An admixture is defined as “a material other than water,aggregates, hydraulic cement, and fiber reinforcement usedas an ingredient of concrete or mortar, and added to the batchimmediately before or during its mixing” (AmericanConcrete Institute 2010; ASTM C125). Chemical admixturesare primarily water-soluble substances used to enhance theproperties of concrete or mortar in the plastic and hardenedstate. These benefits include increased compressive andflexural strength at all ages, decreased permeability andimproved durability, corrosion reduction, shrinkage reduction,initial set adjustments, increased slump and workability,improved pumpability, finish and finishability, rheologymodification, improved cement efficiency, alkali-silicareaction (ASR) reduction, and concrete mixture economy.
An admixture or combination of admixtures may berequired to achieve the specific desired results; however,proper mixture designs are required for optimum benefits. Incertain instances, a desired objective may be best achieved bymixture changes in addition to proper admixture usage.Chemical admixtures are not a substitute for suitable concretemixture proportions and acceptable construction practices.This report deals with commonly used admixtures otherthan those assigned to other ACI committees. Materials,such as mineral admixtures, used to produce concrete are notdiscussed in this report.
The chemical admixtures are classified generically or withrespect to their characteristics. Information to characterizeeach class is presented with brief statements of the generalpurposes and expected effects of each group of materials.The wide scope of the admixture field, the continuedentrance of new or modified materials into this field, and thevariations of effects with different concreting materials andconditions preclude a complete listing of all admixtures andtheir effects on concrete. Summaries of the state of the art ofchemical admixtures include Ramachandran and Malhotra(1984), Ramachandran and Mailvaganam (1992), Mather(1994), Nkinamubanzi and Aïtcin (2004), Collepardi andValente (2006), and “Chemical Admixtures for Concrete,”ACI Education Bulletin E4-03 (ACI Committee E703 2003)