ADMIXTURE GENERAL CLASSIFICATION:
Admixtures are ingredients other than water, aggregates, hydraulic cement, and fibers that are added to the concrete batch immediately before or during mixing. A proper use of admixtures offers certain beneficial effects to concrete, including improved quality, acceleration or retardation of setting time, enhanced frost and sulfate resistance, control of strength development, improved workability, and enhanced finish ability. It is estimated that 80% of concrete produced in North America these days contains one or more types of admixtures. According to a survey by the National Ready Mix Concrete Association, 39% of all ready-mixed concrete producers use fly ash, and at least 70% of produced concrete contains a water-reducer admixture. Admixtures vary widely in chemical composition, and many perform more than one function.
Two basic types of admixtures are available: chemical and mineral.
Chemical admixtures are added to concrete in very small amounts mainly for the entrainment of air, reduction of water or cement content, plasticization of fresh concrete mixtures, or control of setting time. Seven types of chemical admixtures are specified in ASTM C 494, and AASHTO M 194, depending on their purpose or purposes in PCC. Air entraining admixtures are specified in ASTM C 260 and AASHTO M 154. General and physical requirements for each type of admixtures are included in the specifications.
- Type A Water-reducing admixtures;
- Type B Retarding admixtures;
- Type C Accelerating admixtures;
- Type D Water-reducing and retarding admixture;
- Type E Water-reducing and accelerating admixtures;
- Type F Water-reducing, high-range, admixtures; and
- Type G Water-reducing, high-range, and retarding admixtures.
These are of two types
Generally used fly ash and fumed silica are non reactive or slightly reactive type. Mineral admixtures like (fly ash, silica fume [SF]) are usually added to concrete in larger amounts to enhance the workability of fresh concrete; to improve resistance of concrete to thermal cracking, alkali-aggregate expansion, and sulfate attack; and to enable a reduction in cement content.
- Fly Ash
- Silica Fume
- The second type more of the proprietary type or special grades of mineral admixture
- are prepared using a combination of active metal salts. They are inorganic oxidizer of
- micro/macro metal elements contained in the cementitious materials providing electrochemical
- decay of cement grain by electrolysis between inversely charged particles of
- electrolyte and cement grain. Decay-hydration reactions result in maximum volume of
- cementitious paste as a continuous solid phase in which the aggregates are embedded.
TECHNOBUILD Concrete Admixtures
- In construction, concrete is the foundation of many major projects. Therefore, it is
- imperative that concrete used in construction be strong, crack resistant and workable.
- Admixtures are used to improve or change specific properties in concrete and improve
- the quality of concrete construction projects. Technokotes’ concrete admixtures do more
- than just improve the strength of the concrete; they also can be used to add color or
- texture to the concrete for decorative purposes. Technokotes has an extensive portfolio
- of concrete admixtures to ensure that all criteria are met and the finished product meet
- the requirements of the contractor, architect and building/project owner.