Tim Harford is an award-winning journalist, economist, and broadcaster. He is the author of the bestselling The Undercover Economist, Messy, The Undercover Economist Strikes Back, Adapt, and The Logic of Life. A senior columnist at the Financial Times, Harford’s new book is Fifty Inventions That Shaped the Modern Economy.
The Undercover Economist explains why this ancient building material came to dominate the world today—and why that could be a problem in the future.
About 15 years ago, poor families in the Coahuila state in Mexico were offered an unusual handout from a social program called Piso Firme. It wasn’t a place at school, a vaccination, food, or even money. It was $150 worth of ready-mixed concrete.
Workers would drive concrete mixers through poor neighborhoods, stop outside the home of a needy family, and pour out the porridgelike mixture, through the door, right into the living room. Then they would show the occupants how to spread and smooth the gloop, and make sure they knew how long to leave it to dry. And they’d drive off to the next house.
Piso Firme means “firm floor,” and when economists studied the program they found that the ready-mixed concrete dramatically improved children’s education. How so? Previously, most house floors were made of dirt. Parasitic worms thrive in dirt, spreading diseases that stunt kids’ growth and make them sick.
Concrete floors are much easier to keep clean: so the kids were healthier, they went to school more regularly, and their test scores improved. Living on a dirt floor is unpleasant in many other ways: economists also found that parents in the program’s households became happier, less stressed, and less prone to depression when they lived in houses with concrete floors. That seems to be $150 well spent.
Beyond the poor neighborhoods of Coahuila state, concrete often has a less wonderful reputation. It’s a byword for ecological carelessness: concrete is made of sand, water, and cement, and cement takes a lot of energy to produce; the production process also releases carbon dioxide, a greenhouse gas. That might not be such a problem in itself—after all, steel production needs a lot more energy—except that the world consumes absolutely vast quantities of concrete: five tons per person, per year. As a result the cement industry emits as much greenhouse gas as aviation1.
Architecturally, concrete implies lazy, soulless structures: ugly office blocks for provincial bureaucrats; multistory parking garages with stairwells that smell of urine. Yet it can also be shaped into forms that many people find beautiful—think of the Sydney Opera House, or Oscar Niemeyer’s cathedral in Brasilia.
Perhaps it’s no surprise that concrete can evoke such confusing emotions. The very nature of the stuff feels hard to pin down. “Is it Stone? Yes and No,” opined the great American architect Frank Lloyd Wright in 1927. He continued. “Is it Plaster? Yes and No. Is it Brick or Tile? Yes and No. Is it Cast Iron? Yes and No.”2
That it’s a great building material, however, has been recognized for millennia—perhaps even since the dawn of human civilization. There’s a theory that the very first settlements, the first time that humans gathered together outside their kinship groups—nearly 12,000 years ago at Gobekli Tepe in southern Turkey—was because someone had figured out how to make cement, and therefore concrete. It was certainly being used more than 8,000 years ago by desert traders to make secret underground cisterns to store scarce water; some of these cisterns still exist in modern-day Jordan and Syria. The Mycenaeans used it over 3,000 years ago to build tombs you can see in the Peloponnese in Greece.
The Romans were serious about concrete. Using a naturally occurring cement from volcanic ash deposits at Puteoli, near Pompeii and Mount Vesuvius, they built their aqueducts and their bathhouses. Walk into the Pantheon in Rome, a building that will soon celebrate its 1,900th birthday. Gaze up at what was, for centuries, the largest dome on the planet. You’re looking at concrete. It’s shockingly modern.
Many Roman brick buildings are long gone—but not because the bricks themselves have decayed. They’ve been cannibalized for parts. Roman bricks can be used to make modern buildings. But the concrete Pantheon? One of the reasons it has survived for so long is because the solid concrete structure is absolutely useless for any other purpose. Bricks can be reused; concrete can’t3. It can only be reduced to rubble. And the chances of its becoming rubble depend on how well it’s made. Bad concrete—too much sand, too little cement—is a deathtrap in an earthquake. But well-made concrete is waterproof, stormproof, fireproof, strong, and cheap.
That’s the fundamental contradiction of concrete: incredibly flexible while you’re making something, utterly inflexible once it’s made. In the hands of an architect or a structural engineer, concrete is a remarkable material; you can pour it into a mold, set it to be slim and stiff and strong in almost any shape you like. It can be dyed, or gray; it can be rough, or polished smooth like marble. But the moment the building is finished, the flexibility ends: cured concrete is a stubborn, unyielding material.
Perhaps that is why the material has become so associated with arrogant architects and autocratic clients—people who believe that their visions are eternal, rather than likely to need deconstructing and reconstructing as times and circumstances change. In 1954, Soviet leader Nikita Khrushchev delivered a two-hour speech praising concrete, and proposing in some detail his ideas for standardizing it still further. He wanted to embrace “a single system of construction for the whole country.”4 No wonder we think of concrete as something that is imposed on people, not something they choose for themselves.
Concrete is permanent and yet throwaway. It lasts forever. In a million years, when our steel has rusted and our wood has rotted, concrete will remain. But many of the concrete structures we’re building today will be useless within decades. That’s because, more than a century ago, there was a revolutionary improvement in concrete—but it’s an improvement with a fatal flaw.
In the mid–19th century, a French gardener, Joseph Monier, was dissatisfied with the available range of flowerpots. Concrete pots had become fashionable, but they were either brittle or bulky. Customers loved the modern look, but Monier didn’t want to have to lug around cumbersome planters, and so he experimented with pouring concrete over a steel mesh. It worked brilliantly.5
Monier had been rather lucky. Reinforcing concrete with steel simply shouldn’t work, because different materials tend to expand by different amounts when they warm up. A concrete flowerpot in the sun should crack, as the concrete expands by a certain amount and the steel inside expands at a different rate. But by a splendid coincidence, concrete and steel expand in a similar way when they heat up; they’re a perfect pairing6.
But Monier rode his luck: over time he realized that reinforced concrete had many more applications besides flowerpots—railway sleepers, building slabs, and pipes—and he patented several variants of the invention, which he exhibited at the Paris International Exhibition in 1867.
Other inventors took up the idea, testing the limits of reinforced concrete and working out how to improve it. Less than 20 years after Monier’s first patent, the elegant idea of prestressing the steel was patented. The prestressing makes the concrete stronger—it partly counteracts the forces that will act on the concrete when it’s in use. Prestressing allows engineers to use much less steel, and less concrete, too. And it works as well as ever 130 years later1.
Reinforced concrete is much stronger and more practical than the unreinforced stuff. It can span larger gaps, allowing concrete to soar in the form of bridges and skyscrapers. But here’s the problem: if cheaply made, it will rot from the inside as water gradually seeps in through tiny cracks in the concrete and rusts the steel. This process is currently destroying infrastructure across the United States;7 in 20 or 30 years’ time, China will be next. China poured more concrete in the three years after 2008 than the United States poured during the entire 20th century, and nobody thinks all of that concrete is made to exacting standards.
There are many new methods for improving concrete, including special treatments to prevent water from getting through to the steel. There’s “self-healing” concrete, full of bacteria that secrete limestone, which reseals any cracks. And “self-cleaning” concrete, infused with titanium dioxide, breaks down smog, keeping the concrete sparkling white. Improved versions of the technology may even give us street surfaces that clean what’s coming out of car exhausts.
Yet ultimately, there is much more we could be doing with the simple, trusted technology we have already. Hundreds of millions of people around the world live in dirt-floor houses; hundreds of millions of people could have their lives improved with a program like Piso Firme. Other studies have shown large gains from laying concrete roads in rural Bangladesh—improved school attendance, agricultural productivity, and wages of farmworkers.
Perhaps concrete serves us best when we use it simply.
- Vaclav Smil, Making the Modern World: Materials and Dematerialization (London: John Wiley & Sons, 2013), 54–57. ↩a, ↩b
- Adrian Forty, Concrete and Culture (London: Reaktion Books, 2012), 10. ↩
- Stewart Brand, How Buildings Learn: What Happens After They’re Built (New York: Viking, 1994). ↩
- Forty, Concrete and Culture, 150–155. ↩
- Inventors and Inventions (Tarrytown, NY: Marshall Cavendish, 2008), vol. 4. ↩
- Mark Miodownik, Stuff Matters (London: Penguin, 2014), chap. 3. ↩
- The American Society of Civil Engineers noted in its “2017 Infrastructure Report Card” that “56,007—9.1 [percent]— of the nation’s bridges were structurally deficient in 2016,” and that an estimated $123 billion was needed for bridge repair (www.infrastructurereportcard.org). ↩