ACI 116R-00 defines the term admixture as “a material other than water, aggregates, hydraulic cement, and fiber reinforcement, used as an ingredient of a cementitious mixture to modify its freshly mixed, setting, or hardened properties and that is added to the batch before or during its mixing.”
Functions of Admixtures:
- Increase workability without increasing water content or decrease the water content at the same workability;
- Retard or accelerate time of initial setting;
- Reduce or prevent shrinkage or create slight expansion;
- Modify the rate or capacity for bleeding;
- Reduce segregation;
- Improve pumpability;
- Reduce rate of slump loss;
- Retard or reduce heat evolution during early hardening;
- Accelerate the rate of strength development at early ages;
- Increase strength (compressive, tensile, or flexural);
- Increase durability or resistance to severe conditions of exposure, including application of deicing salts and other chemicals;
- Decrease permeability of concrete;
- Control expansion caused by the reaction of alkalies with potentially reactive aggregate constituents;
- Increase bond of concrete to steel reinforcement;
- Increase bond between existing and new concrete;
- Improve impact and abrasion resistance;
- Inhibit corrosion of embedded metal; and
- Produce colored concrete or mortar.
Standards Used for Admixtures:
- Air-Entraining Admixtures ASTM C 260
- Standard Specification for Air-Entraining
- Admixtures for Concrete AASHTO M 154
- Standard Specification for Air-Entraining
- Admixtures for Concrete CRD-C 13
- Chemical Admixtures ASTM C 494
- Standard Specification for Chemical
- Admixtures for Concrete AASHTO M 194
- Standard Specification for Chemical
- Admixtures for Concrete CRD-C 87
- Calcium Chloride ASTM D 98
- Standard Specification for Calcium Chloride AASHTO M 144
- Foaming Agents ASTM C 869
- Admixtures for Shotcrete ASTM C 1141
- Admixtures for Use in Producing
- Flowing Concrete ASTM C 1017
- Grout Fluidifier For Preplaced Aggregate
- Concrete ASTM C 937
- Pigments For Integrally Colored Concrete ASTM C 979
Types of Admixtures:
- Chemical Admixtures:
- Accelerators
- Retarders
- Air entrainments
- Plasticizers
- Pigments
- Corrosion inhibitors
- Bonding agents
- Pumping aids
- Mineral Admixtures:
- Fly ash
- Mineral
- Ground granulated blast furnace slag (GGBFS or GGBS)
- Silica fume
- High reactivity Metakaolin (HRM)
- According to ASTM:
- Type A—Water-reducing admixtures,
- Type B—Retarding admixtures,
- Type C—Accelerating admixtures,
- Type D—Water-reducing and retarding admixtures,
- Type E—Water-reducing and accelerating admixtures,
- Type F—Water-reducing, high range admixtures,
- Type G—Water-reducing, high range, and retarding admixtures, and
- Type S—Specific performance admixtures.
