Admixtures have both beneficial and detrimental effects on the expansion of different types of expansive cement, and sometimes these effects are unpredictable. For this reason, trial mixtures should always be performed to determine their influence on the expansion for a particular mix design. These trial mixtures should use the specified job materials and proportions under simulated ambient conditions.

In general, air entraining admixtures have no effect on expansion. Some water-reducing and water-reducing retarding admixtures (specifically types A, D, F, and G) are not compatible with certain shrinkage-compensating cements, because they accelerate the ettringite reaction causing the expansion to decrease and/or the shrinkage to increase. These effects occur from both normal and high range admixtures, although some high range admixtures may be beneficial to the expansion of shrinkage-compensating concrete. Calcium Chloride, an accelerator admixture, decreases expansion and increases drying shrinkage and should never be used.

Recently, a new admixture, called Tetraguard AS20, has been developed to actually reduce drying shrinkage. It functions by reducing the capillary tension of pore water (one of the primary causes of drying shrinkage) which helps to induce compressive stresses and offset tensile stresses in concrete. Using 2% Tetraguard AS20 admixture by mass of cement in concrete may reduce shrinkage by as much as 80% at 28 days and up to 50% at one year and beyond. Other benefits include: reduction of compressive creep, minimized curling, and reduction of carbonation. See www.masterbuilders.com for more information.