Is there anyone around here who knows how to make concrete? Make it properly, I mean?
We recently heard that 1,700 concrete panels at five stations along the Silver Line extension were poorly manufactured. Two years ago, chunks of concrete fell from the ceiling at the Rhode Island Avenue Metro station. (It’s among stations that will close in the summer for repairs.) And who can forget the Silver Spring Transit Center? Its opening was delayed for five years when it turned out that the concrete — and the facility is basically nothing but a huge pile of concrete — was improperly made.
If you were an ancient Roman, you’d be laughing into your toga. Or weeping.
The Pantheon. The Baths of Diocletian. Trajan’s Market. All made of concrete. All still standing after nearly 2,000 years.
The Loudoun Gateway station, part of the Silver Line extension, is seen in July 2017. Problems have been identified with more than 1,700 precast concrete panels at five stations under construction. (Katherine Frey/The Washington Post)
We can’t get our stuff to last even 40 years.
Marie D. Jackson, a professor in the geology and geophysics department at the University of Utah, studies Roman concrete. It is, she said, really quite wonderful stuff. While concrete seems simple — just three ingredients: powdered cement, aggregate and water — the Romans formulated a material that still wows us today.
“They experimented for at least 100 years with different mix designs before they really perfected quality control and materials selection,” Jackson said. “The really amazing thing is that for the imperial era, from Augustus through the time of Hadrian, they used the same materials in very effective ways.”
They perfected the mix around roughly 30 B.C. and used it over the next two centuries to build impressive structures. The key, Jackson said: the bits of volcanic stone they used as the aggregate and the lime mortar they used to bind it.
The combination of the two reacted to form a new mineral cement, one that gets stronger as time passes, even withstanding Italy’s frequent earthquakes.
“It’s an active, dynamic material,” Jackson said. “When microcracks formed, new mineral cements grew through them and healed the cracks.”
And this all happened without rebar. The steel rods we use today provide reinforcement, but if water gets in, they can rust, expanding and compromising the concrete.
“What we need to recognize is that the Roman imperial administration put an enormous amount of financial and technical support into creating concrete structures that were meant to stand the test of time,” Jackson said.
These ranged from grand public buildings to sturdy piers and sea walls. Each was a physical reminder of the power and accomplishments of the Roman state.
Jackson is among researchers working to find a version of this ancient miracle compound that will work in the United States.
“We can’t go repairing subway stations with Roman concrete,” Jackson said. “That won’t work. They had different structural and architectural needs than we do. But what I’m focused on now is understanding Roman principles so they can be applied to modern prototypes.”
Renato Perucchio, an engineering professor at the University of Rochester who has collaborated with Jackson, said the Romans didn’t face some of the challenges we do now. Their structures didn’t have to withstand modern loads, like a heavy subway train, for example.
Still, it’s hard not to be awed by their work. Take the Baths of Diocletian, a public bathing complex completed in 306 A.D. that featured cold baths, lukewarm baths and hot baths. In the 16th century, the artist and architect Michelangelo was commissioned to transform part of the complex into a church.
“Of the entire structure, only the part added by Michelangelo needs careful tending,” Perucchio said. “The Roman part is intact. Think about that.”
Perucchio said that if an architect today were to file paperwork intending to build the Pantheon — the Roman temple that has a 142-foot-high unreinforced concrete dome, the world’s largest — permission would be denied.
“You would be told, ‘You can’t do it, because the material is not capable of resisting the mechanical stresses, because the material is unreinforced,’ ” Perucchio said. “If you hear that, you must arrive at one of two conclusions: One is that the gravitational field in Roman times did not work as it works today. Or the other conclusion is that we have lost knowledge. And I think we have lost knowledge.”
If only we could resurrect some ancient Romans, I said.
“You have to be careful,” Perucchio said, laughing. “Resurrecting Romans means resurrecting emperors. You need to resurrect the engineers.”
Hey, I’m willing to give it a try. We’re not having much luck on our own.
As published by The Washington Post – John Kelly – 5-14-18