Concrete corrosion

Concrete
is the most widely used constructional
material in the world. In spite of the impressive performance of
concrete in several structures,. Concrete can be defined as the artificial
stone produced when cement (usually Portland cement) is mixed with
fine aggregate (sand), a coarse aggregate (gravel or crushed stones)
and water.
They are classified in three different categories:
■ Low strength – Less than 20 MPa
■ Medium strength – Between 20 and 40 MPa
■ High strength – Greater than 40 MPa.

To obtain maximum properties
from concrete, it must be properly cured.
Following are the basic requirements for curing:
(1) The concrete must contain an adequate water content to complete
the process of hydration.
Moisture losses must be prevented during the setting time (e.g. a
week).
(2) The temperature of the concrete must be maintained above the
freezing point.
(3) The concrete must be protected against external movements and
disturbances to allow the formation of a uniform cohesive mass.
(4) Sufficient time must be allowed to ensure the completion of the
hydration reaction and achieve maximum hardening of the concrete.

English description American (ASTM)
1-Ordinary Portland cement Type I
2- low-heat Portland cement Type II
3-Rapid hardening Portland cement Type III
4-Modified Low heat Portland cement Type IV
5-Sulfate resisting cement Type IIV
Type I cement is most commonly used.
Concrete is produced by mixing the ingredients
in mixers such as rotating drum or horizontal

Concrete made with portland cement has certain
characteristics: it is relatively strong in compression but weak in tension and tends to
be brittle. The weakness in tension can be overcome by the use of conventional rod
reinforcement and to some extent by the inclusion of a sufficient volume of
certain fibres. The use of fibres also alters the behaviour of the fibre-matrix
composite after it has cracked, thereby improving its toughness.

Types of fibre
.1. Glass
Glass fibre has high tensile strength (2 – 4 GPa)
and elastic modulus (70 – 80 GPa) but has brittle
stress-strain
characteristics
(2,5 – 4,8% elongation at break) and low
creep at room temperature.
2-Acrylic
Acrylic fibres have been used to replace asbestos fibre in many
fibre-reinforced concrete products. In this process fibres are
initially dispersed in a dilute water and cement mixture. Acrylic
fibres have also been added to conventional concrete at low
volumes to
reduce the effects of plastic-shrinkage cracking.

3-Aramid
Aramid fibres are two and a half times as strong as glass fibres and five times as
strong as steel fibres, per unit mass. Due to the relatively high cost of these fibres,
aramid-fibre-reinforced concrete has been primarily used as an asbestos cement
replacement in certain high-strength applications.
4-Carbon
Carbon fibre is more expensive than other fibre types. For this reason its
commercial use has been limited.
Carbon fibre has high tensile strength and modulus of elasticity and a brittle
stress-strain characteristic. Additional research is needed to determine the
feasibility of carbon-fibre concrete on an economic basis.
4-Nylon
Nylon is particularly effective in imparting impact resistance and
flexural toughness and sustaining and increasing the load carrying
capacity of concrete following first crack.

5-Polyester
Polyester fibres have been used at low contents (0,1% by volume) to control plastic-
shrinkage cracking in concrete.
6-Polypropylene
Polypropylene fibres are tough but have low tensile strength and modulus of
elasticity; they have a plastic stress-strain characteristic. and a relatively low
modulus of elasticity. Long polypropylene fibres can prove difficult to mix due to their
flexibility and tendency to wraparound
7-Fabric and composite fibre reinforcement
South African manufacturers have been extremely innovative in
developing versions of fibre for use with concrete. To overcome the
bond and elastic modulus problem of polypropylene fibres, one
development has been that of a composite of a core fibre (which can
be polypropylene or a stiffer material such as acrylic, Kevlar, glass or
carbon fibres) around which is spun a fluffy coating of polypropylene
or cellulose.

New Developments
A development of the last few decades has been significant research
activity and increasing application of high-performance fibre-
reinforced cement-based composites (HPFRCC). This has led to design
recommendations being proposed for these materials recently in
Japan. Particular classes are ultra high performance
(UHPFRC) and strain-hardening (SHCC) fibre-reinforced cement-
based composites. These composites are designed for particular
applications varying from the requirement of high strength to that of
high ductility. For instance UHPFRC have been designed for and
applied in thin bridge decks or bridge deck overlays, with
compressive strengths in the range 120 to 180 Mpa and flexural
strengths in the range 20 to 40 MPa
8-Steel
Carbon steels are most commonly used to produce fibres but fibres made from
corrosion-resistant alloys are available. Stainless steel fibres have been used for high-
temperature applications.

Concrete Corrosion
Definition - What does Concrete
Corrosion mean?
Concrete corrosion is the chemical, colloidal or physicochemical
deterioration and disintegration of solid concrete components and
structures, due to attack by reactive liquids and gases
This type of corrosion causes wide spread damage to critical sewage
pipelines, bridges and other critical assets made of concrete

Concrete corrosion is mainly caused by Salt water or acidic ground water
,Microbes in sewer pipes,Sulphates,Chlorides, Industrial waste like slag
and corrosive gases

Influence of cover cracking on corrosion rate
The effect of cracking on corrosion may vary depending on concrete quality, concrete
resistivity, crack width, crack density, and crack orientation. The effect of load-
induced crack width, concrete quality (binder type and w/b ratio) and concrete
resistivity

2Fe → 2Fe+2 + 4e-
O2 + 2H2O + 4e- → 4OH-
2Fe+ + 4OH- → Fe(OH)2
4Fe(OH)2 + 2H2O + O2 → 4Fe(OH)3
2Fe(OH)3 → Fe2O3 + 3H2O

Since the volume of rust products is much higher (about 4 to 6 times) than that of the
iron

But Concrete, can provides protection to steel reinforcement because of the
following two reasons:
(a) Concrete provides a highly alkaline environment to steel reinforcement which
passivates the steel surface and, hence, prevents it from corrosion.
(b) Concrete prevents the ingress of corrosion species, like oxygen, chloride ions,
carbon dioxide and water, in low water–cement ratio
concrete.
Steel Loss
where m = loss of mass
Atm = atomic mass of the reaction ion
(55.85 g/mol for iron)
C = total charge that has passed through
the circuit
= ∫ I(t)dt
F = Faraday‘s constant (96485 C/mol)
z = valence of reaction (assumed to be 2)

Corrosion Rate Prediction Models
1-Alonso et al.’s model (1988)
where kcorr is a constant with
a value of 3 x 104 μA/cm2.kΩ-
cm and ρef is the resistivity of
the concrete at its actual
degree of saturation.
2-Yalcyn and Ergun’s model (1996)
Yalcyn and Ergun proposed a
value of C
as 1.1 x 10-3 day-1 for the
different concrete samples
where icorr is the corrosion rate at
time t, io is the initial corrosion
rate and C is acorrosion constant

3-Katwan et al.’s model (1996)

4-Duracrete model (1998)
where k corr is a constant regression
parameter (104), Fcl, F Galv, F oxide and
F Oxy are factors to take into account the
influence of chloride content, galvanic
effects,
continuous formation and ageing of
oxides and availability of oxygen on I corr
and ρ(t) is the resistivity of concrete (Ω-
m) at time t.
ρ(t) is the resistivity
5-Scott’s model (2004) where f is a slag correction
factor, f = 10(|0.5-S|-0.5+S)
(where S is the slag
concentration expressed as a
decimal e.g. 0.25 for 25%), Cc is
the 90 day chloride
conductivity index value (mS/cm)
and x is the concrete cover depth
(mm).

6-Martinez and Andrade’s model (2009)
Martinez and Andrade’s model can be used to predict an
annual-averaged
representative corrosion rate (icorr,rep).
where icorr,max is the maximum
predicted icorr

Pourbaix Diagrams
Based on thermodynamic data on reactions between metal and water Pourbaix

Costs of Concrete Corrosion
· Cost of additional or more expensive material used to prevent corrosion damage
· Cost of labor attributed to corrosion management activities
· Cost of the equipment required
· Loss of revenue due to troublen in supply of product
· Cost of loss of reliability

corrosion Prevention (CoP)
1-Sealers and Coatings
sealers and coatings do offer a significant increase in life expectancy
when installed before contamination of the concrete.
Sealers work by chemically reacting with the components of concrete
to fill the pores; thus, making it difficult for water to penetrate the
concrete surface.

Hot dip galvanized reinforcement offers significant advantages compared to uncoated
carbon steel under equivalent circumstances. These include: an increase of initiation
time of corrosion; greater tolerance for low cover,
Hot dip galvanizing process
Hot dip galvanizing is a metallurgical process whereby perfectly cleaned steel is totally
immersed into molten zinc at a temperature of approximately 450°C. During this process the
carbon steel metallurgically reacts with the molten zinc forming a series of zinc/iron alloys
together with a top pure zinc layer, chemically bonded to the parent steel. Hot dip galvanized
coating thicknesses are dependent on factors such as immersion time, zinc temperature, speed
of withdrawal and chemical analysis of the carbon steel reinforcement. It is possible that the
chemical composition of the steel could result in coating thicknesses as much as 200 μm.
While such coatings improve corrosion protection, , it is advisable to limit the coating
thickness to <200 μm and avoid excess
Gamma
Layer
(±6 μm)

Bond strength of concrete to hot dip galvanized
reinforcing bars
A further misconception that arises is that due to the formation of insoluble zinc
salts and the evolution of hydrogen formed at the interface between the newly
poured (wet) concrete and the hot dip galvanized reinforcement, is the reduced
bond strength.
Generally it is believed that during the early stages (6 to 10 days) of the concrete curing.
A higher bond with respect to bare steel could be obtained, due to the formation of
calcium hydroxyzincate crystals that fill the interfacial porosity of the cement paste
and act as bridges between the zinc coating and the concrete. the cost of hot dip
galvanizing reinforcement is insignificant compared to the cost of repairing spalling
concrete that results from the corrosion of uncoated reinforcement

Corrosion Inhibitors
Corrosion inhibitors, which are added to the concrete at the time of
mixing, are used to prevent the onset of corrosion in R/C.
mechanisms: by increasing the threshold concentration for
aggressive species necessary for corrosion to occur or by
reducing the rate of corrosion once corrosion has begun.
Corrosion inhibitors, whether admixed or surface applied, exist
in three basic forms: anodic inhibitors, cathodic inhibitors, and
mixed inhibitors. Anodic inhibitors minimize the anodic
component of the corrosion process while cathodic inhibitors
minimize the cathodic component. Mixed inhibitors prevent
both the anodic and cathodic reactions. By forming a film on
the steel, coating the surface of the steel, or by reacting with
the chloride ions, the interaction between the chloride ions and
steel will be prevented.

Cathodic Protection
The basis of corrosion theory is that a measurable difference in
potential exists between the anodic and cathodic areas. Cathodic
protection (CP) makes use of an externally applied potential, which acts
as the anode, to shift all of the reinforcing steel into a cathodic and
protected state. CP provides a high level of corrosion management
by using electrical current to shift the potential of the
reinforcing steel in the negative direction
Cathodic protection by
impressed current method
Sacrificial anode cathodic
protection system

Impressed Current Cathodic Protection
ICCP systems use an external power source that provides the necessary
current, 5 – 20 mA/m2 (0.5 – 1.9 mA/ft2), to mitigate corrosion
activity. An ICCP system consists of ―the reinforcement to be
protected, an anode, a power source, concrete surrounding the steel, a
monitoring system, and cabling to carry the system power and
monitoring signals.‖

Discrete Anode ICCP
The discrete anode system utilizes anodes
that are always embedded in the
concrete structure . The individual
anodes are connected to one another by
titanium feed wire and then connected to
the DC power source.
Mesh Anode ICCP
In the mesh anode system, a metallic
mesh with integrated anodes is attached
to the exposed concrete surface and
connected to a rectifier. A thin layer of
concrete is applied over the mesh and
embeds the anodes into the system.

Conductive Coating ICCP
The conductive coating system
utilizes conductive fillers in the
coating itself . The conductive
coating is applied to the concrete
surface and connected to the
rectifier by means of feed-wires
Thermal Sprayed ICCP
The thermal or arc sprayed metal application includes the melting of
a metal or alloy wire and the spraying of the molten metal to the
concrete with compressed air. To provide cathodic protection, a
connection is made between the rectifier and the thermal sprayed
metal by means of a stainless steel or copper plate that is secured to
the concrete surface prior to spraying. The sprayed metal a zinc.

Galvanic Cathodic Protection with Coatings
To increase the useful life of the sacrificial anodes, the method of
using coatings in addition to sacrificial cathodic protection has been
researched.
Thermal Sprayed
GCP with Coatings

Penetration of Corrosion Species in Concrete
Usually, penetration of a particular substance such as chloride ions into concrete
can be in twoforms: capillary attraction and ionic diffusion, depending on the
degree of saturation in the
The content of chloride ions (not total chloride content, only soluble one) at
steel surface has a great effect on the corrosivity of steel in concrete. The quality of
cover concrete (permeability) and cover depth are the key to determine the ease of
chloride ions reaching the steel surface.Capillary Attraction. While in dry to semi-
dry concrete, ions can migrate along with water under the influence of capillary
attraction. The rate of penetration of chloride ions under capillary
attraction is much faster than that of ionic diffusion

Ionic Diffusion. When concrete is in semi-wet to near-saturation, ionic migration
occurs
primarily through the diffusion process. The diffusion generally follows the Feick’s
second law.
A solution to Fick's second law based on initial and boundary conditions is as
following:

Corrosion Monitoring Techniques
Half-cell Potential
The measurement of the free corrosion potential of the reinforcement
consists of determination of the voltage difference between the steel and reference
electrode in
contact with the concrete .

Time to Cracking Models
1-Cady-Weyers’ Deterioration Model
where S is the bar spacing,D is the diameter
of the bar, ∆ D is the change in diameter of
the bar ,
Jr is the rate of rust production, and ρ is a
function of the mass densities of steel and
rust .
2-Morinaga’s Empirical Equations
where Qcr is the critical mass of corrosion products (10-4g/cm2);
c is the cover to the reinforcement (mm); d is the diameter of reinforcing bars
(mm).
where icor is the corrosion rate in gram
per day ,tcr is the time to cracking in
days.

Using of nano material for improving properties of concrete
Nanoparticle addition to cement paste was found to improve
mechanical, chemical, and thermal properties of cementitious matrix.
There are various types of nanoparticles, especially SiO2 and Fe2O3,
which when incorporated into cement led to considerable
improvement in the compressive strength . Nanosized TiO2 has been
added to accelerate the rate of hydration and increase the degree of
hydration . Moreover, the photocatalytic characteristic of TiO2 helped
to remove the organic pollutants from concrete surfaces, which were
directly exposed to UV radiation . Carbon nanomaterials present a
large group of functional materials with exceptional physical
properties. Extensive research endeavors over the last few years
demonstrated the application potential of various carbon
nanomaterials, mainly carbon nanofiber (CNF) and carbon nanotube
(CNT), in polymeric matrices. This fact has motivated the scientists and
researchers worldwide to use these nanomaterials in concrete as well,
in order to utilize their extraordinary mechanical, electrical, and
thermal properties .

In addition to that, in nanometer length scale, CNFs and CNTs offer the
possibility to restrict the formation as well as growth of nanocracks
within concrete, thus creating a new generation of crack-free
materials. So, concrete reinforcement using carbon nanomaterials is a
rapidly growing research area in recent times. However, there exists a
large difference in the structure and chemistry between a polymeric
and a cementitious, matrix, and, therefore, a great deal of research
activities is being directed towards understanding the interaction
between these nanomaterials and cementitious matrices for their
successful application

Figure SEM image of concrete Without the addition of nanoparticles
(Concrete unusual has high level gaps ( high porosity)
Figure SEM image of concrete With the addition of nanoparticles (Concrete
has low level gaps ( low porosity)
Using of Tio2 for improving properties of concrete

Figure . EDX chart of concrete. Without addtion

Element [wt.%] [norm.wt.%
]
[norm.
at.%]
Compound [norm.wt.%
]
Error in
wt.% (3
Sigma)
Oxygen 24.98095 20.0041 37.91945 -3.2E-16 10.55332
Silicon 1.110329 0.889122 0.960121 SiO2 1.902131 0.27504
Titanium 0 0 0 TiO2 0 0
Calcium 17.82632 14.27485 10.8022 CaO 19.97347 12.13651
Potassium 80.88574 64.7712 50.24245 K2O 78.0237 39.45965
Magnesium 0.075833 0.060725 0.075774 MgO 0.100699 0.098015
Sum: 124.8792 100 100
Table show components of concert without adding of TiO2 nanoparticles

Figure EDX chart of concrete with the addition of TiO2
nanoparticles

Element [wt.%] [norm.
wt.%]
[norm. at.%] Compound [norm.
wt.%]
Error in
wt.% (3
Sigma)
Oxygen 1.058642 20.22818 38.13122 3.05E-15 0.692535
Silicon 0.085465 1.633029 1.753636 SiO2 3.493596 0.099904
Magnesium 0.010778 0.205944 0.255554 MgO 0.341513 0.005055
Potassium 3.489825 66.68242 51.43766 K2O 80.32597 3.167678
Calcium 0.569878 10.88904 8.194291 CaO 15.23602 0.832428
Titanium 0.018913 0.361385 0.227638 TiO2 0.602904 0.063183
Sum: 5.2335 100 100
Table Shows component concert with addition

It has almost twice the compression of
samples without adding material to it
Concrete routinewithout adding Concrete plus TiO2
27.35Mpa 42.15 Mpa
Compression stress
With Add (1% -2%0 g of Tio2

Concrete cancer
concrete degradation caused by the presence of contaminants or the
action of weather combined with atmospheric properties. It includes
rusting of concrete reinforcement bar and any number of concrete
failures, notably carbonatation or the Alkali - silica reaction
Mechanism
Concrete Cancer is caused by many factors:
Including: carbonation, moisture and salt. The initial cause of concrete
cancer is usually water penetration When concrete cracks, water
penetrates through causing the steel reinforcement deep inside to rust.
Rusting steel then sheds its skin forcing the layers of rust to push away
the concrete surrounding it.
This results in large or small pieces of concrete falling away and
allowing steel reinforcement to become even more corroded and may
cause devastating wear on both the steel and the concrete. The use or
presence of Chloride based compounds can cause corrosion of
the reinforcing steel bars then expansion and spalling.

If the cement component is too alkaline, it reacts with atmospheric carbon dioxide,
and the structure will begin to deteriorate as star-shaped cracks appear which allow
rainwater to penetrate. This deterioration is then accelerated by freeze-thaw cycling
of water in the cracks, which, again, causes the surface to spall.
The initial cause of concrete cancer is usually water penetration. When calcium
oxide reacts with water that penetrates the concrete it forms a solution of calcium
hydroxide. The chemical formula for this is:
CaO + H2O → Ca(OH)2
Over time this calcium hydroxide solution will reach the edge of the concrete slab.
When this happens the solution reacts with carbon dioxide in the air and transforms
intocalcium carbonate. On the top of the slab calcium carbonate causes cracks above
the slab (allowing more water penetration) and below the slab
Ca(OH)2 + CO2(g) → CaCO3(s) + H2O.
Alkali-Silica Reaction
During the Alkali-Silica Reaction, a
gel is formed that swells as it draws
Water from the surrounding
cement paste.

Alkali hydroxide + reactive silica gel → reaction product (alkali-silica gel)
The amount of gel formed in the concrete depends on the amount and type of silica
and alkali hydroxide concentration. In absorbing water, these gels expand, thus
inducing pressure and subsequent cracking of the aggregate and surrounding paste:
Gel reaction product + moisture → expansion
Very often, the cracks appear in a star formation. Once this has occurred, water is able
to penetrate the concrete to a deeper level. In winter freeze/thawing actions can cause
the concrete to break up even more
How to prevent ASR damage
*Avoid high alkali content:
*use low alkali portland cement:
*replace cement with low alkali mineral
*Avoid reactive aggregate (amorphous silica)
*Control access to water: use low water to cement ratio, monitor
curing conditions, use admixtures to minimize water contact.
*Use lithium additives prior to placement of concrete or as a
treatment in already existing concrete

Concrete corrosion

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