by Vince Beiser
All of this frenetic construction has made China into the world’s largest consumer of concrete12 and the most voracious consumer of sand in human history. In 2016, China used an estimated 7.8 billion tons of construction sand. That’s enough to cover the entire state of New York an inch deep. In the next few years, that number is projected to grow to nearly 10 billion tons.
All around the world, converting those armies of sand into concrete has in many ways yielded incredible blessings. Concrete has saved countless lives and enriched even more. Concrete dams generate electricity. Concrete hospitals and schools can be built and repaired far more quickly than their counterparts of adobe, wood, or steel. Concrete roads help farmers get their crops to market, students to get to school, sick people to get to hospitals, and medicines to get to villages in all weathers. Research has shown that paving streets increases land values, agricultural wages, and school enrollment.
Just having a concrete floor is a huge improvement for many people. Hundreds of millions of people worldwide live in dwellings with dirt floors. Writing in Foreign Policy magazine,13 economist Charles Kenny pointed out that walking barefoot on such a floor is an excellent way to contract an illness, particularly hookworm disease, a parasitic infection to which children are especially vulnerable. Simply paving those floors massively reduces the risk. According to Kenny, a program in Mexico that provided concrete floors for poor homes cut the rate of parasitic infestations by nearly 80 percent, and halved the number of children with diarrhea in any given month. Sand, it turns out, can not only provide shelter but can be a boon for public health.
All of these countless tons of concrete, however, come at a steep cost. Several types of costs, actually.
Heaping concrete on cities can destroy culture and beauty just as surely as heaping sand on coral reefs kills fish. Shanghai’s shikumen are hardly the only historic architectural type demolished to make room for concrete high-rises. Concrete is a key reason so many places in today’s world look just like every other place. It’s the standardized substrate upon which a million identical office towers, apartment blocks, Starbucks, Marriotts, and eight-lane highways have been propagated the world over. It is the coat of generic gray paint that renders everything the same color and texture. Sure, concrete has some cachet in certain architectural circles, but for the average person it’s the symbol of modernity at its worst, the stuff they used to pave paradise and put up a parking lot.
More pressingly, concrete also inflicts physical harm on people and the planet. Just as it does on a beach, sand in the forms of concrete and asphalt soaks up the sun’s heat. Those miles of warmed-up pavement can raise the ambient temperature of a whole city, creating a phenomenon known as urban heat islands. According to a 2015 study by the California Environmental Protection Agency,14 when combined with the heat generated by motor vehicle engines, paved areas can boost the temperature in some cities by as much as 19 degrees Fahrenheit. That’s more than just unpleasant. Heat exposure can be lethal to children, the elderly, and other vulnerable people. Heat also boosts the formation of air pollutants, especially ground-level ozone, better known as smog. Too much sand on the ground can lead to toxins in the air.
Urban heat islands will only get hotter as climate change grows more acute. And speaking of climate change, concrete is making it worse. The cement industry is one of the world’s leading sources of greenhouse gases. Processing limestone into cement emits carbon dioxide. On top of that, most cement-producing furnaces burn fossil fuels, which spew out even more CO2. Cement is made in at least 150 countries, and produces between 5 and 10 percent of the total carbon dioxide emissions worldwide. That puts cement making in the top three sources of carbon dioxide emissions, behind only coal-fueled power plants15 and the ubiquitous automobile.
Concrete, as we have seen, is also the handmaiden of the automobile. One promotes dependence on the other. The more roads you build, the more traffic you generate, which means more carbon emissions from tailpipes. “Not to mention,” as Charles Kenny writes, “building new roads in a pristine forest is a pretty surefire way to lose that forest to loggers.”
In some places, building with concrete is backfiring in startling ways. Some 30 percent of Texas’s Harris County, in which Houston sits, is covered by roads, parking lots, and other structures; that made the flooding caused by 2017’s Hurricane Harvey much worse.16 All that impervious concrete blocked storm water from seeping into the earth as it would naturally, turning streets into artificial rivers.
While concrete seals off the earth in Houston, it is crushing it in Indonesia. That nation’s capital, Jakarta, and its environs are an urban behemoth of 28 million people, many of them living in the forest of skyscrapers that have sprung up in recent years. But the ground the city sits on is porous and weakened by the extraction of too much water by thirsty residents. As a result, the unfathomable weight of all that concrete is slowly squashing the ground beneath it, making the city sink. Jakarta has sunk by thirteen feet over the past thirty years, and is still dropping three inches per year. Nearly half the city now sits below sea level, protected only by aging sea walls.17 Shanghai and other cities are similarly crushing the ground beneath them.
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Perhaps the most frightening aspect of our dependence on concrete is that the structures we build with it won’t last. The vast majority of them will need to be replaced—and relatively soon.
We tend to think of concrete as being permanent, like the stone it mimics. In its early days, modern concrete was touted as a completely fireproof and earthquake-proof material, one that would never require repairs. “It has made possible a structure which is a guarantee of its own durability, as concrete improves with age,” trilled Scientific American magazine in 1906.18 That same year the San Francisco Chronicle marveled at a new concrete bridge over the San Joaquin River, declaring “the remotest generation of mankind will never have to construct another bridge at that place.”19 Ernest Ransome himself wrote that “the general wear and tear on a well-constructed reinforced concrete building is insignificant and confined to the finish coat of the floor.”20
None of that turned out to be true. Concrete fails and fractures in dozens of ways. Heat, cold, chemicals, salt, and moisture all attack that seemingly solid artificial stone, working to weaken and shatter it from within.
“The disease that will kill your concrete depends on where you live,” said Larry Sutter, a professor of materials science at Michigan Technological University. In his state, it’s the winter cold. Concrete is microscopically porous, so a little water always seeps in. That water expands when it freezes, which can crack the concrete. The chemicals used to deice roads also degrade their concrete surfaces.
In Florida, the number one problem for concrete is corrosion of the internal rebar, caused by salt in the atmosphere. In California, it’s attack by sulfates in the water, “which can turn concrete into mush in a couple of years,” said Sutter. Other potential worries include bacterial and algal growth in humid areas, and acid deposition from pollution in cities. Underground concrete structures like water pipes, storage tanks, and even missile silos have to contend with damaging chemicals that filter down through the earth.21
One of the most pervasive threats to concrete is something called the alkali-silica reaction, which was discovered in 1940. It’s caused by certain types of sand—silica—which when combined with alkali and water in the cement react to form a gel that can expand and crack the concrete from inside. It’s a particularly pervasive problem, found on every continent except Antarctica. In 2009, cracks caused by ASR were found in the walls of a nuclear power plant in New Jersey. Concrete in at least two other nuclear plants has cracked seriously in recent years, according to the US Nuclear Regulatory Commission22; one was damaged so badly it ultimately had to be closed down.
By now builders have developed tactics to prevent ASR, most commonly by including fly ash in the concrete
mix. “But there’s lots of concrete already in place that’s susceptible,” said Sutter. And there’s probably more being put in place. “There are areas in the United States where we have mined all the good aggregate, and so we’re using stuff we would not have used twenty years ago,” an aggregate industry consultant told me—that is, sand and gravel that is susceptible to the alkali-silica reaction.
Reinforced concrete is also made vulnerable by the very component that makes it so strong: the steel rods inside it. “Cracks that occur in a structure may be repaired, but not before air, moisture, and many other possible chemicals seep into the form to cause rust,” Courland writes.23 “As the rebar rusts, several things happen. Not only is the amount of ‘good’ steel reduced, but the diameter of the rebar expands to as much as fourfold its original diameter, causing more cracks and, in due course, pushing out chunks of concrete.” Usually the slow-spreading damage is spotted and the building fixed or condemned, but in the worst cases, the structure may be so badly damaged it collapses.
When a dam or a twenty-story office tower or a parking garage starts to show that kind of stress, the owners call in an outfit like Chicago-based Wiss, Janney, Elstner Associates. WJE specializes in figuring out what’s going wrong with concrete in everything from nuclear power plants to skyscrapers. Its engineers head to the trouble zone with ground-penetrating radar and other sophisticated imaging gear and bore out core samples of the concrete. These men and women have dangled from the tops of skyscrapers and rappelled down the Washington Monument and the St. Louis Arch in pursuit of samples containing information about those structures’ health.
At WJE’s sprawling headquarters north of Chicago, petrographer Laura Powers examines those concrete samples under a powerful microscope to determine, among other details, the quality of the sand used to make it. Powers is a serious arenophile, a sand lover; she collects samples of grains from all over the world, and likes nothing more than to talk about their different qualities. She is often called on to testify in court cases in which contractors are being sued for using substandard aggregate—sand or gravel that was the wrong size or shape, or contained reactive agents that can cause ASR. “We do a lot of evaluations of aging structures,” said Powers. “What worries me are the structures we’re not evaluating.”
Concrete making has developed into a highly sophisticated science to meet the panoply of uses for which it is called upon. There are thousands of different types and mixes of concrete, each with specific properties tailored to specific purposes. The strength required for a chunk of suburban sidewalk, for instance, is very different from that required of a slab of dam holding back a river. Adding chemicals or fibers can make concrete lighter, faster curing, more flexible, resistant to corrosion, or pretty to look at. You might need to add retarders to slow down hardening in hot weather, or accelerators to speed it up in the cold, or superplasticizers to make it more fluid. You might add steel fibers to increase the concrete’s impact resistance, or polypropylene fibers to help keep it from cracking.
Of the utmost importance is deploying the right sand and gravel, the particles that make up the bulk of any concrete. Changing the size, shape, properties, and proportions of the aggregate in the mix gives you concretes of differing strength, durability, ease of use, and cost. Getting the right grains for the job is so important that in 2010 the US military was forced to import sand from Qatar to Iraq.24 There’s certainly no shortage of sand in Iraq, but the local granules weren’t good enough to make the concrete needed to build protective blast walls around government ministries and other important structures.
WJE helps builders develop concrete mixes for specialized purposes. Its campus hosts a warren of labs where they put slabs, cylinders, and chunks of concrete made with various sands from around the world through stress tests simulating its real-world environment. The most punishing testing is carried out by John Pearson, the lean, brush-cut manager of WJE’s cavernous structural testing lab. The lab contains a trailer-truck-sized steel frame, fitted with a hydraulic press capable of exerting 2 million pounds of pressure. WJE researchers use it for testing structural columns. Pearson showed me a video of a recent test. Second by second, as the press applied unimaginable force to a twenty-foot concrete column, fist-sized chunks of concrete started to pop loose. Then suddenly the column exploded in a burst of debris and dust, knocking the camera over. “That kind of sudden failure wouldn’t happen in the real world, except maybe in an earthquake,” Pearson explained. “But slow, gradual deterioration, if it’s not noticed, or not addressed, can lead to collapse.”
Edwin Mah spends his days looking for just such slow, gradual deterioration. Mah, sixty-seven, is a freeway bridge inspector with Caltrans, California’s state transportation agency, charged with checking out how well bridges carrying millions of cars are holding up. He has a lean face with a toothy smile and an accent from his native China, which he left back in 1960. I joined him recently for an inspection of a typical bridge, one built in 1950 to carry the 101 Freeway over Melrose Avenue in central Los Angeles.
It’s a grimy, dusty, noisy corner of the city. The summer heat was just kicking in at 8:30 A.M., and traffic streamed steadily on and off the ramps connecting the freeway with Melrose, a busy four-lane thoroughfare. Underneath the overpass, a bluntly functional span held up by two heavy concrete columns, were vestiges of homeless encampments: an abandoned shopping cart, scattered clothes, a mattress, ashes from a fire. Homeless folk add another risk to concrete overpasses, Mah said. They sometimes steal the steel nuts on the structure to sell as scrap metal, or accidentally set fire to wood reinforcements with their cooking fires. Caltrans inspectors always go out in pairs, Mah explained, especially to spots where homeless folk stay. “A lot of them are very rude,” he says. Sometimes he has to call in California Highway Patrol officers to get them to move so he can do his job.
Mah climbed the slope from the street and stepped out onto the narrow shoulder of the bridge. A relentless fusillade of cars and trucks roared past no more than a foot from him, but Mah didn’t seem to notice. As we walked, he pointed out cracks in the concrete road surface that had been filled in with tarry black sealant, and divots created by spalling—spots where internal expansion had popped off chunks of the concrete, exposing the rebar.
“You see this crack right here? This is very severe,” Mah said, squatting down to point out a long crack snaking across all four lanes. “If we don’t seal that, within five years we’ll have big problems. Pieces coming out. Eventually the whole deck would collapse.” Farther on, the cracks expanded into a fragmented jigsaw. “Look how bad this is. Very bad,” he muttered.
Mah would later write all this up in a report, which would hopefully lead to a Caltrans crew coming out to fill in the cracks. (“Nearly all departments of transportation are understaffed,” said Sutter. “Their ability to identify problems is much better than their ability to solve them.”) With proper maintenance, said Mah, the bridge should last another thirty or forty years, but no more. “Sooner or later it will need to be replaced,” he said. “Material never lasts forever.”
That’s a fact the United States is learning the hard way. The most recent report on America’s infrastructure by the American Society of Civil Engineers gives the nation’s roads a grade of D. One-fifth of America’s highways and one-third of its urban roads are in “poor” condition, inflicting $112 billion worth of extra repair and operating costs on American drivers.25 According to the Federal Highway Administration, nearly one-quarter of all America’s bridges are structurally deficient or functionally obsolete.
How bad can bad roads get? Afghanistan provides an extreme but relevant example. According to The Washington Post, the United States and other Western governments have poured more than $4 billion into building thousands of miles of new roads in that immiserated nation since 2001. Those roads are now in tatters, riddled with giant holes and crumbling pavement. Of course, some of the damage was caused b
y bomb blasts; but much of it is simply because after they were built, the roads got virtually zero maintenance.26
The state of America’s 84,000-odd dams, most of the biggest of which are made with sand-based concrete, is even more unnerving. Their average age is fifty-six years, meaning quite a few are much older. Many were built to specifications far less stringent than those in force today, and so could break under the strain of a floods or earthquake. The American Society of Civil Engineers estimated that as of 2015 some 15,500 dams should be considered “high hazard potential”—meaning a failure would cause deaths. Bringing them up to current standards would cost tens of billions of dollars. Despite this, they don’t get a lot of attention from overstretched state inspectors. Nationwide, there’s only one safety inspector for every 205 dams. As of 2013, according to ASCE, South Carolina had only two people monitoring all of its 2,380 dams, and one of them was part-time.27 So it was as unsurprising as it was tragic when in 2015 heavy rain collapsed 36 of the state’s dams. As many as nineteen people were killed in the resultant flooding, according to The New York Times.28 Scores of other dams around the country have failed since 2010. All told, hundreds of Americans are killed or injured each year due to the failure of the nation’s sand-based roads, bridges, and dams.
Things are far worse in many developing nations, where building standards are low and the regulations that do exist are often ignored. A major Turkish developer told a newspaper a few years ago that during a building boom in the 1970s he routinely used unwashed sea sand to make concrete for buildings in Istanbul and elsewhere. Unwashed marine grains are cheaper to buy, but they are coated with salt that dangerously corrodes rebar. Concrete buildings made with sea sand pancaked by the dozens in Haiti’s 2010 earthquake, and in 2013, Chinese officials halted construction of more than a dozen skyscrapers in Shenzhen that were found to contain unwashed sea sand.
