2. Chemical Reactions
• Acid attack
• Aggressive water attack
• Alkali carbonate reaction
• Alkali silica reaction
• Sulphate attack
Design Errors
• Inadequate structural design
• Poor Design Details
•Plastic
•Drying
Shrinkage
• Internally Generated
• Externally Generated
• Fire
Temperature Changes
Accidental Loadings
Construction Errors
Freezing and thawing
Settlement and Movement
Weathering
Common Causes for Deterioration of Concrete
3. Fire on Concrete
• A fire in concrete structures causes damage. The extent of
which depends up on intensity and duration of the fire.
The principal types of damages are:
• Reduction in strength of concrete
• Cracking and spalling of concrete
• Deflection and deformation members
• Discoloration
• In RC structures fire resistance is depend on type of
concrete and thickness of cover.
• The fire introduces high temperature gradients and as a result
of it surface layers tend to separate and spall from surface.
• The heating of reinforcement expands both laterally and
longitudinally resulting in loss of bond and loss of strength of
reinforcement.
4. Abrasion & Erosion
• Abrasion refers to wearing away of the surface by friction.
• Erosion refers to wearing away of the surface by fluids.
• Cavitations refers to the damage due to non-linear flow of
water.
• The concrete used in the roads , floors, the pavements and
the concrete used in the hydraulic structures should exhibit
resistance against abrasion, erosion and cavitations.
• The more compressive strength the higher the resistance to
abrasion erosion and cavitations.
• The shape and surface texture of aggregate plays an important
part in the abrasion resistance of the concrete.
• Use of steel fibers and polymer based systems in concrete
matrix improves abrasion resistance of concrete.
5. Chemical Causes
• The chemical reactions on the concrete may be classified as
those that occur as the result of external chemicals attacking
the concrete like
1. Acid attack
2. Aggressive water attack
3. Sulphate attack etc.
• Those that occur as a result of internal chemical reactions
between the constituents of the concrete like
1. alkali- silica reaction
2. Alkali carbonate reactions.
6. Carbonation Attack on Concrete
• Carbonation is the effect of carbon dioxide in the air on cement
products mainly the hydroxides in the presence of moisture.
• This is mainly due to reaction of carbon dioxide with the hydrated
cement.
• The calcium hydroxide is converted to calcium carbonate by
absorption of carbon dioxide.
Ca(OH)2+CO2 CaCO3+H2O
• Calcium carbonate is slightly soluble in water and destroying the
permeability system of the concrete. So top layer of concrete
becomes carbonated and this layer is not alkaline to protect
reinforcing steel.
H2O+CO2 H2CO3 ( Carbonic Acid)
• This is due to the reaction between water and carbon dioxide forms
carbonic acid which allows steel to corrode. The corrosion product
occupies much greater volume than original metal which results
surrounding concrete to burst.
7. Influencing Factor
The rate at which carbonation reaches the reinforcement is
dependent on the following factors:
• Time: Rate decreases with increasing time of exposure to
air.
• Cover to reinforcement: the grater the cover, the better the
protection afforded to steel.
• Conc. Of CO2 in atmosphere: Rate increases with
increasing CO2 in the air.
• Alkali content in the Concrete: This depends on cement
content and type of cement.
• Permeability of concrete: Depends on concrete quality.
• Concrete of good quality usually carbonates very slowly.
Carbonation reduced due to reduced moisture content and
reducing the concentration of carbon dioxide in atmosphere.
8. Sulphate Attack on Concrete
• Sulphates are found in most of the soils as calcium, potassium,
sodium and magnesium sulphates. Solid salts do not attack concrete,
but when present in solution they can react with hardened cement
paste. Sulphates are present in seawater, industrial effluents and
some ground water.
• Sulphate reaction is dependent on the following parameters:
1. Concentration of sulphate ions
2. Cations present in sulphate solution
3. C3A content of cement
4. Density, permeability of the concrete
• Chemical Mechanism:
This is mainly due to chemical reaction between sulphate and
hydration products which results changes in the microstructure and
pore size distribution of cement paste.
9. Sulphate Attack on Concrete
• Sulphate converts calcium hydroxide in to large volume of calcium
sulphate (Gypsum).
Na2SO4.10H2O+Ca(OH)2 CaSO4.2H2O+ 2NaOH+8H2O
• The second hydration product C3A hydrate reacts with sulphate
solution to form sulpho aluminates hydrate which has a greater
volume than that of the original compound.
2(3CaO.Al2O3.12H2O)+3(Na2SO4.10H2O) 3CaO.Al2O3.3CaSo4.31H2O+2Al(OH)3+6NaOH+17H2O
• Due to this internal stress is greater enough to cause deformation,
cracking and eventually loss of cohesion. When concrete cracks its
permeability increases and the aggressive water penetrates more
easily in to the interior, thus accelerating the process of
deterioration.
11. Acid Attack
• Portland cement concrete is a highly alkaline material and is not
resistant to attack by acids. The deterioration is mainly due to
reaction between the acid and the products of hydration of
cement.
• The action of acid on concrete is to dissolve away the cement. The
chemical reaction results in formation of water soluble calcium
compounds which are then leached away by the aqueous solutions.
This result in an increase of the porosity and the permeability of the
system.
• Oxalic and Phosphoric acids are exceptions, because the resulting
calcium salts are insoluble in water and the surface of the concrete
becomes coated with the insoluble salt so that reaction ceases.
• If acids or salt solutions are able to reach the reinforcing steel
through cracks or pores in the concrete, corrosion of steel can occur,
which will in turn cause cracking and spalling of the concrete.
• Acid attack is a problem in sewers, at high temperatures, and where
concrete is exposed to rapid flows and considerable volume of acids.
12. Acid Attack
Symptoms:
• Disintegration of the concrete show loss of cement paste and
aggregate from the matrix.
• If reinforcing steel has been reached by the acid, rust staining,
cracking and spalling present.
• All cements except high alumina cement are equally susceptible to
acid attack.
Preventive measures:
• Increasing cement content and reducing w/c ratio.
• Improving concrete cover
• By treating the surface with sodium silicate known as water glass.
13. Alkali Reaction
Mechanism of alkali aggregate reaction (AAR):
• This is also called alkali- carbonate reaction. Carbonates in
aggregates react with the alkalis in cement produces a gel.
• Visual examination of those reactions show map or pattern cracking.
• Alkali carbonate reaction differ from alkali silica reaction is the lack
of silica gel exudations at cracks.
Influence Factors
The reactivity of aggregate depends upon the following factors:
• Size of aggregate particle
• Porosity of aggregate particles
• Alkali content in cement
• Fineness of cement particles
• Alternate wetting and drying
• Temperatures range
14. Alkali-Silica Reaction
• This is due to alkalis produced during the hydration of Portland
cement certain siliceous constituents in the aggregate.
• The alkali-silica gel which is formed imbibes pore fluid causing its
expansion.
• Expansion of gel induces internal stresses and cause cracking of
concrete.
• Visual examination show map or pattern cracking.
• Apart from cracking major effect of ASR is reduction in compressive
strength and modulus of elasticity.
• The resulting damage due to ASR depends on the amount of
moisture available for the ASR gel to expand.
• Testing for presence of alkali-aggregate reaction is conducted by
petrographic examination of concrete.
Preventive measures:
• Use of low alkali cement
• Use of slag cement
• Use of non reactive aggregate
15. Chloride Attack
• Chlorides can be introduced in to concrete by coming
in to contact with environments containing chlorides,
such as seawater or de-icing salts.
Chlorides enter into concrete from following sources:
• Cement of the concrete
• Water mixed in concrete
• Aggregate of the concrete
• Admixtures added to the concrete
16. Chloride Attack
Mechanism
• Concentration of chlorides in contact with the
reinforcing steel will cause corrosion when
moisture and oxygen are present.
• As the rust layer builds, tensile forces generated
by the expansion of the oxide cause the concrete
to crack and delaminate.
• The concentration of chlorides necessary to
promote corrosion and it is effected by concretes
pH.
17. Limits of Chloride content as IS456:2000
S. No Use of concrete Max. chloride
content in Kg/m3
1 Concrete containing metal
and steam cured at high
temp
0.4
2 R.C.C or plain concrete
containing metal
0.6
3 Concrete not containing
embedded metal
3.0
18. Aggressive Water Attack / Soft Water
Attack
• Some waters have extremely low concentration of dissolved
minerals.
• These soft or aggressive waters leach calcium from cement paste or
aggregates. This attack takes place very slowly.
• This attack show a serious effect on hydraulic structures.
• constant supply of aggressive water in contact with concrete washes
away aggregate particles that become loosened as a result of leaching
of the paste.
• Visual examination show concrete surfaces become very rough in
• areas where the paste has been leached.
Prevention
• Areas susceptible to high flows may be coated with a non
Portland cement based coating.
