1. CON 122
Concrete Admixtures
Session 6
Special Admixtures

2. Special Admixtures
 Self-consolidating
concrete admixtures
(SCC):
 Hydration-control
admixtures
 Dampproofing
admixtures
 Pumping Aids
 Bonding admixtures
 Coloring admixtures

3. Special Admixtures
 Liquid admixtures:
 SCC admixtures
 Anti-washout
admixture
 Foaming agent

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. Self-Consolidating Concrete
 Viscosity-Modifying Admixtures
 Rheology-Controlling Admixtures

6. Viscosity-Modifying Admixtures
(VMAs)
“A material added to
concrete, or a cement- 35
30
based mixture, to 25
change (usually 20
15
increase) the viscosity 10
and improve the 5
stability of the mixture.”
0
0 4 8 12
VMA Dosage (fl oz/cwt)

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. 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. 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. 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. Slump Flow

12. Slump Flow Loss Over Time
Slump flow = 28 in. Slump flow = 16 in.
Age = 15 minutes Age = 3 hours

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. 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. Coloring Admixtures (Pigments)
Red and blue pigments were used to color this terrazzo floor.

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. Colors in Bridges

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. Dampproofing Admixtures
 Product types:
 Soaps
 Stearates
 Petroleum Products
 Reduction of moisture transmission
 W/R of less than 0.50 by mass

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. 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. 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. 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. 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. 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. 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