Why Heated Concrete Can Explode Like Popcorn

iStock.com/Salistock
iStock.com/Salistock

Unlike wood, insulation, and other building materials, concrete doesn't burn. Modern civilization has practically built its infrastructure on it, from stairs to floors to office towers. While not bursting into flames is a good thing, concrete does have vulnerability—exposed to high temperatures, it can explode like a bag of microwaved popcorn. And scientists are getting better at understanding why.

A recent paper published in the journal Cement and Concrete Research offered some insight into this unusual phenomenon. Researchers at Empa, the Swiss Federal Laboratories for Materials Science and Technology; the University of Grenoble, and Institut Laue-Langevin conducted an experiment using blocks of concrete, which typically consists of cement, sand, water, and other additives to increase strength or reduce permeability. Heated to 1112°F, portions of the block exploded.

Using neutron tomography, researchers were able to visualize the accumulation of water as the block heats up.

The principle behind it is largely the same as popping popcorn kernels. In both instances, heated water vaporizes and becomes trapped. With nowhere to go, the built-up energy is released, with the concrete becoming pressurized and breaking apart.

Part of the reason the vapor becomes trapped is because water moves away from the heat source—say, a fire in an interior room—and toward the cooler portion of the concrete. In doing so, the water acts as a moisture barrier, preventing vapor from coming through pores. High-performance concrete, which is often used in commercial applications, has few pores, which makes the pressure from the vapor more concentrated. The water in the mix can turn to vapor when temperatures reach 392°F.

Why is understanding this process important? By exploring how and why concrete can burst, additives can be developed to reduce or eliminate the effect. The result will be safer, more fire-resistant buildings.

[h/t Live Science]

10 Facts You Should Know About Mosquitoes

tskstock/iStock via Getty Images
tskstock/iStock via Getty Images

Between the itching and the welts and the fears of mosquito-borne viruses, it's easy to forget that mosquitoes are a wonder of evolution, and that maybe they don't get a fair shake from us. Of more than 3000 known species, only 80 actually bite people, and at least one eats other mosquitoes for us. They grow from egg to adult in just five days, begin mating within minutes of hatching, and possess, by way of their stinging mouthparts, some of the coolest appendages in the animal kingdom.

1. Mosquitoes are excellent flyers in bad weather.

The average raindrop is 50 times heavier than the average mosquito, yet they buzz around in the rain with no problems. If a Boeing 747 got whacked with a similarly scaled-up raindrop, there would be 2375 tons of water coming down on it, and things probably wouldn’t turn out as well as they do for the mosquito. How do the insects do it?

A common urban legend said that the bugs were nimble enough to dodge the drops. A few years ago, a team of engineers from the Georgia Institute of Technology watched real mosquitoes and Styrofoam dummy mosquitoes with a high-speed camera during a rainy flight to see if that’s what was really happening. They found that the bugs don’t fly fast enough to dodge the drops, but their slowness is what keeps them from getting knocked out of the sky. A mosquito’s low mass even at slow speed doesn’t provide enough of a target for a raindrop to splash on collision. Instead, the drop just deforms, and doesn’t transfer enough momentum to the mosquito to disrupt its flight.

2. Texas is the mosquito capital of America.

Of the 3000 species of mosquitoes around the world, at least 150 are found in the United States, and 85 of those call Texas home. When people say everything's bigger in Texas, you can also include the biodiversity of the state's biting, disease-carrying insects.

3. Some mosquitoes are truly dangerous to humans ...

The female mosquito, which is the one that stings and sucks blood, is an incredible transmitter of disease and, because of that, the deadliest animal in the world. Each year, the malaria parasites they transmit kill 2 million to 3 million people and infect another 200 million or more. They also spread pathogens that cause yellow fever, dengue fever, Rift Valley fever, Chikungunya and West Nile disease.

4. ... and some mosquitoes are harmless.

Not every species of mosquito sucks blood from people, and among those that do, not every one transmits disease. The blood suckers don’t even need to bite you for every meal. Males live entirely on nectar and other plant fluids, and the females’ diet is primarily plant-based, too. Most of the time, they only go after people when they’re ready to reproduce, because blood contains lipids, proteins, and other nutrients needed for the production of eggs.

5. MosquitoEs actually help the environment.

When you’re rubbing calamine lotion all over yourself, mosquitoes might not seem to serve any purpose but to annoy you, but many species play important ecological roles. The mosquitoes Aedes impiger and Aedes nigripes, which gather in thick clouds in Arctic Russia and Canada, are an important food source for migrating birds. Farther south, birds, insects, spiders, salamanders, lizards, frogs, and fish also eat different mosquito species regularly. Plants need them, too, and some, like the blunt-leaved orchid and endangered monkeyface orchid, rely on mosquitoes as their primary pollinator.

Some mosquito species are also excellent at mosquito control. Species of the genus Toxorhynchites feed on the larvae and immature stages of other mosquitoes and will sometimes even cannibalize members of their own species.

6. Mosquitoes are amazing hunters (as if we needed to tell you that).

Mosquitoes are adept at picking up on the chemicals given off by their human hosts. They can detect the carbon dioxide in our breath, the 1-octen-3-ol in our breath and sweat, and other organic substances we produce with the 70-plus types of odor and chemical receptors in their antennae. These receptors can pick up traces of chemicals from hundreds of feet away, and once the mosquito closes in, it tracks its meal chemically and also visually—and they’re fond of people wearing dark colors.

7. Mosquitoes can be picky.

If it seems like you’re always covered head to toe by bites while people who were sitting right next to you only have one or two, it’s not just paranoia; the skeeters actually are out to get you. Some people happen to give off more of the odors and compounds that mosquitoes find simply irresistible, while others emit less of those and more of the compounds that make them unattractive to mosquitoes—either by acting as repellents or by masking the compounds that mosquitoes would find attractive.

8. A female mosquito's mouth is primed for sucking blood.

A mosquito doesn’t simply sink its proboscis into your skin and start sucking. What you see sticking out of a mosquito’s face is the labium, which sheaths the mouthparts that really do all the work. The labium bends back when a mosquito bites, allowing these other parts to pass through its tip and do their thing. The sharp, pointed mandibles and maxillae, which both come in pairs, are used to pierce the skin, and the hollow hypopharynx and the labrum are used to deliver saliva and draw blood, respectively.

9. Mosquito saliva prevents blood clotting.

The saliva that gets pumped out from the hypopharynx during a bite is necessary to get around our blood’s tendency to clot. It contains a grab bag of chemicals that suppress vascular constriction, blood clotting and platelet aggregation, keeping our blood from clogging up the mosquitoes' labrum and ruining their meal.

10. Mosquitoes can explode.

Blood pressure makes a mosquito's meal easier by helping to fill its stomach faster, but urban legend says it can also lead to their doom. Story goes, you can flex a muscle close to the bite site or stretch your skin taut so the mosquito can’t pull out its proboscis and your blood pressure will fill the bug until it bursts. The consensus among entomologists seems to be that this is bunk, but there is a more complicated way of blowing the bugs up. To make a blood bomb, you’ve got to sever the mosquito’s ventral nerve cord, which transmits information about satiety. When it's cut, the cord can’t tell the mosquito’s brain that its stomach is full, so it’ll keep feeding until it reaches critical mass. At least one researcher found that mosquitoes clueless about how full they were would keep sucking even after their guts had exploded, sending showers of blood spilling out of their blown-out back end.

Get The Details On All 21 Successful Moon Landings With This Interactive Map

Astronaut Eugene A. Cernan mans a Lunar Roving Vehicle during the Apollo 17 mission.
Astronaut Eugene A. Cernan mans a Lunar Roving Vehicle during the Apollo 17 mission.
NASA, Wikimedia Commons // Public Domain

In light of Apollo 11’s 50th anniversary this week, the world has focused on those historic first few steps on the Moon and everything that led up to them. But how much do you know about the 20 subsequent Moon landings? To fill you in, Smithsonian.com created an interactive map of the Moon with the who, what, where, when, and how of each successful lunar mission.

The map is color-coded: red for Russian Luna missions, green for China’s Chang'e 3 and Chang'e 4, and blue for the U.S.’s Apollo (marked with stars) and Surveyor missions (simple rings). You can click on each icon to expand a paragraph with a short summary of the mission and its notable accomplishments.

After Russia’s unmanned Luna 9 became the first craft to touch down on the Moon in 1966, 18 other triumphant landings followed in just a decade. The 20th didn’t happen until 37 years later, when China achieved its first landing with Chang'e 3 in 2013. The most recent occurred this past January, when China’s Chang'e 4 became the first spacecraft to land on the far side of the Moon. Chang'e 4 and its rover, Yutu 2, are still exploring the Moon as you read this, and China hopes to launch its follow-up mission, Chang'e 5, as early as this year.

Six Apollo missions landed humans on the Moon, and there haven’t been any actual astronauts on its surface since. But the 15 robotic landings have contributed to our lunar knowledge in a safer, more cost-efficient way. If you look at the map, you can see that most of the spacecrafts have landed near the Moon’s equator on the near side, where the terrain is mostly basaltic plains—the far side contains craters and even mountains. With more Chang'e missions to come from China, and NASA’s Artemis missions in the works, Smithsonian.com may soon have to create a 360° version of its map.

[h/t Smithsonian.com]

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