Corrosion of Steel in Concrete

This article discusses the process and causes of corrosion of steel in concrete. It explains how corrosion weakens the structural integrity of buildings and other structures. The article also highlights the research gap in the field and provides an overview of previous and recent studies on corrosion.

Running head - CORROSION OF STEEL IN CONCRETE
Corrosion of Steel in Concrete
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Introduction
Super structures are the fundamental infrastructure that is shaping the modern world.
Engineering marvels are made throughout the decades by making innovation in the construction
industry (Leygraf et al. 2016). One of the most important aspect based on which these mega-
structures are built is concrete. Concrete provide shape and provides the necessary base to these
structures. Concrete could be classified of two types – PCC and RCC. Plain Cement Concrete is
made of fine and course aggregate along with cement being the binding agent (Li et al., 2015).
The following paper would be discussing about the problems in the structural strength of
steel reinforced concrete due to the effect of corrosion. In construction field, corrosion of the
reinforced material is one of the most widely researched topic as the problems that are identified
due to corrosion is devastating. The structural integrity of the materials are weakened as rust
destroys the molecular compaction of the metals. Structures suffer loss in strength due to
corrosion which results in rusting, starting of fire, electrical short-circuit and finally the collapse
of building or any other superstructure.
Discussion
Concept of corrosion
According to Talbot & Talbot (2018), corrosion is classified as a deadly effect to the
metal surface. It destroys the structural integrity of the metal, weakening the molecular
compaction of the metal; which in turn damages the strength of the metal. It is also costly to
solve the problem of corrosion. The effects of corrosion could be devastating as building, bridges
and other structures could collapse due to it (Thomas et al. 2015). Corrosion is classified as a
natural process of conversion, where atoms of metallic compounds are is converted into more

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stable form of in chemical terms like oxides or hydroxide or oxide of sulfides. As discussed by
Perez (2016), the process of corrosion could also be classified as the process of destruction of
metals through the process of electrochemical reaction in the surface of the metal.
Process of corrosion
Metals such as steel and iron are corroded when it comes in contact with acidic
substances like water or moisture, the Fe atoms are oxidized as it comes in direct contact with
them (Xu et al., 2015). Metals like steel when comes in contact with water, the iron atoms
present in steel is lost to the electrolyte present in it. When the iron particle in the steel is
oxidized, formation of Fe++ ions occurs in the anode part of steel. According to (Cui et al.
2018), the Fe++ denotes the loss of two electrons in the surface atoms of steel. Thus, when the
Fe++ atoms are formed, these ions are moved to the cathode area in the steel. Thus, through the
oxidation process, the electrons are forced by the oxygen atoms in the steel to rise up and form
OH ions, better known as hydroxyl ions. These ions react with the Fe++ ions to form hydrous
iron oxide compound; (FeOH) which is known as rust (Dreybrodt, Gabrovšek & Perne, 2016).
Principle of Corrosion
According to (Ramezanzade er al., 2018), there are certain principle of corrosion that
quantifies the process of corrosion. These principle of corrosions could be classified as Half Cell
Reaction, Potential of Electrode and Corrosion rates and polarization.
The half-cell reaction states that in the process of corrosion, two reaction takes place in
the metal in a half and half way (El-Reedy, 2017). The reaction at anode part of the metal which
is also known as the anodic reaction, atoms in the metal are ionized and passed in the solution,
thus leaving the electrons within the original metal surface. The second process, which is

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denoted by cathodic reaction, the free electrons that is present in the metal at that time is
accepted by the oxygen or hydrogen oxide (Cui, Lim & Huang, 2017). The reactions that takes
place are -
Fe + 2H2O = Fe(OH)2 + H2
The anodic reaction – Fe = Fe2+ + 2e-
The Cathodic reaction – 2H2O + 2e- = H2 + 2(OH)-
Thus, the anodic and the cathodic reaction is known as the half-cell reaction principle.
The electrode potentials principle is directly interlinked with the half-cell reaction in the
corrosion process. According to Otieno, Beushausen & Alexander, (2016), the electrode
potentials have values of each of the reactions that is associated with the half-cell reaction and
explains the likelihood of the reaction process. The electrode potential values of the half-cell
reaction are
Reaction Potential (Volts)
Zn = Zn2+ + 2e -0.76
Fe = Fe2+ + 2e -0.44
2H + 2e = H2 0.00
2H2O + 2e = H2 + 2(OH)- 0.40

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The last principle that clarifies the existence of corrosion is the present of potential
difference in between the cathode and the anode at the half-cell region that governs the
generation of current flow (Bertolini et al., 2016).
Occurrence of corrosion in steel
Steel reinforcement that is used in the reinforced cement concrete structure, provides
strength to the concrete due to its tensile bearing capability. However, it also impairs the
longevity and the durability of concrete due to the proneness of steel to corrosion (Broomfield,
2013). Corrosion mainly occurs in the steel that is covered by the concrete at every side. The
formation of corrosion occurs due to the steel coming in contact with water and moisture. When
the compaction of the concrete is not good, bleeding and segregation of the concrete occurs.
Thus, due to segregation and bleeding, air pores are left in the mixture which later creates
honeycomb structure in the concrete. Air and water enters in the concrete due to the permeability
of water, corroding the steel reinforcement in it. Thus, corrosion provides rust on the steel
reinforcement, which in turn destroys the strength bearing capability of steel. These effects in
permanent damage in the molecular strength of steel which slowly starts to decrease the bearing
capacity of steel. Thus, high yields occurs in steel and due to bulking, the steel starts to bend
which results in collapsing of the structure.
Cause of Corrosion in steel
As discussed by Glass & Buenfeld, (2017), steel used in concrete is usually non-
corroding. However, sometimes, due to lack of materials, when steel is used in severe
environments such as sea water or in soil where the salt and moisture content is high, steel gets

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corroded. This occurs due to the present of chlorine in them Chlorine disrupts the layer of
protection in concrete that disrupts the integrity.
Another reason could be the process of carbonation that could corrode steel in concrete.
When the concrete carbonate level increases to a level of steel rebar, the corrosion of steel
occurs.
Research Gap
According to Granju & Balouch, (2015), past researches states that the process of
corrosion in the reinforcement of concrete is usually occurs due to the presence of moisture in
the air. The moisture in the atmosphere oxidizes the surface level atoms of the reinforcement that
is being used in the concrete if only they are exposed to open air.
However, in the recent studies, it is found that, steel also gets corrode due to the presence
of alkaline and other chemical compound. It also have been found out that due the carbonization,
corrosion takes place.
Conclusion
Thus, the study could be concluded by providing a brief overview about the concept of
corrosion and its effects. The study also discusses about the process of corrosion and the
principle of corrosion in details. Process of corrosion and causes of corrosion in the steel
reinforcement of concrete is also thoroughly discussed and explained. There is also discussion of
research gap in the study that explains the previous studies and the recent studies on the
corrosion that indicates the gap in the literature.

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