1. CON 122
Concrete Admixtures
Session 5
High Performance Concrete Admixtures

2. High-Performance Concrete
―Concrete having desired properties
and uniformity which cannot be
obtained routinely using only
traditional constituents and normal
mixing, placing, and curing
practices.‖
- (NIST/ACI Workshop; May, 1990)

3. High-Performance Concrete in
Simple Terms
 Concrete with performance characteristics
over and above what is typically
(“the norm”) that meets the project
requirements.

4. High-Performance Concretes
 Developed to meet construction needs
 Often require combination of admixtures
 Typically, economically viable options

5. Properties of High-Performance
Concretes
 Ease of Placement and Compaction
without Segregation, Low Bleeding, Good
Finishability, & Low Plastic Shrinkage
 High Early-Age Strength
 Volume Stability

6. Properties of High-Performance
Concretes
 Increased Ductility & Energy Absorption
(Toughness)
 Enhanced Long-Term Mechanical
Properties
 Long Life in Severe Environments

7. Properties of High-Performance
Concretes
 Can Be Grouped Into Three General
Categories…
 Enhanced Fresh / Plastic Properties
 Enhanced Mechanical Properties
 Enhanced Durability Properties

8. What’s Next?
 The overview will be limited to only calcium
nitrite and the amine-ester organic corrosion
inhibitor, the two most widely used corrosion
inhibitors in the world.
 Following the Overview, the bulk of the
discussion will focus on the amine-ester
inhibitor, which is now being introduced in
the Middle East.
 Calcium nitrite will extend the setting
characteristics of concrete.

9. Overview
 Corrosion – How Big a Problem in Bridges?
 The Corrosion Process
 Options for Corrosion Protection
 Corrosion-Inhibiting Admixture
 Calcium Nitrite Inhibitors

10. Corrosion of Bridge Structures
Fulton Bridge in Cleveland, Ohio

11. Corrosion: How Big a
Problem?
―The average bridge deck located in a
snow-belt State with reinforcing steel
and 40 mm (1.5 in.) of concrete cover
has shown spalling in about 7 to 10
years after construction and has
required rehabilitation in about 20 years
after construction.‖
Repair / Replacement Cost: ~ $ 20 billion & increasing

12. Corrosion Inhibitors
 Control Corrosion of Steel Reinforcement
 Dosage dependent on anticipated chloride
level

13. The damage to this concrete parking
structure resulted from chloride-induced
corrosion of steel reinforcement.

14. Types of Corrosion Inhibitors
 Calcium Nitrite
 Sodium Nitrite
 Dimethyl Ethanolamine
 Amines
 Phosphates
 Ester Amines

15. Corrosion-Inhibiting System
 Definition: “An admixture (or system) that
will significantly delay the onset and/or rate of
corrosion and, thus, extend the useful service
life of reinforced and pre-stressed concrete
structures.”
 Though there are classical definitions for
corrosion inhibitors in the literature, this simple
definition corrosion inhibitor is the most relevant
from an Owner’s perspective.
 Basically, an Owner is only interested in a
corrosion inhibitor that will effectively delay
corrosion and help achieve the intended service
life of the structure.

16. Most Commonly Used Inhibitor
 The most commonly used corrosion
inhibitor in the world is calcium nitrite.
 Calcium Nitrite is inorganic and comes in a
30% solution.

17. Calcium Nitrite Inhibitor
 30% calcium nitrite
solution
 Anodic corrosion
inhibitor
 Recommended
dosage of 1.0 to 6.0
gal/yd3 (5 -30 L/m3)

18. Corrosion Sequence
 Formation: Ferrous Oxide and Ferric Oxide
 Ferrous oxide reaction with chlorides to
form rust
 Chloride ions continue attack until
passivating oxide layer destroyed
 Volume of rust is greater, thus concrete
cracks.

19. Corrosion of Steel in Concrete
 Electrochemical process that requires:
 Moisture & Oxygen
 Breakdown of Protective Oxide Layer (the
Passive Layer)

20. Consequences of Corrosion in
Concrete
Delamination

21. Consequences of Corrosion in Concrete
Cracking Spalling

22. Corrosion of Steel in Concrete:
Net Effect
 Corrosion by-product (rust) induces
tensile stresses within matrix…..

23. Calcium Nitrite Inhibitor:
Advantages
 Historical data
 Effective with admixed
chlorides
 Can double as an
accelerator in cold
weather applications
 Early concrete
strengths are equal or
better than reference
mixes

24. Calcium Nitrite Inhibitor: Disadvantages
 Accelerating Effect
 Meets ASTM C 494 Requirements for Type C,
Accelerating, Admixture

25. NOTE: ASTM Specification for Corrosion
Inhibiting Admixtures
 ASTM C 1582/ C 1582M:
 Standard Specification for Admixtures to
Inhibit Chloride-Induced Corrosion of
Reinforcing Steel in Concrete

26. Rule #1 for Corrosion Protection
of Steel in Concrete
 Good Concreting Practices
 Good quality concrete
 Low water-cementitious materials ratio
 High-range water-reducing admixture
 Proper placement & consolidation
 Good Curing !!!

27. ACI 318 Classes for Corrosion Exposure
Category
Category Severity Class Condition
Concrete dry or protected
Not Applicable C0
from moisture
Concrete exposed to moisture
C Moderate C1 but not to external sources of
chlorides
Corrosion
Protection of Concrete exposed to moisture
Reinforcement and an external source of
chlorides from deicing
Severe C2
chemicals, salt, brackish
water, seawater, or spray from
these sources

28. ACI 318 Requirements for Concrete for
Corrosion Exposure Category
Min.f
Exposure Max. ’c Additional Minimum Requirements
Class w/cm
(psi)
Max Water-Soluble Chloride
Ion (Cl-) Content in Concrete
(percent by weight of cement) Related
Provisions
Reinforced Prestressed
Concrete Concrete
C0 n/a 2,500 1.00 0.06 None
C1 n/a 2,500 0.30 0.06
C2 0.40 5,000 0.15 0.06 7.7.6, 18.16

29. Sources of Chloride
• De-icing Salts for Snow & Ice Removal
• Groundwater
• Brackish Water
• Seawater & Airborne
• Mixture Ingredients

30. How to Reduce Concrete
Permeability
 Lower Water-Binder  Use Pozzolans & Slag
Ratio & Use High- Cement
Range Water Reducer  Fly Ash & Natural
Pozzolans
 Silica Fume
 Metakoalin

31. Effect of w/cm on Permeability
Coefficient of Permeability
Water-Cement Ratio

32. Alkali Silica Reaction
 Necessary conditions:
 Reactive Aggregates
 Alkali Source: Cement, aggregates, soil, water
 Moisture availability
 Resulting effects:
 Cracking
 Structural movement
 Durability Failure

33. Alkali-Silica Reaction

34. Alkali-Silica Reaction (ASR)
 Contributing factors:
 Reactive forms of silica
in the aggregate
 High-alkali (pH) pore
solution
 Sufficient moisture
Crack
– Reaction Product
Source: PCA

35. Mechanism
 Reactive silica + alkalis Akali-silica gel
OH- OH-
Reactive
Silica
OH- OH-

36. Mechanism
 Silica gel + Water Expansion
H2O H2O
Reactive
Silica
H2O
H2O

37. Mechanism
 Expansion Cracking
H2O H2O
Reactive
Silica
H2O
H2O

38. Cracking and Appearance
of ASR Gel
Source: PCA

39. Alkali-Silica Reaction (ASR)
 Visual Symptoms
 Network of cracks
 Closed or spalled joints
 Relative displacements
Source: PCA

40. Alkali-Silica Reaction (ASR)
Source: PCA

41. Alkali-Silica Reaction (ASR)
 Visual Symptoms
 Fragments breaking out of the surface
(popouts)
 Mechanism
1. Alkali hydroxide + reactive silica gel
reaction product (alkali-silica gel)
2. Gel reaction product + moisture
expansion

42. Alkali-Silica Reaction (ASR)
Pop-outs caused by ASR of sand-sized particles

43. Mitigation of ASR
 Avoid reactive aggregates
 Limit concrete alkali content (low alkali
cement)
 Supplementary cementitious materials
 Fly ash, silica fume, slag, calcined clay
(metakaolin)
 Blended cement
 Use chemical inhibitors, e.g., LiNO3
 Test for effectiveness of mitigation measures

44. ASR Inhibitors
 Lithium nitrate
 Lithium carbonate
 Lithium hydroxide
 Lithium aluminum silicate
 Barium salts

45. ASR Inhibitors—Lithium
Carbonate
 Expansion of
specimens made with
lithium carbonate
admixture.

46. External Sulfate Attack
 Source of sulfate ions
in solution
 Access to cement
paste

47. External Sulfates
 Natural sulfates of
calcium, sodium
magnesium,
potassium
 Soils
 Ground water
 Ponds or rivers
 Seawater
 Sanitary, Industrial,
and Agricultural waste

48. Sulfate Attack Mechanism
 Sulfate ions (SO4-2) react with hydration
products (calcium hydroxide and
aluminate hydrates)
 Reaction products result in swelling
(mechanism is uncertain)

49. Sulfate Attack Mechanism
 Swelling pressures destroy cement matrix
 Affected by:
 Cement type
 Sulfate ion concentration in water or soil
 Permeability of concrete
 Presence water

50. External Sulfate Attack
External to internal
progression of deterioration
50

51. Mitigation of Sulfate Attack
 Use low w/c
 Use sulfate resistant
cement (Type V)
 Use supplementary
cementitious
materials
Source: PCA

52. Effect of w/c
Type V Cement Type V Cement
w/c = 0.65 w/c = 0.39
Visual Rating = 5 @ 12 Visual Rating = 2 @ 16 years
years
Source: PCA

53. Table for Sulfate Attack Class
Water-soluble
Sulfate (SO4) in
Class Desc. sulfate (SO4) in soil,
water, ppm
% by weight
S0 N/A < 0.10 < 150
S1 Moderate 0.10 to 0.20 150 to 1,500
S2 Severe 0.20 to 2.00 1,500 to 10,000
S3 Very Severe > 2.00 > 10,000

54. Shrinkage-Reducing Admixtures
 Potential uses
 Bridge decks
 Critical floors
 Buildings
 Components
 Propylene glycol
 Polyoxyalkylene alkyl esters
 Drying shrinkage reduction: 25%-50%

55. Shrinkage-Reducing Admixtures
 Shrinkage cracks, such as shown on this
bridge deck, can be reduced with the use
of good concreting practices and
shrinkage reducing admixtures.

56. Shrinkage-Reducing Admixtures

57. Shrinkage
 Volume Reduction due to loss of moisture
from a concrete matrix as it hardens and
dries.
 Plastic Shrinkage
 Thermal Contraction
 Drying Shrinkage
 Autogenous Shrinkage
 Carbonation Shrinkage

58. Drying Shrinkage: Mechanism
 Loss of moisture
 Meniscus forms at air-water interface due
to surface tension

59. Drying Shrinkage: Mechanism

60. Drying Shrinkage: Mechanism
 Surface tension forces
exert inward pulling Capillary
force on the walls of Tension
the pores
 Most significant in
pore sizes ranging
from 2.5-50 nm
(micrometers)

61. Reducing Drying Shrinkage
 Lower Cement & Water Contents
 Increase Coarse Aggregate Content &
Topsize
 Shrinkage Compensation
 Shrinkage-Reducing Admixtures

62. Shrinkage-Reducing Admixtures:
Mechanism
 Reduce capillary tension by reducing
surface tension of water
62

63. Shrinkage-Reducing Admixtures:
Mechanism
Reduced
Capillary Capillary
Tension Tension

64. Effect of SRAs on Plastic
Properties of Concrete
 SRAs may increase bleed time and bleed
ratio (10% higher).
 SRAs may also delay final set by 1-2
hours.
 Precautions needed to minimize impact on
air-void system.

65. Effect of SRAs on Hardened
Properties of Concrete
 May experience some loss in strength.

66. SRAs: Benefits
 Reduced drying shrinkage & potential for
subsequent cracking
 Reduced autogenous shrinkage
 Reduced curling
 Improved aesthetics, watertightness &
durability