That Which Is Old Is New Again

A few years ago I heard of the discovery of what made Roman concrete so tough – volcanic ash as part of the mix – but it turns out that was only part of the recipe that made Roman concrete so durable and strong that it lasts for millennia, even in aquatic environments. Researchers at MIT, Harvard University, and two European labs have solved the rest of the mystery, particularly the mystery of how it self-heals microcracks, something modern concrete can’t do.

Researchers have spent decades trying to figure out the secret of this ultradurable ancient construction material, particularly in structures that endured especially harsh conditions, such as docks, sewers, and seawalls, or those constructed in seismically active locations.

Now, a team of investigators from MIT, Harvard University, and laboratories in Italy and Switzerland, has made progress in this field, discovering ancient concrete-manufacturing strategies that incorporated several key self-healing functionalities. The findings are published today in the journal Science Advances, in a paper by MIT professor of civil and environmental engineering Admir Masic, former doctoral student Linda Seymour ’14, PhD ’21, and four others.

The researchers found a number of anomalies in samples of Roman concrete they could explain, one of them being the inclusion of minuscule particles of lime, specifically what is called quicklime. It turns out to be the material that was the secret to the ability to self-heal cracks in the concrete. The were also able to determine part of the mixing process that made Roman concrete so tough.

Studying samples of this ancient concrete, he and his team determined that the white inclusions were, indeed, made out of various forms of calcium carbonate. And spectroscopic examination provided clues that these had been formed at extreme temperatures, as would be expected from the exothermic reaction produced by using quicklime instead of, or in addition to, the slaked lime in the mixture. Hot mixing, the team has now concluded, was actually the key to the super-durable nature.

“The benefits of hot mixing are twofold,” Masic says. “First, when the overall concrete is heated to high temperatures, it allows chemistries that are not possible if you only used slaked lime, producing high-temperature-associated compounds that would not otherwise form. Second, this increased temperature significantly reduces curing and setting times since all the reactions are accelerated, allowing for much faster construction.”

If we have truly rediscovered how to make Roman concrete, the effects on our world could be immeasurable. Looking at our crumbling infrastructure, much of it caused by the decay and failure of modern concrete, replacing that concrete with durable Roman concrete that will last millennia rather than decades can transform our civilization. The need to rebuild our roads, bridges, sewers, water systems, buildings, canals, and any other constructs making use of concrete every few decades would be greatly reduced, if not eliminated. It would save money, increase the long term safety of our roads, highways, bridges, and tunnels. The money saved could be used for other projects rather than heavy maintenance or replacement of existing infrastructure. But there may be those who might not like the idea of concrete that only needs to be replaced every 2000 years.

As one commenter to the Instapundit post linking the MIT article put it, “Sadly, it will never be allowed in the US, because fat lazy bloated road construction unions won't allow it. They wouldn't get [to] rebuild all of I-94 every other year.” I think the commenter understated it as I think any of the construction unions that would be affected by this new ‘old’ concrete might be against it.

Only time will tell.