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Saturday, May 18, 2024

Florida’s Condo Collapse Foreshadows the Concrete Crack-Up

It will likely be many months before we know for sure what caused the catastrophic collapse of the Champlain Towers South building in Surfside, Florida, last week, which killed at least 18 people. But it’s already clear that at least one culprit was failing concrete. In 2018 an engineering firm warned that concrete beneath the building’s pool and entrance drive showed "major structural damage,” and it found “abundant cracking” in the underground parking garage. Just a few months ago, the president of the building’s condominium association wrote that “concrete deterioration is accelerating.”

While this kind of sudden, wholesale building collapse is very rare, the problem of crumbling concrete isn’t at all. It’s a slow-moving crisis that affects much of the world. Billions of tons of concrete in the form of buildings, roads, bridges, and dams may need to be replaced in the coming decades. That will cost trillions of dollars—and generate staggering amounts of climate-change-fueling carbon emissions.


Concrete, which is essentially just sand and gravel glued together with cement, is by far the most widely used building material on earth. We pour enough each year to build a wall 88 feet high and 88 feet wide right around the equator. That’s largely because the number and size of cities is exploding. The number of urban dwellers has more than quadrupled since 1960 to more than 4 billion, and it’s still rising. We’re adding the equivalent of 10 New York Cities to the planet every single year.

There’s no way cities could grow this fast without concrete. It’s an almost magically cheap, easy way to quickly create roads, bridges, dams, and relatively sturdy, sanitary housing for huge numbers of people. An estimated 70 percent of the world’s population now live in structures made at least partly out of concrete.

But none of those structures will last forever. Concrete fails and fractures in dozens of ways. Heat, cold, chemicals, salt, and moisture all attack that seemingly solid artificial rock, working to weaken and shatter it from within. (Rising temperatures and atmospheric carbon levels are expected to make things worse.)

That threatens not just apartment towers, but our concrete-based infrastructure. A 2021 report by the American Society of Civil Engineers found that more than 20,000 concrete bridges across the US are structurally deficient and nearly half the nation’s public roadways are in “poor” or “mediocre” condition.

Things are far worse in many developing nations, where building standards are low and regulations often ignored. To cut costs, builders often use unwashed sea sand to make concrete. Those grains are cheaper, 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. Shoddy concrete was also likely a key reason for the collapse of a factory in Bangladesh in 2013 that killed more than 1,000 people. According to The Financial Times, as much as 30 percent of Chinese cement is so low-grade that it produces dangerously flimsy structures known as “tofu buildings.” Cheaply made concrete is one of the reasons so many schools collapsed in China’s 2008 Sichuan earthquake, killing thousands.

All of which is terrifying, considering that most of the world’s concrete was set in place only in the last few decades, and most of it in the developing world—China first and foremost. China alone used more cement between 2011 and 2013 than the United States used in the entire 20th century. As a result, writes economist Vaclav Smil, “The post-2030 world will face an unprecedented burden of concrete deterioration … The future replacement costs of the material will run into trillions of dollars.”


Digging up the billions of tons of sand and gravel needed to make all that concrete will inevitably damage countless river beds, lake bottoms, and flood plains. Poorly regulated sand and gravel extraction in many countries has wiped out huge numbers of river-dwelling fish and birds, damaged coral reefs, and caused riverbanks to collapse. The industry has even spawned a criminal black market, rife with corruption and violence.

As if all that weren’t enough, manufacturing all that concrete will take a heavy toll on the environment. The cement industry produces 5 to 10 percent of the world’s carbon dioxide emissions, behind only coal-fueled power plants and automobiles as a source of global warming gases.

Unlike fossil fuels, which can be swapped out for solar, wind, and other renewables, there is no complete alternative to concrete. Newish materials like mass timber are helpful, but they can’t be deployed on the scale needed to house upwards of 4 billion city dwellers, let alone the infrastructure they depend on.

Still, there’s a lot we can do to soften concrete’s impact. More rigorous building codes and enforcement around the world could prevent at least some building collapses. On the emissions front, a handful of promising startups offer technologies that lower concrete’s carbon footprint—including a couple that actually use carbon to replace some of the cement in the mix. Powering more cement manufacturing plants with renewable energy would also help. The most effective solution is just to use less concrete in the first place, by making cities more dense, walkable, and generally less car-centric. Think of how much concrete would be saved if just 10 percent of new housing didn’t need to come with a driveway and garage, or even a parking space.

Over the past century, we have built our world on concrete—but we are only now starting to see its true cost. It’s time to start getting thriftier with our favorite building material.

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