How Do Ancient Concrete Buildings Survive When Modern Ones Do Not?

Mayan site in Copan Ruinas, Honduras

Pantheon in Rome

Wars. Climate disasters. Earthquakes. Volcanoes. Time. Wear and tear. Obsolescence. Abandonment. In today’s world of modern commercial building, a concrete and steel structure is expected to last north of 50 years (pushing it, maybe to 100 years), but buildings often face demolition within 30 to 40 years. Stone structures, not particularly durable in earthquake zones, can last a bit longer. Look at the venerable mega-structures built in New York City in the 1930s and beyond. Or even more incredible, the Acropolis in Athens. Their legacy is obviously significantly longer. So, with this basic understanding, it seems puzzling how ancient Roman and Mayan concrete structures are still standing, as the above photos illustrate.

What does this ancient concrete have that modern concrete seems to lack? After all, as Associated Press’ Maddie Burakoff points out (October 10th): “Ancient builders across the world created structures that are still standing, thousands of years later — Roman engineers who poured thick concrete sea barriers, Maya masons who crafted plaster sculptures to their gods, Chinese builders who raised walls against invaders…

“A growing number of scientists have been studying materials from long-ago eras — chipping off chunks of buildings, poring over historical texts, mixing up copycat recipes — hoping to uncover how they’ve held up for millennia.

“This reverse engineering has turned up a surprising list of ingredients that were mixed into old buildings — materials such as tree bark, volcanic ash, rice, beer and even urine. These unexpected add-ins could be key to some pretty impressive properties, like the ability to get stronger over time and ‘heal’ cracks.

“Figuring out how to copy those features could have real impacts today: While our modern concrete has the strength to hold up massive skyscrapers and heavy infrastructure, it can’t compete with the endurance of these ancient materials.” Not to mention another nasty reality of modern cement: “The concrete industry is having a bit of a reckoning. As the world’s most ubiquitous construction material, concrete contributes about 8% of global carbon dioxide emissions. About 30 billion tons of concrete are produced every year, which is three times more than it was 40 years ago.

“This has fueled a slew of innovations as researchers and companies strive to produce lower-carbon alternatives. Some are looking to the past: the deep tech startup Dmat, for example, makes self-healing concrete inspired by Ancient Romans [, as discussed below]. Others are looking to the future: a team of researchers at Northwestern are developing ‘Martian concrete’ that doesn’t require water and is more than twice as strong.” Elissaveta M. Brandon, writing for the October 18th FastCompany.com. Modern construction designers are indeed learning from the ancient builders of these amazing structures that are still standing centuries or millennia later.

“Many researchers have turned to the Romans for inspiration. Starting around 200 BC, the architects of the Roman Empire were building concrete structures that have stood the test of time — from the soaring dome of the Pantheon to the sturdy aqueducts that still carry water today… Even in harbors, where seawater has been battering structures for ages, you’ll find concrete ‘basically the way it was when it was poured 2,000 years ago’ said John Oleson, an archaeologist at the University of Victoria in Canada.

“Most modern concrete starts with Portland cement, a powder made by heating limestone and clay to super-high temperatures and grinding them up. That cement is mixed with water to create a chemically reactive paste. Then, chunks of material like rock and gravel are added, and the cement paste binds them into a concrete mass.

“According to records from ancient architects like Vitruvius, the Roman process was similar. The ancient builders mixed materials like burned limestone and volcanic sand with water and gravel, creating chemical reactions to bind everything together… Now, scientists think they’ve found a key reason why some Roman concrete has held up structures for thousands of years: The ancient material has an unusual power to repair itself. Exactly how is not yet clear, but scientists are starting to find clues.

“In a study published this year, Admir Masic, a civil and environmental engineer at the Massachusetts Institute of Technology, proposed that this power comes from chunks of lime that are studded throughout the Roman material instead of being mixed in evenly. Researchers used to think these chunks were a sign that the Romans weren’t mixing up their materials well enough.

“Instead, after analyzing concrete samples from Privernum — an ancient city outside of Rome — the scientists found that the chunks could fuel the material’s ‘self-healing’ abilities. When cracks form, water is able to seep into the concrete, Masic explained. That water activates the leftover pockets of lime, sparking up new chemical reactions that can fill in the damaged sections.

“Marie Jackson, a geologist at the University of Utah, has a different take. Her research has found that the key could be in the specific volcanic materials used by the Romans… The builders would gather volcanic rocks left behind after eruptions to mix into their concrete. This naturally reactive material changes over time as it interacts with the elements, Jackson said, allowing it to seal cracks that develop.” Brandon. Whatever else is said and done, we can no longer afford to build using the current, environmentally destructive and short-lived standard Portland cement. The arrogance of modernity occasionally must yield to the wisdom of the ancient past. With all the bombing and artillery/missile strikes in major conflicts around the world, there will be a lot of rebuilding in our near future. Will we learn how to do it better now?

I’m Peter Dekom, and in this world of hyper-accelerating transitory reality, it is often a wise investigation to view our history, from political and military turmoil to our most basic building and construction practices.