| Admixtures |  |
Not to be confused with additives, which are added to cements at the finishing stage, admixtures are added during batching, to help modify the fresh, hardening, or hardened properties of concrete (ie. Air). The most commonly used admixtures are manufactured to comply with stringent rules and regulations, depending on country or state where applicable. Concrete admixtures should be supplied by companies operating quality systems in accordance with these regulations. Admixtures are occasionally used which may not be scoped in U.S., British, or Canadian standards, such as pumping aids, water resisting admixtures and dual purpose admixtures e.g. combined air-entrainer's and water-reducing admixtures.
Different cement types may require substantially different dosage rates to achieve the desired effect. This is particularly true for air-entrained concretes where the variation in dosage rates may be substantial. The aggregates also can contribute to this problem. And this is where testing is essential, as concrete is engineered for a maximum resiliency, within a set parameter, and should be tested until the desired air entrainment is met.