Concrete science

PHOENIX, Ariz. — Concrete is the most common artificial material on the planet. It’s used to make roads, bridges and dams. It anchors fence posts and makes durable outdoor stairs. Chances are, concrete forms the foundation of the building you live in. Humans use billions of tons of it each year. That’s enough for each man, woman and child on Earth to have their own personal concrete cube measuring 1.5 meters (nearly 5 feet) across. So it’s little wonder that this building material is the focus of much research, even among teens.

The idea of concrete as a research topic may seem drab and low-tech. After all, it’s been in use since ancient Rome. Yet finding new or better uses for a material, or a better way to make it, is what engineering is all about.

And doing that with concrete brought finalists from three nations to compete at the world’s largest teen science competition. This International Science and Engineering Fair (ISEF) was created by Society for Science & the Public and sponsored by Intel. The 2016 competition brought together more than 1,750 students from 75 countries. (The Society also publishes Science News for Students.) The teens described their research here on May 12.

One of the teams looked at how to reduce the environmental footprint of concrete. Its solution was to use seawater rather than freshwater, which might be better saved for drinking. Another team investigated ways to make concrete safer by making it glow in the dark. The third project focused on a possible use for concrete rubble, which is generated by the renovation or destruction of old buildings or roadways.

Together, these projects show that topics don’t have to be glitzy to yield important results.  

Saving precious water

Concrete is typically made by mixing together several materials. The largest part of thiscomposite material is a binder called cement. It’s made by first heating limestone and clay to very high temperatures. Then, people add small amounts of other minerals before grinding the mix into a powder. They add freshwater  to turn the cement into a slurry. Then they add other ingredients such as gravel and sand. The slurry gradually hardens and binds the other ingredients  together. Engineers can further strengthen concrete by adding steel rods. These reinforcing bars are often called “rebar” for short.

 

This is the slurry of cement, gravel, sand and other minerals that will harden into concrete.

 

Making concrete requires a lot of water. But freshwater is a precious resource in many parts of the world. In many arid locations, drinking water comes not from wells but from seawater that has been treated to remove the salt. That’s especially true in some coastal parts of the Middle East, notes Abdulrahman Mohammed, 18, and Ahmed Elhamamsi, 16. Both attend Ahmad Bin Hanbal Secondary School in Najma, Qatar. Qatar (which somewhat rhymes with the English word “gutter”) is a small oil-rich nation on the shores of the Persian Gulf. Seawater is readily available there. Freshwater, not so much.

Abdulrahman and Ahmed wanted to see what happened if they substituted seawater for freshwater in concrete. So they mixed up samples of each and then compared them. To a few of the samples, they also added a powdered clay mineral called metakaoline (MEH-tah-KAY-oh-leen). (It’s a dehydrated version of the clay mineral used to make porcelain and fine china.)

The teens’ early results are encouraging. Concrete with both metakaoline and seawater appeared to be stronger than that made from the traditional recipe. It resisted about 10 percent more crushing pressure than did the regular stuff. Their data now suggest that in some cases engineers could substitute smaller amounts of concrete made from the new recipe to carry the same load as concrete made with freshwater. 

 

Abdulrahman Mohammed, 18 (left), and Ahmed Elhamamsi, 16, made concrete with seawater rather than freshwater. Not only does it conserve a precious resource in arid regions, but it also improves the final product.

 

Concrete made with seawater could potentially solve another common problem. In areas where freezing temperatures are common, rain and snow can soak into its surface. When that water freezes it expands. That can cause concrete to weaken over the course of many winters. But concrete made from seawater was about 4 percent less permeable. That means smaller amounts of rain would soak into its surface, the teens note. (Temperatures never drop below freezing in Qatar, but they certainly do in many other places.)

Further tests will be needed to make sure concrete made with seawater doesn’t suffer long-term problems, the teens say. For example, salts and other minerals dissolved in the water might cause any rebar inside the concrete to corrode.

Seawater-based concrete could be a boon for Qatar, the boys say. In 2022, their nation will host the World Cup soccer tournament. That means there will soon be a lot of construction in the country (which is about twice the size of the state of Delaware).

Safety first

A lot of concrete goes into making roads. Each year in the United States, about 1.5 million traffic accidents occur when drivers hit animals crossing the road at night. But some of those accidents might be prevented if animals could be seen more clearly against the background. That was just one motivation for the glow-in-the-dark cement created by two students at Saint Joseph’s Academy in Baton Rouge, La.

 

Among glow-in-the-dark coatings for concrete, teens found that a paint-like epoxy coating (right) was the brightest at night. A tough sealant made another (left) was almost as bright but much more wear-resistant.

 

Aniko Nowakowski, 18, and Meredith Guidry, 17, made concrete glow by creating a coating that could be painted onto a road’s exposed surface.

The glow comes from a compound called strontium aluminate. (Its formula is SrAl2O4.) The chemical is phosphorescent(FOSS-for-ESS-ent). That means it absorbs certain wavelengths of sunlight, then re-radiates them as visible light once the sunlight is removed. The glow-in-the-dark coating can be chemically tweaked with different additives to make it give off blue, green or blue-green light. The material can glow for hours after only 20 minutes in full sunlight. It’s still glowing at dawn, although only about half as brightly as at sundown, the teens say.

Aniko and Meredith made a number of different coatings and assessed each one for brightness and durability. The ideal combination should give off plenty of glow but not be worn away quickly by traffic.

In some of their coatings, the teens used large granules of strontium aluminate. In others, they added it as a fine powder. Initially, they thought that the powdered material might mix into the coating better. Plus, powdered strontium aluminate would provide much more surface area per ounce than the larger granules. That also might mean more light.

 

Meredith Guidry, 17 (left), and Aniko Nowakowski, 18, created a glow-in-the-dark coating for concrete to accent backyard landscaping or mark roadways at night. Their tests showed that the brightest glow came, in fact, from a recipe in which large granules of strontium aluminate were mixed into a paint-like epoxy. The second-brightest combination was the powdered material mixed with a tough sealant. This recipe also held up much better to wear  than did the epoxy. So the teens concluded that the sealant-based coating might be the best overall choice among the options they tested.

 

Such coatings could be used in a wide variety of places. A glow-in-the-dark coating could clearly mark parking spots or the edges of driveways. It could decorate patios or poolside surfaces. Hospitals and other public buildings could use the material to highlight safe evacuation routes in case of a power failure. Indeed, the teens argue, the potential benefits of glow-in-the-dark concrete are mind-boggling.

Rubble, be gone!

Durability remains one of concrete’s biggest appeals. The Romans built concrete structures almost 2,000 years ago that still stand today.  These include the Colosseum. But even things made of concrete can wear out, be damaged or outlive their usefulness.  And that old concrete tends to end up as rubble — a large and long-lived waste.

Each year in the United States alone, construction projects and demolition generate about 181 million metric tons (200 million short tons) of waste concrete. About 70 percent of that waste will be recycled to make more concrete. But that leaves more than 54 million metric tons of unrecycled rubble. Much of that gets thrown into landfills.

 

Brynn Cauldwell, 17, came up with an idea for making concrete rubble useful. In the process, it also possibly allows for the recycling of its materials. What if more rubble could be recycled? And what if that recycling got rid of another big environmental problem at the same time? Those were questions asked by Brynn Cauldwell. This 17-year-old attends St. Stithians Boys’ College in Sandton, South Africa.

 

The environmental problem that interested Brynn was how to limit mining operations from poisoning nearby ecosystems. It’s a problem especially when the material being mined (such as coal) includes minerals containing sulfur.

And the problem often gets worse when a mine closes. It can lead to what is known as acid mine drainage. This descriptive term refers to the highly acidic waters that drain from a mine or that run off of mined materials that have been discarded in piles nearby.

When water washes over these mine wastes it dissolves the sulfur-bearing minerals. That creates strong acids that mix with the water and make it highly acidic.

In turn, the  acidic water often dissolves toxic heavy metals present in rocks. This runoff flows downhill into the nearest stream. There, and in areas further downstream, these poisons snuff out living organisms. Fish and other creatures can be replaced by slimy globs of acid-tolerant microbes known as extremophiles (Ex-TREEM-oh-fyles).

Brynn realized that concrete could be a potential solution to this problem. Acids can dissolve the cement that binds concrete together. That cement includes alkaline materials. When it dissolves, it releases acid-neutralizing ions. This process also creates water, which further dilutes the acid.

 

The highly acidic and environmentally devastating waste known as acid mine drainage (seen here) can be largely neutralized by filtering it through concrete rubble, a teen’s research finds. Brynn’s tests confirmed that his idea works. But he has not yet used actual mine drainage. Instead, the teen used a strong solution of hydrochloric acid. He ran the acidic solution through a container full of concrete rubble over and over again. As the cement in the concrete began to dissolve, the acid got weaker and weaker. Eventually the solution’s acidity dropped to a point where it was no longer a threat.

 

Acid mine drainage also tends to contain toxic metals. If Brynn had used it, extra steps might have been needed to remove them from the water, he notes. But eventually, the water should emerge from this system clean enough to irrigate crops, he says. “By combining two wastes, we could end up with something useful,” he concludes.

Not only that, says Brynn, but the sand and gravel left behind after the cement dissolved could be reused to make fresh batches of concrete. That’s less material sent to landfills — recycling at its best.

But wait, there’s more…

The widespread availability of concrete, as well as its low cost, renders it a popular topic for teen research. The projects above were three of several concrete-related projects that earned their way from local competitions to the Intel ISEF finals. And if you think these projects are impressive, you’re right. Abdulrahman and Ahmed received $1,000 for their research. It was provided by the King Abdulaziz and his Companions Foundation for Giftedness and Creativity. That group is based in Riyadh, Saudi Arabia. Brynn took home $3,000 worth of stock in United Technologies Corporation, a company based in Farmington, Conn.

Teens in other science competitions have investigated concrete for their studies too. Take, for instance, Augusta Uwamanzu-Nna of Elmont Memorial High School in New York. In her case, she focused on improving the cement used as a binder. This project won the high school senior a finalist’s spot in the Intel Science Talent Search (anotherSSP program) this past March.

Augusta was turned on by the idea of innovation — even in something as apparently simple as cement. “I was motivated by the need to implement sustainable measures into the cement and concrete industry,” the teen says. She showed that by adding tiny clay particles to its recipe, liquid cement will flow better. And that, she says, might one day help prevent disasters like the Deepwater Horizon oil spill.

One measure of recognition for the value of her findings: This spring the young researcher was accepted into every Ivy League school. She’ll begin her studies at Harvard this fall.      

Power Words

acid    A chemical that releases hydrogen ions when dissolved in a solution. Acids have a sour taste and have a pH ranking of less than 7.0.

acidic   An adjective for materials that contain acid. These materials often are capable of eating away at some minerals such as carbonate, or preventing their formation in the first place.

acid mine drainage    The highly acidic runoff from mines, often mines that have been abandoned. Sometimes brightly colored and full of toxic metals, these liquid wastes form when water from underground sources or precipitation dissolves sulfur-bearing minerals in the materials being mined.

alkaline    An adjective that describes a chemical that produces hydroxide ions (OH-) in a solution. These solutions are also referred to as basic — as in the opposite of acidic — and have a pH above 7.

aquifer   Rock that can contain or transmit groundwater.

arid     A description of dry areas of the world, where the climate brings too little rainfall or other precipitation to support much plant growth.

binder       Something used to bind — hold together — other things. Three-ring binders hold notebook paper securely in one place. Cement binds together the rock and other materials used in concrete.

cement     A finely ground material used to bind sand or bits of ground rock together in concrete. Cement typically starts out as a powder. But once wet, it becomes a mudlike sludge that hardens as it dries.

composite    A material made using two or more different building blocks, which together produce something with new and better features. Carbon fiber reinforced polymers are one example. Embedded in these hard and strong plastics are tiny fibers made from carbon. Engineers use these plastic to build lightweight bodies for race cars and airplanes, among other things.

compound   (often used as a synonym for chemical) A compound is a substance formed from two or more chemical elements united in fixed proportions. For example, water is a compound made of two hydrogen atoms bonded to one oxygen atom. Its chemical symbol is H2O.

concrete    To be solid and real. (in construction) A simple, two-part building material. One part is made of sand or ground-up bits of rock. The other is made of cement, which hardens and helps bind the grains of material together.

dehydrate    To lose a large amount of water.

desalination   The process of removing salt from water. It’s a primary technology for turning seawater into freshwater.

ecosystem      A group of interacting living organisms — including microorganisms, plants and animals — and their physical environment within a particular climate. Examples include tropical reefs, rainforests, alpine meadows and polar tundra.

engineering   The field of research that uses math and science to solve practical problems.

environmental footprint    A term for the energy and resource use that can be linked with given activities (such as air travel or the discarding of old goods versus recycling them), products (cell phones or frozen foods) and lifestyles (eating meat instead of grains or driving to local venues instead of walking). The more resources used, the bigger something’s so-called environmental footprint will be.

epoxy       Short for epoxy resin, this is a material made of a chain of chemical building blocks known as epoxide rings. After heating, these resins turn solid or semi-solid and work like a glue to hold things together.

extremophile      A microorganism that lives in conditions of extreme temperature, acidity, alkalinity or chemical concentration.

freshwater    A noun or adjective that describes bodies of water with very low concentrations of salt. It’s the type of water used for drinking and making up most inland lakes, ponds, rivers and streams, as well as groundwater.

ion     An atom or molecule with an electric charge due to the loss or gain of one or more electrons.

Ivy League       The colloquial name for a group of eight northeastern U.S. colleges and universities. They comprise Brown, Columbia, Cornell, Dartmouth, Harvard, Princeton, the University of Pennsylvania and Yale. They have gained renown for their storied history and the high scholastic rigor required of their students. The term, first coined by a writer with the New York Tribune in 1937, referred to the fact that these schools had so many ivy-covered buildings.

landfill     A site where trash is dumped and then covered with dirt to reduce smells. If they are not lined with impermeable materials, rains washing through these waste sites can leach out toxic materials and carry them downstream or into groundwater. Because trash in these facilities is covered by dirt, the wastes do not get ready access to sunlight and microbes to aid in their breakdown. As a result, even newspaper sent to landfill may resist breakdown for many decades.

metric ton    A unit of weight in the metric system. A metric ton is 1,000 kilograms. By comparison, a short ton, a unit of measurement in the English system, is 2,000 pounds, or a little over 907 kilograms.

mineral     The crystal-forming substances, such as quartz, apatite, or various carbonates, that make up rock. Most rocks contain several different minerals mish-mashed together. A mineral usually is solid and stable at room temperatures and has a specific formula, or recipe (with atoms occurring in certain proportions) and a specific crystalline structure (meaning that its atoms are organized in certain regular three-dimensional patterns).

phosphorescence      Commonly referred to as “glow-in-the-dark,” materials exhibiting this quality absorb energy from certain wavelengths of light (a type of radiation) and store it. Later, after the source of radiation disappears, these materials release the stored energy as visible light. A substance with this ability is said to be phosphorescent.

precipitation   (In meteorology) A term for water falling from the sky. It can be in any form, from rain and sleet to snow or hail.

rebar      Short for reinforcing bar. A steel rod used internally in concrete structures to give them additional strength.

Science Talent Search or STS      An annual competition created and run by Society for Science & the Public (SSP). On May 26, 2016, Regeneron Pharmaceuticals Inc., of Tarrytown, N.Y., took over sponsorship of this competition. Since its beginning in 1950, this event has been bringing 40 research-oriented high school seniors to Washington, D.C. where they compete for awards and showcase their research to the public.

Society for Science and the Public (or SSP)      A nonprofit organization created in 1921 and based in Washington, D.C. Since its founding, SSP has been not only promoting public engagement in scientific research but also the public understanding of science. It created and continues to run three renowned science competitions: The Regeneron Science Talent Search (begun in 1942), the Intel International Science and Engineering Fair (initially launched in 1950) and Broadcom MASTERS (created in 2010). SSP also publishes award-winning journalism: in Science News (launched in 1922) and Science News for Students (created in 2003). Those magazines also host a series of blogs (including Eureka! Lab).

short ton      A unit of weight in the English system. A short ton is 2,000 pounds, or a little over 907 kilograms. A metric ton, by comparison, is 1,000 kilograms.

slurry        A thick (or viscous) mix of liquids and non-dissolving solids.

strong acid        This is an acid that forms when a starting material completely ionizes — each of its molecules donates a proton to a water molecule — in an aqueous solution. Examples of strong acids include hydrochloric acid. This develops when hydrogen chloride ionizes in water to form the hydrochloric acid. Other strong acids include nitric, sulfuric and perchloric. Usually, the water molecules can easily give up the protons to make the starting material again. But in strong acids, this does not generally occur. Strength does not refer to how concentrated or how corrosive an acid is.

toxic   Poisonous or able to harm or kill cells, tissues or whole organisms. The measure of risk posed by such a poison is its toxicity.