How would you describe the process of concrete setting?

Concrete setting is initiated by a process called hydration. Rather than the concrete just 'drying out', the hydration process involves the water added to the materials (stone, sand & cement) reacting with the cement. The water reacts with calcium in the cement to form an alkali paste which bonds the materials together. Adding too little water means not enough cement hydrates to set properly, but too much will cause separation of the materials.