electrodepostion of iron oxide on steel fiber for improved .../67531/metadc700033/m2/1/high... ·...
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APPROVED:
Xun Yu, Major Professor Xu Nie, Committee Member Sheldon Shi, Committee Member Yong Tao, Chair of the Department of
Mechanical and Energy Engineering Costas Tsatsoulis, Dean of the College of
Engineering Mark Wardell, Dean of the Toulouse Graduate
School
ELECTRODEPOSTION OF IRON OXIDE ON STEEL FIBER FOR IMPROVED
PULLOUT STRENGTH IN CONCRETE
Chuangwei Liu
Thesis Prepared for the Degree of
MASTER OF SCIENCE
UNIVERSITY OF NORTH TEXAS
August 2014
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Liu, Chuangwei. Electrodepostion of Iron Oxide on Steel Fiber for Improved Pullout
Strength in Concrete. Master of Science (Mechanical and Energy Engineering), August 2014, 24
pp., 1 table, 10 figures, references, 50 titles.
Fiber-reinforced concrete (FRC) is nowadays extensively used in civil engineering
throughout the world due to the composites of FRC can improve the toughness, flexural strength,
tensile strength, and impact strength as well as the failure mode of the concrete. It is an
easy crazed material compared to others materials in civil engineering. Concrete, like glass, is
brittle, and hence has a low tensile strength and shear capacity. At present, there are different
materials that have been employed to reinforce concrete. In our experiment, nanostructures iron
oxide was prepared by electrodepostion in an electrolyte containing 0.2 mol/L sodium acetate
(CH3COONa), 0.01 mol/L sodium sulfate (Na2SO4) and 0.01 mol/L ammonium ferrous sulfate
(NH4)2Fe(SO4)2.6H2O under magnetic stirring. The resulted showed that pristine Fe2O3 particles,
Fe2O3 nanorods and nanosheets were synthesized under current intensity of 1, 3, 5 mA,
respectively. And the pull-out tests were performed by Autograph AGS-X Series. It is
discovering that the load force potential of nanostructure fibers is almost 2 times as strong as the
control sample.
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Copyright 2014
by
Chuangwei Liu
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ACKNOWLEDGEMENTS
This thesis has been made possible by two important groups of people in my life.
Professors
Firstly, I would like to express the greatest gratitude to my adviser, Dr. Xun Yu. He
taught me a lot of wisdoms, which are not only for study but also for life. Those wisdoms will
guide my whole life. It is my honor to be his students.
Family and Friends
Thank my parents, who gave me life and raised me up. All the glory I got is belonged to
them.
Thank my sister for taking care of our parents during the time I am away.
Thanks my roommate Zhiguang Ding, who gave me help and guides me all the time.
Thanks Zhenghang Zhao, Ying Qiu, Hao Yu for their support.
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TABLE OF CONTENTS
Page
ACKNOWLEDGEMENTS ..............................................................................................................iii
LIST OF TABLES .............................................................................................................................v
LIST OF FIGURES ..........................................................................................................................vi
CHAPTER 1 INTRODUCTION .......................................................................................................1
CHAPTER 2 EXPERIMENTAL AND CHARACTERIZATION ...................................................6
CHAPTER 3 RESULTS AND DISCUSSION ..................................................................................9
3.1 Samples were Produced under Current Intensity of 1 mA ..............................................9
3.2 Samples were Produced under Current Intensity of 3 mA ............................................13
3.3 Samples were Produced under Current Intensity of 5 mA ............................................15
3.4 Samples were Produced under Different Current Intensity at 60 min ..........................17
CHAPTER 4 SUMMARY ..............................................................................................................19
REFERENCES ...............................................................................................................................20
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LIST OF TABLES
Page
Table 2.1: As-prepared samples .......................................................................................................7
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LIST OF FIGURES
Page
Figure 2.1: Preparation process of the nanostructures iron oxide coatings deposited on steel
fiber ......................................................................................................................................6
Figure 2.2: As-prepared samples .....................................................................................................7
Figure 2.3: Universal testing machine .............................................................................................8
Figure 3.1: SEM morphologies of Fe2O3 nanorods grown on steel fiber under current intensity of
1 mA at different time: (A) 30 min, (B) 60 min, (C) 120 min ...........................................10
Figure 3.2: a) Load curve of Fe2O3 steel fibers pull-out test with 1 mA current intensity (A): 30
min, (B): 60 min, (C): 120 min; b) Mean of load force .....................................................11
Figure 3.3: SEM morphologies of Fe2O3 nanorods grown on Steel fiber under current intensity of
3 mA at different time: (A) 10 min; (B) 30 min; (C) 60min..............................................13
Figure 3.4: a) Load curve of Fe2O3 steel fibers pull-out test with 5 mA current intensity (A): 30
min, (B): 60 min, (C): 120 min; b) Mean of load force .....................................................15
Figure 3.5: SEM morphologies of Fe2O3 nanorods grown on steel fiber under current intensity of
5 mA at different time: (A) 10 min; (B) 20 min; (C) 60min..............................................16
Figure 3.6: a) Load curve of Fe2O3 steel fibers pull-out test with 5 mA current intensity (A): 10
min, (B): 20 min, (C): 60 min; b) Mean of load force .......................................................17
Figure 3.7: a) Load curve of Fe2O3 steel fibers pull-out test at 60 min with different current
intensity: 1mA (# 2), 3 mA (# 6), 5 mA (# 9); b) Mean of load force ...............................18
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CHAPTER 1
INTRODUCTION
Reinforced concrete (RC), a mixture of cement and mineral aggregate, is a composite
material commonly used in construction projects such as road surfaces, parking lots,
and airports. But it is a sensitive material compared to others materials in civil engineering.
Concrete, like glass, is brittle, and hence has a low tensile strength and shear capacity [1, 2, 3].
An increase in the strength of concrete causes an increase in its brittleness which makes the
concrete very susceptible to cracking [4, 5]. This cracking creates easy access routes for
deleterious agents leading from early saturation, freeze–thaw damage, scaling, discoloration
and steel corrosion [6]. The low cracking potential of concrete in the early stages of hydration
and in-service life is desirable for designing a durable structure. It has been reported that in fiber
reinforced concrete the crack width and crack spacing reduce, especially at early ages [7, 8]. The
enhancement properties of concrete in fresh and hardened states, durability and its environmental
impact are very interesting topics for research. One method to increase some engineering
properties of concrete is the use of fibers as an additional basic material in the concrete mixture.
At present, there are different materials that have been employed to reinforce concrete. Zube
published the study on the reinforcement of concrete mixtures in 1956 [9]. The paper revealed
various types of wire mesh placed under concrete overlay in an attempt to prevent reflection
cracking. It evaluated that all types of wire reinforcement prevented or greatly delayed the
formation of longitudinal cracks. It suggests that the use of wire reinforcement would allow the
thickness of overlays to be decreased while still achieving the same performance. Recently,
others researches examined the effects of fiber-modified on concrete mixtures utilizing steel,
asbestos, rock wool, glass wool, and cellulose fibers.
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Asbestos is the only mineral substance used as a textile fiber. The substance is found in
fibrous reins of serpentine or amphibole rock [10]. At first, it was tried to use non-synthetic
fibers in pavements; therefore, cotton fibers and asbestos fibers were used, but these were
degradable and were not suitable as the long term reinforcements [11]. Asbestos was also used
until it was recognized as a health hazard [12, 13]. And the results of compared changes in void
contents and hydraulic properties of plain and modified cement mixtures placed on the Nantes
fatigue test crack were published by Huet [14]. A polymer modifier (SBS) was used in two of the
mixtures and a mineral fiber (asbestos) was used in the third one to modify the base mixture.
Plain and SBS modified mixtures showed similar decreases in void content and hydraulic
properties after 1,100,000 load cycles. In contrast, Huet concluded that the mixtures modified
with fibers “had undergone no reduction in void content; its drainage properties were
practically unchanged and rutting was minimal” after the same loading.
The historical origin of glass and glass fibers is uncertain. The fiber-forming substance is
glass. Glass fiber has high strength and its elongation is only 3–4%, but its elastic recovery is
100 percent. Fibers of glass will not burn. However they soften at about 815 ℃ and their strength
begins to decline at temperatures above 315 ℃ [10]. It is thought that adding glass fibers to
concrete mixtures enhances material strength and fatigue characteristics while increasing
ductility. Due to their excellent mechanical properties, glass fibers might offer an excellent
potential for concrete modification. With new developments in producing glass fiber, reinforced
bituminous mixtures can be more cost competitive and cost effective as compared to modified
binders. The use of glass fiber-reinforced concrete mixtures may increase the construction cost,
however this may reduce and save the maintenance cost [15]. The critical stress intensity factor
or fracture toughness for glass FRAC is higher than that for plain concrete which indicates
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stronger resistance to crack propagation. Glass fiber-reinforced concrete can improve the
stability and the deformability of the concrete with no increasing bitumen content of hot mix
concrete (HMA) which will be beneficial to prevent rutting and bleeding in high temperature
degrees during the hot season [16].
Some papers investigated the effects of cellulose fibers on bleeding, void content
reduction, abrasion, and drainage in porous concrete in these studies [17, 18, 19]. Cellulose
fibers in the mixture allowed concrete contents to be increased while drastically decreasing
bleeding of the binder. No changes were observed in either void content or abrasion after adding
cellulose fibers. Full-scale test sections on Belgian roads were monitored for drainage over a six-
month period. Those sections containing fibers retained the same drainage quality over six
months, while the drainage time doubled in sections without fibers [20]. Both loose cellulose
fibers and a pelletized cellulose fiber were evaluated for binder drain-down and resistance to
rutting, low temperature cracking, aging and moisture damage [21]. Drain-down tests illustrated
that all mixtures with fiber drained significantly less than those with polymers or the control.
Fiber modified mixtures were the only ones to meet test specifications for drain down. The
control samples were found to have excellent resistance to rutting and no significant difference
was observed between the control and mixtures with modified binder. Low temperature and
moisture damaging results were inconclusive. Polymer modified mixtures were found to have
better resistance to aging. A cellulosed fiber material was added to recycled concretes (RAC) as a
supplement. The results indicated that adding fiber improves the basic performances of RAC in
terms of resistance to rutting, moisture susceptibility and the cracking as well as its durability. It
was concluded that RAC with modified concrete binder at the recycling rate of 70% is
recommended as a balanced result [22].
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Polypropylene fibers are widely used as reinforcing agents in concrete [23, 24, 25, 26,
27]. The polypropylene fibers provide the three-dimensional reinforcement of the concrete. In
this way, concrete becomes more tough and durable [28, 29]. Polypropylene fibers are vital
components of high-performance concrete [30, 31] . Polypropylene fibers were also used as
modifiers in concrete in the United States. Ohio State Department of Transportation (ODOT) has
published a standard for the use of polypropylene fibers in high-performance concrete [32].
Some researchers conducted a research on concrete overlays modified with
polypropylene fiber. These mixtures together with others that had no fiber were sampled by
coring and taken to the laboratory for further analysis. It was concluded from the laboratory
testing that the fiber modified mixtures were slightly stiffer and showed improved fatigue life.
The biggest problem encountered with polypropylene fibers was the inherent incompatibility
with hot concrete binder due to the low melting point of the fiber. Huang and White also stated
that further research was needed to understand the viscoelastic properties of fiber-modified
concrete mixtures [33, 34].
Compare with the above fibers, steel fiber is the most commonly used for most structural
and non-structural purposes [35, 36]. This is followed by polypropylene (PP), glass; however,
these are not commonly used for structural concrete applications [35]. The reasons for the greater
usage of steel fiber include economics, manufacturing facilities, reinforcing effects and
resistance to environmental aggressiveness [37]. It has been reported that adding steel fiber into
concrete in the amount of 1–1.5% by volume increases its tensile strength by up to 100%,
flexural strength by up to 150–200% and the compressive strength increases by 10–25% [36].
The fiber induces a homogeneous stress distribution in the concrete, which causes better
exploitation of the high strength matrix [38]. Furthermore, the addition of steel fibers improves
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the impact strength and toughness [39] and transforms concrete from a brittle to a more ductile
material [40, 41]. Steel fiber concrete has much higher fracture energy than plain concrete [42].
And a paper reported that both the compressive strength and the strain corresponding to peak
stress increase with the addition of steel fibers [43]. Furthermore, the maximum compressive
strain of steel fiber concrete is higher than plain concrete. In the case of tensile strength, it was
reported that with the same type and volume of steel fiber, the improvement is much more for
lightweight aggregate concrete than normal weight concrete [44].
Nevertheless, despite the many advantages of adding steel fiber to concrete, this fiber has
certain disadvantages, particularly the reduced fracture of fresh concrete because of its high
gravity. It can increase the dead load of a composite [45, 46]. In order to address above the
disadvantages and improve the pull-out force between steel fiber and concrete, the Fe2O3
nanorods were synthesized on the surface of steel fiber by electrodeposition technique. The aim
of this research is to extend a preliminary investigation on the performance of a new fiber-
reinforced concrete composite with Fe2O3 nanorods, and present an extensive study on the use of
industrial Fe2O3 nanorods in reinforced concrete structural applications. The new Fe2O3
nanorods-reinforced concrete material is expected to have a satisfactory physical and great
pressure while allowing for a reduction in the coarse aggregate quantity.
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CHAPTER 2
MATERIALS EXPERIMENTAL AND CHARACTERIZATION
All the reagents and solvents were analytical grade and were used without any further
purification. The experiment of electrochemical deposition was performed in a beaker with two
regular electrode configurations in an electrolyte containing 0.2 mol/L sodium acetate
(CH3COONa), 0.01 mol/L, sodium sulfate (Na2SO4) and 0.01 mol/L ammonium ferrous sulfate
(NH4)2Fe(SO4)2.6H2O under magnetic stirring, where the wire mesh ( 25 cm2 ) were served as
cathode (work electrode) and graphite as counter electrode (Fig. 1). The pH of electrolyte was
adjusted to about 8 by using HNO3 and NH3•H2O. The electrochemical deposition was achieved
at room temperature with different current intensity (1, 3 and 5 mA) for different
electrodeposition times.
Fig. 2.1 Preparation process of the nanostructures iron oxide coatings deposited on steel fiber.
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Table 2. 1 As-prepared samples
Sample Current intensity (mA) Deposition time (min)
# 0 control sample
# 1 1 30
# 2 1 60
# 3 1 120
# 4 3 10
# 5 3 30
# 6 3 60
# 7 5 10
# 8 5 20
# 9 5 60
In the fabrication of concrete, samples were weighed according to mix design and
prepared as per general specifications (water: cement ratio 3:10). Thereafter, Fe2O3 nanorod
fibers were inserting into the concrete about 1 cm. Nine groups specimen (Table 2.1) were
prepared by different current and different electrodeposition times.
Fig. 2.2 As-prepared samples
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The surface morphology of composite coatings was characterized by scanning electron
microscope (SEM, S-4800, Hitachi, Japan). And the pull out forces between Fe2O3 nanorod
fibers and concrete were measured by universal testing machine (Shimadzu
Corporation AutoGraph AGS-X Series, Japan) (Fig. 3.)
Fig. 2.3 Universal testing machine
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CHAPTER 3
RESULTS AND DISCUSSION
3.1 Samples were Produced under Current Intensity of 1 mA
Fig. 3.1 (a) presents the morphology of the pristine Fe2O3 with an average 1μm under
current intensity of 1 mA at 30 min. When there is the electrodeposition time reach 60 min, the
prepared product exhibits a columnar-shaped structure with the size about 400 nm (Fig. 3.1 (b)).
The size of columnar-shaped structure is no significant change when the time reaches 120 min,
but some fluff was appeared on the structure as shown in Fig. 3.1 (c). Compared with the above
samples, the Fe2O3 synthesized with 30 min has a large size, while the sample has a small size
under increase of electrodeposition time. The results indicate that pristine Fe2O3 may experience
a dissolution and recrystallization process, and the addition of electrodeposition time may
enhance the grain refinement. This phenomenon can be explained by the space steric effect,
which increased the diffusion activation energy of the reactants.
Fig. 3.2 shows the results of load force test. The load force of control specimen is about
74 N. Meanwhile, the steel fiber with pristine Fe2O3 can enhance the load force of concrete: the
load forces are approximately 120 N, 122 N and 121 N that are almost 1.6 times as strong as the
control specimen. The main reason is that specific surface area increased the need to increase the
interface between concrete and steel fiber, increasing the force of friction. In addition, increasing
electrodeposition time cannot significant change the pull out force due to these samples have a
similar morphology and same size of pristine Fe2O3.
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Fig. 3.1. SEM morphologies of Fe2O3 nanorod grown on steel fiber under current intensity of 1
mA at different time: (A) 30 min (# 1); (B) 60 min (# 2); (C) 120 min (# 3).
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Fig. 3.2. a) Load curve of Fe2O3 steel fibers pull-out test with 1 mA current intensity (A): 30 min,
(B): 60 min, (C): 120 min; b) Mean of load force.
Cathodic deposition of oxide/hydroxide is based on the generation of OH−
ions at the
working electrode [47, 48]. In nitrate solution, the following electrochemical reactions:
- - -3 2 2NO +H O+2e NO +2OH→ 1
-2 2O +2H O+4e 4OH→ 2
4 2 4 22NH +2H O 2NH OH+H+ → 3
2 22H O+2e 2OH +H−→ 4
may occur at the cathode. These reactions cause an increase in local pH on the surface of the
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cathode and formation of ferric hydroxide. Later ferric hydroxide is converted to form Fe2O3.
The overall reaction can be shown as [49, 50]:
32 3 22Fe +6OH Fe O +H+ − → 5
Due to the low concentration of dissolved oxygen and nitrate ions in solution it seems
that reaction 4 is dominant in the increase of local pH and hydroxide formation. The loose
adhesion of the catholic iron hydroxide deposits to the cathode surface and their spallation have
been reported as common difficulties during electrogeneration of base in aqueous medium. To
overcome this problem, we have noticed that the application of lower bath temperature than
room temperature can offer important advantages such as control of the kinetic energy of
solvents and deposit molecules, in other words at lower temperature the kinetic energy of
molecules is low and the adhesion of deposit is firm, thus the spallation can be prevented. Also at
low temperature the rate of gas bubbling at electrode surface is reduced and the spallation of
deposit into electrolyte would be reduced. Another applied trick for the reduction of the deposit
spallation was addition of a solvent with low dielectric constant to the electrolyte, in this way the
solvation and separation strength of electrolyte reduced and this caused lower spallation of the
deposit. Therefore the certain amount of methanol was added to the electrolyte to reduce the
dielectric constant of solvent.
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3.2 Samples were Produced under Current Intensity of 3 mA
Fig. 3.3. SEM morphologies of Fe2O3 grown on steel fiber under current intensity of 3 mA at
different time: (A) 10 min (# 4); (B) 30 min (# 5); (C) 60min (# 6).
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The morphologies of the coating surface exhibited different kind of crystal characteristics.
The coating takes on a cone approximately 1μm in length were deposited on the steel fiber (Fig.
3.3 a). As electrodepostion time increases, the nanosized iron oxide is uniformly coated on the
steel fiber surface by applying an anodic current intensity of 3 mA in a sulfate bath containing
iron salt. As revealed in the SEM image, the surface morphology of iron oxide deposited on the
steel fiber surface is highly porous and is of nanorod structure. The spaced radial iron oxide
nanorods formed on the steel fiber are about 300 nm in length and the space size of nanorods
about 200 nm. The size of naostructure is no significant change when the time reaches 60 min,
but the part of structure was dissolved and the space size of nanorods reaches to 600 nm, as
shown in Fig. 3.3 (c). This means that enhance the current intensity can refine grain and
increased the diffusion activation energy of the reactants under the same electrodeposition time.
The value of load force in the Fig. 3.4 has the same trend with the Fig. 3.2. But the value
of Fe2O3 nanorods lower than the value of pristine Fe2O3, due to the space size and spaced radial
of Fe2O3 nanorods is too small compare with the size of concrete. The adhesion of nanoroad is
not very well.
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Fig. 3.4. a) Load curve of Fe2O3 steel fibers pull-out test with 3 mA current intensity (A): 10 min,
(B): 30 min, (C): 60 min; b) Mean of load force.
3.3 Samples were Produced under Current Intensity of 5 mA
Microstructures of the Fe2O3 nanorods were revealed through the SEM studies (Fig.
3.5).The surface morphology demonstrate that the shapes of Fe2O3 nanosheets were nearly flake,
approximately 1μm long. Most of nanosheets overlapped one another and were perpendicular to
the substrate. Alternatively, when the electrodepostion time reach to 60 min under the current
intensity of 5 mA. High density and orientation-ordered Fe2O3 nanosheets bundle were observed
on the substrate. The length of the nanosheets increased, and the shape of the nanosheets was
improved with an increasing the time.
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Meanwhile, the load force has significant change more than 135 N under the current
intensity of 5 mA. The main is that the length of nanosheets much more close to the grain size of
concrete than nanorods, and has excellent specific surface than pristine Fe2O3.
Fig. 3.5. SEM morphologies of Fe2O3 nanorod grown on steel fiber under current intensity of 5
mA at different time: (A) 10 min (# 7); (B) 20 min (# 8); (C) 60min (# 9).
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Fig. 3.6. a) Load curve of Fe2O3 steel fibers pull-out test with 5 mA current intensity (A): 10 min,
(B): 20 min, (C): 60 min; b) Mean of load force.
3.4 Samples were Produced under Different Current Intensity at 60 min
Fig. 3.7 shows the results of load force test. The load force of sample 2 is about 122 N.
The load force of sample 6 reduced to 110, the main reason is that the space size of nanorods is
too narrow compare with the diameter of concrete. The load force is about 135 N, when the
current intensity reaches to 5 mA. The main is that the length of nanosheets much more close to
the grain size of concrete than nanorods, and has excellent specific surface than pristine Fe2O3.
Meanwhile, increasing the electrodeposition time can enhance the load force of concrete. The
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main reason is that specific surface area increased the need to increase the interface between
concrete and steel fiber, increasing the force of friction. In addition, reducing the size of grain
can increase the force of friction.
Fig. 3.7. a) Load curve of Fe2O3 steel fibers pull-out test at 60 min: 1 mA (# 2), 3 mA (# 6), 5
mA (# 9); b) Mean of load force.
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CHAPTER 4
SUMMARY
The morphology of the pristine Fe2O3 with an average 1μm. When the electrodeposition
time reaches 60 min, the prepared product exhibits a columnar-shaped structure with a size about
400 nm. Meanwhile, increasing the electrodeposition time can enhance the load force of concrete:
the pull out forces is approximately 119 N, 122 N and 122 N that are almost 1.6 times as strong
as the control specimen.
The Fe2O3 nanorods on the substrate surface were produced and the coating becomes
compact and uniform under the current intensity of 3 mA at 30 min. The size of naostructure has
no significant change when the time reaches 60 min, but the part of coatings were dissolved, as
shown in Fig. 6(c). This means that enhance the current intensity can refine grain and increased
the diffusion activation energy of the reactants. And their load forces are 1.5 times as strong as
the control sample.
Fe2O3 nanosheets were produced under the current intensity of 5 mA, and these samples
have the best performance to improve the behavior of concrete. The main is that the length of
nanosheets much more close to the grain size of concrete than nanorods, and has excellent
specific surface than pristine Fe2O3
In sum, the Fe2O3 coatings were fabricated and the coating becomes compact and
uniform under the same current intensity when the deposition time is increased. As increase in
deposition time would increase the load force. However, the resulted showed that the pull out
force of coating initially decreased but finally increased the increasing the current intensity at the
60 min.
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