After a cold winter, concrete contractors and producers should check leftover admixtures before starting production. Admixtures that are frozen and then thawed can have varying effects on fresh and hardened concrete.

WHY ARE THAWED ADMIXTURES A PROBLEM?

Many admixtures tend to separate into two or more phases during freezing. Water separates from the active ingredients of the admixture creating different concentrations within the storage container. After thawing, the phases tend to remain dispersed, and only after thoroughly remixing do they distribute uniformly.

WHAT IS THE PROPER STORAGE TEMPERATURE?

Most admixtures, except for some waterproofers, nonchloride accelerators, and air-entraining agents, are aqueous solutions that freeze at about 28 degrees Fahrenheit. Since many types of admixtures are manufactured, ask your admixture representative about the lowest recommended storage temperature.

HOW TO REVIVE A FROZEN ADMIXTURE

To thaw an admixture, bring it to at least 50 degrees Fahrenheit and wait until it thaws. Remix by mechanical agitation or by agitation with low-pressure air. Take care when using air because too much air causes some admixtures to foam.

HOW TO CHECK FOR ADMIXTURE UNIFORMITY

After thawing and agitating, run tests on the admixture to ensure it's homogenous. The laboratory can perform the following tests: pH (for air-entraining agents only); specific gravity; residue by oven drying; and infrared analysis.