A Simple Fix for Cement-Admixture Incompatibility

With today’s concrete mixtures becoming more complex, the possibility for cement-admixture incompatibility problems is  increasing.  Cement-admixture incompatibility is simply when the concrete experiences the opposite performance that was expected when a particular cementitious-admixture system is used.  The occurrence of such problems is ever more evident based on the recent creation of ASTM Sub-committee C09/C01.48, which deals with establishing test methods designed to predict and diagnose material incompatibility issues.

The heart of most incompatibility issues concerns how chemical admixtures can alter the balance of sulfate availability (from the inter-ground gypsum) and aluminate reactivity from the C3A and C4AF phases in the cement.

Remarkably, problems such as poor slump increase and rapid slump loss that can occurr with certain cementitious material-admixture combinations, can be essentially eliminated by delaying the addition of admixture sometimes as little as 30 to 60 seconds after the cement and admixture have mixed together. This delay allows the normal sulfate-aluminate reactivity to occur, thus minimizing unexpected performances.


Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s