Deterioration of concrete and causes of concrete deterioratios

1. Module 4
Deterioration of concrete
structures
Wasim Shaikh
AIKTC, New Panvel

2. Deterioration of concrete structures

3. Deterioration of concrete structures
• Defect: An identifiable, unwanted condition that was not part of the
original intent of design.
• Deterioration: A Defect that has occurred over a period of time.

4. SCALING
• Scaling is referred to the loss of the surface portion of concrete
(or mortar) as a result of the freezing and thawing.
• This problem is typically caused by the expansion of water due
to freezing and thawing cycles.
• Scaling happens when the hydraulic pressure from water freezing
within concrete exceeds the tensile strength of concrete
• It is a physical action that usually leaves the aggregates clearly
exposed.
• Usually it start with localized area then extend to larger areas.
• Concrete having decent amount of entrapped air can prevent
scaling damage.

5. DISINTEGRATION
• Disintegration is the physical deterioration (such as scaling) or breaking down of the
concrete into small fragments or particles.
• The deterioration usually starts in the form of scaling and, if allowed to progress beyond
the level of very severe scaling is considered as disintegration.
• Severity
• Light – Loss of surface mortar to a depth of up to 5 mm without exposure of coarse
aggregate;
• Medium - Loss of surface mortar to a depth of 6 to 10 mm with exposure of some coarse
aggregates;
• Severe - Loss of surface mortar to a depth of 11 mm to 20 mm with aggregate particles
standing out from the concrete and a few completely lost.
• Very Severe - Loss of surface mortar and aggregate particles to a depth greater than 20
mm.

6. EROSION
• Erosion is the deterioration of concrete surface
as a result of particles in moving water
scrubbing the surface.
• Similar, damage may be caused by flowing ice.
• Erosion is generally an indication that the
concrete is not durable enough for the
environment in which it has been placed.
• Erosion is sometimes combined with the
chemical action of air and water-borne
pollutants which accelerate the breakdown of
the concrete.

7. CORROSION OF REINFORCEMENT
• Corrosion is the deterioration of steel reinforcement in concrete.
Corrosion can be induced by chloride or carbonation.
• The alkali content in concrete protects the reinforcement from
corrosion.
• when chloride ions above a certain concentration are dissolved in
water and penetrate through the concrete to the reinforcement this
protection breaks down and corrosion starts.
• The formation of rust requires iron, water and oxygen. Although it's a
complex process, the chemical equation is,
4Fe + 3O2 + 6H2O → 4Fe(OH)3.

8. CORROSION OF REINFORCEMENT
• When steel corrodes, the resulting rust occupies a greater volume than the
steel. This expansion creates tensile stresses in the concrete, which can
eventually cause cracking, delamination, and spalling.
• The alkaline environment of concrete (pH of 12 to 13) provides steel with
corrosion protection. At the high pH, a thin oxide layer forms on the steel
and prevents metal atoms from dissolving

9. Role of chloride ions in corrosion of Rebars
• The risk of corrosion increases as the chloride content of concrete
increases.
• When the chloride content at the surface of the steel exceeds a certain
limit, called the threshold value, corrosion will occur if water and
oxygen are also available.
• a threshold limit of 0.20 percent total (acid-soluble) chloride by weight
of cement.

10. Role of Carbonation in corrosion of Rebars
• Carbonation occurs when carbon dioxide from the air penetrates the
concrete and reacts with hydroxides, such as calcium hydroxide, to
form carbonates.
• The reaction with calcium hydroxide, calcium carbonate is formed.
• Ca(OH)2 + CO2 → CaCO3 + H2O
• This reaction reduces the pH of the pore solution to as low as 8.5, at
which level the passive film on the steel is not stable.s

11. Causes of concrete Deterioration
Causes
• Chemical
• Physical
• Mechanical
• Defects

12. Chemical
• Deterioration by carbon dioxide
• Deterioration by sulphates
• Deterioration chlorides
• Deterioration Alkali-aggregates reaction

13. Deterioration by carbon dioxide
• 1) Carbonation
• Carbonation is due to the penetration of CO2 into the concrete.
• This phenomenon consists in the transformation of the lime (Calcium
Hydroxide)
• This lime (Calcium Hydroxide) then converts into Calcium carbonate.
• If the concrete gets carbonated it reduces the ph of the concrete.

14. Effect of corrosion

15. Leaching of the concrete
Formation of lime on the surface
50 to 60 % humidity is very bad.
Can be prevented using air entrapped concrete.

16. Deterioration by sulphates
• The most common soluble sulphates in the ground, in water and in
industrial processes are calcium and sodium.
• may also be found directly in the aggregates as impurities
• They react with calcium hydroxide to form gypsum
• This process increases the volume of the concrete by lamination
process.

17. Lamination of concrete

18. Deterioration by chlorides
Chlorides causes the corrosion of the rebars by
reducing the alkalinity of concrete.
a structure completely immersed in seawater will
have a higher chloride content. However, the
porosity in the concrete will be completely saturated
with humidity, and the oxygen will not be able to
penetrate. Corrosion of the reinforcement rods will
not occur, or will be negligible

19. Deterioration Alkali-aggregates reaction
• Some types of aggregate, such as those which contain reactive silicon,
react with two alkalis contained in the cement, potassium and sodium
• An alkali-aggregates reaction may cause considerable expansion and
serious deterioration of concrete structures.
• This reaction forms a gel which is highly expansive if exposed to
humidity, and the gel creates forces which break the concrete around
the aggregates.

20. Deterioration due to alkali-aggregates
reaction

21. Detection of deterioration due to alkali-
aggregates reaction
• An initial, immediate assessment to detect the presence of an alkali-
aggregates reaction is by carrying out a detailed visual check
• This type of deterioration shows up with cracking in the concrete distributed
like a spider’s web, with an orderly or less orderly distribution pattern
according to the reinforcement present (As shown in previous slide)
• Chemical analysis by means of a colour test using sodium cobalt nitrite is a
certain way to identify the presence of a reaction between alkalis and
reactive aggregates
• The sodium cobalt nitrite reacts with the K (potassium) in the gel to form a
coloured precipitate. Therefore, if there has been a reaction, its colour will
change and will turn yellow, this indicates alkali aggregate reaction.

22. Deterioration by physical elements
Deterioration by physical element can be subdivided into following
three categories.
• Freezing and thawing (Effect of climate)
• High temperatures
• Shrinkage and cracking

23. Deterioration by Freezing and thawing
(Effect of climate)
• Extreme change in change in climatic conditions have adverse
effect on concrete, especially the freezing and thawing cycles.
• If the water present in the pores of concrete freezes, its volume gets
increased by around 9% of volume.
• This increase in volume exerts stress on the concrete and causes
cracks in the concrete as shown in figure below.
• Increase in humidity also increases the amount of water in the
concrete which leads to hydrostatic pressure.
• This hydrostatic pressure may cause lamination of the concrete
surface as explained before.
• To avoid the adverse effect of freezing and thawing use of aerating
admixes is advised. The aerating admixtures fill the concrete pores
with air pockets which do not allow the entrance of water in the
concrete.

24. Deterioration by High temperatures
• The effect of high temperatures on concrete is destructive. The reinforcement rods resist at
temperatures of up to 500°C, while concrete resists at up to 650°C.
• Even if the reinforcement rods are protected by concrete, when they heat up, their volume
increases and they create stresses in the concrete, this may lead to parts of the concrete breaking
off.
• Once the reinforcement is exposed to fire, it expand much more quickly than the concrete in which
they are embedded, causing a loss of bond between concrete and reinforcement.
• Even if the failure temperature is not reached, the concrete may lose its performance characteristics
if it is suddenly cooled down, a condition which usually occurs when fires are extinguished.
• In this situation, the oxide which forms due to the heat is transformed into lime, which
disintegrates the concrete.
• If exposure to fire is prolonged, the reinforcement rods reach their failure temperature and there is
a loss in tensile strength, which causes the entire structure to collapse.

25. Deterioration by mechanical elements
Deterioration by mechanical elements can be subdivided into following
parts
• Abrasion
• Impact
• Erosion
• Cavitation

26. Deterioration by Abrasion
• If a material is repeatedly struck by particles from a harder body,
abrasion takes place. This is due to the friction which the harder
powder particles exercise on the surface of the material.
• It is therefore quite clear that abrasion depends directly on the
characteristics of the materials which make up the concrete.
• As a result, we can improve resistance to abrasion by reducing the
water/ cement ratio or by sprinkling cement mixed with hard admixes
and aggregates on the surface of the concrete

27. Deterioration by erosion
• Erosion is the deterioration of concrete surface as a
result of particles in moving water scrubbing the
surface.
• Similar, damage may be caused by flowing ice.
• Erosion is generally an indication that the concrete
is not durable enough for the environment in which
it has been placed.
• Erosion is sometimes combined with the chemical
action of air and water-borne pollutants which
accelerate the breakdown of the concrete.
• Effects of erosion can be seen in the figure.

28. Effect of loading on serviceability and
durability:
• The response of concrete subjected to loading differs from type of loading,
if the concrete is subjected to impact loading its strength reduces.
• Even under the sustainable loading which remains on concrete for long
duration concrete undergoes deformation due to creep.
• Creep is the deformation in the concrete due to long term loading, the
effects of creep are usually not visible in the fresh structure but it takes
years to show up.
• Creep reduces the service life of the concrete structures.
• Another form of deterioration which arises due to cycling loading i.e.
gradual removal and application of load on the concrete, is called as fatigue.
• Fatigue also a long term deformation usually found on concrete bridges

29. Deterioration by Defects: (Design and
construction errors)
• These are the wide range of deterioration that arises due to design and construction
errors, a list of few of these causes is given below.
• Defects due to bleeding and segregation
• Defects due to improver cover.
• Defects due to poor quality of materials.
• Defects due to poor/incorrect deign of the mix
• Defects due to the wrong composition
• Defects due to incorrect/poor quality installation

30. Examples of defects
Inadequate Cover Segregation of concrete

31. Causes of leakage and seepage in concrete
structures
Following are some major sources of leakage in the concrete structures.
• Structural Causes:
• Non-Structural Causes

32. Structural Causes
• Cracks due to differential settlement of foundations of a building.
• Cracks formed in the RCC slab, beam, walls due to poor design, deficiency, over
loading or poor workmanship resulting in honey combing etc
• Cracks due to thermal extremes, expansion- contraction, shrinkage, creep
including aggressive climatic conditions and lack of joints.
• Cracks due to vegetation growth.
• Cracks due to absence of structural elements like lintels, sill etc
• Cracks between two different materials particularly with different co-efficient of
thermal expansion

33. Non-Structural Causes
• Improper slope of the terrace
• Defective Waterproofing
• Extreme Weather Conditions
• Sub Standard Work Practices
• Poor Quality of Materials
• Poor Quality of Bricks and Plaster:
• Broken tiles on Terrace
• Joints Between Flooring Tiles
• No Plinth Protection
• Leakage of Water from Water Storage Tanks
• Poor Plumbing

34. Non-Structural Causes
• Poor Maintenance
• Chocked Pipes
• Broken Pipes
• Lack of Periodic Checks and Cleaning Arrangements