"An admixture is defined in ACI 116R and in ASTM C 125 as ""a material other than water@ aggregates@ hydraulic cement@ and fiber reinforcement used as an ingredient of concrete or mortar@ and added to the batch immediately before or during its mixing."" This report deals with commonly used admixtures other than those assigned to other ACI committees. Materials such as admixtures used to produce expansive-cement concrete (ACI Committee 223); fly ash and natural pozzolans (ACI Committee 232); silica fume (ACI Committee 234); admixtures for insulating and cellular concrete (ACI Committee 523); and polymers (ACI Committee 548)@ are not discussed in this report. The chemical admixtures are classified generically or with respect to their characteristics. Information to characterize each class is presented along with brief statements of the general purposes and expected effects of using each group of materials. The wide scope of the admixture field@ the continued entrance of new or modified materials into this field@ and the variations of effects with different concreting materials and conditions preclude a complete listing of all admixtures and their effects on concrete. Summaries of the state-of-the-art of chemical admixtures include Ramachandran (1984)@ Ramachandran and Mailvaganam (1992)@ and Mather (1994)."