The term Concrete Admixture can be defined 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”. It can also be stated that “chemical admixtures are used to enhance the properties of concrete and mortar in the plastic and hardened state. These properties may be modified to increase compressive and flexural strength at all ages, decrease permeability and improve durability, inhibit corrosion, reduce shrinkage, accelerate or retard initial set, increase slump and workability, improve pumpability and finish-ability, increase cement efficiency, and improve the economy of the mixture. An admixture or combination of admixtures may be the only feasible means of achieving the desired results. In certain instances, the desired objectives may be best achieved by mixture changes in addition to proper admixture usage”.
Chemical admixtures are materials that are added to the constituents of a concrete mixture, in most cases, specified as a volume in relation to the mass of the cement or total cementitious materials. The admixtures interact with the hydrating cementitious system by physical and chemical actions, modifying one or more of the properties of concrete n the fresh and/or hardened states. Concrete is composed principally of aggregates, hydraulic cement, and water, and may contain other cementitious materials and chemical admixtures. It will contain some amount of entrapped air and may also contain purposely entrained air obtained by use of a chemical admixture or air-entraining cement. Chemical admixtures are also frequently used to accelerate, retard, improve workability, reduce mixing water requirements, increase strength, improve durability, or alter other properties of the concrete. There are many kinds of chemical admixtures that can function in a variety of ways to modify the chemical and physical properties of concrete. This bulletin provides information on the types of chemical admixtures and how they affect the properties of concrete, mortar, and grout.
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