Scientists discover the secret of why Roman concrete was so durable

The former members of the Roman culture They were masters of engineering and construction, as their aqueducts, buildings, and ports have survived, in many cases, for two centuries. A team of scientists has examined the concrete that they used and he believes he has found the key: quicklime.

Researchers have been trying to unlock the secret of this ultra-durable ancient building material for decades, especially in structures that endured particularly harsh conditions, such as piers, culverts and levees, or those built in seismically active locations.

And new study published by Science Advances signed by researchers from the Massachusetts Institute of Technology (MIT), Harvard University and laboratories in Italy and Switzerland has uncovered ancient manufacturing strategies of concrete that incorporated several key functionalities.

For years, it had been believed that the key to the durability of that concrete It was based on an ingredient, the pozzolanic material, a volcanic ash from the Pozzuoli area, in the Bay of Naples (Italy), to which the stories of architects and historians of the time referred.

However, these ancient samples also contain small, distinctive millimeter-scale brilliant white mineral features, which have long been recognized as a ubiquitous component of rock formations. concretes romans.

lime clasts

These white chunks, often referred to as “lime clasts”, come from lime, another key component of the ancient mix of concrete.

Such remains have until now been considered mere evidence of careless mixing or poor-quality raw materials, MIT explains in a statement.

However, the new study suggests that those tiny limestone clasts gave the concrete a hitherto unknown self-repairing ability.

One of the signatories to the research, Admir Masic, from MIT, stressed that if “the romans They put so much effort into making an exceptional building material, why would they put so little effort into ensuring they produce a well-mixed end product?” so I thought there had to be a reason.

Following further characterization of the limestone clasts, using high-resolution multiscale imaging and chemical mapping techniques, the researchers gained new insights into the potential functionality of these limestone clasts.

Historically, it had been assumed that when lime was incorporated into Roman concrete, it first combined with water to form a highly reactive pasty material in a process known as slaking, but that process alone could not explain the presence of the clasts. of lime

So the team wondered if the Romans might have used quicklime, which is a more reactive form of the material. Studying samples of old concrete, they determined that the white particles were indeed made up of various forms of calcium carbonate.

“Super Durable Nature’s Key”

Spectroscopic examination provided indications that they had formed at extreme temperatures, as would be expected from the exothermic reaction produced by the use of quicklime instead of, or in addition to, slaked lime in the mix.

Hot mixing, according to the team, was actually “the key to the super-durable nature” of the concrete due to two factors Masic explained.

On the one hand, when the concrete as a whole is heated to high temperatures, it allows a chemistry that would not be possible if only slaked lime were used, producing compounds associated with those temperatures that would not otherwise form.

In addition, the increase in temperature significantly reduces curing and setting times, as all reactions are accelerated, allowing for much faster construction.

The team decided to prove that this was the mechanism responsible for the durability of the concrete Roman, producing hot mix samples incorporating ancient and modern formulations, cracking them and running water through them.

After two weeks, those openings had completely healed and the water could no longer flow, however, an identical piece of concrete made without quicklime never cured and water continued to flow through the sample.

Masic considered that “it is exciting to think about how these formulas of concrete more durable formulas could extend not only the lifespan of these materials, but also how it could improve the durability of 3D-printed concrete formulations.”

(With information from EFE)


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