Researchers reverse-engineer Roman concrete

Amongst the capabilities lost to antiquity like Damascus steel and Ulfberht swords, Roman concrete with it's Wolverine'esque regenerative capabilities that allows it to weather centuries like no concrete made by modern man; that is till a team of researchers reverse engineered the manufacturing process: Hot mixing, and published their findings in the journal Science Advances:

Ancient Roman concretes have survived millennia, but mechanistic insights into their durability remain an enigma. Here, we use a multiscale correlative elemental and chemical mapping approach to investigating relict lime clasts, a ubiquitous and conspicuous mineral component associated with ancient Roman mortars. 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. Inspired by these findings, we propose that these macroscopic inclusions might serve as critical sources of reactive calcium for long-term pore and crack-filling or post-pozzolanic reactivity within the cementitious constructs. The subsequent development and testing of modern lime clast–containing cementitious mixtures demonstrate their self-healing potential, thus paving the way for the development of more durable, resilient, and sustainable concrete formulations.

Hot mixing: Mechanistic insights into the durability of ancient Roman concrete | Science Advances

Lead author, Admir Masic found that millimeter-scale calcium rich mineral deposits known as "lime clasts" found in Roman concrete will re-cement cracks that restore watertightness to stop the erosive effects of flowing water through the healed crack.

"To prove that this was indeed the mechanism responsible for the durability of the Roman concrete, the team produced samples of hot-mixed concrete that incorporated both ancient and modern formulations, deliberately cracked them, and then ran water through the cracks. Sure enough: Within two weeks the cracks had completely healed and the water could no longer flow. An identical chunk of concrete made without quicklime never healed, and the water just kept flowing through the sample. As a result of these successful tests, the team is working to commercialize this modified cement material."

Riddle solved: Why was Roman concrete so durable? | MIT News

The researchers manufactured samples of "Hot mixing" concrete, cracked them and ran water through the cracks to induce the lime clasts to heal the crack like Flex Tape.

Masic's lab is looking into future possibilities like enhanced 3D printed concrete structures and CO2 absorbing concrete that could help change the global impact of new construction.