Steel-Corrosion Characteristics of an Environmental Inhibitor using Limestone Sludge and Acetic Acid
International Journal of Concrete Structures and Materials
Steel-Corrosion Characteristics of an Environmental Inhibitor using Limestone Sludge and Acetic Acid
Calcium acetate, which can be used in concrete to shorten the construction period and to improve productivity, was manufactured using limestone sludge and acetic acid. Calcium acetate contains a carboxyl group, and it can provide anticorrosive properties by forming a complex with the steel surface. We evaluated the basic performance of a carboxylic early-strength agent produced from industrial by-products (limestone sludge and acetic acid) as a corrosion inhibitor. A comparative evaluation was performed using calcium nitrate, which is a conventional early-strength agent; the corrosion area ratio, corrosion state, and electrochemical performance of a steel plate immersed in aqueous solutions were evaluated. A steel plate immersed in calcium acetate was not substantially corroded. The electrochemical investigations showed a high corrosion potential based on the impedance characteristics. The corrosion current showed anodic values, and no corrosion occurred on the surface of the steel plate because of the adsorption of carboxyl groups. Scanning electron microscopy indicated that the steel plate was covered by a crystalline coating, which suppressed corrosion. We show that it is possible to develop an environmentally friendly recycling method as an early-strength agent and corrosion inhibitor when manufacturing calcium acetate using limestone sludge.
steel; corrosion; inhibitor; limestone sludge; acetic acid
Deicing agents are used in large quantities to remove snow
from road surfaces in winter; chloride-based deicing agents are
the most widely used
(Federal Highway Administration 2002;
. However, chloride accelerates the corrosion of
steel materials and concrete; to prevent these negative effects,
the agent was mixed with a corrosion inhibitor. Wet deicing
agents can be mixed with a liquid corrosion inhibitor, such as
an amine or amino alcohol; however, solid-state deicing agents
are more difficult to handle because they cannot be used with a
liquid corrosion inhibitor. To inhibit the corrosion caused by
chloride-based deicing agents, the use of an acetate compound,
such as calcium magnesium acetate or calcium nitrate, has
been proposed. Currently, these inhibitors are expensive and
their effect is minimal; therefore, strategies to solve these
problems are urgently needed (Shi et al. 2009, 2010).
Concrete agents are chemical materials that improve the
fluidity, hydration, and durability of concrete. Early-strength
concrete agents are important materials for reducing the
construction period. Common early-strength concrete agents
include calcium formate and calcium nitrate
Dodson 1990; NS Berke and ARosenberg 1989; Hoang et al.
2016; Messina et al. 2015; C¸etin et al. 2016)
High early-strength concrete shows a deteriorated
longterm strength and durability because of the rapid formation
(Thamas et al. 2015; Hansen 1987; Han 1991;
Bazant and Baweja 1996)
. Concrete with reduced durability
is characterized by cracks from expansion because of
corrosion of the inner steel reinforcement.
Early-strength agents with carboxyl groups can improve
the compressive strength of concrete by promoting the
hydration of cement. Materials that have carboxyl groups
and can be used as early-strength agents include calcium
acetate and calcium formate. Calcium acetate and calcium
formate can improve the strength of cement by promoting
hydration of the gypsum component and C3A therein
et al. 2014; Le Sao uˆt et al. 2013; Huang and Shen 2014)
These early-strength agents are known to possess
(Monticelli et al. 2000)
Earlier work confirmed that mixing 1% calcium acetate
manufactured from limestone sludge with 1 wt% cement
could accelerate the hydration of cement and improve its
(Kim et al. 2016)
Figure 1 shows the corrosion characteristics of several
types of inhibitors against chloride ions. Amines and
alkanolamines exhibit a moderate efficacy as corrosion inhibitors
(Ormellese et al. 2009)
Corrosion is more likely for higher absolute values of the
corrosion potential. As shown in Fig. 1, when the chlorine ion
concentration is 1.0 mol/L, the carboxyl group exhibits a
higher resistance to corrosion than amines and amino acids.
Carboxylates exhibit the best corrosion resistance
et al. 2009)
. They also show better anti-corrosive properties
than sodium nitrite, which is a conventional corrosion inhibitor.
Quicklime is used to remove gaseous sulfuric acid that is
generated during steel manufacturing. The limestone used for
producing quicklime is pretreated using a washing method to
prevent the powders from clogging the piping and to ensure
that air reaches the kiln. Large amounts of industrial
byproducts are generated during this washing process and are
collectively termed limestone sludge (LSS). A separate process
is required to deal with these by-products
Association 2015; Seo et al. 2014)
. In this study, calcium acetate,
which is the main raw material for carboxylic early-strength
agents, was produced using LSS and an organic acid. We
evaluated the corrosion-inhibiting characteristics of solid-state
carboxyl-based calcium acetate generated by a reaction with an
organic acid that can be used as a corrosion inhibitor with LSS.
Calcium acetate, which can be used as a concrete
earlystrength agent using calcined sludge as an industrial by–
product, was prepared, and its corrosion characteristics were
evaluated. For this purpose, the corrosion area ratio,
corrosion weight loss, and electrochemical corrosion
characteristics were evaluated after an iron plate was corroded using
calcium chloride, calcium nitrate, and calcium acetate.
Further, the surface of the steel sheet was examined using
scanning electron microscopy (SEM).
2.1.1 Lime Stone Sludge
LSS, an industrial by-product, was used to manufacture a
calcium-containing high early-strength agent. The LSS had a
density of 2.97 g/cm3 and an average particle diameter of
approximately 28.70 lm; the calcium carbonate had a
density of 2.93 g/cm3 and an average particle
diameter \ 40 lm.
The X-ray diffraction (XRD) results and chemical
composition analyses of LSS are shown in Fig. 2 and Table 1,
respectively. The XRD patterns of CaCO3 and LSS show a
CaCO3 peak at approximately 29 . The structure of LSS
appears to be the same as that of CaCO3. However, in terms
of the chemical composition, the CaO content of LSS was
roughly 5.84% less than that of CaCO3. Moreover, LSS
contained SiO2 and metallic salts, such as Al2O3 and Fe2O3.
2.1.2 Recycled Acetic Acid
Recycled acetic acid (RAA) was obtained by separating
the acids used in the etching processes. In this study, about
60% RAA was used. Figure 3 shows the Fourier transform
infrared (FT-IR) analysis of RAA. The peaks in the range of
3300–2500 cm-1 are attributed to carboxylic groups. C=O
(1760–1690 cm-1) and C–O (1320–1210 cm-1) groups
were also observed. Some examples of carboxylic acids are
acetic acid, formic acid, gluconic acid, and propionic acid.
2.1.3 Manufacturing of Calcium Acetate
Figure 4 shows the schematic of the process used for
manufacturing calcium acetate. In this study, RAA and LSS
were made to react with each other to yield CA (Eq. 1).
Maximum yield was obtained (1 mol each of CA, water, and
carbon dioxide for every 1 mol of CaCO3) at an acetic
acid:CaCO3 ratio of 2:1.
2CH3COOH + CaCO3 = Ca(CH3COO)2 + H2O + CO2
Table 2 lists the formulation of the aqueous solutions
prepared for the corrosion experiments. The corrosion
characteristics of sodium chloride, calcium nitrate, and the
produced calcium acetate were evaluated.
Fig. 1 Inhibitor specification
(Ormellese et al. 2009)
Fig. 2 XRD results of CaCO3 and LSS.
2.2.2 Corrosion of Steel
The steel material used for the corrosion experiment was
cut into 5 cm (width) 9 10 cm (length) 9 2 mm (thickness)
plates, which were then immersed in a sodium citrate
solution for 3 h to remove fine rust from their surfaces.
Rectangular containers [7 cm (width) 9 15 cm (length) 9 3 cm
(height)] were used to install the steel plates. A 1 mm-thick
sponge was placed under each container, and the steel plates
were placed in the conductors so that their top and bottom
surfaces were in contact with the test solutions. In each of
the installed containers, the aqueous solutions (3%), which
were prepared according to the formulations given in
Table 2, were poured, and the corrosion state was examined
after 1–3 weeks.
2.2.3 Observation of the Corrosion State
The corrosion state was examined by calculating the
corrosion area rate. The corrosion area was measured by
removing the steel plates from the solutions after different
intervals of time (1–3 weeks). Oiled grid papers were placed
on top of the corroded steel plates to calculate the corrosion
area. The weight reduction per unit area resulting from steel
corrosion was obtained by measuring the weights of the steel
material before and after the corrosion test and then dividing
the weight reduction by the area of the material.
Corrosion area rate (area% ) ¼
2.2.4 Evaluation of the Electro-Chemical
Before starting the electrochemical experiments, the steel
rebars were exposed to the aqueous solutions of sodium
chloride, calcium nitrate, and calcium acetate, and their
potentials were stabilized using a potentiostat. These
experiments were conducted in a three-electrode system; the
specimens worked as the working electrode, a platinum wire
acted as the counter electrode, and silver–silver chloride
acted as the reference electrode. A working electrode area of
0.78 cm2 was used for all samples.
Electrochemical impedance spectroscopy studies were
carried out by changing the frequency of a 10 mV sinusoidal
voltage from 100 kHz to 0.1 Hz. DC polarization studies
were performed at a scan rate of 1 mV/s at potentials ranging
from - 0.3 to ? 0.3 V versus an open circuit potential. The
potentiostat used in this study was a VersaSTAT (Princeton
Applied Research, Oak Ridge, TN, USA), and the data were
analyzed using the Metrohm Autolab NOVA 1.10 software
by fitting the experimental data in the constant-phase
element model. All electrochemical studies were carried out at
27 ± 1 C.
SEM images were used to observe the microstructural
changes on the surface of the corroded steel plates.
3. Results and Discussion
3.1 Corrosion Area and Weight Loss
Table 3 lists the corrosion area and weight loss rates
obtained for the sodium chloride, calcium nitrate, and
calcium acetate solutions. The corrosion area in the sodium
chloride solution was measured by immersing a steel plate
into the solution for 1–3 weeks. The corrosion areas were
6.05% after 1 week, 48.68% after 2 weeks, and 100% after
3 weeks. Red and black corrosion were evenly distributed
on the surface.
For calcium nitrate, the corrosion area ratio after 1 week
was 3.96% (lower than that in sodium chloride for the same
duration). However, after 2 weeks, the corrosion area ratio
increased to 95%, which was much higher than that for
sodium chloride. The calcium acetate solution showed no
corrosion for 2 weeks, and a corrosion area ratio of
approximately 1% was observed after 3 weeks. A thin layer
of red corrosion was observed on the surface of the steel
plate in this case.
The steel plate that was immersed in a mixture of calcium
acetate and sodium chloride showed no corrosion after
1 week. Corrosion began to appear after 2 weeks, depending
on the mixing ratio of calcium acetate. After 2 weeks, the
corrosion area ratio decreased as the calcium acetate content
increased. Corrosion ratios of 6.68, 0.83, and 0.71% were
obtained for 10, 30, and 50% calcium acetate substitution,
respectively. The corrosion area ratio for 10% calcium
acetate substitution after 3 weeks was 36.61%.The corrosion
area ratio after 3 weeks at a calcium acetate substitution of
50% was 1.37%, indicating an improvement in the corrosion
The calcium nitrate/calcium acetate solution began to
corrode the steel plate after 2 weeks, which is similar to that
observed for the solution containing calcium acetate and
sodium chloride. The corrosion area ratios were 10.35, 2.41,
and 1.33% for 10, 30, and 50% calcium acetate substitution,
respectively. Carboxyl groups (like amino groups) tend to be
adsorbed onto metal surfaces, thus forming an organic layer.
Calcium acetate with carboxyl groups can form a complex
with ferrous oxide and ferric oxide, and can generate a
strong complex on metal surfaces. Terminal carboxyl groups
can form a coating on metal surfaces to inhibit corrosion.
The slight red color observed when the calcium acetate
solution was used can be attributed to the formation of
carboxyl group complexes, which in turn formed a
corrosion-inhibiting layer on the surface of the steel plate.
Figure 5 shows the oxidation inhibition layer generated by
carboxyl groups on the surface of the steel plate
et al. 2000)
. Complexes with carboxyl groups on the surface
of the steel interfere with the contact and bonding of oxygen
ions and inhibit corrosion in a manner similar to that
provided by a film on passive state metals. Figure 6 shows the
corrosion characteristics as a function of time.
Fig. 5 The oxidation inhibition layer formed by carboxyl
groups on the surface of the steel plate
et al. 2000)
Table 4 presents the weight losses caused by corrosion.
The weight reduction, which varies depending on the nature
of the aqueous solution, was the greatest using the sodium
chloride solution. However, when the specimen was treated
with calcium acetate, the weight increased slightly or did not
change during the corrosion test.
When calcium acetate was mixed with sodium chloride at
a ratio of 1:9, the corrosion-induced weight reduction was
0.81 mg/cm2; at a 50% mixing rate of calcium acetate, there
was almost no weight reduction. When the corrosion area
ratios were compared, the corrosion caused by sodium
chloride was accompanied by a chipping-off phenomenon
after the surface of the steel was corroded; however, when
calcium acetate was mixed in the aqueous solution, no
chipping-off was observed. Calcium acetate changed the
color of the steel surface and prevented corrosion; no steel
weight loss was observed. When calcium nitrate was used,
the weight reduction caused by corrosion was similar to that
provided by the sodium chloride solution, and there was
almost no corrosion prevention. Calcium nitrate likely does
not provide a surface coating effect, resulting in the loss of
steel material by surface corrosion.
3.2 Electrical Corrosion
Figures 7, 8 and 9 show the Nyquist plots of calcium
acetate, a mixture of calcium acetate and sodium chloride,
and calcium nitrate, respectively. A concentric circle was
drawn based on the slope of the impedance curve using the
impedance method, and the area of this concentric circle was
calculated as the corrosion potential value. The maximum
electrode resistance of calcium acetate was approximately
7200, while those of sodium chloride and the mixture of
sodium chloride and calcium acetate were 79.8 and 427,
respectively. This indicates that the corrosion potential
performance of calcium acetate was higher than that of sodium
chloride and that of the sodium chloride/calcium acetate
mixture.The resistance value of calcium nitrate was 124,
which is higher than that of NaCl (79.8). The most favorable
corrosion prevention ingredient was calcium acetate because
its resistance value was lower than that of the calcium
acetate-sodium chloride mixture.
Figure 10 shows the polarization resistance of sodium
chloride and calcium acetate. The figure shows that the
corrosion current value of the solution with 50% calcium
acetate substitution was higher than that of the sodium
chloride solution. The corrosion current of the solution with
50% calcium acetate substitution was close to zero,
indicating a high corrosion potential (Stern and Geary 1957;
Marcus 1993). When 100% calcium acetate was used, the
corrosion current moved to anodic values and no corrosion
was observed. This is because of the reduction reaction
caused by the surface adsorption of carboxylic acid.The
polarization resistance of calcium nitrate was closer to 0 than
that of NaCl, which indicates that its corrosion resistance is
superior to that of sodium chloride.
Figure 11 shows SEM images of the cross-section and
surface of the steel plates after the corrosion experiment. The
steel plate that was immersed in the sodium chloride solution
showed a uniform distribution of an amorphous oxide on its
surface. Furthermore, the wrinkles, which were present on
the surface of the plate before immersion, disappeared and
small oxides covered the surface. The surface layer was
etched by corrosion. For cross-section corrosion caused by
sodium chloride, the corrosion products formed bumps on
the surface after corrosion.
When using the mixture of calcium acetate and calcium
chloride, oxides were observed at the cross-section of the
plate and wrinkles were observed on the surface, indicating
that the corrosion of the surface was less intense. In the case
of calcium acetate, small octahedral grains were evenly
distributed on the surface of the plate, forming an oxide
layer. In this case, surface wrinkles were also observed. A
corrosion inhibition layer formed because of the
complexation of carboxyl groups with the surface of the steel plate.
When using calcium nitrate, the wrinkles on the steel
surface disappeared and a coarse-grained coating layer
formed on the surface. The nitrate ions (from calcium
nitrate) formed an oxide layer of Fe2O3 on the steel surface
to inhibit the progression of corrosion.
Sodium chloride causes surface etching and red corrosion,
while calcium nitrate forms coarse particles on the steel
surface. The increased corrosion loss was due to the physical
properties of the oxide layer, even when the corrosion
potential of calcium nitrate was lower than that of sodium chloride.
While measuring the corrosion area ratio, the weak oxide layer
of calcium nitrate was etched by friction as the surface portion
was cleaned, thereby increasing the corrosion area ratio.
The geometry of the cross section was examined after
treatment with the sodium chloride-calcium acetate
compound; some crystals were observed on the surface, while
many crystallization products were evenly distributed for
calcium acetate. The crystallization products showed smaller
crystal sizes and a more uniform distribution than sodium
chloride; therefore, surface reformation is likely caused by
the generation of complexes, not surface etching.
Calcium acetate was produced using industrial
by-products. The corrosion characteristics of a steel plate immersed
in an aqueous solution of calcium acetate were analyzed by
evaluating its corrosion area ratio, weight loss due to
corrosion, and electrochemical characteristics. SEM images of
the plate were also examined. The results are as follows.
(1) The corrosion experiment using sodium chloride,
calcium nitrate, and calcium acetate solutions showed
that the corrosion area of the steel plate immersed in
calcium nitrate was larger than that of the plate
immersed in sodium chloride. No corrosion was
observed on the plate immersed in calcium acetate.
The corrosion area for the sodium chloride and calcium
nitrate solutions decreased with the addition of calcium
acetate to these solutions.
(2) Among the three solutions used in this study, the
calcium acetate solution showed the largest corrosion
potential area, and the corrosion potential value was
located on the anode, indicating that it was not
susceptible to corrosion. Calcium acetate showed an
excellent corrosion potential because it formed an
organic coating on the surface with complexes
generated by carboxyl groups on metal surfaces.
(3) When a mixture of sodium chloride and calcium
acetate was used, the corrosion crystal products on the
surface of the metal plate surface were different from
those generated in sodium chloride and calcium
acetate. The crystal products generated on the surface
were similar to those generated in the calcium acetate
solution. Here, the surface corrosion caused by sodium
chloride was inhibited by the formation of an organic
coating on the surface of the steel surface by calcium
This research was supported by the Research Grant from
(Hanyang Experiment & Consulting) through the Korea
Agency for Infrastructure Technology Advancement funded
by the Ministry of Land, Infrastructure and Transport of the
Korean government (Project No.: 17CTAP-C115066-02).
This article is distributed under the terms of the Creative
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Fig. 11 SEM images of the cross-section and surface of the
steel plates immersed in various aqueous solutions.
a Non-treated, b NaCl, c Calcium Nitrate, d Calcium
Acetate 50% ? NaCl50%, e Calcium Acetate 100%.
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