Degradation of Mechanical Properties of Graphene Oxide Concrete under Sulfate Attack and Freeze–Thaw Cycle Environment

Abstract

In this paper, firstly, the effects of graphene oxide on the mechanical properties of concrete were investigated. Secondly, the degradation and mechanism of the mechanical properties of graphene oxide concrete (GOC) under sulfate attack and a freeze–thaw environment were investigated. In addition, the dynamic modulus of elasticity (MOEdy) and uniaxial compressive strength (UCS) of the GOC were measured under different environmental conditions. According to the test results, the incorporation of graphene oxide in appropriate admixtures could improve the mechanical properties of concrete in these two working environments. It is worth noting that this effect is most pronounced when 0.05 wt% graphene oxide is incorporated. In the sulfate attack environment, the MOEdy and UTS of the GOC0.05% specimen at 120 cycles decreased by 22.28% and 24.23%, respectively, compared with the normal concrete specimens. In the freeze–thaw environment, the MOEdy and UTS of the GOC0.05% specimen at 90 cycles decreased by 13.96% and 7.58%, respectively, compared with the normal concrete specimens. The scanning electron microscope (SEM) analysis showed that graphene oxide could adjust the aggregation state of cement hydration products and its own reaction with some cement hydration crystals to form strong covalent bonds, thereby improving and enhancing the microstructure density.

Full text

Citation: Qian, J.; Zhou, L.-Q.; Wang,
X.; Yang, J.-P. Degradation of
Mechanical Properties of Graphene
Oxide Concrete under Sulfate Attack
and Freeze–Thaw Cycle Environment.
Materials 2023,16, 6949. https://
doi.org/10.3390/ma16216949
Academic Editor: Carlos Leiva
Received: 19 September 2023
Revised: 12 October 2023
Accepted: 17 October 2023
Published: 29 October 2023
Copyright: © 2023 by the authors.
Licensee MDPI, Basel, Switzerland.
This article is an open access article
distributed under the terms and
conditions of the Creative Commons
Attribution (CC BY) license (https://
creativecommons.org/licenses/by/
4.0/).
materials
Article
Degradation of Mechanical Properties of Graphene Oxide
Concrete under Sulfate Attack and Freeze–Thaw
Cycle Environment
Ji Qian , Lin-Qiang Zhou, Xu Wang and Ji-Peng Yang *
State Key Laboratory of Mountain Bridge and Tunnel Engineering, Chongqing Jiaotong University,
Chongqing 400074, China; jiqian@cqjtu.edu.cn (J.Q.); 611220080025@mails.cqjtu.edu.cn (L.-Q.Z.)
*Correspondence: yangjp@cqjtu.edu.cn
Abstract:
In this paper, firstly, the effects of graphene oxide on the mechanical properties of con-
crete were investigated. Secondly, the degradation and mechanism of the mechanical properties of
graphene oxide concrete (GOC) under sulfate attack and a freeze–thaw environment were investi-
gated. In addition, the dynamic modulus of elasticity (MOE
dy
) and uniaxial compressive strength
(UCS) of the GOC were measured under different environmental conditions. According to the test
results, the incorporation of graphene oxide in appropriate admixtures could improve the mechanical
properties of concrete in these two working environments. It is worth noting that this effect is most
pronounced when 0.05 wt% graphene oxide is incorporated. In the sulfate attack environment,
the MOE
dy
and UTS of the GOC
0.05%
specimen at 120 cycles decreased by 22.28% and 24.23%, re-
spectively, compared with the normal concrete specimens. In the freeze–thaw environment, the
MOE
dy
and UTS of the GOC
0.05%
specimen at 90 cycles decreased by 13.96% and 7.58%, respectively,
compared with the normal concrete specimens. The scanning electron microscope (SEM) analysis
showed that graphene oxide could adjust the aggregation state of cement hydration products and its
own reaction with some cement hydration crystals to form strong covalent bonds, thereby improving
and enhancing the microstructure density.
Keywords:
graphene oxide concrete; sulfate attack; freeze–thaw cycle; mechanical property; scanning
electron microscope
1. Introduction
Concrete is a versatile building material used for construction over the last few decades.
It is made by mixing cement, water, and other materials. On the one hand, to achieve
recycling and reuse, some academics have mixed waste materials (such as waste marble
powder [
1
], coal gangue [
2
], and molybdenum tailings [
3
], etc.) from industrial processes
into the fundamental components of concrete to protect the environment and meet required
criteria. On the other hand, the addition of fibers to concrete is becoming increasingly
popular to enhance the mechanical properties of the concrete. There are many different
types of fibers available today, such as glass fiber [
4
], carbon fiber [
5
], basalt fiber [
6
], steel
fiber [
7
], etc., that have been employed in a wide range of civil applications. Compared with
the ordinary fiber, they have good integration with the construction and help in transferring
the load as well as improving the physical and mechanical performance of the mixture
materials [
8
]. The addition of all graphene and carbon fiber improves the properties of the
concrete in several ways [9].
Cement is widely used in construction projects as the primary constituent of concrete
and mortar. Nevertheless, the presence of brittle cracking defects in concrete and mortar
results in a reduction in their ultimate compressive strength (UCS) and dynamic modu-
lus of elasticity (MOE
dy
) as well as the loss of the internal alkaline environment [
10
,
11
].
Materials 2023,16, 6949. https://doi.org/10.3390/ma16216949 https://www.mdpi.com/journal/materials

Materials 2023,16, 6949 2 of 16
Recently, the burgeoning field of nanomaterial research has prompted an increasing num-
ber of researchers to investigate methods to improve the performance characteristics
(such as mechanical property, durability, and long-term performance) by incorporating
nanomaterials [12,13].
The utilization of nanotechnology in construction presents a cer-
tain degree of complexity [
14
]. Specifically, carbonaceous nanomaterials, nanometals and
metal oxides, and inorganic nanomaterials are the primary nanomaterials currently in-
corporated into concrete, with particular emphasis on graphene oxide as a noteworthy
subject of investigation in the field of nanomaterials in recent times [
15
–
17
]. As shown in
Figure 1, graphene oxide, as a derivative of graphene, exhibits both exceptional strength
and flexibility as well as a substantial specific surface area. Furthermore, the presence of
oxygen-containing functional groups on the surface of graphene oxide enables its disper-
sion in water and enhances its hydrophilicity [
18
]. This property has a significant impact
on the formation of hydration products, as it facilitates the interweaving and penetration of
these products into a uniform and dense microstructure. Consequently, this process leads
to a significant reduction in the occurrence of internal defects, ultimately improving the
strength, toughness, and durability of cement composites [19,20].
Materials 2023, 16, x FOR PEER REVIEW 2 of 17
of elasticity (MOE
dy
) as well as the loss of the internal alkaline environment [10,11].
Recently, the burgeoning field of nanomaterial research has prompted an increasing
number of researchers to investigate methods to improve the performance characteristics
(such as mechanical property, durability, and long-term performance) by incorporating
nanomaterials [12,13]. The utilization of nanotechnology in construction presents a certain
degree of complexity [14]. Specifically, carbonaceous nanomaterials, nanometals and
metal oxides, and inorganic nanomaterials are the primary nanomaterials currently
incorporated into concrete, with particular emphasis on graphene oxide as a noteworthy
subject of investigation in the field of nanomaterials in recent times [15–17]. As shown in
Figure 1, graphene oxide, as a derivative of graphene, exhibits both exceptional strength
and flexibility as well as a substantial specific surface area. Furthermore, the presence of
oxygen-containing functional groups on the surface of graphene oxide enables its
dispersion in water and enhances its hydrophilicity [18]. This property has a significant
impact on the formation of hydration products, as it facilitates the interweaving and
penetration of these products into a uniform and dense microstructure. Consequently, this
process leads to a significant reduction in the occurrence of internal defects, ultimately
improving the strength, toughness, and durability of cement composites [19,20].
(a) (b)
Figure 1. Molecular structure of graphene and graphene oxide. (a) Graphene; (b) Graphene oxide.
Lv et al. [21] investigated the effect of graphene oxide nanosheets on the
microstructural and mechanical properties of cement composites. The results showed that
the incorporation of graphene oxide nanosheets resulted in the modulation of flower-like
crystal formation and a significant improvement in both tensile and flexural strength of
the cement-based materials. Similarly, Indukuri et al. [22] used scanning electron
microscopy (SEM) and X-ray diffraction (XRD) analysis to determine the properties of
cement composites. Then, the influence of graphene oxide on the microstructure and
reinforcing capacity of cement composites containing fly ash and silica fume was
investigated. Jiang et al. [23] investigated the effect of incorporating polyvinyl alcohol
(PVA) fibers and graphene oxide on the mechanical properties, durability, and
microstructure of cement-based materials. The results showed that the incorporation of
both PVA fibers and graphene oxide resulted in a significant improvement in the
mechanical strength and durability of the cement-based materials, exceeding the
performance of control specimens. In addition, Chintalapudi et al. [24] provided a
comprehensive compilation of various studies that reported the enhancement of
compressive strength in graphene oxide specimens. Gong et al. [25], Pan et al. [26], and
Duan et al. [27] have also shown that the incorporation of graphene oxide in cementitious
composites and mortars has a positive influence on their mechanical properties. The
application of GO in concrete can improve the mechanical properties and durability of the
concrete, and it can obtain beer economic benefits under certain additive amount and
use conditions [28,29]. Therefore, the application of GO in concrete has been widely paid
aention to and studied, and it has been applied in many kinds of concrete structures and
Figure 1. Molecular structure of graphene and graphene oxide. (a) Graphene; (b) Graphene oxide.
Lv et al. [
21
] investigated the effect of graphene oxide nanosheets on the microstruc-
tural and mechanical properties of cement composites. The results showed that the incor-
poration of graphene oxide nanosheets resulted in the modulation of flower-like crystal
formation and a significant improvement in both tensile and flexural strength of the cement-
based materials. Similarly, Indukuri et al. [
22
] used scanning electron microscopy (SEM) and
X-ray diffraction (XRD) analysis to determine the properties of cement composites. Then,
the influence of graphene oxide on the microstructure and reinforcing capacity of cement
composites containing fly ash and silica fume was investigated. Jiang et al. [
23
] investigated
the effect of incorporating polyvinyl alcohol (PVA) fibers and graphene oxide on the me-
chanical properties, durability, and microstructure of cement-based materials. The results
showed that the incorporation of both PVA fibers and graphene oxide resulted in a signifi-
cant improvement in the mechanical strength and durability of the cement-based materials,
exceeding the performance of control specimens. In addition,
Chintalapudi et al. [24]
pro-
vided a comprehensive compilation of various studies that reported the enhancement of
compressive strength in graphene oxide specimens. Gong et al. [
25
], Pan et al. [
26
], and
Duan et al. [
27
] have also shown that the incorporation of graphene oxide in cementitious
composites and mortars has a positive influence on their mechanical properties. The ap-
plication of GO in concrete can improve the mechanical properties and durability of the
concrete, and it can obtain better economic benefits under certain additive amount and
use conditions [
28
,
29
]. Therefore, the application of GO in concrete has been widely paid
attention to and studied, and it has been applied in many kinds of concrete structures and
components, such as bridges, tunnels, subways, water conservancy projects, buildings, and
other fields [30–32].

Materials 2023,16, 6949 3 of 16
Sulfate attack has been identified as a prominent factor contributing to the reduced
durability of concrete [
33
,
34
], with documented cases of damage due to sulfate attack
in coastal regions. Degradation of the mechanical properties of concrete due to freeze–
thaw damage in civil engineering practice in cold climates is recognized as the primary
factor [35,36]. Therefore, the development of high-performance concrete is of great impor-
tance in various engineering applications. Yang et al. [
37
] used long-term immersion and
dry–wet cycling as simulation methods to investigate the corrosion resistance of structures
immersed in seawater or groundwater for long periods of time or structures frequently
exposed to dry–wet processes. The results of their tests showed that the incorporation of
graphene oxide in concrete can significantly improve its corrosion resistance coefficient.
This improvement can be attributed to the presence of 3CaO
·
2SiO
2·
3H
2
O (abbreviated as
C-S-H) within the internal structure of the specimens. Similarly, Cheng et al. [
38
] inves-
tigated the durability performance of concrete specimens exposed to both sulfate attack
and dry–wet cycles. The results of their study demonstrated that the recently established
integral area of sulfate ion distribution effectively served as an appropriate indicator for
characterizing the non-uniform degradation patterns observed in sulfate-attacked concrete.
In addition, they presented a novel approach, which is based on homogenization theory,
for predicting the extent of deterioration in compromised concrete structural elements.
Mohammed et al. investigated the effect of graphene oxide on concrete properties through
tests that showed that graphene oxide had improved resistance to chloride ion attack and
to water permeability [
39
]; they also demonstrated that graphene oxide could refine the
pore structure of cementitious materials, making them highly freeze–thaw resistant [40].
There is little research on the durability of GOC with respect to sulfate attack and
freeze–thaw cycles. Because graphene oxide nanomaterials have a significant impact on
the long-term mechanical properties and durability of structures in construction projects,
it is imperative to investigate the degradation patterns and mechanisms that affect the
mechanical properties of GOC in various corrosive environments. The adoption of such
an approach is of immense importance in order to obtain a thorough understanding of
the performance of this novel material and its use in the construction of structures. The
primary objective of this work is to investigate the effect of graphene oxide nanomaterials
on the mechanical properties of concrete, with a particular focus on the degradation
of the mechanical properties of GOC in two corrosive environments (sulfate attack and
freeze–thaw
cycle) during its service life. The influence of different levels of graphene oxide
incorporation on the mechanical properties of the specimens exposed to the environment
was studied using SEM analysis of the microstructure of the concrete.
2. Materials and Experiment
2.1. GOC Material
The specimens were meticulously prepared according to the guidelines of GB/T 50081-
2019 [
41
]. The dimensions of the specimens adhered to the standardized dimensions of
100 mm
×
100 mm
×
100 mm. The GOC specimens were composed of a combination of
complex Portland cement, multilayer graphene oxide dispersion (from Suzhou Tanfeng
Graphene Technology Co., Ltd., Suzhou China), aggregates (including crushed stone (from
Chongqing Hexin Building Materials Co., Ltd., Chongqing, China) for coarse aggregates
and manufactured sand (from Chongqing Hexin Building Materials Co., Ltd., Chongqing,
China) for fine aggregates), and water.
(1)
Complex Portland cement
All the indexes (fineness, stability, mechanical properties, etc.) of P.C. 42.5 (from
Huaxin Cement Co., Ltd., Chongqing, China) complex Portland cement meet the require-
ments of GB175-2020 [
42
]. The compressive strength at 3 d and 28 d is not less than 15 MPa
and 42.5 MPa, respectively. Its chemical composition is shown in Table 1.

Materials 2023,16, 6949 4 of 16
Table 1. The chemical components of the P.C. 42.5.
Components CaO SiO2Al2O3Fe2O3MgO K2O SO3Na2O TiO2P2O5MnO . . .
Percentage (%) 65.32 21.48 4.12 3.22 2.82 0.93 0.68 0.47 0.19 0.10 0.06 . . .
(2)
Multilayer graphene oxide dispersion
The multilayer graphene oxide was subjected to freezing, drying, and dispersing using
the modified Hummers method [
43
]. The resulting product showed no precipitation and
easy dispersion. The dispersion of graphene oxide appeared as a black oily liquid with a
concentration of 10 mg/mL. The parameters and components of graphene oxide are shown
in Table 2.
Table 2. The physical parameters and chemical components of graphene oxide.
Specification Contents
Physical parameters
Purity >95 wt%
Thickness 3.42–7.82 nm
Layers 0.79 nm
Specific surface area 130–260 m2/g
Lamellar diameter 12–40 µm
Chemical components
C 69.26%
O 30.16%
S 0.28%
Si 0.16%
Cl 0.11%
The microstructures of the graphene oxide sheet were investigated using scanning
electron microscopy (SEM) (from Thermo Fisher Scientifi, Waltham, MA, USA) and trans-
mission electron microscopy (TEM) (from Thermo Fisher Scientifi, Waltham, MA, USA), as
shown in Figure 2. Figure 2a shows a thin sheet, revealing the substantial specific surface
area possessed by graphene oxide. Figure 2b shows the presence of numerous folds on the
surface of the graphene oxide sheet.
Materials 2023, 16, x FOR PEER REVIEW 4 of 17
requirements of GB175-2020 [42]. The compressive strength at 3 d and 28 d is not less than
15 MPa and 42.5 MPa, respectively. Its chemical composition is shown in Table 1.
Table 1. The chemical components of the P.C. 42.5.
Components CaO SiO
2
Al
2
O
3
Fe
2
O
3
MgO K
2
O SO
3
Na
2
O TiO
2
P
2
O
5
MnO …
Percentage (%) 65.32 21.48 4.12 3.22 2.82 0.93 0.68 0.47 0.19 0.10 0.06 …
(2) Multilayer graphene oxide dispersion
The multilayer graphene oxide was subjected to freezing, drying, and dispersing
using the modified Hummers method [43]. The resulting product showed no precipitation
and easy dispersion. The dispersion of graphene oxide appeared as a black oily liquid
with a concentration of 10 mg/mL. The parameters and components of graphene oxide are
shown in Table 2.
Table 2. The physical parameters and chemical components of graphene oxide.
Specification Contents
Physical parameters
Purity >95 wt%
Thickness 3.42–7.82 nm
Layers 0.79 nm
Specific surface area 130–260 m
2
/g
Lamellar diameter 12–40 μm
Chemical components
C 69.26%
O 30.16%
S 0.28%
Si 0.16%
Cl 0.11%
The microstructures of the graphene oxide sheet were investigated using scanning
electron microscopy (SEM) (from Thermo Fisher Scientifi, Waltham, MA, USA) and
transmission electron microscopy (TEM) (from Thermo Fisher Scientifi, Waltham, MA,
USA), as shown in Figure 2. Figure 2a shows a thin sheet, revealing the substantial specific
surface area possessed by graphene oxide. Figure 2b shows the presence of numerous
folds on the surface of the graphene oxide sheet.
(a) (b)
Figure 2. SEM and TEM images of the multilayer graphene oxide sheet. (a) SEM image; (b) TEM
image.
Figure 2.
SEM and TEM images of the multilayer graphene oxide sheet. (
a
) SEM image; (
b
) TEM image.
(3)
Concrete aggregates
The GOC specimens use a coarse aggregate consisting of crushed stone graded
5–20 mm
, while the fine aggregate consists of mechanism sand with the specifications
shown in Table 3.

Materials 2023,16, 6949 5 of 16
Table 3. The particle gradation of fine aggregates.
Nominal diameter (mm) 0 0.15 0.3 0.6 1.18 2.38 4.72
Accumulated sieve residue (%) 100 89.34 74.98 52.96 37.45 18.76 0.96
2.2. Experiment
It should be noted that the specimens were cured at a pool with a constant temperature
around 20
±
1
◦
C for 28 days, and were taken out 15 min before the test. The main procedure
of the test in this paper is shown in Figure 3.
Materials 2023, 16, x FOR PEER REVIEW 5 of 17
(3) Concrete aggregates
The GOC specimens use a coarse aggregate consisting of crushed stone graded 5–20
mm, while the fine aggregate consists of mechanism sand with the specifications shown
in Table 3.
Table 3. The particle gradation of fine aggregates.
Nominal diameter (mm) 0 0.15 0.3 0.6 1.18 2.38 4.72
Accumulated sieve residue (%) 100 89.34 74.98 52.96 37.45 18.76 0.96
2.2. Experiment
It should be noted that the specimens were cured at a pool with a constant
temperature around 20 ± 1 °C for 28 days, and were taken out 15 min before the test. The
main procedure of the test in this paper is shown in Figure 3.
Figure 3. Testing process.
2.2.1. Specimen Preparation
The GOC specimens used in the test were prepared with a water–cement ratio of 0.50
and a sand content of 35%. Before the test, graphene oxide dispersions with different mass
ratios (0, 0.02, 0.05, 0.08, 0.11, 0.14, and 0.17 wt%) were first mixed with water. The concrete
mixture was prepared according to the proportions shown in Table 4 and then poured
into triple 100 mm × 100 mm × 100 mm molds. Subsequently, the marked specimens were
placed in a curing room and subjected to standard conditions for the specified time. All
procedures followed the guidelines specified in GB/T50082-2019 [44].
Table 4. Test design and mixture proportion (kg/m
3
).
Specimen Cement
Manufactured
Sand
Crushed Stone Water Graphene Oxide
5–10 mm 10–20 mm
GOC
0%
398 623 450 734 195 0
GOC
0.02%
398 623 450 734 195 0.08
GOC
0.05%
398 623 450 734 195 0.199
GOC
0.08%
398 623 450 734 195 0.318
GOC
0.11%
398 623 450 734 195 0.437
GOC
0.14%
398 623 450 734 195 0.556
GOC
0.17%
398 623 450 734 195 0.675
2.2.2. Test Situation
(1) Basic test
For the basic test, the parameter of interest was the incorporation of graphene oxide
at levels of 0, 0.02, 0.05, 0.08, 0.11, 0.14, and 0.17 wt%. The curing time of the specimens
was set at 28 days. The GOC
0.02%
indicates that the specimen contains 0.02 wt% graphene
oxide.
Figure 3. Testing process.
2.2.1. Specimen Preparation
The GOC specimens used in the test were prepared with a water–cement ratio of 0.50
and a sand content of 35%. Before the test, graphene oxide dispersions with different mass
ratios (0, 0.02, 0.05, 0.08, 0.11, 0.14, and 0.17 wt%) were first mixed with water. The concrete
mixture was prepared according to the proportions shown in Table 4and then poured into
triple 100 mm
×
100 mm
×
100 mm molds. Subsequently, the marked specimens were
placed in a curing room and subjected to standard conditions for the specified time. All
procedures followed the guidelines specified in GB/T50082-2019 [44].
Table 4. Test design and mixture proportion (kg/m3).
Specimen Cement Manufactured Sand
Crushed Stone
Water Graphene Oxide
5–10 mm 10–20 mm
GOC0% 398 623 450 734 195 0
GOC0.02% 398 623 450 734 195 0.08
GOC0.05% 398 623 450 734 195 0.199
GOC0.08% 398 623 450 734 195 0.318
GOC0.11% 398 623 450 734 195 0.437
GOC0.14% 398 623 450 734 195 0.556
GOC0.17% 398 623 450 734 195 0.675
2.2.2. Test Situation
(1)
Basic test
For the basic test, the parameter of interest was the incorporation of graphene oxide at
levels of 0, 0.02, 0.05, 0.08, 0.11, 0.14, and 0.17 wt%. The curing time of the specimens was
set at 28 days. The GOC
0.02%
indicates that the specimen contains 0.02 wt%
graphene oxide.
(2)
Sulfate attack test
The sulfate attack test used a Na
2
SO
4
solution with 10 wt% concentration. The
specimens were subjected to a series of dry–wet cycles, specifically 0, 30, 60, 90, and
120 cycles
, as shown in Table 5. SA
30
-GOC
0.02%
indicates a GOC specimen with 30 wet-dry
cycles and 0.02 wt% graphene oxide.

Materials 2023,16, 6949 6 of 16
Table 5. The dry–wet cycle system for sulfate attack.
Media Injection Soaking Media Discharge Air Curing Heating Cooling
Initial temperature (◦C) 27.0 ±1.0 26.0 ±1.0 26.0 ±1.0 27.0 ±1.0 27.0 ±1.0 80.0 ±5.0
Target temperature (◦C) 26.0 ±1.0 26.0 ±1.0 27.0 ±1.0 27.0 ±1.0 80.0 ±5.0 27.0 ±1.0
Time (h) 0.25 17.5 0.25 0.5 3.5 2
(3)
Freeze–thaw cycle test
The specimens were subjected to a series of freeze–thaw cycles, specifically 0, 30,
60, and 90 cycles, as shown in Table 6. FtC
30
-GOC
0.02%
indicates a GOC specimen with
30 freeze–thaw cycles and 0.02 wt% graphene oxide.
Table 6. The freeze–thaw cycle system for sulfate attack.
Cooling Freezing Thawing
Initial temperature (◦C) 20.0 ±2.0 −19.0 ±1.0 −19.0 ±1.0
Target temperature (◦C) −19.0 ±1.0 −19.0 ±1.0 20.0 ±2.0
Time (h) 0.5 2.0 1.5
2.2.3. Measurement Indexes
The test was performed according to the guidelines of GB/T 50081-2019 [
26
] and
included the measurement of the MOE
dy
and UCS and SEM of the specimens. The detailed
steps are as follows:
a.
Once the number of cycles reached a predetermined test design, the surface moisture
of the removed specimen was dried to assess surface damage.
b.
The resonance method was used to measure the MOE
dy
of the specimen. A layer of
petroleum jelly was applied as a coupling medium on the test surface of the specimen,
which was positioned in the center of the polystyrene plate. Then, the excitation
transducer rod of the DT-20 device (from Tianjin Yida Experimental Instrument
Factory, Tianjin, China) was gently pressed at 1/2 of the center line of the test surface,
while the receiving transducer rod was gently pressed at a distance of 5 mm from the
end of the center line of the test surface. The test results obtained were calculated
and processed according to Equation (1),
Ea=13.244 ×10−4×WL3f2/a4, (1)
where E
a
is the MOE
dy
of the specimen (MPa); ais the cross-sectional length (mm);
Lis the length (mm); Wis the mass (kg); and fis the vibration frequency of the
fundamental frequency (Hz).
c.
The HUT-1000 device (from Jinan Sanqin Testing Technology Co., Ltd., Jinan, China)
was used to measure the UCS of specimens. The specimen was placed in the center
of the lower platen of this device and pressing was started. The loading speed was
1.2 ±0.2 kN/s
. When the load became sharply smaller and the specimen deforma-
tion sharply increased, the setup automatically controlled to stop the loading and
the data were recorded when the specimen was destroyed. The test results were
calculated and processed according to the following Equation (2),
f150 =0.95f100 , (2)
where f
100
is the UCS of the test specimen of 100 mm
×
100 mm
×
100 mm and f
150
is the UCS of the standard specimen of 150 mm ×150 mm ×150 mm.
d.
New fracture surfaces of the specimens were observed using the Quattro setup to
investigate the effect of graphene oxide incorporation on the concrete microstructure
at different cycle counts.

Materials 2023,16, 6949 7 of 16
3. Results and Discussion
The mechanical properties of GOC with different levels of graphene oxide incorpora-
tion (0, 0.02, 0.05, 0.08, 0.11, 0.14, and 0.17 wt%) were investigated. It was observed that
the MOE
dy
and UCS of the GOC basically reached a peak at 0.08 wt% graphene oxide
incorporation. After that, further increases in graphene oxide incorporation did not signifi-
cantly improve the mechanical properties of the GOC. Then, the results of the mechanical
properties of GOC with different levels of graphene oxide incorporation (0, 0.02, 0.05,
and 0.08 wt%) were systematically investigated through sulfate attack and freeze–thaw
cycle tests.
3.1. Results for Basic Test
The UCS of GOC with a curing age of 28 days showed a rapid and then slow increase
with the incorporation of graphene oxide, as shown in Figure 4. The UCS essentially
reached its peak value (51.86 MPa) at the incorporation of 0.08 wt% graphene oxide,
which represents an increase of 14.79% compared with the normal concrete specimen
(GOC
0%
). Thereafter, the UCS did not show a significant further increase with the increasing
incorporation of graphene oxide, with all specimens showing an increase of approximately
15% compared with the normal concrete specimen.
Materials 2023, 16, x FOR PEER REVIEW 7 of 17
where f100 is the UCS of the test specimen of 100 mm ×100 mm × 100 mm and f150 is the
UCS of the standard specimen of 150 mm × 150 mm × 150 mm.
d. New fracture surfaces of the specimens were observed using the Quaro setup to
investigate the effect of graphene oxide incorporation on the concrete microstructure
at different cycle counts.
3. Results and Discussion
The mechanical properties of GOC with different levels of graphene oxide
incorporation (0, 0.02, 0.05, 0.08, 0.11, 0.14, and 0.17 wt%) were investigated. It was
observed that the MOEdy and UCS of the GOC basically reached a peak at 0.08 wt%
graphene oxide incorporation. After that, further increases in graphene oxide
incorporation did not significantly improve the mechanical properties of the GOC. Then,
the results of the mechanical properties of GOC with different levels of graphene oxide
incorporation (0, 0.02, 0.05, and 0.08 wt%) were systematically investigated through
sulfate aack and freeze–thaw cycle tests.
3.1. Results for Basic Test
The UCS of GOC with a curing age of 28 days showed a rapid and then slow increase
with the incorporation of graphene oxide, as shown in Figure 4. The UCS essentially
reached its peak value (51.86 MPa) at the incorporation of 0.08 wt% graphene oxide, which
represents an increase of 14.79% compared with the normal concrete specimen (GOC0%).
Thereafter, the UCS did not show a significant further increase with the increasing
incorporation of graphene oxide, with all specimens showing an increase of
approximately 15% compared with the normal concrete specimen.
0.00 0.02 0.05 0.08 0.11 0.14 0.17
44
46
48
50
52
54
UCS / MPa
The incorporation of graphene oxide / wt%
28d
6.33%
11.02%
14.79%
15.03%
15.14%
15.36%
Figure 4. Mechanical property index of specimens under basic test.
Hardened cement paste is a solid-liquid-gas multiphase system consisting of CH
(Ca(OH)2), C-S-H, eringite (AFt), monosulfate (AFm), hydrated cement particles,
micropores, and water or aqueous solution filled in the micropores. To explain the
obtained results, four representative groups of specimens were selected for
microstructural analysis. The specimens were designated as GOC0%, GOC0.08%, GOC0.14%,
and GOC0.17%, and the SEM images are shown in Figure 5.
Figure 4. Mechanical property index of specimens under basic test.
Hardened cement paste is a solid-liquid-gas multiphase system consisting of CH
(Ca(OH)
2
), C-S-H, ettringite (AFt), monosulfate (AFm), hydrated cement particles, micro-
pores, and water or aqueous solution filled in the micropores. To explain the obtained
results, four representative groups of specimens were selected for microstructural analysis.
The specimens were designated as GOC
0%
, GOC
0.08%
, GOC
0.14%
, and GOC
0.17%
, and the
SEM images are shown in Figure 5.
From Figure 5a, it can be clearly observed that there are a large number of C-S-H,
AFt, and CH in the GOC
0%
specimen, and it can also be observed that some cracks are
distributed around the C-S-H. As shown in Figure 5b, the pore size of the GOC
0.08%
specimen tends to be smaller and the number tends to be reduced, and its graphene oxide
sheet and clusters inhibit the growth and diffusion of surrounding cracks to some extent [
45
].
Compared with the GOC
0%
specimen, the cement hydration products of the GOC
0.08%
specimen are more regular in morphology and arrangement. With a further increase in
graphene oxide incorporation (GOC
0.14%
), as shown in Figure 5c, graphene oxide sheets
and clusters appear in large numbers, and partial agglomeration or clustering [
46
] is already
observed. Excessive graphene oxide instead affects the aggregation and stacking of the
cement hydration products as shown in Figure 5d, which causes some pores in the concrete
and a more pronounced distribution.

Materials 2023,16, 6949 8 of 16
Materials 2023, 16, x FOR PEER REVIEW 8 of 17
(a) (b)
(c) (d)
Figure 5. SEM images of specimens under the basic test. (a) GOC
0%
; (b) GOC
0.08%
; (b) GOC
0.08%
; (d)
GOC
0.17%
.
From Figure 5a, it can be clearly observed that there are a large number of C-S-H,
AFt, and CH in the GOC
0%
specimen, and it can also be observed that some cracks are
distributed around the C-S-H. As shown in Figure 5b, the pore size of the GOC
0.08%
specimen tends to be smaller and the number tends to be reduced, and its graphene oxide
sheet and clusters inhibit the growth and diffusion of surrounding cracks to some extent
[45]. Compared with the GOC
0%
specimen, the cement hydration products of the GOC
0.08%
specimen are more regular in morphology and arrangement. With a further increase in
graphene oxide incorporation (GOC
0.14%
), as shown in Figure 5c, graphene oxide sheets
and clusters appear in large numbers, and partial agglomeration or clustering [46] is
already observed. Excessive graphene oxide instead affects the aggregation and stacking
of the cement hydration products as shown in Figure 5d, which causes some pores in the
concrete and a more pronounced distribution.
At present, some scholars [26] have shown that this adhesion is due to a strong
covalent bond: such chemical reactions can create a strong covalent bond between the
interface of the graphene oxide sheet and the cement matrix, which to some extent
increases the integrity of the graphene oxide sheet as a skeletal lap between the cement
hydration products. This increases the efficiency of load transfer from the cement matrix
to the graphene oxide and thus improves the mechanical properties of the GOC.
In summary, at graphene oxide incorporation levels of 0–0.08 wt%, the graphene
oxide can be well dispersed, participate in and regulate the cement hydration process,
make the formation and aggregation of the cement hydration products more regular and
effective, and reduce the cracks and pores inside the concrete [47,48]. When graphene
oxide incorporation is too high, it is not well dispersed in the cement hydration process,
which generates polymer nano-agglomerations. This change ultimately affects the gap
Figure 5.
SEM images of specimens under the basic test. (
a
) GOC
0%
; (
b
) GOC
0.08%
; (
c
) GOC
0.14%
;
(d) GOC0.17%.
At present, some scholars [
26
] have shown that this adhesion is due to a strong covalent
bond: such chemical reactions can create a strong covalent bond between the interface of the
graphene oxide sheet and the cement matrix, which to some extent increases the integrity
of the graphene oxide sheet as a skeletal lap between the cement hydration products. This
increases the efficiency of load transfer from the cement matrix to the graphene oxide and
thus improves the mechanical properties of the GOC.
In summary, at graphene oxide incorporation levels of 0–0.08 wt%, the graphene
oxide can be well dispersed, participate in and regulate the cement hydration process,
make the formation and aggregation of the cement hydration products more regular and
effective, and reduce the cracks and pores inside the concrete [
47
,
48
]. When graphene oxide
incorporation is too high, it is not well dispersed in the cement hydration process, which
generates polymer nano-agglomerations. This change ultimately affects the gap between
cement hydration crystals and aggregates, increases the porosity of the concrete, and does
not improve the internal microstructural density of the concrete.
3.2. Results of Sulfate Attack Test
3.2.1. Appearance Phenomena
The sulfate attack on concrete can be divided into two main categories: physical and
chemical erosion [
49
]. During the physical attack, the cracking damage of concrete is
caused by the swelling stress generated around the pore walls of the concrete, which is
greater than the tensile strength; the swelling stress results from the pressure generated by
the crystals on the pore walls. During the chemical attack, sulfate ions react with cement

Materials 2023,16, 6949 9 of 16
hydration products to produce swelling products that are about 2.5 times larger than the
initial reaction phase, thus causing swelling cracking of the concrete, as shown in Figure 6.
Materials 2023, 16, x FOR PEER REVIEW 9 of 17
between cement hydration crystals and aggregates, increases the porosity of the concrete,
and does not improve the internal microstructural density of the concrete.
3.2. Results of Sulfate Aack Test
3.2.1. Appearance Phenomena
The sulfate aack on concrete can be divided into two main categories: physical and
chemical erosion [49]. During the physical aack, the cracking damage of concrete is
caused by the swelling stress generated around the pore walls of the concrete, which is
greater than the tensile strength; the swelling stress results from the pressure generated
by the crystals on the pore walls. During the chemical aack, sulfate ions react with
cement hydration products to produce swelling products that are about 2.5 times larger
than the initial reaction phase, thus causing swelling cracking of the concrete, as shown in
Figure 6.
Figure 6. Schematic diagram of damage to concrete under sulfate aack.
This damage usually causes spalling, and many microcracks appear on the surface of
specimens. The specimens show spalling at the edges and corners as the aack becomes
more severe. As shown in Figure 7, the specimens maintained good integrity in the less
severe case (60 cycles). In the case of severe erosion (120 cycles), the normal concrete
specimens were severely damaged compared with the GOC specimens, which had
relatively good integrity and less evidence of sulfate aack.
SA
0
-GOC
0%
SA
0
-GOC
0.05%
SA
60
-GOC
0%
SA
60
-GOC
0.05%
SA
120
-GOC
0%
SA
120
-GOC
0.05%
(a) (b) (c)
Figure 7. The appearance of specimens under the sulfate aack test. (a) 0 cycles; (b) 60 cycles; (c)
120 cycles.
3.2.2. Mechanical Properties
As shown in Figure 8, the MOE
dy
and UCS of the GOC specimens under the sulfate
aack test were both improved compared with the normal concrete specimens. With an
increase in cycle number, the compressive indexes of the specimens showed a trend of
“increases at first, and then decreases”, and the MOE
dy
and UCS of the specimens reached
the maximum at 60 cycles. The MOE
dy
loss rate of the GOC specimens ranged from
Figure 6. Schematic diagram of damage to concrete under sulfate attack.
This damage usually causes spalling, and many microcracks appear on the surface of
specimens. The specimens show spalling at the edges and corners as the attack becomes
more severe. As shown in Figure 7, the specimens maintained good integrity in the
less severe case (60 cycles). In the case of severe erosion (120 cycles), the normal concrete
specimens were severely damaged compared with the GOC specimens, which had relatively
good integrity and less evidence of sulfate attack.
Materials 2023, 16, x FOR PEER REVIEW 9 of 17
between cement hydration crystals and aggregates, increases the porosity of the concrete,
and does not improve the internal microstructural density of the concrete.
3.2. Results of Sulfate Aack Test
3.2.1. Appearance Phenomena
The sulfate aack on concrete can be divided into two main categories: physical and
chemical erosion [49]. During the physical aack, the cracking damage of concrete is
caused by the swelling stress generated around the pore walls of the concrete, which is
greater than the tensile strength; the swelling stress results from the pressure generated
by the crystals on the pore walls. During the chemical aack, sulfate ions react with
cement hydration products to produce swelling products that are about 2.5 times larger
than the initial reaction phase, thus causing swelling cracking of the concrete, as shown in
Figure 6.
Figure 6. Schematic diagram of damage to concrete under sulfate aack.
This damage usually causes spalling, and many microcracks appear on the surface of
specimens. The specimens show spalling at the edges and corners as the aack becomes
more severe. As shown in Figure 7, the specimens maintained good integrity in the less
severe case (60 cycles). In the case of severe erosion (120 cycles), the normal concrete
specimens were severely damaged compared with the GOC specimens, which had
relatively good integrity and less evidence of sulfate aack.
SA
0
-GOC
0%
SA
0
-GOC
0.05%
SA
60
-GOC
0%
SA
60
-GOC
0.05%
SA
120
-GOC
0%
SA
120
-GOC
0.05%
(a) (b) (c)
Figure 7. The appearance of specimens under the sulfate aack test. (a) 0 cycles; (b) 60 cycles; (c)
120 cycles.
3.2.2. Mechanical Properties
As shown in Figure 8, the MOE
dy
and UCS of the GOC specimens under the sulfate
aack test were both improved compared with the normal concrete specimens. With an
increase in cycle number, the compressive indexes of the specimens showed a trend of
“increases at first, and then decreases”, and the MOE
dy
and UCS of the specimens reached
the maximum at 60 cycles. The MOE
dy
loss rate of the GOC specimens ranged from
Figure 7.
The appearance of specimens under the sulfate attack test. (
a
) 0 cycles; (
b
) 60 cycles;
(c) 120 cycles.
3.2.2. Mechanical Properties
As shown in Figure 8, the MOE
dy
and UCS of the GOC specimens under the sulfate
attack test were both improved compared with the normal concrete specimens. With an
increase in cycle number, the compressive indexes of the specimens showed a trend of
“increases at first, and then decreases”, and the MOE
dy
and UCS of the specimens reached
the maximum at 60 cycles. The MOE
dy
loss rate of the GOC specimens ranged from 22.282%
to 28.252% (31.221% for normal concrete specimens), and the UCS loss rate ranged from
24.229% to 25.597% (31.397% for normal concrete specimens) after
120 cycles
. With the
increase in graphene oxide incorporation, the compressive indexes of the GOC specimens
were all improved relative to normal concrete specimens, with the most significant improve-
ment at 0.05 wt% graphene oxide incorporation, indicating that graphene oxide improved
the concrete resistance to sulfate attack.

Materials 2023,16, 6949 10 of 16
Materials 2023, 16, x FOR PEER REVIEW 10 of 17
22.282% to 28.252% (31.221% for normal concrete specimens), and the UCS loss rate
ranged from 24.229% to 25.597% (31.397% for normal concrete specimens) after 120 cycles.
With the increase in graphene oxide incorporation, the compressive indexes of the GOC
specimens were all improved relative to normal concrete specimens, with the most
significant improvement at 0.05 wt% graphene oxide incorporation, indicating that
graphene oxide improved the concrete resistance to sulfate aack.
0306090120
6
9
12
15
18
The number of sulfate attack cycle / time
GOC
0%
GOC
0.02%
GOC
0.05%
GOC
0.08%
MOE
dy
/ GPa
0 306090120
30
40
50
60
GOC
0%
GOC
0.02%
GOC
0.05%
GOC
0.08%
UCS / MPa
The number of sulfate attack cycle / time
(a) (b)
Figure 8. The mechanical properties of specimens under the sulfate aack test. (a) MOEdy; (b) UCS.
3.2.3. SEM
To explain the results obtained in the previous section, the microstructure of
specimens with different graphene oxide incorporation levels was compared and
analyzed under 120 sulfate dry–wet cycles. The SEM images are shown in Figure 9. Figure
9a shows a large number of AFts produced by sulfate aack in normal concrete specimens.
These AFt crystals are randomly arranged, and there are many cracks and pores around
them, which further exacerbate the aack of sulfate ions on the concrete. After
incorporating 0.02 wt% graphene oxide, the concrete microstructure was improved
(Figure 9b), and cracks and pores tended to be refined and reduced. With a further
increase in graphene oxide incorporation, the concrete microstructure was significantly
improved (Figure 9c). Because many graphene oxide clusters are distributed in the pores
as a filling and lapping effect, the pore area inside the concrete is effectively reduced,
resulting in a significant decrease in the number of cracks and pores. When a large amount
of graphene oxide is incorporated, graphene oxide sheets and clusters appear in large-
scale agglomerations or clustering (Figure 9d). Many cement hydration crystals are
distributed around them in a disorganized manner, the number of pores increases, and
the density of the microstructure decreases, which instead affects the concrete resistance
to sulfate aack.
Figure 8.
The mechanical properties of specimens under the sulfate attack test. (
a
) MOE
dy
; (
b
) UCS.
3.2.3. SEM
To explain the results obtained in the previous section, the microstructure of specimens
with different graphene oxide incorporation levels was compared and analyzed under
120 sulfate dry–wet cycles. The SEM images are shown in Figure 9. Figure 9a shows a
large number of AFts produced by sulfate attack in normal concrete specimens. These
AFt crystals are randomly arranged, and there are many cracks and pores around them,
which further exacerbate the attack of sulfate ions on the concrete. After incorporating
0.02 wt%
graphene oxide, the concrete microstructure was improved (Figure 9b), and
cracks and pores tended to be refined and reduced. With a further increase in graphene
oxide incorporation, the concrete microstructure was significantly improved (Figure 9c).
Because many graphene oxide clusters are distributed in the pores as a filling and lapping
effect, the pore area inside the concrete is effectively reduced, resulting in a significant
decrease in the number of cracks and pores. When a large amount of graphene oxide is
incorporated, graphene oxide sheets and clusters appear in large-scale agglomerations or
clustering (Figure 9d). Many cement hydration crystals are distributed around them in a
disorganized manner, the number of pores increases, and the density of the microstructure
decreases, which instead affects the concrete resistance to sulfate attack.
The results show that graphene oxide can reduce the number of products generated
by sulfate attack so that the microstructure of the concrete remains relatively dense when
subjected to sulfate attack. On the other hand, it improves the erosion resistance of concrete
by promoting the formation of regular cement hydration products and optimizing the
crystal arrangement to reduce the size and number of microcracks and pores.
3.3. Results of the Freeze–Thaw Cycle Test
3.3.1. Appearance Phenomena
Freeze–thaw damage in concrete is primarily caused by the freezing of water filling
the capillary pores, which causes the concrete to expand. In turn, this forces the unfrozen
water from the freezing area to flow around the capillary pores, creating a large migration
pressure within the concrete. If the water content in the concrete capillary pore is too high,
the expansion pressure on the pore wall will be significant, creating a large tensile stress
around the pore. If this tensile stress exceeds the ultimate tensile strength of the concrete,
internal microcracks will be generated, causing damage to the concrete structure.

Materials 2023,16, 6949 11 of 16
Materials 2023, 16, x FOR PEER REVIEW 11 of 17
(a) (b)
(c) (d)
Figure 9. SEM images of specimens under the sulfate aack test. (a) SA
120
-GOC
0%
; (b) SA
120
-GOC
0.02%
;
(c) SA
120
-GOC
0.05%
; (d) SA
120
-GOC
0.08%
.
The results show that graphene oxide can reduce the number of products generated
by sulfate aack so that the microstructure of the concrete remains relatively dense when
subjected to sulfate aack. On the other hand, it improves the erosion resistance of
concrete by promoting the formation of regular cement hydration products and
optimizing the crystal arrangement to reduce the size and number of microcracks and
pores.
3.3. Results of the Freeze–Thaw Cycle Test
3.3.1. Appearance Phenomena
Freeze–thaw damage in concrete is primarily caused by the freezing of water filling
the capillary pores, which causes the concrete to expand. In turn, this forces the unfrozen
water from the freezing area to flow around the capillary pores, creating a large migration
pressure within the concrete. If the water content in the concrete capillary pore is too high,
the expansion pressure on the pore wall will be significant, creating a large tensile stress
around the pore. If this tensile stress exceeds the ultimate tensile strength of the concrete,
internal microcracks will be generated, causing damage to the concrete structure.
The freeze–thaw damage in concrete is usually a combination of internal erosion and
surface stripping, and the change in surface appearance is the most intuitive. Concrete
surface damage includes water damage, large holes, pockmarks, cracks, slagging, and
spalling. As shown in Figure 10, the surfaces of the specimens without freeze–thaw cycles
were flat and free of obvious defects, with only a few small pockmarks and small holes.
The surface of the normal concrete specimens showed more and more water stains, cracks,
Figure 9.
SEM images of specimens under the sulfate attack test. (
a
) SA
120
-GOC
0%
; (
b
) SA
120
-GOC
0.02%
;
(c) SA120-GOC0.05%; (d) SA120-GOC0.08% .
The freeze–thaw damage in concrete is usually a combination of internal erosion and
surface stripping, and the change in surface appearance is the most intuitive. Concrete
surface damage includes water damage, large holes, pockmarks, cracks, slagging, and
spalling. As shown in Figure 10, the surfaces of the specimens without freeze–thaw
cycles were flat and free of obvious defects, with only a few small pockmarks and small
holes. The surface of the normal concrete specimens showed more and more water stains,
cracks, pitting, and spalling as the number of freeze–thaw cycles increased, while the
GOC specimens (here, GOC
0.05%
is taken as an example) showed less damage compared
with them.
3.3.2. Mechanical Properties
As shown in Figure 11, the compressive indexes of the specimens (MOE
dy
and UCS)
showed a trend of “first increase, and then decrease” as the number of cycles gradually
increased, reaching a maximum at 30 freeze–thaw cycles. The compressive indexes of
the GOC specimens were improved compared with the normal concrete specimens, and
the compressive indexes improved more obviously with the increase in graphene oxide
incorporation. After 90 freeze–thaw cycles, the MOE
dy
loss rate of the GOC specimens
ranged from 13.960% to 19.140% (21.730% for normal concrete specimens), and the UCS
loss rate ranged from 7.590% to 11.350% (12.740% for normal concrete specimens). The
results showed that graphene oxide improved the frost-resisting durability of concrete.

Materials 2023,16, 6949 12 of 16
Materials 2023, 16, x FOR PEER REVIEW 12 of 17
piing, and spalling as the number of freeze–thaw cycles increased, while the GOC
specimens (here, GOC
0.05%
is taken as an example) showed less damage compared with
them.
FtC
0
-GOC
0%
FtC
0
-GOC
0.05%
FtC
30
-GOC
0%
FtC
30
-GOC
0.05%
(a) (b)
FtC
60
-GOC
0%
FtC
60
-GOC
0.05%
FtC
90
-GOC
0%
FtC
90
-GOC
0.05%
(c)
(d)
Figure 10. The appearance of specimens under the freeze–thaw cycle test. (a) 0 cycles; (b) 30 cycles;
(c) 60 cycles; (d) 90 cycles.
3.3.2. Mechanical Properties
As shown in Figure 11, the compressive indexes of the specimens (MOE
dy
and UCS)
showed a trend of “first increase, and then decrease” as the number of cycles gradually
increased, reaching a maximum at 30 freeze–thaw cycles. The compressive indexes of the
GOC specimens were improved compared with the normal concrete specimens, and the
compressive indexes improved more obviously with the increase in graphene oxide
incorporation. After 90 freeze–thaw cycles, the MOE
dy
loss rate of the GOC specimens
ranged from 13.960% to 19.140% (21.730% for normal concrete specimens), and the UCS
loss rate ranged from 7.590% to 11.350% (12.740% for normal concrete specimens). The
results showed that graphene oxide improved the frost-resisting durability of concrete.
(a) (b)
Figure 11. The mechanical properties of specimens under the freeze–thaw cycle test. (a) MOE
dy
; (b)
UCS.
Figure 10.
The appearance of specimens under the freeze–thaw cycle test. (
a
) 0 cycles; (
b
) 30 cycles;
(c) 60 cycles; (d) 90 cycles.
Materials 2023, 16, x FOR PEER REVIEW 12 of 17
piing, and spalling as the number of freeze–thaw cycles increased, while the GOC
specimens (here, GOC
0.05%
is taken as an example) showed less damage compared with
them.
FtC
0
-GOC
0%
FtC
0
-GOC
0.05%
FtC
30
-GOC
0%
FtC
30
-GOC
0.05%
(a) (b)
FtC
60
-GOC
0%
FtC
60
-GOC
0.05%
FtC
90
-GOC
0%
FtC
90
-GOC
0.05%
(c)
(d)
Figure 10. The appearance of specimens under the freeze–thaw cycle test. (a) 0 cycles; (b) 30 cycles;
(c) 60 cycles; (d) 90 cycles.
3.3.2. Mechanical Properties
As shown in Figure 11, the compressive indexes of the specimens (MOE
dy
and UCS)
showed a trend of “first increase, and then decrease” as the number of cycles gradually
increased, reaching a maximum at 30 freeze–thaw cycles. The compressive indexes of the
GOC specimens were improved compared with the normal concrete specimens, and the
compressive indexes improved more obviously with the increase in graphene oxide
incorporation. After 90 freeze–thaw cycles, the MOE
dy
loss rate of the GOC specimens
ranged from 13.960% to 19.140% (21.730% for normal concrete specimens), and the UCS
loss rate ranged from 7.590% to 11.350% (12.740% for normal concrete specimens). The
results showed that graphene oxide improved the frost-resisting durability of concrete.
(a) (b)
Figure 11. The mechanical properties of specimens under the freeze–thaw cycle test. (a) MOE
dy
; (b)
UCS.
Figure 11.
The mechanical properties of specimens under the freeze–thaw cycle test. (
a
) MOE
dy
;
(b) UCS.
3.3.3. SEM
To explain the results obtained in the previous section, the microstructure of specimens
with different graphene oxide incorporation levels was compared and analyzed under
90 freeze–thaw cycles. The SEM images are shown in Figure 12. The typical damage of
FtC
90
-GOC
0%
specimens under repeated freeze–thaw cycles can be observed in Figure 12a,
where wavy and fish-scale-type cracks are interconnected and tend to expand into a crack
network. In addition, many cracks caused by freeze–thaw stress were distributed inside
the concrete. The microstructure of the concrete was improved after incorporating a
small amount of graphene oxide. As shown in Figure 12b, the graphene oxide sheets
effectively stopped the interconnection, diffusion, and penetration of microcracks in the
FtC
90
-GOC
0.02%
specimens, but some cracks caused by freeze–thaw damage still appeared
distributed on the surface of the cement matrix. With a further increase in graphene oxide
incorporation, small-scale agglomeration or clustering occurred in the FtC
90
-GOC
0.05%
specimens, as shown in Figure 12c, which enabled the concrete to maintain a relatively
dense microstructure under repeated freeze–thaw cycles. Large-scale agglomeration or

Materials 2023,16, 6949 13 of 16
clustering was observed in the FtC
90
-GOC
0.08%
specimen, as shown in Figure 12d. This led
to a large increase in the number of pores distributed around the graphene oxide, which
makes the effect of freeze–thaw damage more pronounced.
Materials 2023, 16, x FOR PEER REVIEW 13 of 17
3.3.3. SEM
To explain the results obtained in the previous section, the microstructure of
specimens with different graphene oxide incorporation levels was compared and
analyzed under 90 freeze–thaw cycles. The SEM images are shown in Figure 12. The
typical damage of FtC
90
-GOC
0%
specimens under repeated freeze–thaw cycles can be
observed in Figure 12a, where wavy and fish-scale-type cracks are interconnected and
tend to expand into a crack network. In addition, many cracks caused by freeze–thaw
stress were distributed inside the concrete. The microstructure of the concrete was
improved after incorporating a small amount of graphene oxide. As shown in Figure 12b,
the graphene oxide sheets effectively stopped the interconnection, diffusion, and
penetration of microcracks in the FtC
90
-GOC
0.02%
specimens, but some cracks caused by
freeze–thaw damage still appeared distributed on the surface of the cement matrix. With
a further increase in graphene oxide incorporation, small-scale agglomeration or
clustering occurred in the FtC
90
-GOC
0.05%
specimens, as shown in Figure 12c, which
enabled the concrete to maintain a relatively dense microstructure under repeated freeze–
thaw cycles. Large-scale agglomeration or clustering was observed in the FtC
90
-GOC
0.08%
specimen, as shown in Figure 12d. This led to a large increase in the number of pores
distributed around the graphene oxide, which makes the effect of freeze–thaw damage
more pronounced.
(a) (b)
(c) (d)
Figure 12. SEM images of specimens under the freeze–thaw cycle test. (a) FtC
90
-GOC
0%
; (b) FtC
90
-
GOC
0.02%
; (c) FtC
90
-GOC
0.05%
; (d) FtC
90
-GOC
0.08%
.
Figure 12.
SEM images of specimens under the freeze–thaw cycle test. (
a
) FtC
90
-GOC
0%
; (
b
) FtC
90
-
GOC0.02%; (c) FtC90-GOC0.05%; (d) FtC90 -GOC0.08%.
The results show that the number of defects in the concrete can be reduced. The
microstructure is relatively dense, and strong covalent bonds with cement hydration
products are formed by incorporating appropriate amounts of graphene oxide. This
practice improves the performance of concrete against freeze–thaw damage and increases
its freeze–thaw durability.
4. Conclusions and Future Directions
4.1. Conclusions
This paper investigates the degradation of the mechanical properties of GOC under
sulfate attack and freeze–thaw cycles. Based on the mechanical behavior of graphene oxide
cement slurry and the microstructure of graphene oxide concrete slurry observed using
SEM, the main conclusions are as follows:
(1) The mechanical properties of GOC specimens are higher than those of normal concrete
specimens, showing a trend of “rapid and then slow increase”, in which the UCS of
0.08 wt% GOC reaches the maximum (51.86 MPa) for the first time, which increases
by 14.79% compared with normal concrete specimens. SEM shows that this increase
is related to the formation of strong covalent bonds.

Materials 2023,16, 6949 14 of 16
(2)
For the sulfate attack environment, the performance of GOC shows a trend of “first
increase, and then decrease” with the increase in the number of cycles. The addition of
graphene oxide significantly improves the mechanical properties of concrete against
sulfate attack, with the most significant improvement being achieved when
0.05 wt%
graphene oxide is added. The MOE
dy
and UTS of the SAGOC
0.05%
specimen under
120 sulfate attack cycles decrease by 22.28% and 24.23%, respectively, compared
with the normal concrete specimen (the decreases in MOE
dy
and UTS of the other
specimens range from 28.25% to 31.22% and 25.57% to 31.39%, respectively). SEM
shows that graphene oxide can improve the microstructure of concrete in a sulfate
attack environment, which is related to the cement matrix’s co-resistance to the
degradation of the concrete’s mechanical properties due to swelling damage from
corrosion products.
(3)
For the freeze–thaw cycle environment, the performance of GOC shows a trend
of “first increase, and then decrease” with increasing cycle times. The resistance
of concrete to mechanical degradation is significantly improved by the incorpo-
ration of graphene oxide, and this improvement is most significant at 0.05 wt%
graphene oxide incorporation. The MOE
dy
and UTS of the FtGOC
0.05%
specimen un-
der
90 freeze–thaw
cycles decrease by 13.96% and 7.58%, respectively, compared with
the normal concrete specimen (the decreases in MOE
dy
and UTS of the other speci-
mens range from 18.99% to 21.72% and 9.30% to 11.36%, respectively). SEM shows that
this is related to the improvement of the concrete microstructure by graphene oxide
and the inhibition of crack propagation and penetration under the
freeze–thaw cycle.
4.2. Limitations and Future Directions
In this paper, the degradation study of the mechanical properties of GOC under a
corrosive environment is still insufficient, and some problems are still to be solved, mainly
in the following aspects:
(1)
The service environment of building structures is complex and variable. The ex-
perimental corrosion environment set up in this paper is only sulfate erosion or
freeze–thaw cycle alone. Therefore, it is necessary to carry out a variety of environ-
mental effects coupled erosion tests in subsequent research, such as the coupling
erosion of chlorides and sulfates, the coupling of freeze–thaw and sulfate erosion, the
coupling of chloride salt and freeze–thaw erosion, etc.
(2)
The erosion of building structures in the actual service environment is a long-term
process. In this paper, only the degradation of the mechanical properties of GOC under
a fixed number of corrosion times set in the laboratory is investigated. Therefore,
long-term erosion tests need to be conducted in subsequent studies.
(3)
In this paper, only standard concrete specimens (100 mm
×
100 mm
×
100 mm)
are used, and the mechanical properties of GOC members (compressive perfor-
mance of columns, flexural performance of beams, etc.) need to be examined in
subsequent studies.
Author Contributions:
Conceptualization, J.Q.; Methodology, J.Q.; Resources, X.W.; Data curation,
X.W.; Writing—original draft, L.-Q.Z.; Writing—review & editing, J.-P.Y. All authors have read and
agreed to the published version of the manuscript.
Funding:
This work was supported by the National Natural Science Foundation of China (Grant
No. 52378283); China Postdoctoral Science Foundation (Grant No. 2021M702782); Natural Science
Foundation of Chongqing, China (Grant No. CSTB2023NSCQ-MSX0633); Team Building Project for
Graduate Tutors in Chongqing (Grant No. JDDSTD2022003).
Institutional Review Board Statement: Not applicable.
Informed Consent Statement: Not applicable.
Data Availability Statement:
The data supporting the article’s findings are available from the
corresponding author upon reasonable request.

Materials 2023,16, 6949 15 of 16
Acknowledgments:
This work was supported by the National Natural Science Foundation of China
(Grant No. 52378283); China Postdoctoral Science Foundation (Grant No. 2021M702782); Natural
Science Foundation of Chongqing, China (Grant No. CSTB2023NSCQ-MSX0633); Team Building
Project for Graduate Tutors in Chongqing (Grant No. JDDSTD2022003).
Conflicts of Interest: The authors declare no conflict of interest.
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