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
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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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Has An Element Ever Been Removed From the Periodic Table?

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lucadp/iStock via Getty Images

Barry Gehm:

Yes, didymium, or Di. It was discovered by Carl Mosander in 1841, and he named it didymium from the Greek word didymos, meaning twin, because it was almost identical to lanthanum in its properties. In 1879, a French chemist showed that Mosander’s didymium contained samarium as well as an unknown element. In 1885, Carl von Weisbach showed that the unknown element was actually two elements, which he isolated and named praseodidymium and neodidymium (although the di syllable was soon dropped). Ironically, the twin turned out to be twins.

The term didymium filter is still used to refer to welding glasses colored with a mixture of neodymium and praseodymium oxides.

One might cite as other examples various claims to have created/discovered synthetic elements. Probably the best example of this would be masurium (element 43), which a team of German chemists claimed to have discovered in columbium (now known as niobium) ore in 1925. The claim was controversial and other workers could not replicate it, but some literature from the period does list it among the elements.

In 1936, Emilio Segrè and Carlo Perrier isolated element 43 from molybdenum foil that had been used in a cyclotron; they named it technetium. Even the longest-lived isotopes of technetium have a short half-life by geological standards (millions of years) and it has only ever been found naturally in minute traces as a product of spontaneous uranium fission. For this reason, the original claim of discovery (as masurium) is almost universally regarded as erroneous.

As far as I know, in none of these cases with synthetic elements has anyone actually produced a quantity of the element that one could see and weigh that later turned out not to be an element, in contrast to the case with didymium. (In the case of masurium, for instance, the only evidence of its existence was a faint x-ray signal at a specific wavelength.)

This post originally appeared on Quora. Click here to view.

Can You Ever Truly Lose Your Accent?

DGLimages, iStock via Getty Images
DGLimages, iStock via Getty Images

You may be able to pull off a Spanish accent when showing off your Antonio Banderas impression, but truly losing your native accent and replacing it with a new one is a lot harder to do. The way you speak now will likely stick with you for life.

According to Smithsonian, our accent develops as early as 6 months old—accents being the pronunciation conventions of a language shaped by factors like region, culture, and class. When a baby is learning the words for nap and dad and play, they're also learning how to pronounce the sounds in those words from the people around them. Newborn brains are wired to recognize and learn languages just from being exposed to them. By the time babies start talking, they know the "right" pronunciations to use for their native language or languages.

As you get older, your innate understanding of foreign accents and languages gets weaker. If you're an English speaker raised in Boston, you may think that the way someone from Dallas speaks English sounds "wrong" without being able to articulate what it is that makes them sound different. This is why pulling off a convincing foreign accent can be so difficult, even if you've heard it many times before.

Around age 18, your ability to learn a second language takes a steep nosedive. The same may be true with your ability to speak in a new accent. If you immerse yourself in a foreign environment for long enough, you may pick up some ticks of the local accent, but totally adopting a non-native accent without making a conscious effort to maintain it is unlikely as an adult.

There is one exception to this rule, and that's Foreign Accent Syndrome. Following a head injury or stroke, some people have reported suddenly speaking in accents they didn't grow up using. The syndrome is incredibly rare, with only 100 people around the world having been diagnosed with it, and medical experts aren't sure why brain injuries cause it. But while patients may be pronouncing their words differently, they aren't exactly using foreign accents in the way most people think of them; the culprit may be subtle changes to muscle movements in the jaw, tongue, lips, and larynx that change the way patients pronounce certain vowels.

[h/t Smithsonian]

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