In search of the lost art of ancient Roman concrete

Concrete is an affordable material that can be poured to fit any shape and dries to be as strong as rock. Unfortunately it is very porous and sucks up water, which freezes in cold months and causes cracks. While some concrete structures can last 50-60 years, these cracks can appear within the first few years after construction and can be devastating to the integrity of a structure.

Roman concrete, however, is much longer lasting. Structures built with the ancient Roman recipe still stand today and retain their structural integrity. They have stood for 2,000 years and in all that time they’ve only grown stronger. The only problem is, the Romans’ recipe was lost long ago.

Now, The Guardian reports, scientists are closer than ever to uncovering the mystery. Analysis has revealed the ingredients include: a mix of volcanic ash, lime (calcium oxide), seawater and lumps of volcanic rock. That’s right, the seawater that has been crashing into it for two millennia was part of the hardening process:

[Marie Jackson] said this revealed another process that was also at play. Over time, seawater that seeped through the concrete dissolved the volcanic crystals and glasses, with aluminous tobermorite and phillipsite crystallising in their place. These minerals, say the authors, helped to reinforce the concrete, preventing cracks from growing, with structures becoming stronger over time as the minerals grew. By contrast, modern concrete, based on Portland cement, is not supposed to change after it hardens – meaning any reactions with the material cause damage.

Scientists are continuing to experiment with their findings, but are still uncertain as to the exact formula to recreate the ancient Roman recipe.