What's the Difference Between Cement and Concrete?

Vladimir Kokorin/iStock via Getty Images
Vladimir Kokorin/iStock via Getty Images

Picture yourself walking down a city block. The sidewalk you follow may be obscured by shuffling feet and discarded gum, but it’s clearly made from something hard, smooth, and gray. What may be less clear is the proper name for that material: Is it concrete or cement? Is there even a real difference between the two words?

Though they’re often used interchangeably, concrete and cement describe different yet related elements of the blocks, flooring, and walls that make up many everyday structures. In simple terms, concrete is the name of the gray, gritty building material used in construction, and cement is an ingredient used in concrete.

Cement is a dry powder mixture that looks much different from the wet stuff poured out of so-called cement trucks. It’s made from minerals that have been crushed up and mixed together. Exactly what kind of minerals it’s made from varies: Limestone and clay are commonly used today, but anything from seashells to volcanic ash is suitable. After the ingredients are mixed together the first time, they’re fired in a kiln at 2642°F to form strong new compounds, then cooled, crushed, and combined again.

Cement
Cement
lior2/iStock via Getty Images

This mixture is useless on its own. Before it’s ready to be used in construction projects, the cement must be mixed with water and an aggregate, such as sand, to form a moldable paste. This substance is known as concrete. It fills whatever mold it’s poured into and quickly hardens into a solid, rock-like form, which is partly why it’s become the most widely-used building material on Earth.

So whether you’re etching your initials into a wet sidewalk slab, power-hosing your back patio, or admiring some Brutalist architecture, you’re dealing with concrete. But if you ever happen to be handling a chalky gray powder that hasn’t been mixed with water, cement is the correct label to use.

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Why Did Noon Used to Mean 3 p.m.?

3 p.m. is basically noon for people who wake up at 12 p.m.
3 p.m. is basically noon for people who wake up at 12 p.m.
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If you’re a late sleeper, you might find yourself thinking 12 p.m. seems way too early to be considered midday, and the word noon would much better describe, say, 3 p.m. It turns out that ancient Romans would have agreed with you, if only for etymological reasons.

As Reader’s Digest explains, the days in ancient Rome were split into four periods of three hours each. The first hour was at sunrise around 6 a.m.—called prime, for first—followed by 9 a.m. (terce, denoting the third hour), 12 p.m. (sext, for sixth), and 3 p.m. (none, for ninth).

According to Merriam-Webster, Middle and Old English borrowed the time-keeping tradition, along with the Latin word for ninth, which was changed to nōn and eventually noon. Though we’re not sure exactly when or why noon started referring to 12 p.m. instead of 3 p.m., it could have something to do with Christian prayer traditions. In the Bible, Jesus’s crucifixion is said to have taken place at the ninth hour, and that’s when worshippers partook in their second of three daily prayers; the others were in the morning and evening. It’s possible that hungry monks were behind noon’s gradual shift from 3 p.m. to 12 p.m.—since their daily fast didn’t end until after the midday prayer, they had a built-in motive for moving it earlier.

While we didn’t exactly stay true to the original Latin meaning of noon, there’s another important remnant of ancient Rome hiding in the way we tell time today. Romans referred to 12 p.m. as meridiem, for midday, and so do we. A.M. is an abbreviation for ante meridiem, or before midday, and P.M. means post meridiem, or after midday.

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