Water reducer
An admixture that makes concrete more workable without adding water, allowing the same placeability at a lower water-cement ratio and therefore higher strength.
What does water reducer mean?
Water reducers work by dispersing cement particles that would otherwise clump, freeing trapped water to lubricate the mix. They can be used three ways: to cut water and gain strength, to cut cement and save money, or to raise slump at the same strength. Mid-range products have become the everyday default in ready-mix, with high-range products reserved for flowing or pumped concrete.
In practice
When a supplier says they can send a wetter mix without hurting strength, this admixture is what they mean.