Roman concrete is absolutely amazing stuff. It is among the main reasons we know so much about Roman architecture today. Many buildings built by the Romans still stand, in some form, thanks to them Ingenious concrete and construction techniques.
However, there is still a lot we don’t understand about how the Romans could make such strong concrete or build all those impressive buildings, houses, public baths, bridges and roads.
Now, a New study — led by researchers from the Massachusetts Institute of Technology (MIT) and published in the journal Nature Communications — sheds new light on Roman concrete and building techniques.
This is thanks to details obtained from partially constructed rooms at Pompeii, a work site abandoned by workers when Mount Vesuvius erupted in 79 AD.
New evidence about the concrete industry
Discovering this very thing Construction site It hit the news early last year.
The builders were repairing a house in the center of the city, when Mount Vesuvius exploded in the first century AD.
This unique find included tiles sorted for recycling and wine containers known as amphorae that were reused to transport building materials.
Importantly, it also included evidence of dry material preparation prior to mixing for concrete production.
This dry matter is the focus of the new study. Access to the actual materials before mixing represents a unique opportunity to understand the concrete making process and how these materials react when water is added.
This has rewritten our understanding of the Roman concrete industry.
Self-healing concrete
The researchers behind this new paper studied the chemical composition of materials found at the site and identified some key elements: tiny bits of quicklime that are changing our understanding of how concrete is made.
Quicklime is calcium oxide, which is produced by heating high-purity limestone (calcium carbonate).
The authors of this study explain that the concrete mixing process took place in the hallway of this house. The workers mixed dry lime (ground lime) with… Pozzolana (ash).
When water is added, the chemical reaction produces heat. In other words, it was Exothermic reaction. This is known as “hot mixing” and results in a very different type of concrete than what you get from the hardware store.
Adding water to quicklime results in the formation of what is called hydrated lime, in addition to generating heat. Within the hydrated lime, researchers identified small, undissolved “lime fragments” that retained the reactive properties of quicklime. If this concrete forms cracks, the lime chips react with water to heal the crack.
In other words, this form of Roman concrete can be literal Heal himself.
Old and new technologies
However, it is difficult to know how widespread this method was in ancient Rome.
Much of our understanding of Roman concrete is based on the writings of the ancient Roman architect Vitruvius.
He had advised this Use pozzolana mixed with limeBut it was assumed that this text did not refer to hot mixing.
However, if we look at another Roman author, Pliny the Elder, we find a clear description of the reaction of quicklime with water which is the basis of the theory. Exothermic reaction Involved in mixing hot concrete.
So the ancients had knowledge of hot mixing but we know little about how widespread this technique was.
Perhaps the most important thing is the detail in the texts of the various experiments A mixture of sand, pozzolana and limeWhich resulted in the combination used by the builders at Pompeii.
The research team was at the Massachusetts Institute of Technology Previously found lime blocks (those little pieces of quicklime) in the Roman remains at Perevernum, about 43 kilometers north of Pompeii.
It is also worth noting Healing of cracks This has been observed in the concrete of the tomb of noblewoman Cecilia Metella outside Rome on the Via Appia (a famous Roman road).
Now this is the new Pompeii He studies After proving that hot mixing occurred and how it helped improve Roman concrete, scientists can look for examples where concrete cracks were healed in this way.
Questions remain
Overall, this new study is exciting – but we should resist the assumption that all Roman construction was manufactured to a high standard.
The ancient Romans could make exceptional concrete mortar, but as Pliny the Elder noted, Poor mortar It caused the collapse of buildings in Rome. So just because they can make a good slurry, doesn’t mean they always did.
Questions, of course, remain.
Can we generalize from the single example of this new study from 79 AD Pompeii to explain all forms of Roman concrete?
Does it show an advance from Vitruvius, who wrote earlier?
Was the use of quicklime to make stronger concrete in this 79 AD house in Pompeii a reaction to the presence of earthquakes in the area and the expectation of future cracks?
To answer any of these questions, more research is needed to find out the prevalence of lime crumbs in Roman concrete in general, and to determine where Roman concrete itself has healed.
This edited article was republished from Conversation Under Creative Commons license. Read Original article.