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Concrete Admixtures that Control Cracking

Reducing Drying or Shrinkage Cracking

Hydrated cement paste shrinks as it loses moisture from its extremely small pores. As the moisture is lost in these small pores, the surface tension of the remaining water tends to pull the pores together which results in a loss of volume over time.

Shrinkage reducing admixtures (SRAs) are designed to decrease the effects of drying shrinkage by reducing the surface tension in these pores.

It should be noted that the type of aggregate and the cement properties themselves can influence the amount of cracking that can occur. Thus, it is important to test local project-specific materials if doing shrinkage testing.

Curing also affects cracking. In slabs, the top tends to dry out first and shrinks while the lower sections still have a higher moisture content. This difference in moisture can be altered by use of Shrinkage Reducing Admixtures, which alter the way water migrates through the concrete and results in a more uniform moisture profile.