The document discusses the issue of corrosion in reinforced concrete structures, particularly focusing on carbon steel reinforcement in Brazilian urban and marine environments. It covers assessment techniques, monitoring methods, and prevention and rehabilitation strategies to mitigate corrosion risks, emphasizing factors like concrete characteristics and exposure conditions that influence durability. The text also provides insights into the electrochemical processes involved in corrosion and the impact of environmental factors, such as chloride ions and moisture content, on corrosion rates.

1. Reinforcement Corrosion in Exposed
Concrete: Assessment, Monitoring,
Prevention and Rehabilitation Techniques
Adriana de Araujo
Institute for Technological Research - IPT
Corrosion and Protection Laboratory
São Paulo, May, 2019

2.  Introduction
– Corrosion in concrete structure
 Assessment:
– Visual inspection and non destructive techniques
 Monitoring:
– Embedded reference electrodes and sensors
 Prevention and Rehabilitation Techniques
– Prevent and corrosion mitigation techniques
AGENDA

3. Corrosion of carbon steel reinforcing is a major
problems for the durability of civil constructions in
marine and urban atmospheres of Brazilian cities
Durability is related to:
 Conception of the project;
 Characteristics of the concrete mixture and
thickness of the rebar cover;
 Exposure and climatic conditions;
 Preventive and corrective maintenance.
Service life
was
reduced!

4. Corrosion Initiation stage
Concrete and
carbon steel
interaction
Chemichal protection:
Passive Layer Formation
Ingress of
aggressive
agents
• CO2
• chloride ions
Breaking the
passive layer: the
onset of
corrosion
• pH reduction
• critical chloride
content
Sánchez-Moreno et al.,2009; Du Plooy, 2013
internal layer: mixed iron oxides
like magnetite (Fe3O4)
external layer: Fe(III) oxide like
hematite (Fe2O3)

5.  Physic protection: the concrete cover acts as a barrier
between the steel and the external environment, limiting
the access of aggressive agents.
 Chemistry protection: the high alkalinity of the pore
solution (pH of order of 12.5) induces the passivation
of the carbon steel.
Potential
+281 mV Ag|AgCl|KCl 3 mol/L
(+491 mV SHE)
Pourbaix (1974) pH 12,5
Immunity
Potential
-1032 mV Ag|AgCl|KCl 3 mol/L
(-822 mV SHE)
PassivityCorrosion
Passivity... if the corrosion
products are insoluble and form
a compact and adherent layer...
Fe3O4 + 8H+ + 8e-  3Fe + 4H2O
O2 + 2H2O + 4e-  4OH-
Ag|AgCl|KCl 3 mol/L = 210 mV SHE

6. 2H+ + 2e-  H2
O2 + 2H2O + 4e-  4OH-
2Fe3O4 + H2O  3Fe2O3 + 2H+ + 2e-
3Fe + 4H2O  Fe3O4 + 8H+ + 8e-
H2  2H+ + 2e-
4OH-  O2 + 2H2O + 4e-
2Fe3O4 + H2O  3Fe2O3 + 2H+ + 2e-
3Fe + 4H2O  Fe3O4 + 8H+ + 8e-
H2  2H+ + 2e-
3Fe2O3 + 2H+ + 2e-  2Fe3O4 + H2O
O2 + 2H2O + 4e-  4OH-
pH 12,5
Fe3O4 + 8H+ + 8e-  3Fe + 4H2O
Fe3O4 + 8H+ + 8e- 
3Fe + 4H2O
O2 + 2H2O + 4e-  4OH-
2H+ + 2e  H2

7. Schematic representation of the corrosion conditions of passive steel in
concrete under different conditions of moisture content
534
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Corrosion
negligible
Lower oxygen availability:
Potential
below -366 mV Ag|AgCl|KCl 3 mol/L
(+156 mV SHE)
Current density: about 0.1 mA/m2
(0,01 µA/cm2 = 10-8 A/cm2)
Immunity
Verythinfilmofiron
oxide(passivefilm)
BERTOLINI et al., 2004
need for
oxygen to
maintain
passivity
Aerated pore water:
Corrosion potential (Ecorr)
between +134 mV and -166 mV
Ag|AgCl|KCl 3 mol/L (+344 to +44 mV SHE)
Concrete and carbon steel interaction

8. Adaptadode
WARTHAetal.2012
Anode
Fe  Fe2+ + 2e-
Blue solution
Cathode
O2 + 2H2O + 4e-  4OH-
Pink solution
Corrosion products
(FeOOH e Fe3O4)
Breaking the passive layer:
Corrosion cell

9. Carbon steel
Anodic region
Anode (+) Cathode (-)
Fe2+
Fe2+
Fe2+
Fe2+
Fe2+
Fe2+
Fe2+
Fe2+
Fe2+
Fe2+
Fe2+
Fe2+
Fe2+
Fe2+
Fe2+
Fe2+
Fe2+
Fe2+
Fe2+
Fe2+
Fe2+
Fe2+
Fe2+
Fe2+
Fe2+
Fe2+
Fe2+
Solution: Ionic current
Diffusion transport
Carbon steel
Cathodic region or
noble metal
2H2O+O2+4e-4OH-
FeFe+2+2e-
The cathodic
process involves the
transport of O2
to the cathodic sites
and the movement
of OH- away from
these sites
O2
OH-
OH-
O2
OH-
O2
H2O
H2O
H2O
Positive ions (cations) migrate in the direction of the cathode;
Negative ions (anions) migrate in the direction of the anode
Metal: Electronic current
OH-
OH-OH-
OH-
O2

10. Fe2+
Fe2+
Fe2+
Fe2+
Fe2+
Fe2+
Fe2+
Fe2+
Fe2+
Fe2+
Fe2+
Fe2+
Fe2+
Fe2+
Fe2+
Fe2+
Fe2+
Fe2+
Fe2+
Fe2+
Fe2+
Fe2+
Fe2+
Fe2+
Fe2+
Fe2+
Fe2+Fe3+
Fe3+
Fe3+
Fe3+
Fe3+
Fe3+
Carbon steel
Anodic region
Carbon steel
Cathodic region or
noble metal
Anode (+) Cathode (-)
2H2O(l)+O2(g)+4e-4OH-
(aq)
Fe(s)Fe2+
(aq)+2e-
4Fe2 +
(aq) + O2 + 2H2O + 8OH-  4 Fe(OH)3(s)
Fe3+
(aq) + 3OH-
(aq)  Fe(OH)3(s)
Fe2+
(aq)  Fe3+
(aq) + e-

11. Green product
(incipient oxidation by
restriction of oxygen in
the solution)
Product brown
orange and reddish brown
oxide or hydroxide of Fe3+
(presence of oxygen in the
solution)
Black product
magnetite
(oxygen restriction)
Presence of ferrous ions (Fe2+),
which, in the presence of
oxygen, pass to ferric (Fe3+)
Fe2+
(aq)  Fe3+
(aq) + e-

12. Cao et al..2013; Laurens et al., 2016; Ji et al., 2015; Gehlen et al.; 2010
Microcell
Uniform corrosion
The anode regions and the cathodic
regions are so close that the effect of
electrolyte electrical resistance is low.
Each electron produced by the anodic
reaction is consumed by a cathodic
reaction at an immediately adjacent
site. There is no current in the volume
of the concrete mass, and the open
circuit potential appears uniform along
the metal surface.
Typical corrosion induced by uniform
carbonation of the cover concrete or
severe corrosion by chloride attack!
Also called generalized
corrosion
Corrosion cell
Electrolyte
Steel
microstructure
GRAIN
CATHODE
GRAIN
ANODE
2e-
Fe+2
OH-
Fe(OH)2
Fe2O3

13. Macrocell corrosion is
characterized by the
presence of an anodic area (A) and a cathodic
area (C), physically separated and
macroscopically visible.
It occurs when there is a localized breakdown of the
passive layer, being induced by the non-uniform
carbonation of the concrete or the local high
concentration of chloride ions!
Corrosion cell
Macrocell
localized corrosion
Also called corrosion by
differential concentration
Corrosion cell

14. Schematic representation of the corrosion conditions of a
passive and an active rebar and determination of the
driving voltage (∆E) available for the macrocell
∆E
Ecorr,
C
Ecorr
A
Anode
Cathode
BERTOLINI et al., 2004

15. Macrocell
 Macrocell corrosion frequently proceeds first since concrete is a
heterogeneous material. Generally, severe corrosion takes place
locally, causing the spalling of the concrete cover.
Miyagawa, 1985
 Macrocell corrosion is also common in the
repair region. Its happen because the
electrochemical incompatibility between the
repair material and the original concrete
(carbonated or contaminated with chloride).
 Preferential path of the aggressive agents by the
smooth interface formed between the mortar and
the concrete by the deep mechanical cut, bigger
than necessary (5 mm) to guarantee a minimum
thickness of the repair mortar.

16. Ingress of
aggressive
agents
Carbonation: chemical reaction that involves the dissolution of
atmospheric CO2 in the pore water and the formation of a weak
carbonic acid which dissociates and reacts with hydrated
compounds (mainly portlandita and C–S–H gel) resulting calcium
carbonate and water. This reaction reduces the alkalinity of the
concrete, depassivating the steel reinforcement
diffusion of CO2 by means of
interconnected capillary pores,
micro fissures and air bubbles
Junior,A. 2013
pH 12,5 pH ≤ 10,5 pH ≤ 9
Carbonation front:!
pH of concrete drops
below nine at the
reinforcement

17. Relative humidity:
between 50 and 70 %
favored the
carbonation process.
The higher content
of Ca++, the slower
should be the
advance of the
carbonation front.
The higher the
permeability, the
higher should be
the diffusion of CO2
The moisture condition of
the concrete surface and
the degree of saturation
control the advance of
the carbonation front!
Parrott, 1990

18. 2H+ + 2e-  H2
Fe2+ + 2e  Fe
O2 + 2H2O + 4e-  4OH-
O2 + 4H+ + 4e  2H2O
2H+ + 2e  H
Fe  Fe2+ + 2e
H2  2H+ + 2e
O2 + 2H2O + 4e-  4OH-
O2 + 4H+ + 4e  2H2O
Fe  Fe2+ + 2e
H2  2H+ + 2e
2H2O  O2 + 4H+ + 4e
Iron has a tendency to
oxidation at potentials
more positive than the
equilibrium!
Fe2+ + 2e-  Fe
O2 + 2H2O + 4e-  4OH-
pH 8
3Fe2O3 + 2H+ + 2e-  2Fe3O4 + H2O

19. Changes the physical and
chemical properties of
the concrete cover of the
reinforcement
Corrosion rate is under resistive
control (ionic current flow between the anodic
and cathodic sites of the corrosion cell):
• periodic wetting drawing cycle
• relative humidity
Breaking the passive layer
Carbonation front first reaches
only part of the perimeter
(outermost section), and
corrosion increases when it
reaches the entire perimeter.

20. EN 206:2013
XC4 - Cyclic wet and dry:
water contact,
not within exposure class XC2
(long-term water contact)
ABNT NBR 6118:2014
Class II – moderate
aggressive:
Urban atmosphere
Relative humidity > 65 %,
outdoor (exposition to
rain water)
Tropical
climate

21. Carbonation rate as a function of w/cm for concretes Portland cement
and blend cement (slag 50 %)
Mac-Donald, D.B., 2011,
Collepardi, M., S. Collepardi, et al.
(2004).
Concretes were exposed to air (20 oC; RH of 60 %) after a curing of 28 days
ABNT NBR 6118: Class II
(W/C ≤ 55 and cover 30 mm)
C= 4 mm/year ~55 years

22. ~ 80 % RH !
ABNT NBR 6118: Class II
(W/C ≤ 50 and cover 30 mm)
C= 5,2 mm/year (slag 50 %) ~33 years;
Old structure, cover 20 mm ~25 years
uniform corrosion induced by
carbonation
variable cover thickness
failure in the repairs execution

23. 534
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PotentialAg|AgCl|KCl3mol/L
Below 70 %, the corrosion rate falls, respectively, by 1
and 2 orders of magnitude
Elseneretal.,2004;Bertolinietal.,2004.
As the moisture content
decreases in concrete, the
ohmic-drop contribution
increasesohmic-drop
Humid, carbonated concrete:
Corrosion potential (Ecorr)
between +209 and -291mV
Ag|AgCl|KCl 3 mol/L
(+100 to -400 Cu/CuSO4 sat)
Corrosion rate is under resistive control:
ionic current flow between the anodic and cathodic sites of the corrosion cell
Potential of oxygen reduction is
approximately 200 mV higher than at the
pH of alkaline concrete
70 % RH
80 % RH
95 % RH
10 µmA/m2

24. Chloride ions (Cl-)
 The presence of Cl- favors the absorption
and retention of water in the concrete due
to its hydrophilic characteristic;
 The presence of Cl- dissolved in pore solution decreases the
electric resistivity of the concrete, consequently, the
corrosion rate increases;
 In the presence of Cl-, there is formation of soluble iron
corrosion product complexes, damaging the precipitation of
protective corrosion products.
Ingress of
aggressive
agents
Corrosion is a concern in Brazil because it has a
large coastal area, occupied by various
constructions in reinforced concrete
Broomfield, 2007; Laurens et al., 2015, Qian, Zhang, 2013

25. Concrete Containing Chlorides
Apostolopoulos, Demi, Papadakis, 2013; Bertolini et al., 2004
Breakdown potential
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PotentialAg|AgCl|KCl3mol/L
potential in structures
exposed to the atmosphere:
between +566 mV and -66 mV
Ag|AgCl|KCl 3 mol/L
Pitting

26. Protection potential:
pitting can propagate
but not initiate
Protection potential:
pitting cannot initiate
nor propagate

27. Pedeferri, 1996

28. The chloride threshold varies
from one region to another
due to the heterogeneity of
the concrete and the interface
conditions.
Angst et al., 2009, Bertolini et al., 2004
The establishment of a significant corrosive process may take
months or years, implying in some difficulty to establish the end of
the period of initiation of corrosion.

29. Tabela da Nace do critério
Interface steel/
concrete
Factors related to concrete
Other factorsCement
and Cement
replacement
Concrete
Properties of steel,
superficial condition
and electrochemical
potential;
Chemical composition,
oxygen availability and
pH of pore water
Amount of voids
CH layer (Buffering
capacity)
Type and amount.
C3A %, slag
Silica fume,
metacauline
Pore structure
(w/C);
Cure;
Superficial crack
Macro and micro
environment:
(relative humidity,
temperature,
precipitation
frequency)
Geometric Factors
(deposited salts,
water puddles)
Figueiredo, Meira, 2014; Angst et al., 2011; SAGUES, 2001
The chloride threshold

30. EN 206:2013
XS1 - AIRBONE
XS3- spray zone
ABNT NBR 6118:2014
Class III or IV: high or
very high aggressive
marine atmosphere
Apparent concrete
Salt spray exposition

31. Chloride corrosion
Leaching of corrosion
products in concrete
gelatinous
precipitate of
greenish
coloration

32. Chloride

33. Chloride corrosion

34. Corrosion propagation stage
Breaking the
passive layer
Induced damage processes
(highly dependent on the cathodic area, as well as the
moisture, air and water contents of the concrete):
key governing
parameters :
• Water content
• Dissolved oxygen Rust and stress
build-up
Surface cracking
(that accelerates the
rate of corrosion);
Concrete
disbonding;
Loss of adhesion
steel/concrete
Internal
cracking
Corrosion stain
X
Cusson, Lounis & Daigle, 2011;Mac-Donald, 2011
Tuutti, 1982; Bertolini et al., 2004
Repair/
Strengthening
Fatalities, injuries,
circulation interruption,
socioeconomic
impacts
Corrosion rate
≥ 0,2 µA/cm2

35. < 2 µm/year
< 0,2 µA/cm2
Bertolini et al., 2004
Low
(2 and 5)
Moderate
(5 and 10)
High
(50 and 100)
Very high
> 100
Brazil
1 µA/cm2

36. ~ 25 μm of corrosion products may cause
cracking in the concrete!
Corrosion carbon steel coupons (pipe line)
NACE Standard RP0775
Uniform corrosion rate
Corrosion level
mm/year µm/year
< 0.025 < 25 low
0.025 a 0.12 25 a 120 Moderate
Corrosion level icorr vcorr
A/cm2
μA/cm2 mm/year µm/year
Negligible ≤ 10-7
≤ 0.1 ≤ 0.00116 ≤ 1.16
low 10-7 a 5x10-7
0.1 a 0.5 0.00116 a 0.0058 1.16 a 5.8
Moderate 5x10-7a 10-6
0.5 a 1 0.0058 a 0.0116 5,8 a 11,6
high > 10-6
> 1 > 0.0116 > 11.6
ANDRADE; ALONSO, 2004
ACI 365-1R, 2017
Possible damages:
10 - 15 years for icorr 0.5 - 2.7 μA/cm2
2 -10 years for icorr 2.7 - 27 μA/cm2
up to 2 years for icorr above 27 μA/cm2

37. AGENDA
 Introduction
– Corrosion in concrete structure
 Assessment:
– Visual inspection and non destructive techniques
 Monitoring:
– Embedded reference electrodes and sensors
 Prevention and Rehabilitation Techniques
– Prevention and corrosion mitigation techniques

38. Maintenance
Durability
Service life
Inspection
Design
Construction
Design construction: Indicate the maintenance activities
and the periodicity with which it should be performed and
ensure access to building parts for maintenance.
Inspection: evaluate the conservation of the
structure and other components against the
conditions of use and exposure over time
Maintenance: procedures that are carried
out periodically for conservation.
Durability: the performance over
time and the expression of the
durability of a product is its SERVICE
LIFE: TIME PERIOD IN WHICH A BUILDING
AND / OR ITS SYSTEMS PROVIDE TO THE ACTIVITIES
FOR WHICH THEY WERE DESIGNED, CONSIDERING THE
PERIODICITY AND CORRECT PERFORMANCE OF MAINTENANCE

39. Maintenance
Inspection
ABNT NBR 16230: defines who is able to perform this service,
standardizes the requirements that the professional must fulfill to
issue the reports of concrete structures
ABNT NBR 15575: performance of residential
buildings. It presents indispensable
characteristics such as comfort, accessibility,
performance and maintenance
ABNT NBR 5674: Requirements for the
maintenance management system
ABNT NBR 9452: requirements for
conducting inspections of bridges,
overpasses and concrete walkways and for
the presentation of the results of these
inspections.

40. Bungey; Millard; Grantham, 2006
Cracking Spalling Erosion Early Long-term
Structural deficiency × × × ×
Reinforcement
corrosion
× × ×
Chemical attack × × × ×
Frost damage × × × ×
Fire damage × × ×
Freeze–thaw × × ×
Internal reactions × × ×
Thermal effects × × × ×
Shrinkage × × ×
Creep × × ×
Rapid drying × ×
Plastic settlement × ×
Physical damage × × × × ×
Age of appearanceSymptoms
Cause
Visual inspection
recognizing concrete defects
 Tables of record of symptoms (in
each element with their identification,
quantification and location):
 Structural distress symptoms;
 Corrosion related symptoms;
 Construction defects;
 Chemical attack, etc
Identify risks and testing methods
which are needed to a proven value
for the determination of the extent of
degradation
 Sketch and photograph
 Report:
 addressing the nature, extent
and evolution of the problem
 recommendations of systems
of repair, strength and
prevention of corrosion or
mitigation techniques

41. The first signs of corrosion in the
concrete surface are cracks
(coincident with the reinforcement
position), rust stains (brown and red
colors), delamination and spalling.
These corrosion damages are
detected in field inspection relaying
on visual examination of the whole
structure.
The extent of corrosion on the
structure elements and its rate can
be known by application of
electrochemical techniques.
Visual inspection - corrosion

42. Corrosion potential – half-cell potential - Ecorr
Malhotra; Carino, 2004When there is active corrosion, current
flow through the concrete between
anodic and cathodic sites is accompanied
by an electric potential field surrounding
the corroding bar.
The equipotential lines intersect the
surface of the concrete and the potential
at any point can be measured.
Elsener et al., 2003
Reference electrode - CSEVoltmeter
pure copper rod completed
immersed in saturate CuSO4
solution
CuSO4 crystals
Porous extremity
(wood)

43. Potential map
The Ecorr is measured on the concrete
surface on a grid pattern relative or not to
the reinforcement position.
Areas with high potential gradient (> 150 mV)
are indicative of a greater risk of
reinforcement corrosion.

44. NACE International Publication
11100 (NACE, 2000)
RILEM TC 154 (Elsener et al., 2004)
The condition of the concrete such as moisture level, the amount of carbonation and
salt concentration will affect the reading and can lead to an erroneous judgment.

45. Field testing – corrosion
 Electric resistivity test
 Moisture content
 Corrosion rate
 Rebar visual inspection
 Fenofthaleina test (carbonation front)
 Free chlorate profile (chloride front)
 Sound testing
 Cover thickness and position of bars (metal detector)
 Loss of bar section

46. Böhni (2005)
Moisture content:
Microwave moisture measurement using the reflection
principle. Measurements on a grid pattern lead to
meaningful images of the moisture distribution in the
surface and volume layer
• Moist 210B
Concrete resistivity:
The four equally spaced electrodes are electrically
connected to the concrete surface. The outer
electrodes are connected to a source of alternating
current, and the two inner electrodes are
connected to a voltmeter.
• Resipod

47. Corrosion rate :
• Gecor 10:
RILEM TC 154 Polarization resistance (2004).
For a small perturbation about the Ecorr, there is
a linear relationship between the change in voltage (ΔE),
and the change in applied current (Δi).
This ratio is called the polarization resistance (Rp)
• CorroMap:
Modified Randles system:
Malhotra; Carino, 2004

48. AGENDA
 Introduction
– Corrosion in concrete structure
 Assessment:
– Visual inspection and non destructive techniques
 Monitoring:
– Embedded reference electrodes and sensors
 Prevention and Rehabilitation Techniques
– Prevention and corrosion mitigation techniques

49. voltmeter
Steel
Concrete porous
water (electrolyte)
Interface
Reference
electrode
Mn/MnO2/NaOH-
0.5 mol/L Ag/AgCl/KCl 0,5 mol/L
Titanium activated with
an iridium enriched
mixed metal oxide
electrode
Solid reference
electrode
The measurement of the corrosion
potential is essential for monitoring the
corrosion process of reinforcing steel,
and various embeddable references
have been used.
Reference electrode
Interface

50. Galvanic sensors
Macrocell devices are widely used to monitor the risk of
reinforcement corrosion, with corrosion initiation shown by a sharp increase
in the macrocell current.
Ladder systems are common type
CorroWatch Multisensor Anode LadderCL Ladder Probe
CO2
Cl-O2
Surface
rebar
Anode
H2O
Cathode
The bars from de sensor
are the anodes and a single
nobler element is the
cathode. In practice, the
whole macrocell is
embedded in the concrete
cover above the
reinforcement.

51. Research project - IPT
Cement
CP II 32
(kg/m³)
Quartz
sand
(kg/m³)
Artificial
sand
(kg/m³)
gravel
(kg/m³)
Water
(L/m³)
Adva
Cast®
(kg/m³)
360 519 519 857 245 0.175
•Water-cement ratio: 0.68
•Compressive strength: 30 MPa
•pH: 12.4
Expansion Ring Anode
Multiring
electrode
Concrete exposed to
chloride solution
CPA, CPB and CPC

52. The half-cell potential of embedded MnO2, Ag/AgCl
and Ti/MMO reference electrodes was found to be
stable and comparable with conventional surface
mounted system for indicated the passive state.
The test do not showed the well established theories of
liquid junction and IR drop problem in concrete media due
to the high internal resistance and the heterogeneity of the
concrete

53. CorroWatch Multisensor
The galvanic current
was high although
the potential values
still indicated a
passive state of
corrosion

54. Most bars maintained a
low corrosion rate.
The exceptions were the
outermost bar (A1) on the
CPA and CPB specimens
and the following bars (A2
and A3) on the CPA.
During the test, these bars
showed increased
corrosion rate.
This result is in agreement
with those obtained in the
monitoring of the
potential
CL Ladder Probe