Water Reducing Admixtures

Water-reducing admixtures reduce the quantity of water required to produce concrete of a certain slump. They also:

  • Reduce the water-cement ratio
  • Reduce cement content
  • increase slump

Typically, water reducing admixtures reduce the water content by approximately 5 – 10% for the same strength properties.

Effect on Strength

Generally, an increase in strength is obtained with water reducing admixtures, because the water-cement ratio is reduced. All other properties being the same, the 28 day strength of a water-reduced concrete can be 10 – 25% greater than concrete without the admixture.

Despite the reduction in water content, water reducing admixtures can cause an increase in drying shrinkage, resulting in cracks or non-uniformity with adjacent building components.

Water reducing admixtures have little or no effect on bleeding.

Specifications

The specification for water reducing admixtures is ASTM C494 or the equivalent AASHTO M194.

Materials

Water reducing admixtures can contain the following materials:

  • Lignosulfonates
  • Hydroxylated carboxylic acids
  • Carbohydrates
  • Polycarboxylates

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