this presentation provided by Emad Behdad

1. CORROSION AND PROTECTION OF STEEL
REINFORCED CONCRETE
PROVIDED BY: EMAD BEHDAD
LECTURER: PROF.SHAMS

2. OUTLINE
• INTRODUCTION
• CORROSION PROCESS
• TYPES OF CORROSION
• CAUSES OF CORROSION
• PROTECTION METHODS
• CONCLUSION

3.  ASTM terminology (G 15) defines corrosion as “the
chemical or electrochemical reaction between a material,
usually a metal, and its environment that produces a
deterioration of the material and its properties.” For steel
embedded in concrete, corrosion results in the formation
of rust which has two to four times the volume of the
original steel and none of the good mechanical properties.
Corrosion also produces pits or holes in the surface of
reinforcing steel, reducing strength capacity as a result of
the reduced cross-sectional area.

4. Electrochemical process of steel
corrosion in concrete

5. Volumetric change

6. • Ca, Na, K hydroxides in
hydrated cement raise the pH
to ~13.5
 A dense protective ferric
oxide (Fe2O3) passive film
forms around the
reinforcement Passive film develops on the bar surface
• This passive film stops iron
dissolution, and is stable at
pH >10
pH >13

7. Yes if:
(a) Concrete is always dry, then there is no H2O to form rust.
Also aggressive agents cannot easily diffuse into dry concrete.
(b) Concrete is always wet, then there is no oxygen to form
rust.
(c) Cathodic protection is used to convert all the
reinforcement into a cathode using a battery. This is not easy
to implement because anodic mesh is expensive, and this
technology is not easy to install and maintain

8. (d) A polymeric coating is applied to the concrete
member to keep out aggressive agents. These are
expensive and not easy to apply and maintain.
(e) A polymeric coating is applied to the
reinforcing bars to protect them from moisture and
aggressive agents. This is expensive and there is
some debate as to its long- term effectiveness.
(f) Stainless steel or cladded stainless steel is used
in lieu of conventional black bars. This is much
more expensive than black bars.

9. Can we avoid corrosion?
No, not entirely:
Concrete is not usually under water or
continuously dry. Aggressive agents such
as carbon dioxide, de-icing agents and/or
sea water can diffuse into the best of moist
concrete, and corrosion will eventually
result.

11. COMMON CORROSION TYPES
1) Crevice Corrosion
Crevice corrosion is a localized form of corrosion usually
associated with a stagnant solution on the micro-environmental
level. Such stagnant microenvironments tend to occur in crevices
(shielded areas). Oxygen in the liquid which is deep in the crevice
is consumed by reaction with the metal. Oxygen content of liquid
at the mouth of the crevice which is exposed to the air is greater,
so a local cell develops in which the anode, or area being attacked,
is the surface in contact with the oxygen-depleted liquid.

12. Crevice Corrosion of Rebar Has Some
Similarities with Filliform Corrosion
The head of the advancing filament becomes
anodic, with a low pH and a lack of oxygen,
as compared with the cathodic area
immediately behind the head where oxygen
is available through the semipermeable
film. Corrosion proceeds as the cathode
follows behind the anodic head (from
Corrosion Basics NACE).

14. 2) Pitting
Theories of passivity fall into two general categories, one based on adsorption and
the other on presence of a thin oxide film. Pitting in the former case arises as
detrimental or activator species, such as Cl-, compete with O2 or OH- at specific
surface sites. By the oxide film theory, detrimental species become incorporated
into the passive film, leading to its local dissolution or to development of
conductive paths. Once initiated, pits propagate auto-catalytically according to the
generalized reaction, M+n + nH2O + nCl- → M(OH)n + nHCl, resulting in acidification
of the active region and corrosion at an accelerated rate (M+n and M are the ionic
and metallic forms of the corroding metal).

16. Chlorides
Airborne, marine, industrial, groundwater, cast-in
Cl– can penetrate through the passive film
At Cl- > “threshold”, passive film breaks down, corrosion
initiates
Cl- “threshold” value is typically 0.05% by wt of concrete
(0.02% prestressed concrete)
Pitting corrosion
Chlorides are main cause of reinforcement corrosion

17. Carbonation
Ca(OH)2 + CO2 → CaCO3 + H2O

18. EFFECT OF CARBONATION
 It can cause soft surface, dusting and color
change
 It reduces quality concrete
 It reduces the concrete ability to protect
reinforcement from corrosion (in an exposed
environment)
 It will result in additional shrinkage in
carbonated region.

19. DETECTING CARBONATION
 Depth of carbonation can be detected using
an indicator.
 A chemical such as Phenolphthalein sprayed
on to freshly broken concrete.
 Areas remaining alkaline will turn in a bright
purply-pink color.
 Carbonated areas of concrete will remain
unchanged in color.

20. Cl- Cl-
+ve Ions +ve Ions
e- Fe Fe++ e-
e- e-
Rebar Rebar

21. Reinforcing steel corrosion
Migration of chlorides, H20 Corrosion of the steel
and O2 into the concrete, no reinforcement and
corrosion and no damage to cracking and/or spalling
concrete of concrete
Degree of Corrosion
Initiation Propagation
(corrosion)
Critical chloride
threshold
I
Time

22. Cl- Cl-
. Cl-. .- . Cl- .- Cl-
. Cl- . Cl Cl . - . Cl- . Cl- Cl- . -. Cl
Cl- Cl- . . . .
pH >~10 . . . Cl
.
Cl-
.
.
. . Cl- . - . - .- . .- . . . .
. . . Cl -
Cl Cl . Cl Cl- Cl
e e
- -
Cathode .
Cathode
. . . Anode .
. . . . .
. . .
ClElectrolyte
- . Cl- . Cl-
. . Cl . - Cl- . Cl-
Cl- Cl.
- .
Cl- .
Cl- Cl- Cl-
Iron Oxygen Moisture
Corrosion = Iron + Oxygen + Moisture
Either
 the pH falls due to carbonation or other chemicals
 chlorides reach the steel above the threshold concentration
 an electrical charge destroys the natural protection of the steel
 Electrons flow and ions migrate
 Rust expansion causes cracking
 Rapid deterioration
 Spalling

23. Rebar
Spalling loss
Cracks
with
Rust Delamination
Staining

24. Abandoned Electric Pole

25. KISH ISLAND

26. BANDAR ABBAS

28.  chloride induced
reinforcement corrosion
in concrete exposed to
seawater
Corroded rebar from cracked concrete of a
parking structure exposed to deicing salts

29. Reinforced steel in concrete cracking

30. CORROSION PREVENTION METHODS
 REBAR COATING
 SCARIFIED & PATCHED DECK AWAITS ANODE MESH
 FLY ASH
 HOT-DIP GALVANIZING
 WIRELESS SENSOR FOR MONITORING CHLORIDE IN
CONCRETE
 INHIBITORS

31. REBAR COATING

32. EPOXY COATING PREVIEW MODEL

35. EPOXY‐COATED BARS
Anode Cathode
Reduces anode area Reduces cathodic area
Increases threshold*
REDUCED CORROSION
Electrical Connection Ionic path
• Electrical path between anode
and cathode Makes ionic pathway longer

36. thermally sprayed coatings of
Zn and Al, combat corrosion
 For atmospheric, buried, and marine environment corrosion protection, Zn
(TSZ), Al (TSA), and their alloys have proven that they provide long term
corrosion protection and outperform most all other methods.
 Anodic (TSZ/TSA) metal coatings applied to steel cathodes (more noble than
Zn or Al), are referred to as cathodic or sacrificial protection coating
systems.
 These thermal spray coatings provide corrosion protection by excluding the
environment (or electrolyte) and acting as a barrier coating (like paints,
polymers, and epoxies), but unlike typical barrier coatings they also provide
sacrificial anodic protection.

37. Zinc and zinc alloys are also sprayed directly onto concrete to protect the
steel rebar within
Arc spraying of zinc on a concrete bridge pier
in the Florida Keys. In this case the zinc acts as
sacrificial anode, although it is more frequently
used in impressed-current systems. Three
impressed-current zinc systems have already
been installed by the Ministry of
Transportation of Ontario in Toronto
Sacrificial cathodic protection of steel in
concrete by thermal zinc spraying

38. FLY ASH
 using a Fly Ash concrete with very low permeability, which will delay the
arrival of carbonation and chlorides at the level of the steel reinforcement.
 Fly Ash is a finely divided silica rich powder that, in itself, gives no benefit
when added to a concrete mixture, unless it can react with the calcium
hydroxide formed in the first few days of hydration. Together they form a
calcium silica hydrate (CSH) compound that over time effectively reduces
concrete diffusivity to oxygen, carbon dioxide, water and chloride ions. By
reducing ion diffusion, the electrical resistance of the concrete also
increases

39. CATHODIC PROTECTION
Impressed current (active)
Sacrificial anode (passive)

40. TITANIUM ANODE MESH
A. TYPICALLY ATTACHED TO THE CONCRETE SURFACE AND
THEN ENCAPSULATED IN CEMENTITIOUS MATERIALS.
B- EASILY CONFORMS TO THE STRUCTURE GEOMETRY.
C- MOST USED IMPRESSED CURRENT ANODE FOR CONCRETE.

41.  Mixed Metal Oxide activated Titanium Anodes in the form of a ribbon
mesh can be installed in close proximity and parallel to the
reinforcement bars (rebar).
MMO Ribbon Mesh

43. 1. Simple to Install.
2. No Power Supply Needed.
3. No Wiring or Conduit.
4. No Long-Term Monitoring or Maintenance

44. Conventional Patch Repair

45. Embedded Zinc Anode for Patch Repair

47. CATHODIC PROTECTION SACRIFICIAL ANODE

49. REFRENCES
 Concrete Society Technical Reports TR 36 and 37

50.  www.corrocell.co.uk