CON 122 Session 6 - Special Admixtures

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CON 122 Session 6 - Special Admixtures

  1. 1. CON 122Concrete AdmixturesSession 6Special Admixtures
  2. 2. Special Admixtures Self-consolidating concrete admixtures (SCC): Hydration-control admixtures Dampproofing admixtures Pumping Aids Bonding admixtures Coloring admixtures
  3. 3. Special Admixtures Liquid admixtures: SCC admixtures Anti-washout admixture Foaming agent
  4. 4. Self-Consolidating Concrete (SCC) Self-Consolidating Concrete (SCC) is highly flowable, non-segregating concrete that can spread into place, fill the formwork, and encapsulate the reinforcement without any mechanical consolidation. ACI 237
  5. 5. Self-Consolidating Concrete Viscosity-Modifying Admixtures Rheology-Controlling Admixtures
  6. 6. Viscosity-Modifying Admixtures (VMAs)“A material added toconcrete, or a cement- 35 30based mixture, to 25change (usually 20 15increase) the viscosity 10and improve the 5stability of the mixture.” 0 0 4 8 12 VMA Dosage (fl oz/cwt)
  7. 7. How Does A VMA Work Thickening-Type: thickens mixture making it cohesive Binding-Type: binds water in mixture  more potent  controls bleeding  adds thixotropic properties
  8. 8. Binding-Type VMA The active cellulosic polymer binds up the free water within any given mixture holding the material together. This makes the concrete, grout, or cement slurry very cohesive preventing the blending of external water with the matrix or the internal water from leaving the matrix.
  9. 9. Binding-Type VMA The active polymer binds up the free water within the mixture, holding the material together VMA 2 VMA 2 H2 O H2 O H2 O VMA 2 H2 O VMA 2 VMA 2 VMA 2 H2 O H2 O VMA 2 VMA 2 H2 O H2 O VMA 2 VMA 2 H2 O H2 O VMA 2 VMA 2 VMA 2 VMA 2 H2 O H2 O VMA 2 VMA 2
  10. 10. Slump Flow Typical Slump Flow for SCC: 26 to 30 in. Recommended slump flow for shafts: 18 to 24 in.  (Note: 16 in. slump flow ≈ 9 in. slump)
  11. 11. Slump Flow
  12. 12. Slump Flow Loss Over TimeSlump flow = 28 in. Slump flow = 16 in. Age = 15 minutes Age = 3 hours
  13. 13. Hydration-Control Admixtures Two part system:  Stabilizer or retarder stops hydration  Activator reestablishes normal hydration Suspends hydration up to 72 hours Reuse of returned concrete Stabilized for long hauls
  14. 14. Coloring Admixtures Natural and synthetic materials Colors: Black, Red, Yellow, Tan, Green, Blue 6%-10% addition by weight cement Special applications: buried electrical or gas lines, special floors, residential concrete
  15. 15. Coloring Admixtures (Pigments)Red and blue pigments were used to color this terrazzo floor.
  16. 16. Colored Concrete is Cost- Effective Can be installed and finished like regular concrete  Eliminates separate finishing or staining, thus minimizing cost of installation Generally less expensive than painting costs over service life of structure.
  17. 17. Colors in Bridges
  18. 18. Curing Colored Concrete Uneven Curing = Uneven Drying = Uneven Color Use curing compounds specifically recommended for colored concrete. Water cure, membrane sheets, or non-approved curing compounds can discolor concrete.
  19. 19. Dampproofing Admixtures Product types:  Soaps  Stearates  Petroleum Products Reduction of moisture transmission W/R of less than 0.50 by mass
  20. 20. Pumping Aids Improve pumpability Aids increase viscosity or cohesion Some aids may increase water demand, reduce compressive strength, increae air entrainment, retard setting
  21. 21. Bonding Admixtures and Bonding Agents Bonding Admixtures Water emulsions:  Rubber  Polyvinyl chloride  Polyvinyl acetates  Acrylics  Styrene butadiene copolymers Added to concrete for bond strength  Rate of addition 5%-20% Bonding agents help glue materials  Restoration/repair work  Latex, grouts, copolymers
  22. 22. Grouting Admixtures Use of Portland Cement Grouts  Stabilize Foundations  Set Machine Bases  Fill Cracks and Joints  Cement Oil Wells  Fill Masonry Walls  Grout Pre-stress tendons/anchor bolts  Fill Voids in preplaced aggregate concrete
  23. 23. Gas-Forming Admixtures Added to Concrete and Grout to Cause slight expansion Use to complete grouting  Machine Bases  Post-tension ducts of prestressed concrete Aluminum Powder/other gas forming materials
  24. 24. Fungicidal, Germicidal, and Insecticidal Admixtures Control of Bacteria and Fungal growth  Types of materials  Polyhalogenated Phenols  Dieldrin emulsions  Copper Compounds  Effectiveness is temporary/ high dosage
  25. 25. Antiwashout Admixtures Increase the cohesiveness of concrete Allows placement of concrete in water and underwater Admixture increases viscosity of water resulting in increased thixotropy and resistance to segregation Types of materials: Cellulose ether or acrylic polymers
  26. 26. Admixture Compatibility Due to Cement-Admixture Incompatibility Fresh Concrete Properties  Slump Loss  Air Loss  Early Stiffening Long-term Hardened Properties  Compressive strength  Placement Poor correlation with lab test to conditions experienced in the field

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