What process is responsible for the initial hardness of concrete?

The initial hardness of concrete is primarily achieved through the process known as setting. This is the phase in which the chemical reaction between the cement and water begins, leading to the formation of complex compounds that create a solid structure. During the setting phase, the paste transitions from a fluid state to a solid state, which is essential for the development of the concrete's early strength and durability.

Setting involves two main stages: initial set and final set. The initial set marks the beginning of the loss of workability, after which the concrete can no longer be easily molded or formed. The final set indicates that the concrete has reached sufficient hardness to support some load, though it may not have achieved its full strength yet.

This process forms the backbone of concrete’s initial structural integrity, which is crucial for any subsequent steps in construction, like curing, which further enhances the concrete’s final strength and durability over time. Thus, the setting process is fundamental in establishing the first stage of hardness in concrete immediately after it is poured.