Scientists from MIT, IMM and Harvard have caused ripples through the internet with their most recent publication on the durability of ancient Roman concrete  in relation to a 1000-2000 year old Roman settlement. They have shown how clumps made from lime, which were previously thought as bad mixing, were in fact reservoirs of reactive calcium that was used to fill-in cracks. Upon the formation of a crack, water would trickle through the lime clump and into the crack, creating a calcium rich solution that would react to fill-in the crack space. This process, called Self-Healing, is a naturally occurring process in most cementitious materials and happens due to the precipitation of minerals through natural reactions. Still, the use of these lime clumps is a way of improving the materials to self-heal faster, better and more consistently to extend the service life of concrete structures

Furthermore these clumps, or lime casts, have also been found elsewhere in other sites. Also, the surface and internal differences of the clasts, show that these reservoirs are formed within the concrete matrix through a process called “hot mixing". This mixing process, lets the calcium oxide or lime react in the moment the mixture of cement is being prepared rather than allowed to react previously as modern lime productions do. Lastly, it was observed that these clasts had a higher frequency of crack intersection, due to being softer than the rest of the material, allowing for better access to the lime reservoir.

All-in-all, this shows the understanding and widespread use of this mixing technology by the Romans to create more durable concrete structures. Discoveries such as these, show that past technologies can provide insights relevant to our current day challenges, in this case, how to develop longer-lasting are resilient structures.

Prof. Nele De Belie has commented on this discovery and the potential lessons to be learnt for current developments in self-healing concrete, in a newspaper interview, published in De Standaard, 10 January 2023