1
FACTORS AFFECTING THE NANO-SCALE INVESTIGATION OF
PASSIVE LAYER FOR CORRODING STEEL BARS IN CONCRETE
UNDER SEVERE ENVIRONMENTAL CONDITIONS
Raja Rizwan HUSSAIN (1), Abdulrahman ALHOZAIMY (2), Abdulaziz Al
NEGHEIMISH (3) and Rajeh Al ZAID (4)
(1) Asst. Professor, Center of Excellence for Concrete Research and Testing, Civil
Engineering Department, King Saud University, Riyadh, Saudi Arabia.
(2) Professor, Center of Excellence for Concrete Research and Testing, Civil Engineering
Department, King Saud University, Saudi Arabia.
(3) Executive Director and Associate Professor, Center of Excellence for Concrete Research
and Testing, Civil Engineering Department, King Saud University, Riyadh, Saudi Arabia.
(4) Professor, Center of Excellence for Concrete Research and Testing, Civil Engineering
Department, King Saud University, Riyadh, Saudi Arabia.
Keywords:
Nanotechnology, Corrosion, Passive Layer, SEM, XRD, EDS, Reinforced Concrete.
Author contacts
Authors E-Mail Fax Postal address
First Author [email protected] +966-1-4696355
PO Box: 800, CoE-CRT,
King Saud University,
Riyadh, 11421, Saudi Arabia.
Second Co-author +966-1-4696355
PO Box: 800, CoE-CRT,
King Saud University,
Riyadh, 11421, Saudi Arabia.
Third Co-author +966-1-4696355
PO Box: 800, CoE-CRT,
King Saud University,
Riyadh, 11421, Saudi Arabia.
Fourth Co-author +966-1-4696355
PO Box: 800, CoE-CRT,
King Saud University,
Riyadh, 11421, Saudi Arabia.
Contact person for the paper: Dr. Raja Rizwan Hussain, Asst. Professor, Center of Excellence
for Concrete Research and Testing, Civil Engineering Department, King Saud University.
e-mail: [email protected], Tel:+966-562-556969, Fax: +966-1-4696355,
Postal address: PO Box: 800, Riyadh, 11421, Saudi Arabia.
2
FACTORS AFFECTING THE NANO-SCALE INVESTIGATION OF
PASSIVE LAYER FOR CORRODING STEEL BARS IN CONCRETE
UNDER SEVERE ENVIRONMENTAL CONDITIONS
Raja Rizwan HUSSAIN (1), Abdulrahman ALHOZAIMY (2), Abdulaziz Al
NEGHEIMISH (3) and Rajeh Al ZAID (4)
(1) Asst. Professor, Center of Excellence for Concrete Research and Testing, Civil
Engineering Department, King Saud University, Riyadh, Saudi Arabia.
(2) Professor, Center of Excellence for Concrete Research and Testing, Civil Engineering
Department, King Saud University, Saudi Arabia.
(3) Executive Director and Associate Professor, Center of Excellence for Concrete Research
and Testing, Civil Engineering Department, King Saud University, Riyadh, Saudi Arabia.
(4) Professor, Center of Excellence for Concrete Research and Testing, Civil Engineering
Department, King Saud University, Riyadh, Saudi Arabia.
Abstract
The presence of ambient hot weather and chloride ions in the soil, ground water, as well as in
the concrete raw materials is a major cause of corrosion in reinforced concrete structures.
Chloride ions and high temperature break the passive film on the reinforcement steel surface
in concrete protecting the steel from corrosion which is believed to be in nanometers and
primarily composed of iron oxides. However, little is known about the chemical composition
and the structure of the passive film as well as its breaking process. This makes it difficult to
classify corrosion, proven by the fact the chloride threshold value of steel measured by
conventional electro-chemical techniques under variable temperature conditions can vary
greatly. While this technique measures corrosion in a macro scale, the growth and
deterioration of passive film actually takes place on nano-scale and is governed by the
elemental compositions and nano-microstructure of the steel as well as the chemistry of the
concrete pore solutions around the rebar. This paper focuses on factors and limitations
affecting the characterization of passive layer at the nano-scale using different techniques. To
address these key issues, factors and limitations affecting the nano-techniques (such as SEM,
XRD, EDS/EDX, XRF, Metallography) have been addressed to obtain a more precise
characterization of passive film as well as its breaking in terms of nano-micro structural
material properties. The nano-scale investigations conducted in this paper revealed that the
steel bars with passive oxide layer have an orderly structure in contrast to what was expected.
A comparison of steel bar with passive layer showed a uniform repeating pattern in contrast to
the surface without passive layer at the nano-level. This is an interesting and novel finding
which will be further explored and reported in the future. Three Iron-oxides (β-Fe2O3, Fe0.92O
3
and Fe3O4) as well as Iron hydroxide (Fe (OH)3) were identified in this passive layer.
However, the results presented in this paper are preliminary and will be elaborated in detail in
the future.
1. INTRODUCTION
Despite the substantial amount of research work reported, quantitative nano-scale
investigation of passive layer characterization and its breakdown for corroding steel in
concrete under severe coupled environmental conditions of chloride and high temperature has
yet to be fully explored. Furthermore, it was found from the previous data that there exists a
difference of opinion among various researchers. Conducted at the level of the atom and
molecule, the scale of such research is generally ten times the diameter of a water molecule,
i.e., one billionth of a meter: a nanometre. Corrosion damage investigation in RC (reinforced
concrete) structures has become important field of study in civil engineering, with the goal of
continuous and periodic assessment of the safety and integrity of the corroded civil
infrastructure. For decades, the struggle to deal with the detrimental effects of several
environmental loadings on RC structures such as hot weather in countries like Gulf region has
been a major area of concern for researchers. In the recent past, the authors of this paper have
been involved deeply in the research related to the corrosion of reinforced concrete structures
under variable environmental actions from macro to micro scale [1-11]. In this research paper,
problems regarding the study of passive layer, its break down and corrosion products at the
nano-scale level using nano technology have been analysed which has limited research data in
the past.
Several nano-techniques are available for analysing materials at the nano-scale level in
the present era. However, nano-scale investigation of passive layer complete characterization
as well as its breakdown and corrosion products formation for reinforced concrete under
several environmental actions is yet to be fully explored [12, 13]. In the previous research
[14], the behaviour and evolution of passive films generated on AISI 304L has been studied at
the nano-scale for a long immersion time in chloride containing media. A theoretical
impedance function was deduced by the use of nanotechnology [15] for a proposed
mechanism of passive film formation of steel in contact with alkaline aqueous media
involving two reaction intermediates: mixed oxide with similar stoichiometry to magnetite
and Fe(III)-oxides. In one of the previous reported researches [16], the corrosion resistance of
C+Mo dual-implanted H13 steel was studied using multi-sweep cyclic voltammetry and
nanotechnology. Evolution of the passive films formed on AISI 304L and duplex stainless
steel SAF 2205 in NaOH 0.1M was investigated by C. M Aberu et. al. at nano-scale [17]
using X-ray photoelectron spectroscopy (XPS). The effect of chloride and nitrite ions on the
passivity of steel in alkaline solutions was also investigated at the nano-scale [18]. The
influence of stress on passive behaviour of steel bars in concrete pore solution was studied
with electrochemical impedance spectroscopy and X-ray photoelectron spectroscopy [19]. X-
ray photoelectron spectroscopy (XPS) had also been used to study the properties of passive
oxide film that form on carbon steel in saturated calcium hydroxide solution and the effect of
chloride on the film properties [20].
However, the nano-scale techniques used in all the above reported research studies have
several limitations, difference of opinion and factors affecting the quality, repeatability,
4
reproducibility and reliability of nano-scale investigation results which needs to be clearly
pointed out and remains for future studies. This leads to the objectives of this research paper.
2. EXPERIMENTATION
A general plan of experimental program is outlined including the broad design and
methodology that has been adopted in this research. Various nano-technological experimental
testing techniques were employed in this research. Scanning Electron Microscopy (SEM) -
both Tungsten and Field Emission imaging was used from micro to nano scale for steel
passive layer and corrosion products as well as the Interfacial Transition Zone (ITZ) between
the embedded steel and concrete. Energy Dispersive Spectroscopy/Energy Dispersive X-ray
(EDS/EDX) elemental analysis was carried out for passive layer and interfacial transition
zone characterization. X-ray Diffraction (XRD) peak location and compound identification of
passive layer as well as the corrosion products was performed at low angle (2θ) special
attachment for thin film analysis. FT-IR material orientation analysis was also conducted to
observe the geometry and arrangement of particles. Photo Electron Spectroscopy for material
characterization and elemental constituent analysis of metals was conducted for various types
and brands of steel available in the local market of gulf region. Along with that,
metallographic analysis for steel reinforcement x-section was also conducted to reveal TM
and PF rings in TMT bars which are very important for passive layer successive
characterization. The Nano-Experimental techniques have been used by many researchers in
the past to study the surface characteristics of many materials at the nanometer scale.
However, in this research, nano-scale studies on the characteristics of iron oxide surface
passive films formed on steel rebars in concrete pore solution have been reviewed which have
limited data in the past and there exists a difference in opinion as well between various
researchers with regards to this passive iron oxide nano-layer.
Material Properties
The materials used and their properties are as follow:
• Reinforcing Steel: Steel bars were procured from five different locally available sources
namely; 1. Sabic Hadeed Steel 2. Ittefaq Steel 3. Muhaidib Steel 4. China Steel and 5.
Korean Steel which is deliberately named as steel source A, B, C, D and E in this paper
(Details are provided in the following sections).
• 20 mm coarse aggregates, procured from Saudi Ready Mix Company, North Riyadh,
KSA, Bulk Specific Gravity: OD basis = 2.58, Absorption, % = 1.56.
• 10 mm coarse aggregates, procured from Saudi Ready Mix Company, North Riyadh,
KSA, Bulk Specific Gravity: OD basis = 2.62, Absorption, % = 1.17.
• Crushed sands, procured from Saudi Ready Mix Company, North Riyadh, KSA, Bulk
Specific Gravity: OD basis = 2.58, Absorption, % = 2.00, Fine Modulus = 4.41.
• Silica sands, procured from Saudi Ready Mix Company, North Riyadh, KSA, Bulk
Specific Gravity: OD basis = 2.58, Absorption, % = 0.376, Fine Modulus = 1.04.
• Cement, procured from Al-Yammamah Cement Company, KSA with chemical
composition satisfying ASTM C-150 for Type I cement.
5
• Sodium Chloride: 99.9% pure sodium chloride was obtained from VWR Chemicals as a
source for chloride ions in concrete and pore solution.
• Water: Tap water available at King Saud University, Civil Engineering Department,
KSA.
Specimen Preparation
Mild Steel (MS) rebar specimens were prepared from a 12 meter long as received deformed
and plain black steel rebars from five different production sources, measuring 6-14 mm in
nominal diameter. The rebars were cut into 1000mm, 10mm and 2 mm segments (Fig. 1) to
suffice the requirement of various SEM and XRD machines as well as their sample holders.
The five steel sources commercially available in the gulf region are being tested under three
types of surface conditions including as received with black oxide mill scale, polished and
brown rust condition (Fig. 2). In general, concrete ingredients were mixed by following
ASTM C-192 “Standard Method of Making and Curing Concrete Test Specimens in the
Laboratory”. Aggregates together with absorption water were added into the mixer first, and
after a few revolutions of the mixer, the cement and the remaining water were added. The
mixer was run for 3 minutes after all ingredients were added into it, then left to rest for 3
minutes, and finally was run for another 2 minutes. After preparation of concrete mixes,
standard tests were performed including: Slump test based on ASTM C-143 “Standard Test
Method for Slump of Portland Cement Concrete” and setting time tested as per ASTM C-403
“the Standard Test Method for Time of Setting of Concrete Mixtures by Penetration
Resistance”.
Preparation of Pore Solutions
Simulated Concrete Pore Solution: Synthetic pore solution was prepared consisting of 7.4 g
NaOH and 36.6 g KOH per litre of saturated calcium hydroxide solution. The solution was
saturated with Ca(OH)2 to simulate conditions in ordinary portland cement concrete. Prior to
its use, the solution was kept for 24 h under continuous magnetic stirring (Fig. 3) and then
filtered on Wattman paper of No. 15 grade. This was necessary to remove insoluble CaO from
the solution.
Cement Extracts: Ordinary Portland cement was sieved through 150µm sieve and extract was
prepared as 100 g of the cement was mixed with 100ml of distilled water and shaken
vigorously using a microid flask mechanical shaker for about 1 hour. The extracts were then
collected by filtration.
Concrete Leached Pore Solution: Another technique was considered to extract the pore
solution from the concrete itself. A concrete prism was cast with a cylindrical hole throughout
the specimen having diameter just equal to the actual steel bar to be tested. Then the steel bar
was inserted into the concrete prism hole and the hole was filled with distilled water. The idea
was to leach the actual pore solution from the concrete in the very small fitting gap between
the steel bar under investigation and the concrete prism hole inner periphery. PH meter is used
to monitor the leached pore solution.
NaCl Pore Solution: Another set of solution was prepared as above and NaCl was added to
these solutions to simulate aggressive conditions prone to corrosion. The oxygen
6
concentration of the stagnant solutions was monitored during the experiments. The
concentration of oxygen was sufficiently high in the solutions (>1 mg/L) for the oxygen
reduction reaction to take place; therefore, oxygen bubbling in the solutions was not required
in general. All reagents were of at least ACS grade and the solutions were prepared with
distilled water with conductivity of 0.8µS/cm. The pH of solutions was carefully checked by a
Methron pH meter and was found to be around 12.3.
Fig.1 1mm, 10mm and 2mm Fig. 2 As received, polished Fig. 3 Pore solution under
rebar samples and brwon rusted rebars continuous magnetic stirring
3. RESULTS AND DISCUSSIONS
The chemical composition and structure of steel rebars was determined. At first SEM-EDXA
analysis was performed for various sources of rebars to find out the elemental composition of
rebars but it was observed that the elemental composition of lighter elements such as ‘Carbon’
was difficult to determine with EDXA analysis. Therefore, Photo-Electron Spectroscopy was
conducted to find out the exact chemical composition of all the elements present in steel bars
obtained from different local production sources. Along with that, metallographic technique
was also used to further study the surface texture of steel bars. All this data is important in the
sense that the successive passive layer which will be developed on the steel after immersion in
alkaline pore solution environment will be influenced by all these properties of steel bars.
The steel samples were cut, polished and prepared in resin moulds as shown in Fig. 4.
The results of Photo-Electron Spectroscopic analysis carried out to determine the elemental
constituents of various steel sources available in the Kingdom are presented in the following
Table 1. The bar ‘A’ was found to have the lowest carbon content which makes it more
resistant to corrosion. Steel ‘C’ & ‘E’ had intermediate carbon content. While, the bar ‘B’ &
‘D’ had maximum percentage of carbon which makes them more prone to corrosion. The
sulphur content in steel source ‘D’ is 0.04 % which is relatively high and the rebar will be
even more prone to corrosion due to the presence of MnS inclusions in the steel as compared
to other steel sources. Regarding the role of steels on nature of passive film, the micro level
observations are quite evident. It can be seen from the metallographic images of etched steel
samples shown in Fig. 5 that TM (Tempered martensite) ring of rebars which plays very
important role on corrosion rate, differ to a great extent in steels produced by different
companies.
7
Table.1: Elemental Composition of Various Steel Bars
Element % A B C D E
C 0.11 0.25 0.13 0.26 0.14
Si 0.13 0.21 0.12 0.19 0.14
Mn 0.34 0.85 0.57 0.92 0.59
P 0.032 0.019 0.018 0.016 0.015
S 0.030 0.021 0.017 0.040 0.019
Cr 0.024 0.018 0.015 0.060 0.020
Ni 0.009 0.005 0.012 0.051 0.014
Mo 0.004 0.001 0.003 0.009 0.004
Al 0.001 0.001 0.002 0.001 0.002
V 0.003 0.001 0.003 0.002 0.002
Sn 0.026 0.001 0.005 0.019 0.005
Fig. 4 Various Steel Samples Prepared for Analysis
sample “A” sample “B” sample “C”
sample “D” sample “E”
Fig. 5 Metallographic Images of Various Steel Sources
Characterization of Passive Layer Developed on Steel Rebars in Pore Solutions
The characterization of passive layer developed on steel bars under pore solution environment
was carried out. The constituent compound analysis as well as growth of passive layer was
investigated under various conditions. The steel samples embedded in concrete were cut
around the steel bar in small squares to fit in the limited space of SEM (scanning electron
8
microscope) and analyzed for the passive layer development around steel bar in the natural
alkaline environment of concrete (Fig. 6).
Fig. 6 Steel embedded in Concrete Being Tested in SEM
As a first trial, SEM was employed to observe the passive layer around the periphery of steel
bar type ‘C’ and images were taken at different resolutions as shown in Fig. 7. These images
proved to be very helpful to reveal the interface of concrete and steel where passive layer is
developed. It was observed that the surface of steel bar which seemed very smooth at macro
level was still very non-uniform at micro and nano level which definitely affects the quality of
passive layer.
It was decided to carry out sensitivity analysis using EDXA technique around the passive
layer to study the surrounding area and its influence on the passive layer itself. For this
purpose, block and spot spectrums were taken at different locations around the passive layer
as shown in Fig. 8. As a first step, block spectrum was taken in the concrete area around the
passive layer as shown in Fig. 8 (a). It is to be noted that as already discussed, carbon ‘C’
being a lighter element was difficult to detect correctly by EDXA-FEM analysis and should
be ignored throughout the analysis considering the carbon content as erroneous and a
limitation of EDS analysis. Taking a spectrum on the steel surface close to the passive layer
for EDS analysis (Fig. 8(b)), it was observed that the number of elements reduced. The
amount of ‘O’ also became much less confirming the fact that the analysis was being targeted
in the steel area close but not in the passive layer. The percentage of iron also increased
substantially and that of calcium decreased as compared to the Fig. 8 (a) again confirming the
above said. This sensitivity analysis provided confidence and hands on experience on the
machine. Again, it was noticed that the amount of carbon was much higher than expected and
was therefore erroneous.
The EDS sensitivity analysis was repeated several times to obtain expertise and
confidence in the hands on experience and confidence for the exact location of analysis on the
periphery of steel concrete to obtain accurate and averaged conclusion. Another idea was to
zoom in to the nano-scale, close to 10 nm and then repeat the above steps. In the light of
observations obtained from sensitivity analysis performed in Fig. 8, a more systematic
approach was adopted to identify the passive layer. A certain point was fixed in the SEM and
then was zoomed inside the reach the passive layer without changing the coordinates (Fig. 9).
But, unfortunately it was observed that the tungsten filament SEM being used in this analysis
did not have enough resolution to show images in beyond 200 nm as shown in the Fig. 10. It
can be concluded here that tungsten filament SEM is not capable of performing the passive
9
layer analysis and need was felt to utilize FE-SEM (Field Emission scanning electron
microscope) having enough resolution to focus deep into the nano-scale. Also, XRD analysis
was tried but since it cannot be focused on a small area of periphery of steel bar having
passive layer, satisfactory results were not obtained. Raman spectra seem to be a suitable
option and should be adopted under the above circumstances.
Fig. 7 SEM Image of Steel Concrete Interface (Passive layer Orientation)
135
Element Weight% Atomic%
C K 6.49 11.32
O K 48.05 62.94
Na K 0.43 0.39
Mg K 0.91 0.79
Al K 1.68 1.30
Si K 6.26 4.67
S K 0.73 0.48
K K 0.38 0.20
Ca K 32.07 16.77
Ti K 0.14 0.06
Fe K 2.87 1.08
Totals 100.00
Fig. 8(a) EDXA Analysis of Steel Concrete Interface (Passive Layer)
136
Element Weight% Atomic%
C K 9.77 29.37
O K 6.41 14.47
Mg K 0.27 0.41
Al K 0.19 0.26
Si K 1.46 1.88
Ca K 2.57 2.31
Mn K 0.51 0.33
Fe K 78.81 50.96
Fig. 8 (b) EDXA Analysis of Steel Concrete Interface (Passive Layer)
Fig. 8 FEM-EDXA Analysis of the X-section side of passive layer
10
Fig. 9 SEM Imaging of Passive layer Fig. 10 Sensitivity Analysis of steel
existing in steel-concrete Interface concrete interface to locate the passive layer
The above discussion was for the case of steel embedded in concrete and being observed from
the X-section side. In the next step, steel bars immersed in the simulated concrete pore
solution (SPS) were analyzed under SEM from the top surface for passive layer EDXA
analysis. The corresponding systematic SEM images are as shown in Fig. 11 and 12. A
surface texture of passive layer developed on steel immersed in pore solution at high
resolution (Fig. 12) showed deposits of pore solution on the passive layer as contamination
and should be ignored during analysis. Also, it was observed that the penetration of electrons
from the SEM were deep enough to bypass the thickness of passive layer and SEM-EDS
analysis may not represent the passive layer but the layer beneath it. It should be kept in mind
that this sensitivity analysis was done merely for hands on experience and understanding of
machine operations and specimen behavior. Several EDS sensitivity analyses were conducted
as already described in the previous section and similar conclusions were drawn. To avoid
repetition, only representative results are presented in Fig. 13.
Fig. 11 SEM Imaging of Steel surface bearing passive layer in simulated pore solution
(SPS)
11
Fig. 12 SEM Imaging of Steel surface bearing passive layer in SPS
169
Element Weight%
C K 56.09
O K 15.00
Al K 2.85
Si K 0.64
Cl K 3.95
Ca K 0.66
Fe K 20.80
Totals 100.00
Fig. 13 SEM-EDXA analysis of sample with passive layer
(Washed and Desiccated)
After obtaining the above results, it was concluded that Field Emission SEM (FE-SEM) must
be fetched and involved in passive layer nano-scale analysis so that the very fine passive layer
(in nano-meters) can be completely analyzed and its structure understood properly. Fig. 14
and Fig. 15 below show the FE-SEM images of steel bar with and without passive layer at the
nano-scale. A unique and repetitive symmetrical pattern was found in the structure of passive
layer at the nano-scale developed on polished steel bars while taking images under FEG SEM.
This is a rather new and very interesting finding of this research project which has not been
reported in the past that the passive oxide layer on the steel surface actually does have a
uniform repeating pattern instead of just being a random non-uniformly structured layer.
Images (Fig. 16) taken with FE-SEM at the nano-scale revealed an interesting observation
that the steel bar even without the passive layer is not so uniformly structured over the surface
as was thought and gives a similar non-uniform surface structural look as found in case of
concrete when zoomed to the nano-scale. In fact the field emission scanning electron
12
microscope images (Fig. 15) obtained at the nano-scale revealed that the steel bars with
passive oxide layer have even more orderly structure in contrast to what was expected.
1.5kV, 60,000x, SEI,
6.3mm WD
1.5kV, 100,000x, SEI
6.3mm WD
Fig. 14 Steel Surface without Passive Layer (nano-scale) FE-SEM Images
1.5kV, 60,000x, SEI,
6.2mm WD
1.5kV, 100,000x, SEI
6.2mm WD
Fig. 15 Steel Surface with Passive Layer (nano-scale) FE-SEM Images
1.5kV, 60,000x, SEI,
6.2mm WD
(With passive layer)
1.5kV, 60,000x, SEI,
6.3mm WD
(Without passive layer)
Fig. 16 FE-EM Images of Steel Bar Surface (nano-scale)
13
After revealing the above interesting information, X-ray diffraction (XRD) analysis was
conducted on the passive layer to understand the compound analysis of this oxide layer
formed on the steel surface under alkaline conditions. The XRD pattern and possible material
identification is presented in Fig. 17. It was found that most of the materials present in the
passive layer were not easily identifiable and needed advanced and complete set of data-base
for the XRD peaks to be identified satisfactorily. This is our present limitation that the
complete database required for such sophisticated material analysis is not available. The
materials identified in the passive layer comprised of various oxides of iron in different
phases, such as Hematite, Magnetite, Wuestite, PIstite, Magnesioferrite etc. along with some
other compounds as shown in Fig. 17.
It was seen from the XRD peaks of various steel sources that the passive layers developed on
various steel sources under simulated pore solution environment are different from each other.
This opens areas of future research in this project to explore the various possibilities and
reasons for these differences in the composition of passive layers developed on different steel
sources shown in Fig. 18. The qualitative comparison of various XRD patterns show that the
peaks observed in case of steel ‘A’, ‘B’ and ‘C’ are not same but similar probably belonging
to the different phases of the same family.
Visible Ref.Code Score Compound Name Displ.[°2Th] Scale Fac. Chem. Formula
* 01-073-0603 45 Hematite, syn 0.922 0.919 Fe2 O3
01-086-2316 17 Wuestite, syn 0.720 0.053 Fe0.902 O
01-074-0953 23 Fe-Ringwoodite, syn 0.742 0.083 Fe2 ( Si O4 )
01-074-1886 32 Wuestite, syn 0.981 0.020 Fe O
00-042-1468 UM alumina 1.353 0.514 Al2 O3
01-088-0840 4 Hawaiite 0.982 0.311 ( Mg , Fe , Al , T..
01-079-1968 32 W\PIstite, syn 1.346 0.018 Fe.945 O
01-079-2177 33 W\PIstite, syn 1.232 0.019 Fe0.92 O
00-019-0605 5 Enstatite, ferroan 1.031 0.240 ( Mg , Fe ) Si O3
00-025-1376 UM Magnetite 1.119 0.034 ( Fe , Mg )
( Al ,..
00-002-1044 UM Magnesioferrite 1.049 0.480 Mg Fe2 +3 O4
Fig. 17 XRD Results for Passive Layers Developed on Steel Rebar
14
20 30 40 50 60 70 80 902Theta (°)
0
400
1600
3600
6400
10000
Inte
ns
ity
(c
ou
nts
)
Fig. 18 X-Ray Diffraction Analysis of Passive Layer (Qualitative)
Along with the qualitative analysis discussed above, quantitative XRD analysis was also
carried out to identify the exact chemical compositions and phases of peaks observed in
various spectra (Fig. 19). While going through the analysis of XRD peaks presented in Figure
19, it is found that except steel source ‘D’, where peaks of beta-Fe2O3 are observed; in no
other case any compound of iron is identified. In all the other cases, the peaks of CaO are
recorded. It is suspected that the reason for this observation lies in the presence of possible
concrete pore solution layer over the passive layer formations in which the steel samples were
immersed. In the future, samples will be washed and desiccated carefully to be analyzed under
XRD to avoid such problems. In another trial, a couple of steel samples were analyzed under
XRD for varying incidence angles of 0.5, 1.0 and 1.5 respectively as shown in Figs. 20. The
three spectra were overlapped and then compared with each other for possible variations due
to different phase angles. The identified compounds along with their chemical formulas are
shown in the figures 19 and 20. X-ray diffraction is a good technique to identify the phases in
the top layer of samples. Grazing incidence diffraction was performed on two samples with
different incidence angles. Iron (Fe), 3 Iron-oxides (Fe2O3, Fe0.92O, Fe3O4) as well as Iron
hydroxide (Fe(OH)3) were identified.
Fig. 19 XRD peak Identification for steel source (Quantitative)
15
Fig. 20(a) XRD spectra of steel ‘D’ at 0.5º Fig. 20(b) XRD spectra of steel ‘D’ at 1.0º
Fig. 20(c) XRD spectra of steel ‘D’ at 1.5º Fig. 20(d) XRD spectra of steel ‘D’ at
superimposed 0.5, 1.0 and 1.5º omega
Fig. 20(f) XRD spectra of steel ‘C’ at 0.5º Fig. 20(g) XRD spectra of steel ‘C’ at 1.0º
Fig. 20(h) XRD spectra of steel ‘C’ at 1.5º Fig. 20(i) XRD spectra of steel ‘C’ at
superimposed 0.5, 1.0 and 1.5º omega
Fig. 20 Incident angle sensitivity analysis for XRD compound and peak identification
16
4. CONCLUSIONS
Despite of the fact that different techniques have been used for nano-scale studies of
extremely thin and delicate iron oxide passive films on steel rebars in concrete, the results are
not consistent and strongly depend on the type of exposure conditions, method of sample
preparation, equipment employed, analysis scale, standard library database available, skill of
the worker, precision and accuracy of measurement, insitu testing technique etc. It should be
noted that there are a number of challenges associated with these techniques when used for
non-uniform naturally developed layers (passive layer on steel reinforcement in conrete) that
can account for the lack of consistency and accurate information. A slight negligence in any
of the above factors can lead to entirely different experiment and analysis results. Especially,
a lot of care is need for sample preparation that minimizes damage to the specimen,
conducting in-situ test, proper interpretation of results and inherited limitations of the devices
used in these nano-techniques. Even though the minimization of the errors associated with
these challenges may provide an insight into the properties of passive oxide film developed on
steel reabrs in concrete and its behavior under circumstances comparable to the actual
exposure conditions, it is not practically possible to eliminate all these experimental
limitations. Therefore, multiple techniques that complement each other must be used to study
these phenomena for future concrete.
5. ACKNOWLEDGEMENTS
This research project has been supported by King Abdulaziz City for Science and Technology
(KACST), Long Term Comprehensive National Plan for Science, Technology and Innovation
(NPST), Project No. 09-NAN674-02, Riyadh, Saudi Arabia, 2009-2011.
6. REFERENCES
[1] Hussain Raja Rizwan, Tetsuya Ishida (2010) Influence of Connectivity of Concrete Pores
and Associated Diffusion of Oxygen on Corrosion of Steel under High Humidity,
Construction and Building Materials Journal, Vol. 24, Issue 6, pp.1014–1019.
[2] Hussain Raja Rizwan and Tetsuya Ishida (2010) Development of Numerical Model for
FEM Computation of Oxygen Transport through Porous Media Coupled with Micro-Cell
Corrosion Model of Steel in Concrete Structures, Computers and Structures Journal, Vol. 88,
Issues 9-10, pp.639–647.
[3] Hussain Raja Rizwan and Tetsuya Ishida, Experimental Investigation of Time Dependent
Non Linear 3D Relationship Between Critical Carbonation Depth and Corrosion of Steel in
Carbonated Concrete, Journal of Corrosion Engineering, Science and Technology (2010),
doi: 10.1179/147842210X12659647007086.
[4] Hussain Raja Rizwan and Tetsuya Ishida (2010) Investigation of Volumetric Effect of
Coarse Aggregate on Corroding Steel Reinforcement at the Interfacial Transition Zone of
Concrete, submitted to KSCE Journal of Civil Engineering, Vol. 15, Issue 1, pp. 153-160.
[5] Hussain Raja Rizwan and Tetsuya Ishida, Enhanced electro-chemical corrosion model for
reinforced concrete under severe coupled environmental action of chloride and temperature,
Construction and Building Materials Journal (2010), Vol. 25, Issue 3, pp. 1305-1315.
[6] Hussain Raja Rizwan and Tetsuya Ishida (2009) Critical Carbonation Depth for Initiation
of Steel Corrosion in Fully Carbonated Concrete and the Development of Electrochemical
17
Carbonation Induced Corrosion Model, International Journal of Electrochemical Science
IJES, Vol. 4, Issue 8, pp. 1178-1195.
[7] Hussain Raja Rizwan, Tetsuya Ishida (2010) Novel Approach Towards Calculation of
Averaged Activation Energy Based on Arrhenius Plot for Modeling of the Effect of
Temperature on Chloride Induced Corrosion of Steel in Concrete, Journal of ASTM
International, Vol. 7, Issue 5, pp. 1-8, doi: 10.1520/JAI102667.
[8] Hussain, R.R., Effect of moisture variation on oxygen consumption rate of corroding steel
in chloride contaminated concrete, Cement & Concrete Composites (2010), Vol. 33, Issue 1
(January 2011) pp. 154–16.
[9] Hussain Raja Rizwan and Tetsuya Ishida (2010) Induced Macro-Cell Corrosion
Phenomenon in the Simulated Repaired Reinforced Concrete Patch, Australian Journal of
Civil Engineering, Vol. 8, No. 1, pp. 53-60, Australia.
[10] Raja Rizwan Hussain, Underwater Half-Cell Corrosion Potential Bench Mark
Measurements of Corroding Steel in Concrete influenced by a Variety of Material Science and
Environmental Engineering Variables, Measurement Journal (2010), Vol. 44, pp. 274-280.
[11] Hussain Raja Rizwan (2010) Enhanced Mass Balance Electrochemical Computational
Model for Corrosion Rate of Steel coupled with CO2 Transport Model in Extremely
Carbonated Concrete, International Journal of Computers and Concrete, Vol. 8, No.2, April
2011, pp. 177-192.
[12] Rita Ghosh and D.D.N. Singh, Kinetics, mechanism and characterization of passive film
formed on hot dip galvanized coating exposed in simulated concrete pore solution, Surface &
Coatings Technology 201 (2007) 7346–7359.
[13] DDN Singh and Rita Ghosh, Corrosion Performance of Steel Rebars Embedded in
Chloride Contaminated Concrete Mortars-Role of Surfance Pre-Treatments, Metals A4aterials
And Processes, 2003, Va/. 16, No. 2-3, pp. 313-326.
[14] C.M. Abreu, M.J. Cristobal, R. Losada, X.R. Novoa, G. Pena, M.C. Perez, Long-term
behaviour of AISI 304L passive layer in chloride containing medium, Electrochimica Acta 51
(2006) 1881–1890
[15] M. Sanchez-Moreno, H. Takenouti, J.J. García-Jareno, F. Vicente, C. Alonso, A
theoretical approach of impedance spectroscopy during the passivation of steel in alkaline
media, Electrochimica Acta 54 (2009) 7222–7226.
[16] Zhang Tonghe, WU Yuguang, YI Zhongzhen, Zhang Xu & Wang Xiaoyan, Nano-
phases and corrosion resistance of C +Mo dual implanted steel, Vol. 44 No. 4 Science in
China (Series E) August 2001.
[17] C.M. Abreu, M.J. Cristóbal, R. Losada, X.R. Nóvoa, G. Pena and M.C. Perez,
Comparative study of passive films of different stainless steels developed on alkaline medium,
Electrochimica Acta 49 (2004) 3049–3056.
[18] M.B. Valcarce, M. Vazquez, Carbon steel passivity examined in alkaline solutions: The
effect of chloride and nitrite ions, Electrochimica Acta 53 (2008) 5007–5015.
[19] Xingguo Feng, Yuming Tang, Yu Zuo School of Materials Science and Engineering,
Beijing University of Chemical Technology, Beijing 100029, China Corrosion Science 53
(2011) 1304–1311.
[20] P. Ghodsa, O.B. Isgora,∗, J.R. Brownb, F. Bensebaac, D. Kingstonc a Carleton
University, Ottawa, Canada b CANMET Materials Technology Laboratory, Ottawa, Canada c
National Research Council, Ottawa, Canada Applied Surface Science 257 (2011) 4669–4677.