Corrision effects the concrete and its durability properties

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. • 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
• This passive film stops iron
dissolution, and is stable at pH
>10
Passive film develops on the bar surface
pH >13

7. 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.

9. 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).

10. 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
Chlorides

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

12. 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.

13. 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.

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

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

16. Cl-
Cl- Cl-
Cl-
Cl-
Cl-Cl-
Cl-
Cl-
Cl-
Cl-
Cl-
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Electrolyte
Cl-
Cl- Cl-
Cl-Cl-
Cl-
Cl-
Cl-
Cl-
Cl-
Cl-
Cl-
Cl-
Cl-
Cl-
Cl-
Cl-
Cl-
Cl-
Cl-
Cl-
Cl- Cl-
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
pH >~10
Anode CathodeCathode
e
-
e
-
MoistureOxygenIron

17. Spalling
Cracks
with
Rust
Staining
Rebar
loss
Delamination

18. Abandoned Electric Pole

19. KISH ISLAND

20. BANDAR ABBAS

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

22. Reinforced steel in concrete cracking

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

24. REBAR COATING

25. EPOXY COATING PREVIEW MODEL

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

29. 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.

30. 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

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

32. 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.

33.  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

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

35. Conventional Patch Repair

36. Embedded Zinc Anode for Patch Repair

38. CATHODIC PROTECTION SACRIFICIAL ANODE