The Constructor

Shrinkage Reducing Concrete Admixture: Mechanism, and Applications

Shrinkage Reducing Admixture

Reading time: 1 minute

Shrinkage-reducing concrete admixture promote expansion of the concrete at about the same volume that normal drying shrinkage is contracting it. The net change in length of the hardened concrete is small enough to prevent shrinkage cracks. Shrinkage reducing concrete mixture is typically comprised of polyoxyalkylene alkyl ether or similar composition.

When such admixture is added to concrete during the batching stage, it can significantly reduce both the early and long-term drying shrinkage; reductions of 30 to 50% can be achieved. This is achieved by treating the ‘cause’ of drying shrinkage within the capillaries and pores of the cement paste.

This type of admixture should not be confused with shrinkage compensating materials which are normally added at above 5% on cement and function by creating an expansive reaction within the cement paste to treating the ‘effects’ of drying shrinkage.


Shrinkage reducing admixtures are mainly based on ethylene glycol derivatives. These organic liquids are totally different to most other admixtures, which are water-based solutions.

The admixtures are normally 100% active and are water soluble. They have a characteristic odor and a specific gravity of less than 1.00.

Mechanism of Shrinkage Reduction

The mechanism by which shrinkage reducing admixtures operate is unique. When excess water begins to evaporate from the concrete’s surface after placing, compacting, finishing and curing, an air/water interface or “meniscus” is set up within the capillaries or pores of the cement paste of the concrete.

Fig. 1: Shrinkage in Hardened Concrete

Because water has a very high surface tension, this causes a stress to be exerted on the internal walls of the capillaries or pores where the meniscus has formed.

This stress is in the form of an inward pulling force that tends to close up the capillary or pore. Thus, the volume of the capillary is reduced leading to shrinkage of the cement paste around the aggregates, leading to an overall reduction in volume.

The shrinkage reducing admixtures operates by interfering with the surface chemistry of the air/water interface within the capillary or pore, reducing surface tension effects and consequently reducing the shrinkage as water evaporates from within the concrete.

Fig. 2: Shrinkage Reducing Mechanism


Usage rates vary with batch designs and water content but typically range from 8 to 25%. Selection, of an appropriate dosage would depend on the level of shrinkage desired, the degree of set retardation that is acceptable, and curing conditions.

Effects on Fresh Concrete

Effects on Hardened Concrete

Fig. 3: Affects on Hardened Concrete



  1. Architectural precast
  2. Pneumatically applied concrete
  3. Water-retaining structures Majority of horizontal slab applications such as floors, roofs, and parking decks.
Exit mobile version