ASTM C494 specifies admixtures that affect the fresh properties of concrete. These include set accelerators and retarders, water reducers and superplasticizers. The use of these admixtures can help solve problems created by weather or site conditions.
For example, a temperature drop of 20o F can cut slump about 1”, increase concrete water requirements and lower the 28-day compressive strength by as much as 25%. To combat this, concrete producers can add an ASTM C494 Type A set accelerating admixture or a Type D combination of retarder and water reducer to the mix.
Chloride-containing set accelerators have been used in the past but are being replaced with non-chloride admixtures that meet ASTM C 494 Type B and can also act as an ASTM C 494, Type E, water reducer. These allow the concrete to be poured at higher temperatures for quicker placement, vibration or compaction without affecting initial or longer term strength.
High-range water reducers are referred to as superplasticizers and help to produce very thick concrete with little segregation. These admixtures typically meet ASTM C 1017 Types F and G and can be used with portland cement, fly ash, slag or silica fume to improve workability and strength.