Concrete Admixtures

What is an Admixture?

An admixture is anything added to concrete other than aggregates, cement, water, or fibers.

Why Use Admixtures?

Admixtures allow the attributes of the concrete to be adjusted based on the conditions of the project site or to achieve desirable characteristics during the finishing and curing phases. Some of the benefits admixtures can achieve include:

  • Increased Workability
  • Decreased Water Content
  • Addition of Entrained Air
  • Reduced Weight
  • Reduced Rate of Slump Loss
  • Reduced Segregation
  • Slowed Down or Sped Up Setting Time
  • Increased Strength
  • Improved Aesthetics

Main Admixture Classifications:

  • Water reducing admixtures (ranging from normal to high range) can reduce the water content in concrete from 5% to 12% on average while still providing a high level of workability during the finishing process. The decrease in water will permit the concrete to achieve a higher end strength and reduce the overall shrinkage that occurs during the curing phase.
    • Normal
    • Mid Range
    • High Range
  • Set controlling admixtures allow the concrete contractor to control the rate at which the concrete will harden. This is especially important to the finishing process during summer and winter months when the temperature of the concrete can be directly affected. During the summer, a retarding admixture will likely be used to decrease the set time, while an accelerating admixture will be used in the winter to speed up the rate of hardening.
    • Retarding
    • Accelerating
  • The most common type of durability enhancing admixture used in concrete construction consists of air entraining admixtures used to increase freeze-thaw resistance in the winter. The other admixtures within this category are typically only used in special circumstances outside of residential applications and include the following:
    • Corrosion Inhibiting
    • Shrinkage Reducing
    • Crack Reducing
    • Integral Waterproofing
    • ASR Inhibitors