Concrete
Concrete is a composite construction material composed primarily of aggregate, cement, and water. There are many formulations, which provide varied properties. The aggregate is generally a coarse gravel or crushed rocks such as limestone, or granite, along with a fine aggregate such as sand. The cement, commonly Portland cement, and other cementitious materials such as fly ash and slag cement, serve as a binder for the aggregate. Various chemical admixtures are also added to achieve varied properties. Water is then mixed with this dry composite, which enables it to be shaped (typically poured) and then solidified and hardened into rock-hard strength through a chemical process called hydration. The water reacts with the cement, which bonds the other components together, eventually creating a robust stone-like material. Concrete has relatively high compressive strength, but much lower tensile strength. For this reason it is usually reinforced with materials that are strong in tension (often steel). Concrete can be damaged by many processes, such as the freezing of trapped water.
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Famous quotes containing the word concrete:
“Don’t feel guilty if you don’t immediately love your stepchildren as you do your own, or as much as you think you should. Everyone needs time to adjust to the new family, adults included. There is no such thing as an “instant parent.”
Actually, no concrete object lies outside of the poetic sphere as long as the poet knows how to use the object properly.”
—Johann Wolfgang Von Goethe (1749–1832)
“Babies are necessary to grown-ups. A new baby is like the beginning of all things—wonder, hope, a dream of possibilities. In a world that is cutting down its trees to build highways, losing its earth to concrete ... babies are almost the only remaining link with nature, with the natural world of living things from which we spring.”
—Eda Le Shan (b. 1922)
““The city’s grotesque iron skeletons
Would knock their drunken penthouse heads together
And cake their concrete dirt off in the streets.””
—Robert Frost (1874–1963)