Researchers gained new insights into the durability of ancient Roman concrete

The new findings suggest that the white lime chunks, being a key component of the roman concrete mixture, provide concrete with a self-healing capability.

The test samples came from the ancient city of Privernum, near Rome, Italy. By conducting several experiments, a team of researchers determined:

Together, these analyses provide new insights into mortar preparation methodologies and provide evidence that the Romans employed hot mixing, using quicklime in conjunction with, or instead of, slaked lime, to create an environment where high surface area aggregate-scale lime clasts are retained within the mortar matrix.

Quicklime is produced by heating naturally-occurring limestone rock, which contains calcium carbonate.

During the hot mixing process, the lime clasts develop a characteristically brittle nanoparticulate architecture, creating an easily fractured and reactive calcium source, which, as the team proposed, could provide a critical self-healing functionality.

In reaction with water the solution turns into calcium carbonate and quickly fill the crack or react with pozzolanic materials to further strengthen the composite material. These spontaneous reactions automatically heal the cracks before they spread over the concrete.

The experiment showed that an identical chunk of concrete made without quicklime never healed. The team aims to commercialize this manufacturing strategy:

“It’s exciting to think about how these more durable concrete formulations could expand not only the service life of these materials, but also how it could improve the durability of 3D-printed concrete formulations.”