Highly focused X-Ray beams have revealed the molecular make-up of concrete from a Roman pier, revealing how it gained its strength and longevity. The work could fill in one of the biggest missing pieces of our understanding on how to stop the world from heating up.
Superior engineering contributed to the Roman Empire's success, but of course, we have long since surpassed their technology. Concrete, is the big exception, however. The ancient product was in many ways more advanced than the one we build with today, as demonstrated by the survival of some 2000-year-old roads and buildings, even in earthquake zones.
Moreover, Roman concrete didn't cook the planet, having a fraction of the environmental impact. Unfortunately, we still haven't worked out how it was made. In a quest to learn the secret Roman sauce, Professor Marie Jackson of the University of Utah used the Berkeley Lab's Advanced Light SourceX-Rays to examine concrete taken from a 2000-year-old pier from Orbetello, Italy. Jackson said in a statement. "We can identify the various minerals and the intriguingly complex sequences of crystallization at the micron scale."
In American Mineralogist, Jackson reveals that crystals of a layered material called "aluminous tobermorite" provided structural strength. The same crystals are seen in rocks formed when volcanic eruptions produced the island of Surtsey off Iceland in the 1960s but were thought to require high temperatures. "No one has produced tobermorite at 20º Celsius," Jackson said in a statement. "Oh - except the Romans!"
Roman concrete is known to have included lime (CaO) volcanic ash, and seawater. Replicating the formula sufficiently precisely that engineers will feel comfortable using it for structures that must last decades has proved challenging, however. Since their chemistry was rudimentary, it is thought the Romans stumbled on the formula by watching volcanic ash turn to stone on exposure to seawater. Tragically, however, the details were lost sometime after Rome fell to less technologically attuned invaders. Work like Jackson's to identify the contents could help us reverse engineer it.
Modern concrete, including the vital ingredient Portland cement, is a major emitter of greenhouse gasses, accounting for around 5 percent of human-induced emissions. If that doesn't sound like much, consider the vast and increasingly successful efforts to replace larger sources with clean technologies. Yet a world run on renewable energy and electric cars could still be brought undone if our ever-growing thirst for carbon-emitting concrete eats up our remaining carbon budget.
A third of concrete's damage is done by the heat needed to fire the kilns in which the cement is made, while half comes from carbon dioxide released when limestone (CaCO3) is heated. The Roman process reacted the lime with carbon dioxide in seawater, actually reducing its concentration. But it's not like the Romans ever did much for us.