Q. ZHOU et al.: PERFORMANCE CHARACTERISTICS OF THERMOSETTING POLYURETHANE MODIFIED ASPHALT BINDER ...
595–605
PERFORMANCE CHARACTERISTICS OF THERMOSETTING
POLYURETHANE MODIFIED ASPHALT BINDER AND ITS
MIXTURES
UPORABNE LASTNOSTI TERMI^NO STABILNEGA
POLIURETANA ZA MODIFIKACIJO ASFALTNEGA VEZIVA IN
ME[ANIC
Qian Zhou
1
, Fan Yang
1,2,*
, Liming Yang
1
, Shiguang Tang
3
1
Guangxi Communications Design Group Co., Ltd., Nanning, China
2
College of Transportation Engineering, Chongqing Jiaotong University, Chongqing, China
3
Guangxi Transportation Engineering Testing Co., Ltd., Nanning, China
Prejem rokopisa – received: 2023-07-04; sprejem za objavo – accepted for publication: 2023-09-18
doi:10.17222/mit.2023.923
A new thermosetting polyurethane modified asphalt (TPUA) pavement material was developed to solve the unbalanced perfor-
mance of traditional bridge deck pavement materials. Compared with the conventional bridge deck pavement materials, this
work comprehensively evaluates the pavement performance of the TPUA binder and its mixture. The results indicate that the
TPUA binder gradually shows elastic material properties at high temperatures and has excellent deformation resistance. The
low-temperature flexibility of the TPUA binder is much better than that of SBS asphalt and epoxy asphalt (EA) binders. The
TPUA binder is a viscoelastic material at low temperatures, and its creep meets the Burgers constitutive model. Moreover, the
TPUA binder also has excellent mechanical properties and flexibility. In addition, the TPUA mixture has excellent mechanical
properties, high-temperature deformation resistance and moisture stability. Its crack resistance at room temperature and low
temperature is much better than those of SBS asphalt and EA mixture. This work will help us continue the development and per-
formance research of TPUA pavement materials.
Keywords: thermosetting polyurethane, modified asphalt, mixture, bridge deck pavement, pavement performance
Avtorji opisujejo novo vrsto s termi~no stabilnim poliuretanom modificiranega asfalta (TPUA; angl.: thermosetting polyure-
thane modified asphalt), uporabnega kot re{itev oziroma zamenjava za neuravnote`en (slabe kakovosti) konvencionalni material
za prevleke plo~nikov na mostovih. Avtorji so med seboj primerjali konvencionalni material s termi~no stabilnim
poliuretanskim vezivom modificirani material. Rezultati raziskave so pokazali, da ima termi~no stabilno poliuretansko vezivo
elasti~ne lastnosti tudi pri visokih temperaturah in posledi~no odli~no odpornost proti deformacijam. Nizko temperaturna
fleksibilnost (elasti~nost) termi~no stabilnega poliuretana je mnogo bolj{e vezivo kot so SBS asfaltna in/ali epoksidna asfaltna
(EA) veziva. TPUA je viskoelasti~ni material pri nizkih temperaturah in proces njegovega lezenja opisuje Burgerjev
konstitutivni model. Poleg tega ima TPUA odli~ne mehanske lastnosti in prilagodljivost, visoko temperaturno odpornost proti
deformacijam in stabilnost v vlagi. Njegova odpornost proti pokanju pri vseh temperaturah uporabe je mnogo bolj{a kot jo imata
SBS asfalt in EA me{anice. Izvedena raziskava bo lahko slu`ila tudi drugim raziskovalcem pri razvoju novih kvalitetnih s
termi~no stabilnim poliuretanskim vezivom modificiranih materialov za prevleke plo~nikov.
Klju~ne besede: termi~no stabilni poliuretan, modifikacija asfalta, me{anice, asfaltne prevleke plo~nikov za mostove, lastnosti
in kvaliteta plo~nikov
1 INTRODUCTION
A bridge deck pavement layer plays a role in protect-
ing a bridge deck, providing driving comfort and dispers-
ing vehicle loads, but it is one of the critical factors af-
fecting the durability of a bridge deck.
1–4
The existing
bridge deck pavement systems include poured asphalt
concrete, asphalt mastic concrete, and epoxy asphalt
(EA) concrete, which can be divided into two main cate-
gories based on the type of asphalt binders: thermoplas-
tic polymer modified asphalt
5,6
and thermosetting resin
modified asphalt.
7,8
The former is a thermoplastic mate-
rial. Although polymers (SBS, SBR, rubber powder, etc.)
can improve the viscoelasticity of asphalt, the perfor-
mance of modified asphalt is still greatly affected by
temperature. The latter is a thermosetting material, and
the representative material is EA. In China, epoxy as-
phalt concrete has been further applied to other
large-span bridges since its successful application at
Nanjing Yangtze River Second Bridge in 2000. Although
epoxy resin can significantly improve the mechanical
properties, high-temperature deformation resistance and
fatigue performance of asphalt, the EA pavement mate-
rial has poor flexibility and a high risk of cracking.
9
The
imbalance in the pavement performance of the existing
pavement materials has also led to distresses such as
cracking, pushing and rutting in the pavement layer,
which affects the durability of a bridge deck.
Thermosetting polyurethane is a polymer material
with a continuous carbamate (-NHCOO-) structure
formed by the reaction of the isocyanate group (-NCO)
Materiali in tehnologije / Materials and technology 57 (2023) 6, 595–605 595
UDK 678.664: 665.775.4 ISSN 1580-2949
Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 57(6)595(2023)
*Corresponding author's e-mail:
1452445527@qq.com (Fan Yang)

and polyol (-OH). It has excellent mechanical properties,
flexibility, high elasticity, chemical stability resistance
and other advantages. It is considered to be the next gen-
eration of asphalt modifiers and is widely researched be-
cause its molecular structure and performance are easy to
control.
10–13
Thermosetting polyurethane modified as-
phalt (TPUA) refers to a high-performance material with
a certain strength PU skeleton structure formed by add-
ing a high amount of the PU modifier into the asphalt
through a polymerization reaction. Scholars conducted
an in-depth research of the modification mechanism of
TPUA and its binder properties. Yang et al.
14
analyzed
the polymerization process and modification mechanism
of thermosetting polyurethane in asphalt and found that
small-molecule modifier monomers can undergo a poly-
merization reaction in asphalt to form a polyurethane
skeleton structure. Moreover, the isocyanate group in
polyurethane can react with the active hydrogen group in
asphalt, proving a chemical modification. Zhang et al.
15
studied the effects of the curing temperature and diluents
on the viscosity change of the TPUA system. The results
indicate that the curing temperature can significantly in-
crease the viscosity growth rate and shorten the construc-
tion reservation time of the TPUA system, while the ef-
fect of the diluent is opposite to that of the curing
temperature. In addition, it is also found that thermoset-
ting polyurethane can significantly improve the
high-temperature and mechanical properties of asphalt,
while its high-temperature rutting resistance and tensile
strength are significantly better than those of SBS modi-
fied asphalt. He et al.
16
prepared composite modified as-
phalt using thermosetting polyurethane and epoxy resin
and found that the composite modified asphalt has excel-
lent high- and low-temperature stability and waterproof
performance. Cong et al.
17
studied the polymerization
process, microstructure and macroscopic properties of
the TPUA binder. The microstructure showed that the
modifier is dispersed in the form of particles in the as-
phalt during the initial solidification stage. As the reac-
tion progresses, the modifier gradually undergoes cross-
linking and forms a network structure, while the
mechanical properties of TPUA are positively correlated
with the conversion rate of isocyanates.
Previous studies indicated that thermosetting poly-
urethane can significantly improve the mechanical prop-
erties, high-temperature deformation resistance and
low-temperature stability of asphalt. However, current
research mainly focuses on analyzing the pavement per-
formance of the TPUA binder, while exploration of the
comprehensive performance of its mixture is limited.
This work compared traditional bridge deck paving ma-
terials, analyzed the rheological properties, low-tempera-
ture flexibility, mechanical properties and crack resis-
tance of the TPUA binder and its mixture, and
Q. ZHOU et al.: PERFORMANCE CHARACTERISTICS OF THERMOSETTING POLYURETHANE MODIFIED ASPHALT BINDER ...
596 Materiali in tehnologije / Materials and technology 57 (2023) 6, 595–605
Table 1: Basic properties of asphalts
Properties
Virgin asphalt SBS asphalt
Test methods
Test value Specification Test value Specification
Penetration (25 °C, 0.1 mm) 65.1 60–80 50.2 40–60 T 0604
Softening point (°C) 48.0  46 76.3  60 T 0606
Ductility (15 °C, cm) >100  40 >100 — T 0605
Viscosity (cp, 135 °C) 226 — 926  3000 T 0625
Density (15 °C, g/cm
3
) 1.012 — 1.008 — T 0603
Table 2: Basic properties of PTMG
Molecular weight Viscosity (cp, 40 °C) Melting point (°C)
Hydroxyl value
(mgKOH/g)
Molecular structure
2000 1225 32 54.7–57.5 H-(OCH2
CH
2
CH
2
CH
2
)
n
-OH
Table 3: Basic properties of BDO
Molecular weight Density (g/cm
3
) Melting point (°C) Boiling point (°C) Molecular structure
90.12 1017 16 230 HO-CH2
CH
2
CH
2
CH
2
-OH
Table 4: Basic properties of isocyanate
NCO (%) Equivalent weight Viscosity (cp, 23 °C) Diluent Appearance
23.0 183 1200 Solvent-free Water clear
Table 5: Aggregate gradation
EA-10
Passing rate/%
13.2 9.5 4.75 2.36 1.18 0.6 0.3 0.15 0.075
Upper limit 100 100 85 70 55 40 32 23 14
Lower limit 100 95 65 50 39 28 21 14 7
Target gradation 100 99 72.1 60.9 47.7 32.7 22.8 16.4 10.7

comprehensively evaluated the pavement performance of
TPUA bridge deck paving materials.
2 EXPERIMENTAL DESIGN
2.1 Raw materials
This work used traditional SBS asphalt and epoxy as-
phalt (EA) as control groups to comprehensively evalu-
ate the pavement performance of the TPUA binder and
its mixture. The PG64-22 virgin asphalt binder was used
as the raw material for preparing TPUA in this research,
and SBS asphalt (5 % SBS) was used as the control
group, both from Shanghai Urban Construction Rili Spe-
cial Asphalt Co., Ltd. The thermosetting polyurethane
modifier system consists of polytetrahydrofuran glycol
(PTMG-2000), 1, 4-butanediol (BDO, AR) and
polyisocyanates, respectively, provided by BASF (China)
Co., Ltd. and Covestro Polymer (China) Co., Ltd. Two
component epoxy asphalt (EA) from ChemCo Systems
in the United States was also used as the control group.
The aggregates in this work are all limestone and meet
the requirements of JTG F40-2004 specifications. The
mixture gradation was selected from the commonly used
EA-10 for bridge deck pavement. The basic properties
and gradation of raw materials are shown in Tables 1–5.
2.2 Preparation
The TPUA binder used in this paper consists of com-
ponents A and B. Component A is a mixture of
PTMG-2000, BDO and virgin asphalt, while Component
B is polyisocyanate. The proportion of raw materials is
consistent with the previous research.
14
The dosage of
thermosetting polyurethane is 50 % (polyurethane:as-
phalt = 1:1). The preparation process of the TPUA mix-
ture is as follows: 1) Place the dry aggregate in a
100–110 °C oven for at least4hofinsulation; 2) Heat
component A to 100 °C and component B to 60 °C;
3) Mix components A and B evenly in proportion, then
mix them with the aggregate and form a test piece;
4) Place the test piece in a 100 °C oven for 7 h before
conducting relevant performance tests. The preparation
process is shown in Figure 1. The polymerization reac-
tion of thermosetting polyurethane involves the reaction
of isocyanate (-NCO) with hydroxyl groups (-OH) in
PTMG and BDO, as shown in Equation (1):
nOCN–R–NCO+nHO–R’–OH –(CONH–R–NHCOO – R’ – O)
n
– (1)
Component I of the EA binder is epoxy-based, and
component II is composed of the curing agent, asphalt
and additives. The preparation of the EA mixture is as
follows: 1) Heat the aggregate to 120–130 °C; 2) Heat
components I and II to 85 °C and 120 °C, respectively,
and mix them in a ratio of I:II = 1:4; 3) Mix the EA
binder with the aggregates and compact the specimens.
Place the test piece in a 120 °C oven for 4 h before con-
ducting relevant performance tests. The preparation pro-
cess is shown in Figure 1.
The preparation process of the SBS asphalt mixture
was based on the JTG E20-2011 specification. To make
the performance of the three mixtures comparable, all se-
lected mixtures had an asphalt content of 7.3 %.
2.3 Methods
2.3.1 Asphalt binder
A dynamic shear rheometer (DSR) was used to study
the high-temperature deformation resistance of SBS as-
phalt, EA and TPUA binder. Referring to ASTM D638,
tensile testing was applied to test the mechanical proper-
ties of the EA and TPUA binder. According to ASTM
D6648, the low-temperature crack resistance perfor-
mance of the three modified asphalt binders was ana-
lyzed using a bending beam rheometer (BBR), and their
low-temperature creep constitutive model was studied
based on the Burgers model. The Burgers model com-
prises the Maxwell and Kelvin models
18–20
in a series, as
shown in Figure 2.
Q. ZHOU et al.: PERFORMANCE CHARACTERISTICS OF THERMOSETTING POLYURETHANE MODIFIED ASPHALT BINDER ...
Materiali in tehnologije / Materials and technology 57 (2023) 6, 595–605 597
Figure 1: TPUA or EA mixture preparation process

The Burgers creep constitutive model is shown with
Equation (2):

  =++−
⎛ ⎝ ⎜ ⎜ ⎞ ⎠ ⎟ ⎟ ⎡ ⎣ ⎢ ⎢ ⎤ ⎦ ⎥ ⎥ −
0
112
11
1
2
2
E
t
E
e
Et
(2)
where  represents the strain,  0
represents the constant
stress, E
1
and  1
represent the elastic and viscous pa-
rameters of the Maxwell model, and E
2
and 2
represent
the elastic and viscous parameters of the Kelvin model,
respectively.
Due to the relationship between stiffness modulus
S(t, T) and creep compliance J(t, T) satisfying Equation
(3), the constitutive model of creep compliance under
constant temperature conditions is shown in Equation
(4).
21
StT
JtT
tT
(, )
(, )
,
==
⎛ ⎝ ⎜ ⎞ ⎠ ⎟ 1   (3)
J(t)
EE
e
t
Et
=+−
⎛ ⎝ ⎜ ⎜ ⎞ ⎠ ⎟ ⎟ +
−
11
1
12 1
2
2
  (4)
2.3.2 Asphalt mixture
The mechanical properties, moisture stability,
low-temperature crack resistance and other pavement
performance of the above three asphalt mixtures were
tested with reference to the JTG E20-2011 specification.
According to ASTM D8844, a semi-circular bending test
(SCB) was conducted to analyze the crack resistance
performance of the three mixtures. Firstly, a 150 mm ×
170 mm cylindrical specimen was prepared with the ro-
tary compaction method and cut into a semi-circular
specimen with a thickness of 50 mm. Secondly, a crack
with a depth of 15 mm and a width of 1.5 mm was cut at
the center of the semi-circular specimen. Finally, after
leaving the specimen at room temperature for 4 h, its
crack resistance was tested using a MTS machine at a
loading rate of 50 mm/min. The maximum tensile stress
and fracture energy were calculated as follows in Equa-
tions (5) and (6):
22,23
 t
=
4976 . F
BD
(5)
G
W
BD a
f
f
=
− (/ ) 2
(6)
Q. ZHOU et al.: PERFORMANCE CHARACTERISTICS OF THERMOSETTING POLYURETHANE MODIFIED ASPHALT BINDER ...
598 Materiali in tehnologije / Materials and technology 57 (2023) 6, 595–605
Figure 2: Burgers model
Figure 3: Variation patterns of high-temperature deformation resistance performance of different binders: a) complex modulus, b) rutting factor,
c) storage modulus, d) phase angle

where t
is the tensile strength, F is the maximum load-
ing force, B is the thickness of the specimen, D is the
diamete of the specimen, a is the depth of the incision,
G
f
is the fracture energy, W
f
is the fracture work
(WF u
f
d =
∫
) and u is the displacement at fracture.
3 RESULTS AND DISCUSSION
3.1 Performance analysis of the binders
3.1.1 High-temperature deformation resistance
The surface temperature of bridge deck pavement is
higher than that of traditional asphalt pavement under
high-temperature weather in summer, which puts for-
ward higher requirements for the high-temperature sta-
bility of bridge deck pavement materials. The rheologi-
cal properties of SBS asphalt, EA and TPUA binder were
studied using the time scanning mode within 52–88 °C.
Due to the high modulus of EA and TPUA, rheological
properties were studied using 8 mm parallel plates. The
test results are shown in Figure 3.
Figure 3a shows that the complex modulus of ther-
mosetting resin modified asphalt binders such as epoxy
asphalt and TPUA varies little with the temperature at
high temperatures. The research results of Kang et al.
24,25
also indicated that after the temperature exceeds 50 °C,
the complex modulus change curve of thermosetting
resin modified asphalt tends to be horizontal (the plat-
form zone). The main reason for the above results is that
a high dosage of thermosetting resin modifiers can form
a skeleton structure with a certain mechanical strength in
asphalt, causing the physical properties of asphalt to
change from viscoelasticity to elasticity at high tempera-
tures. On the contrary, the complex modulus of SBS as-
phalt significantly decreases with an increasing tempera-
ture. The test results of the storage modulus (Figure 3b)
also indicate that EA and TPUA binders exhibit elastic
characteristics at high temperatures, while SBS asphalt
still exhibits significant viscous characteristics.
26
The rutting factor index is often used to evaluate the
high-temperature deformation resistance of modified as-
phalt. The larger the rutting factor, the better is the
high-temperature stability. The rutting factor curves of
three asphalt binders with temperature are shown in Fig-
ure 3c. As the temperature increases, the rutting factor of
these two binders gradually increases as well. This result
is very different from that for general asphalt viscoelastic
materials. It seems to be contrary to the fact that the rut-
ting factor of traditional asphalt materials decreases with
an increase in the temperature. This is because a high
thermosetting resin content forms a continuous network
structure in asphalt, and the performance of asphalt at
high temperatures exhibits the elastic properties of modi-
fiers. From Figure 3d, it can also be concluded that the
phase angle of the EA and TPUA binder gradually de-
creases and approaches 0° with an increasing tempera-
ture. This conclusion is consistent with the research re-
sults by Zhou et al.,
27
that is, thermosetting resin modi-
fied asphalt gradually exhibits the characteristics of an
elastic material at high temperatures, and the phase angle
gradually decreases. Due to a slight change in the com-
plex modulus of thermosetting resin modified asphalt at
high temperatures and the gradual decrease in the phase
angle, the rutting factor of the EA and TPUA binder
gradually increases with temperature. In summary, the
high-temperature deformation resistance of the EA and
thermosetting resin modified asphalt binders such as
TPUA is much better than that of traditional thermoplas-
tic polymer modified asphalt, and the traditional rutting
factor indicators cannot be used to evaluate their
high-temperature deformation resistance performance.
3.1.2 Low-temperature creep performance
Studying the constitutive model of asphalt is signifi-
cant for understanding its viscoelasticity. The BBR test
was used to test the low-temperature (–24 °C) crack re-
sistance of SBS asphalt, EA and TPUA asphalt binders,
and each group included 4 samples. Based on the Bur-
gers model, the low-temperature creep constitutive mod-
els of the three modified asphalt binders were analyzed.
The experimental results are shown in Figure 4, and the
model fitting parameters are shown in Table 6.
As shown in Figure 4a, all three types of binders ex-
hibit creep under a constant stress. The stiffness modulus
of the EA binder is much higher than that of the other
modified asphalt. This is caused by the poor low-temper-
ature flexibility of epoxy resin modifiers. Table 6 shows
that the stiffness modulus of the TPUA binder is much
lower than the other two types of asphalt, indicating that
the TPUA binder has excellent low-temperature flexibil-
ity.
The Burgers viscoelastic constitutive model was used
to study the low-temperature creep characteristics of the
three asphalt binders mentioned above, as shown in Fig-
ures 4b–d. The Burgers creep model has an excellent fit-
ting effect on the creep curves of the three asphalt bind-
ers (R
2
is greater than 0.98). It is also indicated that the
three types of modified asphalt still exhibit viscoelastic
material properties at low temperatures.
24,25
Table 6
shows that the viscoelastic parameters of the EA binder
are much greater than those of the SBS asphalt and
TPUA binder, indicating that the EA binder has a larger
modulus. This conclusion was also verified with Xue’s
research,
28
showing that the viscoelastic parameters of
epoxy asphalt are significantly greater than those of the
traditional asphalt materials because epoxy resin signifi-
cantly increases the modulus of asphalt, which theoreti-
cally explains the reason for the high brittleness of epoxy
asphalt. In addition, the viscoelastic parameters of the
TPUA binder are also lower than the other two types of
asphalt binder, with the best low-temperature flexibility.
The reason is that the soft segment of the PU modifier
uses polyether polyols and theoretically its glass transi-
tion temperature is lower than –80 °C. Therefore, the PU
Q. ZHOU et al.: PERFORMANCE CHARACTERISTICS OF THERMOSETTING POLYURETHANE MODIFIED ASPHALT BINDER ...
Materiali in tehnologije / Materials and technology 57 (2023) 6, 595–605 599

modifier maintains high elasticity and flexibility at the
testing temperature.
3.1.3 Tensile mechanical properties
The thickness of a general bridge deck pavement
layer is less than 80 mm, causing greater stress on the
bridge deck pavement under load, thus also putting
higher requirements on the mechanical performance of
the bridge deck pavement.
29
SBS asphalt undergoes sig-
nificant deformation before demolding and testing due to
its soft material, resulting in inaccurate final test results.
This work only used direct tensile testing to analyze the
mechanical properties of the EA and TPUA binder, and
each group includes 5 samples. The results are shown in
Figure 5 and Table 7.
The macroscopic stretchability of polymer chains
strongly relies on the structural evolution during the
elongational flow. Different polymer chains (i.e., short
chain, long chain, very long chain, among others) play
different roles in the stretching process.
30
Figure 5 shows
that the stress-strain curves of the TPUA and epoxy as-
phalt binder are similar to those of an ideal crosslinked
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600 Materiali in tehnologije / Materials and technology 57 (2023) 6, 595–605
Figure 5: Stress-strain curves of the tensile test
Table 7: Tensile test results
EA TPUA
Strength
/MPa
Elonga-
tion
/%
Fracture
energy
/J·m
–2
Strength
/MPa
Elonga-
tion
/%
Fracture
energy
/J·m
–2
7.3 270 2.18 × 10
5
3.2 460 1.71 × 10
5
Figure 4: Change curves of the stiffness modulus and creep compliance of different binders: (a) stiffness modulus, (b) EA, (c) SBS asphalt, (d)
TPUA
Table 6: Low-temperature crack resistance and Burgers model parameters
Asphalt
Low-temperature crack resistance(60 s) Model parameters
Stiffness modulus/MPa Creep rate E1/MPa E
2/MPa  1/MPa·s  2/MPa·s R
2
EA 865 0.095 1203.9 3377.9 1152920.2 64097.2 0.989
SBS asphalt 404 0.243 771.3 985.4 175212.8 28916.3 0.998
TPUA 34 0.216 62.6 81.4 18814.8 2366.5 0.997

rubber.
31
Although the tensile strength of the TPUA
binder is lower than that of the EA binder, its elongation
at break is much higher than that of the EA binder. The
stress-strain curve of TPUA can be divided into three
stages: elastic, yield, and strengthening ones. In the elas-
tic stage, the stress-strain curve of TPUA tends to a
straight line at minor strains in accordance with Hooke’s
law. The research by Vaidya et al. shows that polymers
only meet Hooke’s law when subjected to small defor-
mations (strain less than5%orevenlo wer).
32
During the
yield stage, the strain significantly increases while the
stress slowly increases. The main reason is that the
crimped PTMG soft segments in the PU molecular struc-
ture are straightened and gradually arranged in order. At
this stage, the stress change rate with the strain is rela-
tively low. In the strengthening stage, the stress of TPUA
increases rapidly with the increase in the strain. This is
because breaking the TPUA binder requires a greater
force. When the ultimate stress is reached, the material is
destroyed. Although the tensile strength of TPUA is
lower than that of the EA binder, the difference in the
fracture energy between the two materials is not signifi-
cant. Therefore, TPUA has excellent flexibility and frac-
ture resistance.
3.2 Evaluation of asphalt mixture pavement perfor-
mance
3.2.1 Mechanical properties
The thickness of bridge deck pavement is thinner
than that of traditional pavement, causing the pavement
material to undergo greater tensile and compressive
stresses under repeated loads and temperatures. The
study investigated the mechanical properties of tradi-
tional bridge deck pavement materials and TPUA mix-
tures based on a Marshall test and splitting test, and each
group includes 4 samples. The results are shown in Fig-
ure 6.
Thermosetting resin modified asphalt (e.g., TPUA
and EA) is a composite material with a continuous skele-
ton structure formed by the polymerization reaction of
small molecule modifier monomers in the asphalt.
8,14
Traditional thermoplastic polymer modified asphalt is a
mixture with a certain network structure formed due to a
simple dispersion of polymers in asphalt. The former is a
chemical crosslinking of the modifier in asphalt, while
the latter is a physical crosslinking of the polymer.
Therefore, the strength of a thermosetting resin modified
asphalt mixture is several times higher than that of ther-
moplastic polymer modified asphalt. The research by Liu
and Wei et al.
33,34
found that the Marshall stability of an
epoxy asphalt mixture is over 50 kN. Figure 6 shows
that the mechanical properties of the TPUA mixture are
between those of SBS asphalt and EA mixture. Its Mar-
shall stability exceeds 50 kN, and its splitting strength is
greater than 2 MPa, demonstrating excellent mechanical
properties. Although the mechanical properties of the
TPUA mixture are slightly lower than those of the EA
mixture, its Marshall stability is five times that of a tradi-
tional SBS asphalt mixture, and its splitting strength is
also close to three times that of the SBS asphalt mixture,
far exceeding the mechanical performance requirements
of an asphalt mixture. Therefore, the TPUA mixture is a
high-strength paving material.
3.2.2 High-temperature stability
Due to the small thickness of bridge deck pavement
and great impact of the temperature field, it is significant
for rutting damage in high-temperature environments. It
also puts forward higher requirements for the high-tem-
perature deformation resistance of bridge deck pavement
materials. GB/T 30598-2014 requires the dynamic stabil-
ity of epoxy asphalt mixture at 60 °C to be greater than
8000 cycles/mm. JTG F40-2004 requires the dynamic
stability of the SBS asphalt mixture to be greater than
3000 cycles/mm. This paper analyzes the high-tempera-
ture stability of the TPUA mixture and its control groups
using the rutting test, and each group includes 3 samples.
The results are shown in Figure 7.
The traditional bridge deck pavement layer must
meet the requirements of a dense structure, so the con-
tent of the binder used in the pavement material is rela-
tively large. It adversely affects the high-temperature sta-
bility of traditional thermoplastic polymer modified
asphalt mixtures. As shown in Figure 7, the dynamic
stability of the SBS asphalt mixture is only 3089 cy-
cles/mm. Although it meets the pavement performance
requirements, more is needed for a bridge deck pavement
in complex environments. The dynamic stability of the
TPUA and EA mixture exceeds that of the SBS asphalt
mixture by one order of magnitude, and their rut depth is
also close to 0 mm. This also indicates that the TPUA
and EA mixture can maintain the deformation resistance
of bridge deck pavement under continuous high-tempera-
ture conditions. The reason for the above results is the
high-performance thermosetting resin modified asphalt.
Q. ZHOU et al.: PERFORMANCE CHARACTERISTICS OF THERMOSETTING POLYURETHANE MODIFIED ASPHALT BINDER ...
Materiali in tehnologije / Materials and technology 57 (2023) 6, 595–605 601
Figure 6: Mechanical properties of three asphalt mixtures

The research by Xue and Qian et al.
35,36
also indicated
that after the formation of a network structure by thermo-
setting resin modifiers, the dynamic stability of the mod-
ified asphalt mixture is higher than 10,000 cycles/mm.
The above results also reveal that the high-temperature
stability of thermosetting resin modified asphalt pave-
ment materials is much better than that of thermoplastic
polymer modified asphalt.
3.2.3 Moisture stability
At present, the distresses of a bridge deck pavement
are mostly directly or indirectly related to the moisture
stability of the pavement material. This work used the
immersion Marshall test to analyze the TPUA mixture
and its control groups, and each group includes 4 sam-
ples. The results are shown in Figure 8.
Thermosetting resins are mostly polymerized from
polar small molecule monomers, which also endows
them with strong polarity. Therefore, thermosetting res-
ins have strong adhesion to substrates, especially polar
substrates. In addition, thermosetting resins can also im-
prove the polarity of modified asphalt and its adhesion to
aggregates, thereby improving the moisture stability of
the mixture.
14,27
Qian et al.
35,36
found that the moisture
stability of a thermosetting resin modified asphalt mix-
ture is much higher than that of a traditional SBS asphalt
mixture, and its Marshall residual stability and indirect
tensile strength ratio are not less than 90 %. Figure 8
shows that the Marshall residual stability of SBS asphalt,
TPUA and EA mixtures is 88.4, 91.3 and 93.8 %, respec-
tively, much higher than the specification requirements
(not less than 80 %). After immersion, the TPUA and EA
mixtures still have a much better mechanical strength
than the SBS asphalt mixture, meeting the bridge deck
pavement’s high bearing capacity requirements. This in-
dicates that thermosetting resin modified asphalt pave-
ment materials have excellent moisture stability. The rea-
son is that thermosetting resin modifiers can form a
denser skeleton structure in asphalt and prevent water
from entering the interior of the mixture. In addition,
thermosetting resin modifiers are mostly polar materials,
able to improve the adhesion between asphalt and aggre-
gate and reduce water erosion on the cement aggregate
interface.
3.2.4 Crack resistance
Cracking distresses caused by repeated effects of
temperature fields, loads and other factors account for
over half of bridge deck pavement distresses. After being
subjected to loads and environmental factors, asphalt
pavement with existing cracks will experience stress con-
centration at the top of the cracks. If the strength and
toughness of the asphalt mixture are insufficient, cracks
will extend along the weak areas of the mixture until
they penetrate the entire road surface. Traditional fatigue
tests make evaluating the crack resistance performance
of asphalt mixtures after existing cracks difficult. ASTM
D8044 indicates using semi-circular bending (SCB) test-
ing to evaluate the cracking resistance of asphalt mix-
tures at intermediate temperatures. Gong and Jiang found
that using fracture energy indicators in SCB tests, they
can effectively evaluate the crack resistance performance
of asphalt mixtures.
22,23
Therefore, a SCB test was used
to study the crack resistance performance of TPUA and
its control group mixtures in the presence of cracks, and
each group included 4 samples. The results are shown in
Figure 9.
As shown in Figure 9a, the force of the EA mixture
significantly increases with displacement during the
loading process. The ultimate strength is reached at a
displacement of about 1 mm, and the loading force rap-
idly decreases. At this point, the specimen undergoes
brittle fracture. This result is consistent with Fan’s re-
search findings, which indicate that the EA mixture ex-
hibits strong resistance to crack initiation and weak resis-
tance to crack propagation (similar to brittle fracture).
37
On the contrary, the stress of the SBS asphalt and TPUA
mixture slowly decreases after reaching their ultimate
strength. The fracture mode is a ductile fracture. The
above results also indicate that the EA mixture has a
Q. ZHOU et al.: PERFORMANCE CHARACTERISTICS OF THERMOSETTING POLYURETHANE MODIFIED ASPHALT BINDER ...
602 Materiali in tehnologije / Materials and technology 57 (2023) 6, 595–605
Figure 8: Immersion Marshall test results
Figure 7: Rutting test results

high stiffness due to the epoxy resin modifier’s high
crosslinking density and rigid structures containing ben-
zene rings in the molecules. Figure 9b shows that the
tensile strength of the TPUA mixture is between those of
the SBS asphalt mixture and the EA mixture. However,
the fracture energy of the TPUA mixture is significantly
greater than those of the other two mixtures. Therefore,
the TPUA mixture has excellent crack resistance perfor-
mance.
3.2.5 Low-temperature flexibility
Traditional asphalt pavement materials gradually lose
their viscosity and toughness at low temperatures and ex-
hibit the brittleness and hardness of elastic materials, sig-
nificantly increasing the risk of cracking.
38
A bridge deck
pavement, especially a steel deck pavement, will experi-
ence significant deformation under load and environmen-
tal factors. At low temperatures, a steel bridge deck
pavement is more at risk of cracking. A bending creep
test was used to study the low-temperature flexibility
(–10 °C) of the TPUA mixture and control groups, and
each group included 4 samples. The results are shown in
Figure 10.
As shown in Figure 10, the bending stiffness modulus
of EA, SBS asphalt and TPUA mixtures is 8.71 × 10
3
MPa,
2.85 × 10
3
MPa, and 1.31 × 10
3
MPa, respectively, which
is consistent with the test results from Section 2.2. As the
molecular structure of the epoxy resin modifier in the EA
binder contains more benzene rings, the stiffness modu-
lus of the EA mixture is much higher than those of the
other two mixtures, reducing the low-temperature flexi-
bility of the binder. The research by Han and Qian et
al.
36,39
also indicates that the low-temperature flexibility
of epoxy asphalt mixtures is lower than that of traditional
SBS asphalt mixtures. In addition, GB/T 30598-2014 re-
quires that the low-temperature requirement for an epoxy
asphalt mixture is also relatively low, not less than
2000 με. The stiffness modulus of the TPUA mixture is
much lower than those of the other two mixtures because
there are more flexible chain segments (PTMG) in the
thermosetting polyurethane modifier, which can maintain
the flexibility even at lower temperatures. From Figure
10, it can also be seen that the TPUA mixture exhibits
excellent low-temperature crack resistance performance.
The ultimate bending and tensile strains of EA, SBS as-
phalt and TPUA mixture are 3.23 × 10
3
με, 4.82 × 10
3
με
and 9.95 × 10
3
με, respectively. The crack resistance of
the TPUA mixture is more than three times that of the
EA mixture and more than two times that of the SBS as-
phalt mixture. The reason is that the thermosetting PU
modifier has a lower glass transition temperature and
still has good ductility at low temperatures. The thermo-
setting PU modifier can significantly improve the
low-temperature stability of its modified asphalt mixture.
4 CONCLUSIONS
We studied the high-temperature deformation resis-
tance, low-temperature flexibility and mechanical prop-
erties of the TPUA binder. We comprehensively evalu-
ated the pavement performance of the TPUA mixture by
comparing it with traditional bridge deck paving materi-
als. The conclusions are as follows:
(1) The traditional rutting factor index is unsuitable
for evaluating the thermosetting resin modified asphalt
Q. ZHOU et al.: PERFORMANCE CHARACTERISTICS OF THERMOSETTING POLYURETHANE MODIFIED ASPHALT BINDER ...
Materiali in tehnologije / Materials and technology 57 (2023) 6, 595–605 603
Figure 9: SCB test results: a) force-displacement curve, b) tensile me-
chanical properties
Figure 10: Low-temperature stability test results

binder. TPUA and EA binders gradually exhibit the char-
acteristics of elastic materials under high-temperature
conditions and have excellent high-temperature deforma-
tion resistance.
(2) The TPUA mixture has excellent mechanical
properties. The Marshall stability and splitting strength
of the TPUA mixture are five times and more than three
times that of the SBS asphalt mixture, respectively. Its
dynamic stability also exceeds that of the SBS asphalt
mixture by one order of magnitude and it has excellent
high-temperature deformation resistance. The moisture
stability of the TPUA mixture is between those of the
SBS asphalt mixture and the EA mixture, which is much
higher than the standard requirements.
(3) Under low-temperature conditions, the TPUA
mixture has excellent low-temperature crack resistance
performance; its fracture energy is more than three times
that of the EA mixture and more than two times that of
the SBS asphalt mixture.
Acknowledgment
This study was sponsored by the Guangxi Science
and Technology Research Program (Gui Ke Gong
14124004-4-13) and the KeyR&DProgram of Guangxi
(GUI KE AB20159036).
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