Concrete is a symbol of modern civilization. In a far shorter time than it took to replace houses of earth and straw with brick, it created the city skylines that soar into the sky. Paradoxically, concrete also best shows the destruction of civilization. Is there any scene that speaks more eloquently of the terror of earthquakes or war than piles of collapsed concrete? The moment concrete caves in, the dreams of the people who lived within it vanish too.
Admir Masic, a professor in the Department of Civil and Environmental Engineering at the Massachusetts Institute of Technology (MIT), is a refugee who fled Bosnia to escape war. Having witnessed the destruction of civilization as a child, Masic grew into a scientist who dreams of concrete that does not fail. The idea is for concrete to heal its own cracks. Concrete also contributes to global warming. Eight percent of the greenhouse gases emitted by humanity during manufacturing come from it. If concrete lasts longer, it can help curb warming.
The clue was found in ancient Rome. Roman buildings, aqueducts, and breakwaters made of concrete have retained their form even after 2,000 years. Augustus, who became Rome's first emperor in 27 B.C., said, "I found Rome a city of brick and left it a city of marble." Marble was only a finish; the real support holding up the Pantheon and the Colosseum to this day was concrete. Even the breakwaters in the sea remain as they were.
Concrete made by modern people crumbles in less than 50 years. The secret to the longevity of Roman concrete was its self-healing ability. On the 9th, Masic reported in the international journal Nature Communications that ancient Romans manufactured concrete differently from today, allowing cracks to repair themselves. He found the method of making ancient Rome's "super concrete," different from the modern one.
Roman concrete that splits yet fuses back together
Concrete is made by mixing cement from limestone with sand, gravel, and water. If sand and gravel are the aggregate that fill a building's volume and increase its strength, cement acts as an adhesive that hardens by reacting with water. The way ancient Romans made concrete was similar. So why are ancient Roman concrete structures so sturdy?
Romans also fired limestone with calcium carbonate (CaCO₃) and ground it into powder to make cement. That is quicklime, or calcium oxide (CaO). Mixing this with water makes slaked lime, or calcium hydroxide (Ca(OH)₂). The Roman architect Vitruvius wrote in the 1st century B.C. in De architectura that they first added water to lime to make a paste-like material and then mixed it with other materials such as volcanic ash. In other words, slaked lime came first, and then other materials were added. The principle is not much different from today's concrete manufacturing.
In 2023, Masic published an analysis of a 4th-century B.C. concrete city wall. Examining a wall discovered at the archaeological site of Privernum in central Italy, he found millimeter-scale small lime lumps inside. He had identified the self-healing component of ancient concrete. When cracks form in concrete and rainwater enters, these lime lumps dissolve and then re-harden as limestone, filling and sealing the gaps.
The problem was that following Vitruvius' description did not produce the lime lumps observed in ancient concrete. Masic concluded that, contrary to Vitruvius' record, ancient Romans first mixed quicklime with volcanic ash and then added water. That triggers an intense chemical reaction and generates tremendous heat. This is the hot mixing method.
When heat is generated during mixing, concrete sets faster and becomes stronger. In that process, parts reached up to 400 degrees Celsius and formed small lime lumps. That created the very component that "treats" cracks.
Proving the new theory with a time capsule preserved in Pompeii
Vitruvius' words carried authority that no one questioned in his time or later. His theory of human proportions is representative. In De architectura, Vitruvius said that when a person stretches out arms and legs in a large X, the fingertips and toes touch a circle's circumference and the navel sits at the circle's center. Height equals arm span, so the body also fits into a square with all sides equal.
Actual human proportions differed from his claims, but later artists did not dare object. When drawing diagrams of human proportions, they twisted the body to force it into the circle and square to match Vitruvius. The person who challenged Vitruvius' argument was the quintessential genius of the Renaissance, Leonardo S.p.A..
Drawing the Vitruvian Man, Da Vinci, based on direct observation, set the square slightly outside the circle. Inside the circle he drew a man with arms and legs splayed so the navel was at the center, as Vitruvius said. But he also superimposed a figure standing with feet together so they touched the base of the square. And the center of the square was not the navel but near the genitals.
Masic also sought evidence to challenge Vitruvius' authority by directly studying Roman sites. Those lime lumps from the concrete wall came first. But it was still possible they were merely impurities, not made intentionally. Stronger proof was needed. Masic found decisive evidence at the Pompeii site re-excavated in 2023.
Buried under 6 meters of volcanic ash, the Pompeii site vividly showed a scene of repairing dwellings when Mount Vesuvius erupted in A.D. 79. As Masic had argued earlier, materials in which quicklime and volcanic ash were mixed before water entered were found. Walls made later by adding water to this mix were also found. Construction tools turned up as well. It was, in effect, a time capsule of an ancient Roman construction site. "I will never forget the feeling that, by opening a time capsule, I was time-traveling to watch people making concrete in A.D. 79," Masic said.
A war refugee boy who found hope in science
Masic founded a company to commercialize ancient Rome's concrete technology and set out to solve problems facing humanity today. The construction industry has been identified as a culprit in warming. That is because large amounts of greenhouse gases are emitted when making cement, the main material. In the process of firing limestone at temperatures above 1,500 degrees Celsius, carbon dioxide, which accounts for 44% of its mass, is released. Carbon dioxide is also emitted in obtaining the energy to maintain those high temperatures.
Concrete made in the Roman way lasts longer, so usage can be reduced compared to now. That much greenhouse gas emissions can also be cut. Concrete would be reborn as an eco-friendly material. The researchers confirmed the possibility through experiments.
They made concrete in the ancient Roman way and deliberately created cracks. When water was run through, as expected, the cracks completely sealed within two weeks and water no longer flowed. Concrete made by the modern method left the cracks as they were and water kept passing through. Masic said he will develop not only long-lasting, self-healing concrete but also concrete that absorbs carbon dioxide.
Masic said science had been his hope since childhood. Just before he entered high school, the Bosnian War broke out. When tanks destroyed his home, he fled with his family to neighboring Croatia. He said he discovered "magic" that gave him hope in a refugee camp. It was chemistry. Refugees could not attend regular school, but with a teacher's help, he was allowed to sit in on classes. He absorbed scientific knowledge like a sponge. Six months after he began auditing classes, he entered a local chemistry competition and won.
Later, thanks to a change in the law, he officially graduated from high school, entered an Italian university, and earned a Ph.D. in chemistry. By coincidence, his doctoral research focused on parchment containing the wisdom of ancient Romans. He later founded a company for restoring old documents. It was no accident that he uncovered the secret of ancient concrete.
To share his experience, in 2017 Masic established at MIT the Refugee Action Hub (ReACT), a computer science education program for refugees. Every year, thousands have gone through this program and found jobs at global information and communications technology (ICT) corporations such as Microsoft and Meta. Perhaps among them, a world-class scientist will emerge.
Omar Yaghi, a professor at the University of California, Berkeley, won the 2025 Nobel Prize in chemistry for discovering metal-organic frameworks that adsorb moisture from the air. Like Masic, he grew up in a Palestinian refugee family in Jordan.
In media interviews after the Nobel announcement, he said, "As a child, every single drop of water was truly precious," and "We had to wake up at dawn and open the valve to get water that we could use for only a couple of hours a week." The searing experiences of a refugee boy led to solving humanity's water shortage problem. They say hope was the last thing to come out of Pandora's box, which released all manner of evils. Having grown from war refugees into scientists who may save the world, could they be that hope?