durabillty of concrete case study

1. DURABILITY OF
CONCRETE
ARJUN R KURUP 14MST1041
AROMAL CHOLAPURATH 14MST1047
GIRISH S 14MST1021
SHABEER AZEEZ 14MST1045

2. WHAT IS DURABILITY OF CONCRETE?
The ability of concrete to resist weathering action,
chemical attack, and abrasion while maintaining its
desired engineering properties.

3. FACTORS AFFECTING DURABILITY
• ABRATION
• BIOLOGICAL FACTORS.
• TEMPERATURE EFFECT
• ENVIRONMENTAL RELATED PHYSICAL PROBLEMS
• FREEZING AND THAWING
• CHEMICAL ATTACKS

4. ABRATION
• Concrete is resistant to the abrasive affects of
ordinary weather
• Abrasion resistance is directly related to the strength
of the concrete

5. ABRATION
• Examples of severe abrasion and erosion are
particles in rapidly moving water, floating ice, or
areas where steel studs are allowed on tires
• For areas with severe abrasion, studies show that
concrete of grade M80 and above work well.

6. BIOLOGICAL FACTORS
• Mosses and lichens
these plants of a higher order, cause significant
damage to concrete. These plants produce weak acids
in the fine hair roots. The acids that are produced will
attack the cement paste and cause the concrete to
disintegrate and scale

7. BIOLOGICAL FACTORS

8. FIRE

9. FREEZING AND THAWING
• The most potentially destructive weathering factor
is freezing and thawing while the concrete is wet
• Deterioration is caused by the freezing of water and
subsequent expansion in the paste, the aggregate
particles, or both.

10. FREEZING AND THAWING
• With the addition of an air entrainment admixture,
concrete is highly resistant to freezing and thawing
• the microscopic air bubbles in the paste provide
chambers for the water to enter and thus relieve the
hydraulic pressure generated

11. FREEZING AND THAWING
• Air-entrained concrete with a low water-cement
ratio and an air content of 5 to 8% will withstand a
great number of cycles of freezing and thawing
without distress

12. CHEMICAL ATTACKS
• Carbonation
• Chloride Attack
• Acid Attack
• Sulphate Attack

13. CARBONATION OF CONCRETE
It is a process by which CO2 from the air penetrates
into concrete and reacts with calcium hydroxide to
form calcium carbonates in presence of water.
CH + CO2-------------------------- CACO3 + WATER

14. CARBONATION OF CONCRETE

15. CHLORIDE ATTACK
• Chloride attack is particularly important because it
primarily causes corrosion of reinforcement.
• Statistics have indicated that over 40 per cent of
failure of structures is due to corrosion of
reinforcement.

16. CHLORIDE ATTACK
• Due to high alkalinity of concrete a protective oxide
film is present on the surface of steel reinforcement.
• This protective passivity layer can be lost due to
carbonation and chloride in presence of H2O and O2

17. CHLORIDE ATTACK
• Chloride enters the concrete from cement, water,
and aggregate and sometimes from admixtures.
S.No. Type of Use of Concrete
Maximum Total acid soluble
chloride content. Expressed as
kg/m3 of concrete
1 Concrete containing metal and steam cured at elevated
temperature and prestressed concrete. 0.4
2 Reinforced concrete or plain concrete containing
embedded metal. 0.6
3 Concrete not containing embedded metal or any
material requiring protection from chloride. 3.0
According to IS 456-2000

18. CHLORIDE ATTACK
Prevention measures:
• Use supplementary cementitious materials to reduce
permeability
• Increasing the concrete cover over the steel
• use of corrosion inhibiting admixtures
• epoxy-coated reinforcing steel, surface treatments, concrete
overlays, and cathodic protection

22. ACID ATTACK
Concrete is susceptible to acid attack because of its
alkaline nature. The components of the cement paste
break down during contact with acids.

23. ACID ATTACK
Most pronounced is the dissolution of calcium
hydroxide which occurs according to the following
reaction:
2 HX + Ca(OH)2 -> CaX2 + 2 H2O
(X is the negative ion of the acid)

24. SULPHATE ATTACK
• Sulphates can attack concrete by reacting with
hydrated compounds in the hardened cement paste
• Result in disintegration of the concrete

25. SULPHATE ATTACK
• It combines with the C-S-H, or concrete paste, and
begins destroying the paste that holds the concrete
together. As sulphate dries, new compounds are
formed, often called Ettringite. (calcium
sulphoaluminate hydrate)

26. SULPHATE ATTACK
• These new crystals occupy empty space, and as
they continue to form, they cause the paste to
crack, further damaging the concrete

27. SULPHATE ATTACK
• The sulphate ion + hydrated calcium aluminate
and/or the calcium hydroxide components of
hardened cement paste + water = ettringite

28. SULPHATE ATTACK
• C3A.CS.18H + 2CH +2S+12H = C3A.3CS.32H
ettringite.
• C3A.CH.18H+ 2CH +3S +11H = C3A.3CS.32H

29. SULPHATE ATTACK
EFE or harmless ettringite formation happens, for instance,
when gypsum reacts with anhydrous calcium aluminate in
a through solution reaction and acts as a set retarder in
Portland cement mixtures

30. SULPHATE ATTACK
Under proper restraint, Calcium aluminate sulphate (C4A3S)
hydrates within few days producing ettringite uniformly
distributed and then homogeneous expansion throughout the
hardened concrete

31. SULPHATE ATTACK

32. SULPHATE ATTACK
• the sulphate ion + hydrated calcium aluminate
and/or the calcium hydroxide components of
hardened cement paste + water = gypsum (calcium
sulphate hydrate)
• Na2SO4+Ca(OH)2 +2H2O = CaSO4.2H2O +2NaOH
• MgSO4 + Ca(OH)2 + 2H2O = CaSO4.2H2O + Mg(OH)2

33. SULPHATE ATTACK
ETTRINGITE

35. SULPHATE ATTACK
External Sources:
• Soil - gypsum - harmless (0.01-0.05)
• Groundwater-high-manganese and alkali sulphates
• Agricultural soil and water-Ammonium sulphate
• Furnaces - high sulphur fuel
• Furnaces-Chemical industry-sulphuric acid.

36. SULPHATE ATTACK
Internal source:
• Portland cement might be over-sulphated.
• presence of natural gypsum in the aggregate.
• Admixtures also can contain small amounts of
sulphates.

37. SULFATE ATTACK
• Cement type and content:
The most important mineralogical phases of cement
that affect the intensity of sulfate attack are: C3A,
C3S/C2S ratio and C4AF
• Cements with low C3A content are less vulnerable to
sulfate attack.

38. SULPHATE ATTACK
Control of sulphate attack:
The quality of concrete, specifically a low permeability, is the
best protection against sulphate attack.
• Adequate concrete thickness
• High cement content
• Low w/c ratio
• Proper compaction and curing

39. SULPHATE ATTACK
• The addition of a pozzolanic admixture such as flyash
• Use of chloride ions:
the solubility of sulfate ettringite in sodium and calcium
chloride solutions is about 3 times more, than in water
• Use of low C3A content cement

40. SULPHATE ATTACK
Exposure Concentration of
water-soluble
sulphates in soil per
cent
Concentration of
water-soluble
sulfates in water
ppm
Mild <0.1 <150
Moderate 0.1 to 0.2 150 to 1500
Severe 0.2 to 2 1500 to 10000
Very severe >2 >10000
Exposure conditions:

41. SULPHATE ATTACK

42. SULPHATE ATTACK

43. SULPHATE ATTACK

44. Alkali-Silica Reaction:
“The Cancer of Concrete”

45. Alkali-Silica Reaction
The alkali–silica reaction (ASR) is a reaction which
occurs over time in concrete between the highly
alkaline cement paste and reactive non-crystalline
(amorphous) silica, which is found in many common
aggregates.

46. Alkali Silica Reaction (ASR)
Alkalis
+
Reactive
Silica
+
Moisture
ASR
Gel
which
expands
Concrete
expansion
and
cracking
What is ASR?

47. Concrete failure due to ASR

49. • Concrete quality
• Loss of strength, stiffness, impermeability
• Premature failure of concrete structures
• Economic/Environmental impacts
• ASR decreases concrete service life
• Reconstruction has both environmental and economic
impacts. ex. cement production produces 7% of the
world’s CO2 emissions (a greenhouse gas)
Why is it important to study ASR?

50. Creation of alkali-silica gel

51. Reactants: alkalis, reactive silica, and water
Alkalis
Main cations:
• Sodium (Na+)
• Potassium (K+)
Common sources:
• Portland cement
• Deicing agents
• Seawater
Creation of alkali-silica gel

52. Reactive Silica
Silica
tetrahedron
Amorphous Silica Crystalline Silica
Creation of alkali-silica gel contd…

53. Creation of alkali-silica gel contd….
Amorphous or disordered silica
(most chemically reactive)

54. Common reactive minerals:
Chalcedony Cherts

55. Common reactive minerals: contd…
Strained Quartz

56. Opal
Common reactive minerals: contd…

57. Obsidian
Common reactive minerals: contd…

58. Common reactive minerals: contd…
Tridymite

59. Common reactive minerals: contd…
Cristobalite

60. Cryptocrystalline volcanic rocks
Common reactive minerals: contd…

61. Water
Found in pore spaces in concrete
Sources:
• Addition of water to concrete mixture
• Moist environment / permeable concrete
Creation of alkali-silica gel contd….

62. 1. Siliceous aggregate in solution
Creation of alkali-silica gel contd....

63. 2. Surface of aggregate is attacked by OH-
H20 + Si-O-Si Si-OH…OH-Si
Creation of alkali-silica gel contd…

64. 3. Silanol groups (Si-OH) on surface are broken down by OH-
into SiO- molecules
Si-OH + OH- SiO- + H20
Creation of alkali-silica gel contd…

65. 4. Released SiO- molecules attract alkali cations in pore
solution, forming an alkali-silica gel around the aggregate.
Creation of alkali-silica gel contd…
Si-OH + Na+ + OH- Si-O-Na + H20

66. 5. Alkali-silica gel takes in water, expanding and exerting an
osmotic pressure against the surrounding paste or
aggregate.
Creation of alkali-silica gel contd…

67. 6. When the expansionary pressure exceeds the tensile
strength of the concrete, the concrete cracks.
Creation of alkali-silica gel contd…

68. 7. When cracks reach the surface of a structure,
“map cracking” results.
Creation of alkali-silica gel contd…

69. 8. Once ASR damage has begun:
Creation of alkali-silica gel contd…
Expansion and cracking of concrete
Increased permeability
More water and external alkalis penetrate concrete
Increased ASR damage

70. Images of ASR damage

71. Images of ASR damage contd…

72. How to prevent ASR damage
• Avoid high alkali content:
• use low alkali Portland cement: Na20eq < 0.69
• replace cement with low alkali mineral admixtures
• 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
Alkalis + Reactive Silica + Moisture ASR Gel

73. Alkali-Silica Reaction
Chemical reactions in ASR
• Ca(OH)2 + H4SiO4 → Ca2+ + H2SiO4
2− + 2 H2O →
CaH2SiO4 · 2 H2O

74. Alkali-Silica Reaction

75. ASR Optical Image

76. Repairing ASR Damage to a
Concrete Dam
Typical Options:
•Monitoring
•Slot cut
•Upstream face membrane
•Roller compacted concrete
•Decrease the reservoir
•Dam Removal

77. ASR Damage Examples
Built in 1965, this deteriorated bridge is located 9.7 miles west of Lee
Vining at 9400 feet elevation on the eastern slope of the Sierra Nevada.

78. Cracks in concrete
• Plastic Shrinkage Cracks.
• Settlement cracks.
• Bleeding.
• Delayed Curing.
• Constructional effects.
• Early Frost Damage.
• Unsound Materials.
• Shrinkage.
• Drying Shrinkage.
• Thermal Shrinkage.

79. PLASTIC SHRINKAGE CRACKS
• When the loss of water from surface of concrete is
faster than the migration of water from interior to
the surface, the surface dries up.
• It depends upon the rate of evaporation of water
from the surface of concrete

80. PLASTIC SHRINKAGE CRACKS
Prevention measures:
• Moisten the formwork.
• Erect temporary wind breakers to reduce the wind
velocity over concrete.
• Erect temporary roof to protect green concrete from
hot sun.
• Reduce the time between placing and finishing. if
there is delay cover the concrete with polythene
sheets

81. PLASTIC SETTLEMENT CRACKS
• Plastic concrete when vibrated or otherwise settles.
If the concrete is not free to settle uniformly, then
cracks are formed.
• Non Uniform settlement caused due to large piece
of aggregates or reinforcement.

82. PLASTIC SETTLEMENT CRACKS

83. THERMAL EXPANSION AND
SHRINKAGE
• Expansion and contraction of concrete subjected to
ambient increase or decrease in temperature results
concrete cracking.
• Ex: roof slabs, road or airfield pavements , bridge
decks etc.

84. CONCLUSIONS
FACTORS AFFECTING DURAILITY OF CONCRETE
• ENVIRONMENTAL FACTORS
• QUALITY OF CONSTITUENT MATERIALS
• QUANTITY OF CONSITUENT MATERIALS
• QUALITY OF WORKMANSHIP
• COVER TO THE REINFORCEMENT
• INADEQUATE DESIGN
• IMPROPER USE OF STRUCTURE

85. CONCLUSIONS
Physical stress:
• Abrasion (traffic, friction, flow etc.)
• Wear
• Weathering - wind, sun, rain
• Freeze - thaw
• Water pressure
• Temperature

86. CONCLUSIONS
Chemical stress:
• pH value < 6.5:
corrosion of concrete
• Dissolved sulphates (soil, sewage, exhaust etc.):
penetration and reaction with unhydrated
C3A
formation of Ettringit (increase of volume)
spalling
• Acids:
dissolving of calcium hydroxide

87. CONCLUSIONS
Chemical stress conti….
• Chlorides:
yield corrosion of reinforcement steel
• Ammonium and magnesium salts:
may attack calcium hydroxide of the
cement paste
• Grease and oil:
may build acids and react with calcium
hydroxide

88. THANK YOU