What does 'initial set' refer to in the context of concrete?

The term 'initial set' in the context of concrete refers to the point at which the mixture begins to transition from a plastic (flowable) state to a solid (hardened) state. This stage marks the beginning of the hardening process, where the chemical reactions of hydration are taking place, and the concrete gains its initial strength. At this point, the concrete is no longer workable and cannot be molded or shaped.

Understanding this concept is crucial for construction applications because knowing when the initial set occurs helps crews manage timelines for pouring and finishing concrete, ensuring that work can be adjusted based on how quickly the concrete is setting. This phase is distinct from full curing, which involves the entire hydration and strength-gaining process that occurs over time after the initial set.