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Recipe for Success

5/25/2016

Milk, lard, eggs, and cactus juice sound like ingredients for a recipe. They are just some of the ingredients used by various civilizations over thousands of years as admixtures in concrete.

Admixtures have long been recognized as important components of concrete used to improve its performance. According to ACI E4-12, Chemical Admixtures for Concrete, materials used in early concrete and masonry included milk and lard by the Romans; eggs during the middle ages in Europe; polished glutinous rice paste, lacquer, tung oil, blackstrap molasses, and extracts from elm soaked in water and boiled bananas by the Chinese; and in Mesoamerica and Peru, cactus juice and latex from rubber plants.

More recently chemical admixtures have been used to help concrete producers meet sustainability requirements often included in modern construction. For concrete these requirements can be related to extended life cycles, use of recycled materials, storm water management, and reduced energy usage. Chemical admixtures are used to facilitate the increased use of supplementary cementitious materials, lower permeability, and improved long term durability of concrete.

As defined by the new ACI 212.3R-16 Report on Chemical Admixtures for Concrete, an admixture is a material other than water, aggregates, cementitious materials, 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.

This new report reviews several categories and types of chemical admixtures and their use in unique concrete technologies. They are classified into 12 groups: air-entraining; normal, mid- and high-range water-reducing; accelerating; set-retarding; extended set-control; workability-retaining; viscosity- and rheology-modifying, shrinkage-reducing and shrinkage-compensating, and corrosion-inhibiting; lithium admixtures to reduce deleterious alkali-silica reaction; permeability-reducing; and miscellaneous.

Chemical admixtures are used on a daily basis in the cast-in-place and precast concrete industries. Mixtures that use using multiple chemical admixtures are more common today. Their successful use requires compatibility, setting times, and early strengths that are appropriate to the placing environment.

ACI 212.3R-16 Report on Chemical Admixtures for Concrete is available as a printed document, PDF, ePub, or Kindle.

More ACI Resources on Chemical Admixtures

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