Description

Chemical admixtures, which are primarily water-soluble substances, are discussed in detail and, in this report, are classified into 13 groups: airentraining; accelerating; water-reducing and set-retarding; admixtures for flowing concrete; admixtures for self-consolidating concrete; cold weather admixture systems; admixtures for very high-early-strength concrete; extended set control; shrinkage-reducing; corrosion-inhibiting; lithium; permeability-reducing; and miscellaneous. Chemical admixtures are used on a daily basis in the cast-in-place and precast concrete industries. Twelve categories of admixtures are described in detail as to type, current usage, and their effect on concrete in the plastic and hardened state. Their benefits and common usage are outlined.

Each category of admixture addresses the benefits obtainable with their use in a properly proportioned concrete mixture, types of batching systems, control measures, and test placements for mixture design verification. Mixture designs using multiple chemical admixtures have become more common. Their successful usage requires proper compatibility and, often, setting times and early strengths that are proper for the placing environment. The potential benefits are highlighted to all members of the concrete team, concrete contractor, concrete producer, admixture supplier, and testing personnel.

Finely divided mineral admixtures are addressed by ACI 232.2R “Use of Fly Ash in Concrete,” ACI 232.1R “Use of Raw or Processed Natural Pozzolans in Concrete” and ACI 234R “Guide for the Use of Silica Fume in Concrete.”

Keywords: accelerating; admixture; admixture system; air-entraining; alkali-aggregate reaction; flowing concrete; high-range water-reducing admixture; permeability-reducing admixtures; self-consolidating concrete; shrinkage-reducing; water-reducing and set-retarding.