUPER20 obtained a smaller permeability coefficient, while
FIGURE 5 SMA20 was between SUPER20 and AC20. This phenomenon
Permeability coefficient versus gradation type.
would be interpreted as follows: SAC20 contained more coarse
aggregates and formed a structural skeleton through stone-to-
stone contact. Therefore, more air voids may have been
constant nominal maximum aggregate size. The failure stiffness of generated between the structural skeleton during the hot mix
the SMA20 mixture was less than that of SAC20, SUPER20, and asphalt mixture forming process, which eventually led to the flow
AC20. It is worth noting that the failure stiffness of SUPER20 was of water through the voids and yielded a larger water permeability
not between SMA20 and SAC20 as expected. This is mainly because coefficient. AC20 has a suspended dense structure with fewer

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FIGURE 6
Rutting and cracking resistance of mixtures with different asphalt binders: (A) dynamic stability and (B) failure strain.

internal voids, while SMA20 and SUPER20 have a thicker asphalt resistance of the dense-graded mixes more significantly, which
film, which makes it difficult for water to penetrate through the was mainly attributed to the excellent elasticity and flexibility of
mixture. For the LSA30 mixture, more coarse aggregates formed the the polymer SBS. When the temperature was high, the viscosity of
skeleton and created more voids that could not be filled with a small the SBS-modified asphalt was much higher than that of the
amount of asphalt; thus, it had the largest permeability coefficient. conventional base asphalt, which effectively prevented the asphalt
Furthermore, when the aggregate gradation type was the same, from flowing. In addition, the excellent elasticity of SBS enabled the
such as AC, increasing the nominal maximum aggregate size would asphalt mixture to deform and recover moderately after wheel
significantly enlarge the water permeability coefficient of the loading, reducing the amount of permanent deformation and
mixture because as the particle size increased, the internal voids thus improving the high-temperature rutting resistance of the
of the mixture gradually increased, and water penetrated more mixture. At the same time, the excellent flexibility of SBS-
easily. Consequently, both the type of aggregate gradation and modified asphalt allowed it to withstand greater bending and
the nominal maximum aggregate size affected the permeability tensile deformation at low-temperature, thus improving the low-
performance of the mixture. temperature cracking resistance of the mixture.

3.5 The effect of asphalt binders 4 Conclusion

Figure 6 presents the effect of different asphalt binders on the On the basis of laboratory test results and analysis, the following
high-temperature rutting resistance and low-temperature cracking conclusions were drawn.
resistance of the mixtures. Figure 6A shows that the SBS-modified
asphalt imparted greater dynamic stability to the mixture when the • Dense-graded mixtures AC20 and SUPER20 exhibited greater
aggregate gradation was the same (AC). For AC13, the dynamic stability and smaller flow values than SMA20 and SAC20.
stability of the mixture increased sharply from 969 to 6,300, an When the gradation type was fixed, the optimum asphalt
increase of 550%, when the asphalt binder was adjusted from content of the mixture decreased with increasing nominal
ordinary base asphalt (Pen 60/80) to SBS-modified asphalt (SBS maximum aggregate size.
MA). This change also was applicable to AC20. • Wheel tracking tests confirmed that better high-temperature
Figure 6B demonstrates that the SBS-modified asphalt was also rutting resistance was obtained for SMA20 and SAC20,
able to significantly improve the low-temperature failure strain of followed by SUPER20 and AC20. For the AC mixtures, the
the mixture, thus enhancing the low-temperature cracking rutting resistance of the asphalt mixtures increased with the
resistance of the mixture. Similarly, the failure strain of the increase in nominal maximum aggregate size.
AC13 mixture increased rapidly from 0.00471 to 0.00643, an • Wheel tracking tests with water immersion showed that
enhancement of nearly 37%, as the asphalt binder was changed SAC20 possessed a larger stripping ratio, while AC20 had
to SBS-modified asphalt. less moisture damage. LSA30 and AC13 yielded the largest
The aforementioned variations in mixture performance and smallest stripping ratios, respectively. The moisture
confirmed that SBS-modified asphalt significantly improved the sensitivity of the mixtures increased with increasing nominal
high- and low-temperature performance of the mixtures. In maximum aggregate size when the gradation types were
particular, SBS MA enhanced the high-temperature rutting the same.

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• The three-point bending test illustrated that SMA20 obtained Author contributions
the maximum low-temperature failure strain (best low-
temperature cracking resistance). SAC20 had the least failure TJ: acquisition of data; PH and JL: revised the manuscript
strain, while SUPER20 was between SMA20 and SAC20. critically for important intellectual content; HS and KY: analysis
LSA30 had the worst low-temperature performance. For of data; HL: drafted the manuscript; DW and RK: acquisition of
dense-graded mixtures, the low-temperature performance data.
decreased with increasing nominal maximum aggregate size.
• The permeability tests showed that when the nominal
maximum aggregate size was the same, the permeability Conflict of interest
coefficient was the highest for SAC20, followed by
SMA20 and AC20, and the lowest for SUPER20. For the Authors TJ, HS and RK were employed by Henan Airport Group
AC mixtures, the permeability coefficient increased with Co, LTD. Authors KY and DW were employed by Northwest Civil
increasing nominal maximum aggregate size. Aviation Airport Construction Group Co, LTD.
• Compared with the common base asphalt (Pen 60/80), SBS- The remaining authors declare that the research was conducted
modified asphalt improved both the high-temperature rutting in the absence of any commercial or financial relationships that
resistance and low-temperature cracking resistance of dense- could be construed as a potential conflict of interest.
graded asphalt mixtures. In particular, it was more effective in
enhancing the high-temperature performance of the mixtures.
Publisher’s note
Data availability statement All claims expressed in this article are solely those of the authors and
do not necessarily represent those of their affiliated organizations, or
The original contributions presented in the study are included in those of the publisher, the editors, and the reviewers. Any product that
the article/supplementary material; further inquiries can be directed may be evaluated in this article, or claim that may be made by its
to the corresponding author. manufacturer, is not guaranteed or endorsed by the publisher.

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