What process causes concrete to set and become hardened?

The process that causes concrete to set and become hardened is hydration. This is a chemical reaction that occurs when water is added to cement, which is a key ingredient in concrete. During hydration, the water molecules react with the cement particles, producing hydroxides and other compounds that lead to the formation of a solid structure. This process not only contributes to the strength of the concrete but also plays a crucial role in its durability.

As hydration progresses, the concrete transitions from a plastic, workable state to a rigid, hardened material. The strength of the concrete continues to increase over time as the hydration reactions continue, even long after the initial setting has occurred.

While evaporation can affect the curing process and might lead to surface cracking if water is lost too quickly, it is not the primary mechanism for setting and hardening concrete. Cooling does not directly involve the chemical changes necessary for hardening, and compressive strengthening is a description of the capacity of hardened concrete to withstand loads rather than a process of setting. Thus, hydration is the essential process that causes concrete to set and harden effectively.