U.S. patent application number 14/872081 was filed with the patent office on 2017-03-30 for method of ascertaining fully grown passive film formation on steel rebar embedded in concrete.
The applicant listed for this patent is KING SAUD UNIVERSITY. Invention is credited to ABDULAZIZ AL-NEGHEIMISH, ABDULRAHMAN ALHOZAIMY, RAJA RIZWAN HUSSAIN, DDN SINGH.
Application Number | 20170089851 14/872081 |
Document ID | / |
Family ID | 58408758 |
Filed Date | 2017-03-30 |
United States Patent
Application |
20170089851 |
Kind Code |
A1 |
HUSSAIN; RAJA RIZWAN ; et
al. |
March 30, 2017 |
METHOD OF ASCERTAINING FULLY GROWN PASSIVE FILM FORMATION ON STEEL
REBAR EMBEDDED IN CONCRETE
Abstract
The method of ascertaining fully grown passive film formation on
steel rebar embedded in concrete utilizes electrochemical impedance
spectroscopy (EIS) to determine, in situ, the degree of passive
film formation on steel rebar embedded in concrete. A length of
steel rebar and a counter electrode are both embedded in a concrete
slab. A reservoir is supported on an external face of the concrete
slab and filled with an electrolytic solution. A reference
electrode is then positioned in the electrolytic solution, and the
length of steel rebar, the counter electrode and the reference
electrode are electrically connected an EIS test instrument to
perform electrochemical impedance spectroscopy. The quality of
passive film formation on the length of steel rebar is determined
based on comparison of the electrochemical impedance spectroscopy
results with known passive film formation data.
Inventors: |
HUSSAIN; RAJA RIZWAN;
(RIYADH, SA) ; ALHOZAIMY; ABDULRAHMAN; (RIYADH,
SA) ; AL-NEGHEIMISH; ABDULAZIZ; (RIYADH, SA) ;
SINGH; DDN; (JAMSHEDPUR, IN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
KING SAUD UNIVERSITY |
Riyadh |
|
SA |
|
|
Family ID: |
58408758 |
Appl. No.: |
14/872081 |
Filed: |
September 30, 2015 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G01N 17/02 20130101;
G01N 27/026 20130101; G01N 33/20 20130101 |
International
Class: |
G01N 27/02 20060101
G01N027/02; G01N 33/20 20060101 G01N033/20; G01N 17/02 20060101
G01N017/02 |
Claims
1. A method of ascertaining in situ fully grown passive film
formation on steel rebar embedded in concrete by analyzing both
open circuit potentials and electrochemical impedance spectra
(EIS), the method consisting of: embedding a length of steel rebar
in a concrete slab to form a working electrode; embedding a
graphite counter electrode in the concrete slab, the counter
electrode being positioned adjacent and parallel to the length of
steel rebar; supporting a reservoir on an external face of the
concrete slab; filling the reservoir with an electrolytic solution
with simulated concrete pore solution; immersing a reference
electrode in the electrolytic solution, wherein the working
electrode, the graphite counter electrode, the concrete slab, and
the reference electrode immersed in electrolytic solution defining
a three-electrode electrochemical impedance spectroscopy (EIS) test
cell adapted for connection to an EIS test instrument; electrically
connecting the electrodes to the EIS test instrument; obtaining
data from open circuit potentials; performing and obtaining data
from electrochemical impedance spectroscopy to generate a plot of
impedance as a function of frequency for the length of steel rebar
and the counter electrode; matching the plot to a known plot of
passive film formation on steel rebar and reviewing the data
obtained from the open circuit potentials; and determining a degree
of passive film formation on the length of steel rebar in situ
based on passive film formation associated with the matched
plot.
2-3. (canceled)
4. The method of ascertaining fully grown passive film formation on
steel rebar embedded in concrete as recited in claim 1, wherein the
reference electrode comprises a saturated calomel electrode.
5. A steel rebar and concrete electrochemical impedance
spectroscopy test cell, comprising: a concrete prism; a length of
steel rebar embedded in the concrete prism; a counter electrode
embedded in the concrete prism, the counter electrode being
positioned adjacent and parallel to the length of steel rebar; a
reservoir supported on an external face of the concrete prism, the
reservoir being adapted for receiving a volume of an electrolytic
solution; and a reference electrode positioned in the electrolytic
solution in the reservoir, the working electrode, the counter
electrode, the concrete prism, and the reference electrode immersed
in electrolytic solution defining a three-electrode electrochemical
impedance spectroscopy (EIS) test cell adapted for connection to an
EIS test instrument.
6. The steel rebar and concrete electrochemical impedance
spectroscopy cell as recited in claim 5, wherein the counter
electrode comprises a graphite electrode.
7. The steel rebar and concrete electrochemical impedance
spectroscopy cell as recited in claim 6, wherein the electrolytic
solution comprises simulated concrete pore solution.
8. The steel rebar and concrete electrochemical impedance
spectroscopy cell as recited in claim 7, wherein the reference
electrode comprises a saturated calomel electrode.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to procedures for testing
structural materials used in the construction industry, and
particularly to a method of ascertaining fully grown passive film
formation on steel rebar embedded in concrete using electrochemical
impedance spectroscopy (EIS).
[0003] 2. Description of the Related Art
[0004] Electrochemical impedance spectroscopy (EIS) (sometimes also
referred to as "dielectric spectroscopy" or "impedance
spectroscopy") is a technique for measuring the dielectric
properties of a medium as a function of frequency. EIS is based on
the interaction of an external electric field with the electric
dipole moment of a sample, typically expressed by electrical
permittivity. EIS is often used as an experimental method for
characterizing electrochemical systems. The technique measures the
impedance of a system over a range of frequencies, and therefore
the frequency response of the system (including the energy storage
and dissipation properties) is revealed. Typically, data obtained
by EIS is expressed graphically in a Bode plot or a Nyquist
plot.
[0005] FIG. 2 illustrates a conventional three-electrode
electrochemical cell for electrochemical impedance measurement by
EIS. Cell 100 contains an electrolyte solution 108 in which a
working electrode 102 and a counter electrode 104 are immersed.
Typically, the working electrode 102 and the counter electrode 104
are parallel plate electrodes. In addition to the working electrode
102 and the counter electrode 104, a third voltage reference
electrode 106 is placed close to the polarization layer (i.e., the
region of positive polarization 110 near the working electrode 102)
and measures the voltage difference of the polarization double
layer capacity to the working electrode 102. The working electrode
102 is made of the metal to be characterized in combination with
the electrolyte 108. The reference electrode 106 may be, for
example, an open-tipped glass capillary filled with a standard
electrolyte coupled to a standard metal in order to create a
defined electrochemical potential to the electrolyte.
[0006] The total potential drop across the cell is summed up by all
contributions of the chemical process, including mass transport,
chemical and adsorption steps, electron transfer, etc. By measuring
the impedance spectrum:
V REF * ( .omega. ) I s * ( .omega. ) ##EQU00001##
over angular frequency range .omega. and fitting it with an
equivalent circuit model, the several process contributions can be
separated from each other. The typical evaluation includes
determination of Warburg impedance related to mass transport,
electron transfer resistance, electrolyte resistance and double
layer capacity, As the electrochemical reaction takes place on the
working electrode 102, it is necessary to keep the DC potential
V.sub.REF at a defined value, or alternatively, apply a constant DC
current to the cell. This is often performed with a
potentiostat/galvanostat DC circuit.
[0007] Electrochemical impedance spectroscopy has been used to
characterize the nanoscale passive film formation on steel rebar in
concrete at different stages of exposure in simulated concrete pore
solution (SPS). However, since the rebar is placed in SPS, rather
than an actual concrete environment, the EIS results are typically
not representative of the actual behavior. It would be desirable to
be able to characterize nanoscale passive film formation on steel
rebar in its actual concrete environment.
[0008] Thus, a method of ascertaining fully grown passive film
formation on steel rebar embedded in concrete solving the
aforementioned problems is desired.
SUMMARY OF THE INVENTION
[0009] The method of ascertaining fully grown passive film
formation on steel rebar embedded in concrete utilizes
electrochemical impedance spectroscopy (EIS) to determine, in situ,
the degree or quality of passive film formation on steel rebar
embedded in concrete. A length of steel rebar and a counter
electrode, such as a graphite electrode, are both embedded in a
concrete slab, the counter electrode being positioned adjacent and
parallel to the length of steel rebar. For electrochemical
impedance spectroscopy, the length of steel rebar acts as a working
electrode. A reservoir is supported on an external face of the
concrete slab and filled with an electrolytic solution, such as
simulated concrete pore solution. A reference electrode, such as a
saturated calomel electrode, is then positioned in the electrolytic
solution, and the length of steel rebar, the counter electrode and
the reference electrode are electrically connected to an EIS test
instrument to perform electrochemical impedance spectroscopy in
order to generate a plot of impedance as a function of frequency
for the coupled length of steel rebar and the counter electrode.
The plot is then matched to a known plot of passive film formation
on steel rebar, and a degree or quality of passive film formation
on the length of steel rebar is determined based on passive film
formation associated with the matched plot.
[0010] These and other features of the present invention will
become readily apparent upon further review of the following
specification.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is a schematic diagram illustrating a steel rebar and
concrete electrochemical impedance spectroscopy cell for performing
a method of ascertaining fully grown passive film formation on
steel rebar embedded in concrete according to the present
invention.
[0012] FIG. 2 is a schematic diagram illustrating a conventional
prior art electrochemical impedance spectroscopy cell.
[0013] FIG. 3 is an exemplary graph showing measured potential as a
function of time for a length of steel rebar embedded in concrete
using the method of ascertaining fully grown passive film formation
on steel rebar embedded in concrete according to the present
invention.
[0014] Unless otherwise indicated, similar reference characters
denote corresponding features consistently throughout the attached
drawings.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0015] The method of ascertaining fully grown passive film
formation on steel rebar embedded in concrete utilizes
electrochemical impedance spectroscopy to characterize nanoscale
passive film formation on steel rebar while it is embedded in its
actual concrete environment. As shown in FIG. 1, a three-electrode
electrochemical impedance cell 10, similar to cell 100 of FIG. 2,
is established, using steel rebar 12 embedded in concrete 20 as the
working electrode. A counter electrode 14, which may be formed from
any suitable conductive material, such as graphite, is embedded in
the concrete 20 parallel to the steel rebar working electrode 12. A
reservoir 22 is supported on an external face 24 of the concrete
slab 20 and contains an electrolyte solution 18. A reference
electrode 16 is immersed in the electrolyte solution 18, as
shown.
[0016] The reference electrode 16 may be, for example, a saturated
calomel electrode (SCE). An SCE, as is well known in the art, is a
reference electrode based on the reaction between elemental mercury
and mercury(I) chloride. The aqueous phase in contact with the
mercury and the mercury(I) chloride (Hg.sub.2Cl.sub.2 or "calomel")
is a saturated solution of potassium chloride in water. The
electrode is normally linked via a porous frit to the solution in
which the other electrode is immersed, where the porous fit is a
salt bridge. The steel rebar working electrode 12, the counter
electrode 14 and the reference electrode 16 are each in electrical
communication with an EIS test instrument or controller 26, which
supplies voltage, measures the impedance and calculates the
electrochemical impedance spectroscopy results. It should be
understood that EIS test instruments are available in many
different configurations, and in the drawings, controller 26
represents any suitable type EIS test instrument known in the art,
which may include a computer, programmable logic controller,
digital signal processor, or other data processing device
programmed to perform EIS calculations and output EIS results.
Using electrochemical impedance spectroscopy to measure the degree
or quality of corrosion in metals is well known. An example is
shown in U.S. Patent Application Publication No. 2008/0179198,
which is hereby incorporated by reference in its entirety.
[0017] In use, the length of steel rebar 12 and the graphite
counter electrode 14 are both embedded in a concrete slab 20, the
counter electrode 14 being positioned adjacent and parallel to the
length of steel rebar 12, as shown in FIG. 1. A terminal portion of
each electrode 12, 14 extends from the concrete slab 20 for
connection to the controller 26 by suitable wires/cables. For
electrochemical impedance spectroscopy, the length of steel rebar
12 acts as a working electrode. A reservoir 22 is mounted on an
external face 24 of the concrete slab 20 and filled with an
electrolytic solution 18, such as simulated concrete pore solution.
A reference electrode 16, such as a saturated calomel electrode, is
then positioned in the electrolytic solution 18, and the length of
steel rebar 12, the counter electrode 14 and the reference
electrode 16 are electrically connected to the controller 26 to
perform electrochemical impedance spectroscopy in order to generate
a plot of impedance as a function of frequency for the coupled
length of steel rebar 12 and the counter electrode 14. The plot is
then matched to a known plot of passive film formation on steel
rebar, and the degree or quality of passive film formation on the
length of steel rebar 12 is determined based upon passive film
formation associated with the matched plot.
[0018] In order to evaluate the present method, the results from
the cell 10 of FIG. 1 were compared against results performed in a
simulated concrete pore solution (SPS). The steel reinforcement
bars used in the experiments each had lengths of 300 mm, and were
descaled by abrading, followed by having their surfaces embedded in
concrete. Type I cement, in compliance with the requirements of
ASTM C150, was used. Coarse aggregates in the cement include a
blend of 20 mm and 10 mm crushed limestone, which were obtained
from quarries near Riyadh, Saudi Arabia. The fine aggregates were a
blend of natural red sand and manufactured sand obtained from the
crushed limestone. The mix proportions used in the concrete
specimens are shown in Table 1 below.
TABLE-US-00001 TABLE 1 Concrete Mix Proportions Material
Proportions (kg/m.sup.3) Cement 350 20 mm Aggregates 735 10 mm
Aggregates 315 Crushed Sand 195 Silica Sand (Red Sand) 585
[0019] In the experiments, a typical water-to-cement ratio (w/c) of
0.50 was used. Standard laboratory curing conditions were used, in
which standard prism specimens in plastic molds were stored in a
laboratory environment at standard room temperature for the first
24 hours, followed by demolding before the start of testing.
Corresponding to the diagrammatic illustration of FIG. 1, the
experimental reinforced concrete prismatic specimen 20 had
dimensions of 100 mm.times.100 mm.times.250 mm. As shown in FIG. 1,
the first 25 mm of exposed rebar surface of each rebar electrode
(adjacent the opening edge of the concrete specimen 20) was blocked
with a tight cover of Teflon.RTM. tape 30, secured with a layer of
epoxy resin. These end blocks 30 ensured a crevice-free entering
end of each rebar electrode in the concrete specimen 20. After
demolding the specimen, the pond reservoir 22 was made atop the
concrete 20, filled with the simulated concrete pore solution
(i.e., the electrolytic solution 18) for use in the electrochemical
impedance studies. Open circuit potentials and electrochemical
impedance spectra were evaluated via controller 26 every 24 hours
for a period of 32 days.
[0020] A set of data were generated from the reinforcement bar
samples embedded in solid concrete, as described above, and the
resultant potential vs. time plot is shown in FIG. 3. Here, the
changes in corrosion potentials developed at the concrete-rebar
interfaces were monitored for 32 days. As can be seen in FIG. 3, a
systematic ennobling in potential over time takes place up to 20
days of exposure. Beyond this period, the change is relatively slow
with movement of potentials in the active direction.
[0021] The initial shift of potential (in the nobler direction) is
attributed to the thickening of the oxide, resulting in anodic
polarization of the reaction taking place at the rebar/concrete
interface. The fluctuation of the potential in the active direction
beyond 20 days is most likely due to cathodic polarization caused
by the limited supply of oxygen at the interface. After initial
hydration and other reactions, concrete becomes denser with the
passage of time after casting, which limits the supply of oxygen at
the rebar/concrete interface, resulting in polarization of cathodic
reaction.
[0022] It can be further seen in FIG. 3 that the drifting of the
potential remains mostly in the range of -90 mV to -120 mV. As per
ASTM C876-09, this potential is in the range of protective
potential for steel exposed in concrete. These results reveal the
passive film on steel rebars becomes a fully protective film after
20 days of exposure. This period is longer than the protective
potential attained by the rebar exposed to SPS. These results
suggest that the film formation and growth is slower in solid
concrete compared to the simulated pore solution. The presence of a
higher content of oxygen and alkalinity in the simulated pore
solution in comparison to solid concrete may have contributed to
the rapid nucleation and growth of the passive film in the case of
rebars exposed to SPS.
[0023] It is to be understood that the present invention is not
limited to the embodiments described above, but encompasses any and
all embodiments within the scope of the following claims.
* * * * *