Water-reducing admixtures have a fluidifying effect on concrete that reduces the amount of water needed for ease in placement. The admixtures break up clusters of cement grains, freeing water trapped within the clusters and dispersing the cement. There are three ways in which water reducers may be used: to increase slump, to lower the water-cement ratio or to reduce cement content. The main components in commercially produced water-reducing admixtures are water soluble organic compounds that can be divided into three groups. Lignosulfonates are the most widely used raw materials in the production of water reducers. Hydroxylated carboxylic acid salts reduce the water content by 5 to 8 percent. Carbohydrates include natural sugars and hydroxylated polymers. The American Society for Testing and Materials (ASTM) classifies water reducers according to how they affect the setting characteristics of concrete. "Specifications for Chemical Admixtures for Concrete," ASTM C 494, gives specifications for three types: Type A (normal setting), Type D (retarding), and Type E (accelerating).

While the use of water reducers typically permits water reductions ranging from 5 to 10 percent or more, several factors will affect the amount of water reduction: dosage; cement properties; cement content; and the use of fly ash.