Expanding on what x3n0ph3n3 said, concrete doesn&#x27;t harden because the water in it evaporates away. Rather, the water is consumed in a chemical reaction. In fact, you have to be careful that the water doesn&#x27;t evaporate too much during the curing process. It&#x27;s very common to hose down a curing sidewalk and keep it covered for 30 days.<p>Incidentally, the chemical reaction is exothermic. That&#x27;s one of the reasons why you can&#x27;t pour a concrete dam all at once: the heat generated would be enormous.