CON 122 Session 5 - High Performance Concrete Admixtures


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CON 122 Session 5 - High Performance Concrete Admixtures

  1. 1. CON 122Concrete AdmixturesSession 5High Performance Concrete Admixtures
  2. 2. High-Performance Concrete―Concrete having desired propertiesand uniformity which cannot beobtained routinely using onlytraditional constituents and normalmixing, placing, and curingpractices.‖ - (NIST/ACI Workshop; May, 1990)
  3. 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. 4. High-Performance Concretes Developed to meet construction needs Often require combination of admixtures Typically, economically viable options
  5. 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. 6. Properties of High-Performance Concretes Increased Ductility & Energy Absorption (Toughness) Enhanced Long-Term Mechanical Properties Long Life in Severe Environments
  7. 7. Properties of High-Performance Concretes Can Be Grouped Into Three General Categories…  Enhanced Fresh / Plastic Properties  Enhanced Mechanical Properties  Enhanced Durability Properties
  8. 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. 9. Overview Corrosion – How Big a Problem in Bridges? The Corrosion Process Options for Corrosion Protection Corrosion-Inhibiting Admixture  Calcium Nitrite Inhibitors
  10. 10. Corrosion of Bridge Structures Fulton Bridge in Cleveland, Ohio
  11. 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. 12. Corrosion Inhibitors Control Corrosion of Steel Reinforcement Dosage dependent on anticipated chloride level
  13. 13. The damage to this concrete parkingstructure resulted from chloride-inducedcorrosion of steel reinforcement.
  14. 14. Types of Corrosion Inhibitors Calcium Nitrite Sodium Nitrite Dimethyl Ethanolamine Amines Phosphates Ester Amines
  15. 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. 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. 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. 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. 19. Corrosion of Steel in Concrete Electrochemical process that requires: Moisture & Oxygen Breakdown of Protective Oxide Layer (the Passive Layer)
  20. 20. Consequences of Corrosion in Concrete Delamination
  21. 21. Consequences of Corrosion in Concrete Cracking Spalling
  22. 22. Corrosion of Steel in Concrete: Net Effect Corrosion by-product (rust) induces tensile stresses within matrix…..
  23. 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. 24. Calcium Nitrite Inhibitor: Disadvantages Accelerating Effect  Meets ASTM C 494 Requirements for Type C, Accelerating, Admixture
  25. 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. 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. 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 moistureReinforcement and an external source of chlorides from deicing Severe C2 chemicals, salt, brackish water, seawater, or spray from these sources
  28. 28. ACI 318 Requirements for Concrete for Corrosion Exposure Category Min.fExposure 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. 29. Sources of Chloride• De-icing Salts for Snow & Ice Removal• Groundwater• Brackish Water• Seawater & Airborne• Mixture Ingredients
  30. 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. 31. Effect of w/cm on Permeability Coefficient of Permeability Water-Cement Ratio
  32. 32. Alkali Silica Reaction Necessary conditions:  Reactive Aggregates  Alkali Source: Cement, aggregates, soil, water  Moisture availability Resulting effects:  Cracking  Structural movement  Durability Failure
  33. 33. Alkali-Silica Reaction
  34. 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. 35. Mechanism Reactive silica + alkalis Akali-silica gel OH- OH- Reactive Silica OH- OH-
  36. 36. Mechanism Silica gel + Water Expansion H2O H2O Reactive Silica H2O H2O
  37. 37. Mechanism Expansion Cracking H2O H2O Reactive Silica H2O H2O
  38. 38. Cracking and Appearance of ASR Gel Source: PCA
  39. 39. Alkali-Silica Reaction (ASR) Visual Symptoms  Network of cracks  Closed or spalled joints  Relative displacements Source: PCA
  40. 40. Alkali-Silica Reaction (ASR) Source: PCA
  41. 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. 42. Alkali-Silica Reaction (ASR)Pop-outs caused by ASR of sand-sized particles
  43. 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. 44. ASR Inhibitors Lithium nitrate Lithium carbonate Lithium hydroxide Lithium aluminum silicate Barium salts
  45. 45. ASR Inhibitors—Lithium Carbonate Expansion of specimens made with lithium carbonate admixture.
  46. 46. External Sulfate Attack Source of sulfate ions in solution Access to cement paste
  47. 47. External Sulfates Natural sulfates of calcium, sodium magnesium, potassium  Soils  Ground water  Ponds or rivers  Seawater Sanitary, Industrial, and Agricultural waste
  48. 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. 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. 50. External Sulfate Attack External to internalprogression of deterioration 50
  51. 51. Mitigation of Sulfate Attack Use low w/c Use sulfate resistant cement (Type V) Use supplementary cementitious materials Source: PCA
  52. 52. Effect of w/c Type V Cement Type V Cement w/c = 0.65 w/c = 0.39Visual Rating = 5 @ 12 Visual Rating = 2 @ 16 years years Source: PCA
  53. 53. Table for Sulfate Attack Class Water-soluble Sulfate (SO4) inClass Desc. sulfate (SO4) in soil, water, ppm % by weightS0 N/A < 0.10 < 150S1 Moderate 0.10 to 0.20 150 to 1,500S2 Severe 0.20 to 2.00 1,500 to 10,000S3 Very Severe > 2.00 > 10,000
  54. 54. Shrinkage-Reducing Admixtures Potential uses  Bridge decks  Critical floors  Buildings Components  Propylene glycol  Polyoxyalkylene alkyl esters Drying shrinkage reduction: 25%-50%
  55. 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. 56. Shrinkage-Reducing Admixtures
  57. 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. 58. Drying Shrinkage: Mechanism Loss of moisture Meniscus forms at air-water interface due to surface tension
  59. 59. Drying Shrinkage: Mechanism
  60. 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. 61. Reducing Drying Shrinkage Lower Cement & Water Contents Increase Coarse Aggregate Content & Topsize Shrinkage Compensation Shrinkage-Reducing Admixtures
  62. 62. Shrinkage-Reducing Admixtures: Mechanism Reduce capillary tension by reducing surface tension of water 62
  63. 63. Shrinkage-Reducing Admixtures: Mechanism Reduced Capillary Capillary Tension Tension
  64. 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. 65. Effect of SRAs on Hardened Properties of Concrete May experience some loss in strength.
  66. 66. SRAs: Benefits Reduced drying shrinkage & potential for subsequent cracking Reduced autogenous shrinkage Reduced curling Improved aesthetics, watertightness & durability