The ancient Romans were brilliant engineers who built extensive networks of roads, aqueducts, ports, and enormous buildings, the ruins of which may still be seen today.
Numerous of these buildings were made of concrete, including Rome’s renowned Gods and goddesses, which has the largest concrete dome.
Other historic Roman canals still carry water to Rome today.
Many contemporary concrete buildings have disintegrated within a few decades.
Researchers have been studying this resilient ancient building material for decades, especially in docks, sewers, seawalls, and other structures. That was built in seismic active areas or that had to resist particularly hard conditions.
It was once believed that when lime was mixed with water then it created a paste-like substance. This procedure is known as slaking.
But the existence of the lime clasts, small solid pieces, that originated from original limestones, could not be explained by this process alone.
Admir Masic thinks that Romans used quicklime direct on buildings and other things.
Significance of this research
Admir Masic thinks that this research will help to reduce the harmful impact of cement manufacturing on the environment. At present cement manufacturing is responsible for around 8% of global greenhouse gas emissions.
Apart from it, this research will help to discover other ideas for concrete manufacturing that can collect carbon dioxide from the air, which is another current research priority of the Masic group.
How is this research conducted?
These ancient Roman concrete samples also contain small, distinct millimeter-scale bright, white mineral features, which is a common component of Roman concrete.
The current study claims that these tiny lime clasts are responsible for the self-healing power.
Using high-resolution multiscale imaging and chemical mapping methods that are developed in the research lab of Masic. He and his team examined samples of this old concrete and the white inclusions were formed of different kinds of calcium carbonate.
As per the expectation, in the spectroscopic examination, when scientists use quicklime in place of or in addition to the slaked lime in the mixture then exothermic reaction occurs.
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This is an indication that these had been formed at extremely high temperatures. Maybe this hot mixing is the secret to the durability of concrete.
During the hot mixing process, a readily broken and reactive calcium supply formed, which developed a distinctive brittle nanoparticulate architecture. Scientists supposed that this is the reason for self-healing activity in the concrete.
Small cracks that develop in the concrete can pass through the lime clasts because of their large surface areas.
Then this substance can combine with water to produce a calcium-saturated solution, which can quickly fill the fracture by recrystallizing it as calcium carbonate, or it can mix with pozzolanic substances to reinforce the composite material even more. These spontaneous reflexes stop the cracks from spreading.
This theory has already received support from the investigation of other Roman concrete samples that had cracks filled with calcite.
The scientists created samples of hot-mixed concrete that combined both traditional and recent formulations and then let water flow through the cracks to demonstrate the process that gave the Roman concrete its long-lasting quality.
The water stopped flowing after two weeks and the cracks had fully healed.
An identical piece of quicklime-free concrete never recovered, and the water just continued to seep through the test.
This research was published in the journal Science Advances.