Why doesn’t water poured onto hard concrete make it soft again?
—John Stratton, Baltimore, Md. Concrete is made by mixing hard or rocky materials—such as sand and gravel or crushed stone—w ith cement, then adding water. Cement is a powdery adhesive substance that reacts to water by hardening, even underwater. So the mixture hardens because water was added, not because it evaporates. In fact, concrete usually must be kept wet for about a week (called “curing”) so the cement has enough time to harden the mixture thoroughly. Other factors—such as air temperature—are important, too. Concrete just gets harder as time goes by. Let it rain! By the way, there’s no such thing as a cement mixer or a cement sidewalk. The correct terms are concrete mixer and concrete sidewalk. WordTeaser This week’s word is: ETUI What’s the definition? A) A sound made out of disgust. B) Julius Caesar’s dying words to Brutus. C) A petite case for little items in use every day. D) Any of several odd words that are overused in crossword puzzles. E) An extremely short musical comp
