Special Admixtures Liquid admixtures: SCC admixtures Anti-washout admixture Foaming agent
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
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)
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
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.
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
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)
Slump Flow Loss Over TimeSlump flow = 28 in. Slump flow = 16 in. Age = 15 minutes Age = 3 hours
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
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
Coloring Admixtures (Pigments)Red and blue pigments were used to color this terrazzo floor.
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.
Colors in Bridges
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.
Dampproofing Admixtures Product types: Soaps Stearates Petroleum Products Reduction of moisture transmission W/R of less than 0.50 by mass
Pumping Aids Improve pumpability Aids increase viscosity or cohesion Some aids may increase water demand, reduce compressive strength, increae air entrainment, retard setting
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
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
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
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
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
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